The Space Infrared Telescope Facility (SIRTF) was successfully launched on August 25, 2003. SIRTF is an observatory for infrared astronomy from space. It has an 85cm diameter beryllium telescope operating at 5.5 K and a projected cryogenic lifetime of 4 to 6 years based on early flight performance. SIRTF has completed its in-orbit checkout and has become the first mission to execute astronomical observations from a solar orbit. SIRTF's three instruments with state of the art detector arrays provide imaging, photometry, and spectroscopy over the 3-180 micron wavelength range. SIRTF is achieving major advances in the study of astrophysical phenomena from the solar system to the edge of the Universe. SIRTF completes NASA's family of Great Observatories and serves as a cornerstone of the Origins program. Over 75% of the observing time will be awarded to the general scientific community through the usual proposal and peer review cycle. SIRTF has demonstrated major advances in technology areas critical to future infrared missions. These include lightweight cryogenic optics, sensitive detector arrays, and a high performance thermal system, combining radiative and cryogenic cooling, which allows a telescope to be launched warm and to be cooled in space. These thermal advances are enabled by the use of an Earth-trailing solar orbit which will carry SIRTF to a distance of ~0.6 AU from Earth in 5 years. The SIRTF project is managed for NASA by the Jet Propulsion Laboratory which employs a novel JPL-industry team management approach. This paper provides an overview of the SIRTF mission, telescope, cryostat, instruments, spacecraft, orbit, operations and project management approach; and this paper serves as an introduction to the accompanying set of detailed papers about specific aspects of SIRTF.

The Cryogenic Telescope Assembly (CTA) on the Spitzer Space Telescope employs a revolutionary warm launch design. Unlike previous space cryogenic telescopes, the Spitzer telescope is mounted outside of the cryostat and was launched at ambient temperature. The telescope was cooled through a combination of passive radiation and controlled vapor cooling from the superfluid helium cryostat. Launched in August 2003 with 49 kg of helium, the 0.85-meter telescope cooled to below 5.5 K within the initial 45 days of flight in accordance with analytical predictions. Despite an aggressive schedule of instrument initialization and checkout testing during the first two months of flight, the CTA met the temperature requirements for all checkout activities. The transient flight performance of this multi-stage thermal/cryogenic system has been found to agree well with pre-launch predictions over the broad temperature range. With an emphasis on early flight cool-down behavior, this report highlights the pre-launch cryostat preparation, the thermal behavior during cryostat blow-down, comparisons to pre- and post-launch model predictions, and in-flight helium mass measurement. The post cool down performance and rate of helium use is also discussed.

The Spitzer Space Telescope (formally known as SIRTF) was successfully launched on August 25, 2003, and has completed its initial in-orbit checkout and science validation and calibration period. The measured performance of the observatory has met or exceeded all of its high-level requirements, it entered normal operations in January 2004, and is returning high-quality science data. A superfluid-helium cooled 85 cm diameter telescope provides extremely low infrared backgrounds and feeds three science instruments covering wavelengths ranging from 3.6 to 160 microns. The telescope optical quality is excellent, providing diffraction-limited performance down to wavelengths below 6.5 microns. Based on the first helium mass and boil-off rate measurements, a cryogenic lifetime in excess of 5 years is expected. This presentation will provide a summary of the overall performance of the observatory, with an emphasis on those performance parameters that have the greatest impact on its ultimate science return.

The Multiband Imaging Photometer for Spitzer (MIPS) provides long wavelength capability for the mission, in imaging bands at 24, 70, and 160 microns and measurements of spectral energy distributions between 52 and 100 microns at a spectral resolution of about 7%. By using true detector arrays in each band, it provides both critical sampling of the Spitzer point spread function and relatively large imaging fields of view, allowing for substantial advances in sensitivity, angular resolution, and efficiency of areal coverage compared with previous space far-infrared capabilities. The Si:As BIB 24 micron array has excellent photometric properties, and measurements with rms relative errors of 1% or better can be obtained. The two longer wavelength arrays use Ge:Ga detectors with poor photometric stability. However, the use of 1.) a scan mirror to modulate the signals rapidly on these arrays, 2.) a system of on-board stimulators used for a relative calibration approximately every two minutes, and 3.) specialized reduction software result in good photometry with these arrays also, with rms relative errors of less than 10%.

The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 μm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center.

The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.

We present the on-orbit performance results of the Pointing Calibration and Reference Sensor (PCRS) for the Spitzer Space Telescope. A cryogenic optical (center wavelength 0.55 um) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from Spitzer's star tracker and gyroscopes to obtain the actual pointing of the Spitzer telescope. The PCRS calibrates out thermomechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. By using only 16 pixels, the PCRS provides high precision centroiding with extremely low (~64 uW) power dissipation, resulting in minimal impact to Spitzer's helium lifetime. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-s radial, which represents ~1/100 pixel centroiding. The Spitzer Space Telescope was launched on 25 August, 2003 and completed its In-Orbit Checkout phase two months later; the PCRS has been operating failure-free ever since.

Wide Field Camera 3 (WFC3) is a panchromatic UV/visible/near-infrared camera whose development is currently nearing completion, for a planned installation into the Hubble Space Telescope. WFC3 provides two imaging channels. The UVIS channel features a 4096 × 4096 pixel CCD focal plane with sensitivity from 200 to 1000 nm and a 160 × 160 arcsec field of view. The UVIS channel provides unprecedented sensitivity and field of view in the near ultraviolet for HST. The IR channel features a 1014 × 1014 pixel HgCdTe focal plane covering 800 to 1700 nm with a 139 × 123 arcsec field of view, providing a substantial advance in IR survey efficiency for HST. The construction of WFC3 is nearly complete, and the instrument is well into its integration and test program. At the time of this writing (July 2004) the manned HST Servicing Mission 4 that was intended to install WFC3 and other hardware has been cancelled, but a robotic servicing possibility is under intensive investigation. We present the current status and performance of the instrument and also describe some aspects of WFC3 that are relevant to a robotic installation.

Temperature variations in the NICMOS detectors arise from a variety of thermal sources. These thermal variations lead to several image artifacts which must be removed before making quantitative scientific measurements from NICMOS data. Future instruments would do well to minimize sources of thermal instabilities in their detectors. A related problem is the inability to directly measure detector temperature from bias due to the instability of the low-voltage power supply in NICMOS. Identifying ways to directly monitor detector temperatures would be an important benefit for future missions.

ASTRO-F is the Japanese infrared astronomical satellite. The mission purpose is the infrared sky survey with much higher sensitivities and spatial resolutions than those of the previous survey mission IRAS. The ASTRO-F has a liquid-helium cooled telescope with an aperture of 68.5 cm. The lightweight liquid helium cryostat has been developed for the ASTRO-F. The use of cryocoolers and other design features will realize the cryogen life of 550 days in orbit with only 170-liter liquid helium. The attitude control system provides capabilities of a continuous sky survey and also pointing observations. The absolute accuracy of the attitude control is approximately 10 arcsec, and the stability is better than 1 arcsec. The astronomical data will be sent to the ground in the rate of 4 Mbps through the X-band link. The telemetry data amount to more than 2 GB per day. The planned launch date was February 2004, but it has delayed because of a failure in the mirror support mechanism of the telescope system. Though the new launch date has not been decided formally, the launch in 2005 summer is now targeted.

The Infrared Camera (IRC) is one of the focal-plane instruments on board the Japanese infrared astronomical space mission ASTRO-F. It will make wide-field deep imaging and low-resolution spectroscopic observations over a wide spectral range in the near- to mid-infrared (2-26um) in the pointed observation mode of the ASTRO-F. The IRC will also be operated in the survey mode and make an all-sky survey at mid-infrared wavelengths. It comprises three channels. The NIR channel (2-5um) employs a 512x412 InSb array, whereas both the MIR-S (5-12um) and the MIR-L (12-26um) channels use 256x256 Si:As impurity band conduction (IBC) arrays. The three channels will be operated simultaneously. All the channels have 10'x10' fields of view with nearly diffraction-limited spatial resolutions. The NIR and MIR-S share the same field of view, while the MIR-L will observe the sky about 25' away from the NIR/MIR-S field of view. The IRC will give us deep insights into the formation and evolution of galaxies, the properties of brown dwarfs, the evolution of planetary disks, the process of star-formation, the properties of the interstellar medium under various physical environments, as well as the nature and evolution of solar system objects. This paper summarizes the latest laboratory measurements as well as the expected performance of the IRC.

An all-sky survey in two mid-infrared bands which cover wavelengths of 5-12um and 12-26μm with a spatial resolution of ~9" is planned to be performed with the Infrared Camera (IRC) on board the ASTRO-F infrared astronomical satellite. The expected detection limits for point sources are few tens mJy. The all-sky survey will provide the data with sensitivities more than one order of magnitude deeper and with spatial resolutions an order of magnitude higher than the Infrared Astronomical Satellite (IRAS) survey. The IRC is optimally designed for deep imaging in pointing observations. It employs 256x256 Si:As IBC infrared focal plane arrays (FPA) for the two mid-infrared channels. In order to make observations with the IRC during the survey mode of the ASTRO-F, a new operation method for the arrays has been developed - the scan mode operation. In the scan mode, only 256 pixels in a single row aligned in the cross-scan direction on the array are used as the scan detector and sampled every 44ms. Special cares have been made to stabilize the temperature of the array in the scan mode, which enables to achieve a low readout noise compatible with the imaging mode (~30 e^-). The flux calibration method in the scan mode observation is also investigated. The performance of scan mode observations has been examined in computer simulations as well as in laboratory simulations by using the flight model camera and moving artificial point sources. In this paper we present the scan mode operation method of the array, the results of laboratory performance tests, the results of the computer simulation, and the expected performance of the IRC all-sky survey observations.

The Far-Infrared Surveyor (FIS) is a focal plane instrument of the ASTRO-F satellite, and is designed primarily to achieve far-infrared all sky survey with four photometric bands in wavelength range of 50 - 200um. Compared to IRAS, the FIS has higher sensitivity, higher spatial resolution, and longer wavelength coverage. The FIS also has spectroscopic capability with a Fourier transform spectrometer (FTS). In order to assemble these two kinds of instrument into a small and light body, we have developed new compact detector arrays and adopt the unique optical design. In the first half year of the ASTRO-F mission, the all sky survey is performed intensively, and is completed in the following half year. In addition to this survey, the telescope can be kept to a specific direction during 10 minutes for pointing observations. In pointing observations, we can take deep photometric images by using the photometric mode, or can take spectra by using the FTS. According to the laboratory calibration, it is expected that the detection limit of the all sky survey is almost one order of magnitude better than the IRAS one. The FTS could take spectra with full spectral resolution for about two orders of magnitude brighter sources than the detection limit of the all sky survey for one pointing observation. Due to the imaging FTS, the observing efficiency is much improved for the extended sources. The FIS will provide us unique and valuable observational data in the far-infrared wavelength region.

Herschel is the fourth cornerstone mission in the European Space Agency (ESA) science programme. It will perform imaging photometry and spectroscopy in the far infrared and submillimetre part of the spectrum, covering approximately the 57-670 μm range. The key science objectives emphasize current questions connected to the formation of galaxies and stars, however, having unique capabilities in several ways, Herschel will be a facility available to the entire astronomical community. Herschel will be equipped with a 3.5 metre diameter passively cooled telescope. The science payload complement - two cameras/medium resolution spectrometers (PACS and SPIRE) and a very high resolution heterodyne spectrometer (HIFI) - will be housed in a superfluid helium cryostat. The ground segment will be jointly developed by the ESA, the three instrument teams, and NASA/IPAC. Herschel is scheduled to be launched into a transfer trajectory towards its operational orbit around the Earth-Sun L2 point by an Ariane 5 (shared with the ESA cosmic background mapping mission Planck) in 2007. Once operational Herschel will offer a minimum of 3 years of routine observations; roughly 2/3 of the available observing time is open to the general astronomical community through a standard competitive proposal procedure.

SPIRE, the Spectral and Photometric Imaging Receiver, is one of three scientific instruments which will fly on the European Space Agency's Herschel Space Observatory. SPIRE contains two sub-instruments: a three-band imaging photometer operating at 250, 360 and 520 microns, and an imaging Fourier Transform Spectrometer (FTS) covering 200-670 microns. The detectors are arrays of feedhorn-coupled NTD spider-web bolometers cooled to 300 mK. The photometer field of view of is 4 x 8 arcminutes, observed simultaneously in the three spectral bands. An internal beam steering mirror allows spatial modulation of the telescope beam and will be used to jiggle the field of view in order to produce fully-sampled images. Observations can also be made by scanning the telescope without chopping. The FTS has an approximately circular field of view with a diameter of 2.6 arcminutes, and employs a dual-beam configuration with broad-band intensity beam dividers to provide high efficiency and separated output and input ports. The spectral resolution can be adjusted between 0.04 and 2 cm^-1 (λ/Δλ = 20 - 1000 at 250 microns). The instrument design, operating modes, and estimated sensitivity are described, and the current status of the project is reported.

The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments for ESA's far infrared and submillimetre observatory, Herschel. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 x 25 pixels, each, and two filled Si bolometer arrays with 16 x 32 and 32 x 64 pixels, respectively, to perform imaging line spectroscopy and imaging photometry in the 57-210 micron wavelength band. In photometry mode, it will simultaneously image two bands, 60-85 micron or 85-130 micron and 130-210 micron, over a field of view of ~ 1.75'x3.5', with full beam sampling in each band. In spectroscopy mode, it will image a field of ~ 50"x50", resolved into 5 x 5 pixels, with an instantaneous spectral coverage of ~ 1500 km/s and a spectral resolution of ~ 75 - 300 km/s. In both modes background-noise limited peformance is expected, with sensitivities (5σ in 1h) of ~3 mJy or 3-10x10^-18 W/m², respectively.

The future ESA space mission Planck Surveyor mission will measure the Cosmic Microwave Background temperature and polarisation anisotropies in a frequency domain comprised between 30GHz and 1THz. On board two instruments, LFI based on HEMT technology and HFI using bolometric detectors. We present the optical solutions adopted for this mission, in particular the focal plane design of HFI, concept which has been applied already to other instruments such as the balloon borne experiment Archeops.

PLANCK represents the third generation of mm-wave instruments designed for space observations of Cosmic Microwave Background anisotropies within the new Cosmic Vision 2020 ESA Science Programme. The PLANCK survey will cover the whole sky with unprecedented sensitivity, angular resolution, and frequency coverage. The expected scientific return will be enormous, both for the cosmological constraints that will be set and for the gold mine of information contained in the astrophysical foregrounds. To reach these ambitious scientific goals, the control of systematic effects is mandatory and a careful instrument design is needed, as well as an accurate knowledge of instrumental characteristics. The Low Frequency Instrument (LFI), operating in the 30 ÷ 70 GHz range, is one of the two instruments onboard PLANCK Satellite, sharing the focal region of a 1.5 meter off-axis dual reflector telescope together with the High Frequency Instrument (HFI) operating at 100 ÷ 857 GHz. We present a detailed study carried out by the LFI team on the performances of the PLANCK telescope coupled with LFI feed horns, both in the main beam and in the sidelobe region.

The JWST project at the GSFC is responsible for the development, launch, operations and science data processing for the James Webb Space Telescope. The JWST project is currently in phase B with its launch scheduled for August 2011. The project is a partnership between NASA, ESA and CSA. The U.S. JWST team is now fully in place with the recent selection of Northrop Grumman Space Technology (NGST) as the prime contractor for the telescope and the Space Telescope Science Institute (STScI) as the mission operations and science data processing lead. This paper will provide an overview of the current JWST architecture and mission status including technology developments and risks.

The scientific requirements of the James Webb Space Telescope fall into four themes. The End of the Dark Ages: First Light and Reionization seeks to identify the first luminous sources to form and to determine the ionization history of the Universe. The Assembly of Galaxies seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and active nuclei within them evolved from the epoch of reionization to the present. The Birth of Stars and Protoplanetary Systems seeks to unravel the birth and early evolution of stars, from infall onto dust-enshrouded protostars, to the genesis of planetary systems. Planetary Systems and the Origins of Life seeks to determine the physical and chemical properties of planetary systems including our own, and investigate the potential for life in those systems. These themes will guide the design and construction of the observatory.

JWST will be used to help understand the shape and chemical composition of the universe, and the evolution of galaxies, stars and planets. With a 6.5 meter primary mirror, the Observatory will observe red shifted light from the early history of the universe, and will see objects 400 times fainter than those seen from large ground-based telescopes or the current generation of space-based infrared telescopes. NASA Goddard Space Flight Center (GSFC) manages JWST with contributions from a number of academic, government, and industrial partners. The contract to build the space-based Observatory for JWST was awarded to the Northrop Grumman Space Technology (NGST)/Ball/Kodak/ATK team.

The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope and to the Spitzer Space Facility, will yield astounding breakthroughs in the realms of infrared space science. The science instrument suite for this Observatory will consist of a Near-Infrared Camera, a Near-Infrared Spectrograph, a Mid-Infrared Instrument with imager, coronagraph and integral field spectroscopy modes, and a Fine Guider System Instrument with both a Guider module and a Tunable Filter Module. In this paper we present an overview of the optical designs of the telescope and instruments.

The NIRCam science objectives are the detection and identification of "first light" objects, the study of star and brown dwarf formation, and the detection and characterization of planetary systems and their formation. These three science programs are also the key objectives of the JWST program as a whole. The NIRCam instrument design is optimized for these objectives within the mission constraints. NIRCam consists of two optics modules, each with a field of view of 2.2 arcmin square. The modules are identical except for the mechanical layout. Each module consists of two channels divided by a dichroic beamsplitter. The short wavelength channel has a band pass of 0.6 - 2.3 microns, with pixels sized for Nyquist sampling of the PSF at 2.0 microns. The long wavelength channel has a band pass of 2.4 - 5.0 microns, with pixels sized for Nyquist sampling at 4.0 microns. Selections of wide (R~4), intermediate (R~10), and narrow (R~100) bandwidth filters are provided in each of the four channels, along with coronagraphic occulting masks and pupil stops. A refractive optical design results in a smaller instrument volume and mass, provides good images at the pupils for wavefront sensing and coronagraphy, allows good access to the pupils and focal planes, and relaxes the alignment requirements compared to a reflective design. The NIRCam instrument is funded by NASA/GSFC under contract NAS5-02105.

The James Webb Space Telescope (JWST) will be equipped with a Near Infrared Multi-Object Spectrograph (NIRSpec), in order to record simultaneously several hundred spectra in a single observation run. The selection of the objects in the field of view will be done by a micro-elecro-mechanical system (MEMS): a micro-shutter array. This array is easily reconfigurable and can generate any slit mask geometry. At the Laboratoire d’Astrophysique de Marseille, we have developed since several years different tools for the modeling and the characterization of these MOEMS slit masks. Our model, based on Fourier theory, addresses two key parameters for the MOS performance: contrast and spectral photometric variation (SPV). The integration in a single model of the JWST telescope, the micro-shutter slit mask, the spectrograph and the detector is proposed. The JWST telescope simulator assess pupil shape with low, mid and high frequencies aberrations on the whole telescope as well as on each segment. Additional wavefront aberrations generated by the fore-optics and the spectrograph are also taken into account. NIRSpec performance is then calculated as function of multiple parameters such as telescope pupil shear, object position in the field, plate scale, object location within the slit, pupil oversizing, wavelength, and dithering strategy. Evaluation of the encircled energy is also presented, including the spectrograph aberrations.

The Near Infrared Spectrograph (NIRSpec) for the James Webb Space Telescope (JWST) is a multi-object spectrograph operating in the 0.6-5.0 μm spectral range. One of the primary scientific objectives of this instrument is to measure the number and density evolution of galaxies following the epoch of initial formation. NIRSpec is designed to allow simultaneous observation of a large number of sources, vastly increasing the capability of JWST to carry out its objectives. A critical element of the instrument is the programmable field selector, the Microshutter Array. The system consists of four 175 x 384 close packed arrays of individually operable shutters, each element subtending 0.2” x 0.4”on the sky. This device allows simultaneous selection of over 200 candidates for study over the 3.6’ x 3.6’ field of the NIRSpec, dramatically increasing its efficiency for a wide range of investigations. Here, we describe the development, production, and test of this critical element of the NIRSpec.

The MIRI is the mid-IR instrument for JWST and provides imaging, coronography and low and medium resolution spectroscopy over the 5-28μm band. In this paper we provide an overview of the key driving requirements and design status.

The science instrumentation for the James Webb Space Telescope (JWST) has concluded its Phase A definition stage. We have developed a concept for the JWST Fine Guidance Sensor (FGS), which will form the Canadian contribution to the mission. As part of the JWST re-plan in early 2003, the FGS design was recast to incorporate a narrow-band (R~100) science-imaging mode. This capability was previously resident in the NIRCam instrument. This FGS science mode makes use of tunable filters and filter wheels containing blocking filters, calibration sources and aperture masks. The science function of the FGS Tunable Filters (FGS-TF) remains complementary to the NIRCam science goals. Narrow-band FGS-TF imaging will be employed during many of the JWST deep imaging surveys to take advantage of the sensitivity to emission line objects. The FGS-TF will also provide a coronagraphic capability for the characterization of host galaxies of active galactic nuclei and for the characterization of extra solar planets. The primary function of the FGS remains to provide the sensor data for the JWST Observatory line-of-sight stabilization system. We report here on the overall configuration of the FGS and we indicate how the concept meets the performance and interface requirements.

The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) is a segmented, cryogenic telescope scheduled for launch in 2011. In September of 2002, NASA selected prime contractor Northrop Grumman Space Technology (NGST) to build the observatory including management of the OTE. NGST is teamed with subcontractors Ball Aerospace, Alliant Techsystems (ATK), and Kodak. The team has completed several significant design, technology, architecture definition, and manufacturing milestones in the past year that are summarized in this paper.

The James Webb Space Telescope (JWST) conducted a phased down select for its primary mirror. Using the results of the Advanced Mirror System Demonstrator (AMSD) as a basis, the Mirror Recommendation Board (MRB) assessed the suitability for JWST of candidate mirrors in the areas of performance, schedule, cost and risk. Beryllium was selected for the JWST primary mirror. This paper summarizes the evaluation and selection process.

The 1.4-meter semi-rigid, beryllium Advanced Mirror System Demonstrator (AMSD) mirror completed initial cryogenic testing at Marshall’s X-ray Calibration Facility (XRCF) in August of 2003. Results of this testing show the mirror to have very low cryogenic surface deformation and possess exceptional figure stability. Additionally, the mirror substrate exhibits virtually no change in surface figure over the James Webb Space Telescope (JWST) operational temperature range of 30 to 62 Kelvin. The lightweighted, semi-rigid mirror architecture approach demonstrated here is a precursor to the mirror technology being applied to the JWST observatory. Testing at ambient and cryogenic temperatures included the radius of curvature actuation system and the rigid body displacement system. These two systems incorporated the use of 4 actuators to allow the mirror to change piston, tilt, and radius of curvature. Presented here are the results of the figure change, alignment change, and radius change as a function of temperature. Also shown will be the actuator influence functions at both ambient and cryogenic temperatures.

The Northrup-Grummann/Ball/Kodak team is building the James Webb Space Telescope (JWST), scheduled for launch in 2011. Part of Ball’s responsibility is to develop the wavefront sensing and control (WFS&C) algorithms and software that will be used to provide the level of imaging performance needed to support the mission’s science objectives. Wavefront sensing on JWST differs from that performed on many ground-based telescopes in that it is conducted entirely within the focal plane of it’s chief science camera, the Near Infrared Camera (NIRCam). In a sense, the complexity of a conventional wavefront sensor is eliminated, in favor of rather complex image processing performed on the ground, to extract the wavefront information. This paper will describe the algorithms being developed for JWST. Specifically, we will describe algorithms for the coarse alignment of the primary mirror segments and the secondary mirror, the coarse phasing of the primary mirror segments, and the fine phasing of the entire telescope. We will also present algorithms for monitoring the wavefront quality throughout the JWST mission.

Dispersed Fringe Sensing (DFS) is an efficient and robust method for coarse phasing of a segmented primary mirror such as the James Webb Space Telescope (JWST). Results from testbed experiments and modeling have shown that among the many factors that affect the performance of DFS, the diffraction from segment aperture and the interference between the segment wavefronts have the most intrinsic influence on the DFS performance. In this paper, modeling and simulations based on diffraction are used to study the formation of DFS fringe and fringe properties such as visibility. We examine the DFS piston detection process and explore the limitation of DFS wavefront piston detection accuracy and the DFS dynamic range under different segment aperture geometries, aperture orientations, and image samplings.

Stellar Imager (SI) is a potential NASA space-based UV imaging interferometer to resolve the stellar disks of nearby stars. SI would consist of 20 - 30 separate spacecraft flying in formation at the Earth-Sun L2 libration point. Onboard wavefront control would be required to initially align the formation and maintain alignment during science observations and after array reconfiguration. The Fizeau Interferometry Testbed (FIT) is a testbed currently under development at the NASA/Goddard Space Flight Center to develop and study the wavefront control methodologies for Stellar Imager and other large, sparse aperture telescope systems. FIT consists of 7 articulated spherical mirrors in a Golay pattern, expandable up to 30 elements, and reconfigurable into multiple array patterns. FIT’s purpose is to demonstrate image quality versus array configuration and to develop and advance the wavefront control for SI. FIT uses extended scene wavelength, focus and field diversity to estimate the wavefront across the set of apertures. The recovered wavefront is decomposed into the eigenmodes of the control matrix and actuators are moved to minimize the wavefront piston, tip and tilt. Each mirror’s actuators are 3 degrees of freedom, however, they do not move each of the mirrors about a point on each mirrors surface, thus the mapping from wavefront piston, tip/tilt to mirror piston, tip/tilt is not diagonal. We initially estimate this mapping but update it as part of wavefront sensing and control process using system identification techniques. We discuss the FIT testbed, wavefront control methodology, and show initial results from FIT.

Large deployable space telescopes like the James Webb Space Telescope (JWST) may have large errors after deployment that must be corrected in situ. One approach is to correct the errors successively. In this paper, we present a new approach to correct large phase aberrations during the coarse figuring stage of the initial alignment. Intensity data is obtained from multiple planes: pupil plane and additional planes in the nearfield of the pupil plane. The irradiance transport equation is used in a new manner used to estimate the phase aberrations at the pupil. The technique was demonstrated in the lab to estimate phase aberrations approaching 20 waves.

The SPICA (Space Infrared Telescope for Cosmology and Astrophysics), which is a Japanese astronomical infrared satellite project with a 3.5-m telescope, is scheduled for launch in early 2010s. The telescope is cooled down to 4.5 K in space by a combination of mechanical coolers with an efficient radiative cooling system. The SPICA telescope has requirements for its total weight to be lighter than 700 kg and for the imaging performance to be diffraction-limited at 5 µm at 4.5 K. Two candidate materials, silicon carbide (SiC) and carbon-fiber-reinforced SiC (C/SiC composite), are currently under investigation for the primary mirror. A monolithic mirror design will be adopted in both cases because of the technical feasibility and reliability. This paper reports the current design and status of the SPICA telescope together with some of our recent results on laboratory cryogenic tests for the SiC and C/SiC composite mirrors.

Placed on the L2 Lagrangian point, the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) will operate in the 5 to 200 μm wavelength range, at 4.5K. The large aperture telescope (3.5m diameter in a single piece) requires a strong manufacturing mastering, associated with high technical performances. The background acquired by EADS-Astrium (France) on the 3.5m Silicone Carbide Herschel Telescope is a key for the success of the SPICA development. EADS-Astrium has been awarded by the Japan Aerospace Exploration Agency (JAXA) and Sumitomo Heavy Industries to assess the feasibility of the 3.5m all SiC telescope through a design phase contract. The Telescope driving requirements are the large diameter of 3.5m especially critical for the manufacturing aspects, and the Wave Front Error which has to be kept below 350nm rms over a large temperature range from ambient to the operational temperature of 4.5K which requires a strong mastering of the distortions.

SiC (silicon carbide) lightweight mirrors are used for a large number of space telescopes, and SiC is also candidate as hopeful material for segmented mirrors of the next generation ground based telescopes from 30 to 100 m in diameter. However, an SiC mirror is difficult to shape because the material is very hard and brittle. We are developing an SiC mirror by means of the ELID (ELectrolytic In-process Dressing) grinding method, a grinding machine with rotary table of 800 mm in diameter and precision of 10 nm in control resolution, and computational simulations. The ELID grinding method is versatile for fabrications of very hard materials. In this study, we introduce test fabrications of SiC mirrors with 360 mm in diameter and equilateral triangle rib structures in the rear face. We developed a support tool with air actuator and oil pressure clamp for suppression of the mirror deformation for manufacturing of the thin mirror.

The technology associated with the use of silicon carbide (SiC) for high-performance mirrors has matured significantly over the past 10-20 years. More recently, the material has been considered for cryogenic applications such as space-based infrared telescopes. In light of this, NASA has funded several technology development efforts involving SiC mirrors. As part of these efforts, three lightweight SiC mirrors have been optically tested at cryogenic temperatures within the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC). The three mirrors consisted of a 0.50 m diameter carbon fiber-reinforced SiC, or C/SiC, mirror from IABG in Germany, a 0.51 m diameter SiC mirror from Xinetics, Inc., and a 0.25 m diameter SiC mirror from POCO Graphite, Inc. The surface figure error was measured interferometrically from room temperature (~290 K) to ~30 K for each mirror. The radius-of-curvature (RoC) was also measured over this range for the IABG C/SiC & Xinetics SiC mirrors. This paper will describe the test goals, the test instrumentation, and the test results for these cryogenic tests.

Many authors have endorsed the concept of assembly of large optics in space and have pointed out the technology needs for astronauts, infrastructure, robots and the observatories themselves. In this paper, we consider the technical issues associated with the integration and test in space of large optics during the next 15 years or so, when human activity is largely confined to low Earth orbit (LEO). We identify technical areas that need development and define a first version of the processes that might be used to create successful telescope missions that are tested in space. We identify a pathway that supports scalable solutions for very large systems necessary for imaging planets in other solar systems and other magnificent science. The investment in space integration and testing technology will return important dividends to designers of large space optics of the future. This approach to space optics testing is attractive because it overcomes the limits of ground testing associated with large test chambers, star simulators and the effects of gravity. It also directly benefits from, and supports, the technology and infrastructure investments about to be made by the new NASA Exploration Systems Enterprise, allowing both observatories and exploration missions to be assembled.

The National Aeronautics and Space Administration (NASA) is planning future deep space missions requiring space-based imaging reconnaissance of planets and recovery of imagery from these missions via optical communications. Both applications have similar requirements that can be met by a common aperture. The Johns Hopkins University Applied Physics Laboratory in collaboration with commercial and academic partners is developing a new approach to deploying and controlling large aperture (meter-class) optical telescopes on spacecraft that can be rapidly launched and deployed. The deployment mechanism uses flexible longeron struts to deploy the secondary. The active control system uses a fiber-coupled laser array near the focal plane that reflects four collimated laser beams off of the periphery of the secondary to four equally-disposed quad cell sensors at the periphery of the primary to correct secondary-to-primary misalignments and enable motion compensation. We describe a compensation technique that uses tip/tilt and piston actuators for quasi-static bias correction and dynamic motion compensation. We also describe preliminary optical tests using a commercial Schmidt-Cassegrain telescope in lieu of an ultra-lightweight composite Cassegrain, which is under development by Composite Mirror Applications, Inc. Finite element and ray trace modeling results for a 40 cm composite telescope design will also be described.

Inspired by a paper by Hyde (1999) (H99) we propose a 30-m diffractive Fresnel lens of ultra-high molecular-weight polyethylene (UHMW-PE) as the Primary Lens (L1) of a large cold far-IR and submillimetre space telescope. The design comprises Lens (L1) and Instrument (ISC) spacecraft 3 km apart, orbiting the Sun-Earth second Lagrangian point L2. In the Instrument S/C an off-axis Ritchey-Chretien Field Optical system (FO) re-images L1 onto a Fresnel corrector (FC). Achromatic over a bandpass λ/Δλ ~7.5 at a basic wavelength of 1.2mm and its harmonics, the design offers diffraction-limited performance from ~20 to ~700μm and a 1'x4' FOV. Positional tolerances appear to allow deployment of the lens by very simple means (we suggest using Shape Memory Alloys and pneumatic pressure). The most serious technical challenge may be material homogeneity. Behind an effective sunshade L1 should cool to ~10K by radiation to space in ~1y: its dominant heat source will be the zodiacal emission. GISMO resolves the FIR background at λ ~ 200μm: an all-sky survey to ~100μJy could in principle take <1y. GISMO should equal or outperform the 10m, 4K conceptual design for SAFIR (the Single-Aperture Far-IR and submillimetre mission, currently under study by NASA) in all observing modes and may offer a simpler (cheaper) and more capable alternative design “flavour” for this flagship future mission.

The solar optical telescope onboard the Solar-B is aimed to perform a high precision polarization measurements of the solar spectral lines in visible wavelengths to obtain, for the first time, continuous sets of high spatial resolution (~0.2arcsec) and high accuracy vector-magnetic-field map of the sun for studying the mechanisms driving the fascinating activity phenomena occurring in the solar atmosphere. The optical telescope assembly (OTA) is a diffraction limited, aplanatic Gregorian telescope with an aperture of Φ500mm. With a collimating lens unit and an active folding mirror, the OTA provides a pointing-stabilized parallel beam to the focal plane package (FPP) with a field of view of about 360x200arcsec. In this paper we identify the key technical issues of OTA for achieving the mission goal and describe the basic concepts in its optical, mechanical and thermal designs. The strategy to verify the in-orbit performance of the telescope is also discussed.

The SUNRISE balloon project is a high-resolution mission to study solar magnetic fields able to resolve the critical scale of 100 km in the solar photosphere, or about one photon mean free path. The Imaging Magnetograph eXperiment (IMaX) is one of the three instruments that will fly in the balloon and will receive light from the 1m aperture telescope of the mission. IMaX should take advantage of the 15 days of uninterrupted solar observations and the exceptional resolution to help clarifying our understanding of the small-scale magnetic concentrations that pervade the solar surface. For this, IMaX should act as a diffraction limited imager able to carry out spectroscopic analysis with resolutions in the 50.000-100.000 range and capable to perform polarization measurements. The solutions adopted by the project to achieve all these three demanding goals are explained in this article. They include the use of Liquid Crystal Variable Retarders for the polarization modulation, one LiNbO₃ etalon in double pass and two modern CCD detectors that allow for the application of phase diversity techniques by slightly changing the focus of one of the CCDs.

NASA has decided to move forward with two complementary Terrestrial Planet Finder (TPF) missions, a visible coronagraph and an infrared formation flying interferometer in collaboration with ESA. These missions are major missions in the NASA Office of Space Science Origins Theme. The primary science objectives of the TPF missions are to search for, detect, and characterize planets and planetary systems beyond our own Solar System, including specifically Earth-like planets.

The Terrestrial Planet Finder (TPF) seeks to revolutionize our understanding of humanity's place in the universe - by searching for Earth-like planets using reflected light, or thermal emission in the mid-infrared. Direct detection implies that TPF must separate planet light from glare of the nearby star, a technical challenge which has only in recent years been recognized as surmountable. TPF will obtain a low-resolution spectra of each planet it detects, providing some of its basic physical characteristics and its main atmospheric constituents, thereby allowing us to assess the likelihood that habitable conditions exist there. NASA has decided the scientific importance of this research is so high that TPF will be pursued as two complementary space observatories: a visible-light coronagraph and a mid-infrared formation-flying interferometer. The combination of spectra from both wavebands is much more valuable than either taken separately, and it will allow a much fuller understanding of the wide diversity of planetary atmospheres that may be expected to exist. Measurements across a broad wavelength range will yield not only physical properties such as size and albedo, but will also serve as the foundations of a reliable and robust assessment of habitability and the presence of life.

One of humanity's oldest questions is whether life exists elsewhere in the universe. The Terrestrial Planet Finder (TPF) mission will survey stars in our stellar neighborhood to search for planets and perform spectroscopic measurements to identify potential biomarkers in their atmospheres. In response to the recently published President's Plan for Space Exploration, TPF has plans to launch a visible-light coronagraph in 2014, and a separated-spacecraft infrared interferometer in 2016. Substantial funding has been committed to the development of the key technologies that are required to meet these goals for launch in the next decade. Efforts underway through industry and university contracts and at JPL include a number of system and subsystem testbeds, as well as components and numerical modeling capabilities. The science, technology, and design efforts are closely coupled to ensure that requirements and capabilities will be consistent and meet the science goals.

Terrestrial Planet Finder Coronagraph, one of two potential architectures, is described. The telescope is designed to make a visible wavelength survey of the habitable zones of at least thirty stars in search of earth-like planets. The preliminary system requirements, optical parameters, mechanical and thermal design, operations scenario and predicted performance is presented. The 6-meter aperture telescope has a monolithic primary mirror, which along with the secondary tower, are being designed to meet the stringent optical tolerances of the planet-finding mission. Performance predictions include dynamic and thermal finite element analysis of the telescope optics and structure, which are used to make predictions of the optical performance of the system

The Hubble Space Telescope (HST) provides the most versatile high contrast imaging capabilities of any current telescope. It allows high resolution, high dynamic range imaging from the near-ultraviolet to the near-infrared with both direct and coronagraphic methods. Its main advantage over ground-based systems is its stable point spread function. A review of the performance of HST as a high contrast imaging system is presented, including the abilities of all of the current HST cameras. Special emphasis is placed on items that are important to future missions (e.g. the Terrestrial Planet Finder), including mid-spatial frequency wavefront stability, coronagraphic system alignment, and observing methods.

The direct detection of Earthlike planets in the visible is a very challenging goal This paper describes a new concept for visible direct detection of Earths using a nulling interferometer instrument behind a 4m telescope in space. The basic concept is described along with the key advantages of the nulling interferometer over more traditional approaches, an apodized aperture telescope or coronagraph. In the baseline design, a 4 beam nuller produces a very deep theta^4 null. With perfect optics, the stellar leakage is less than 1e-11 of the starlight at the location of the planet. With diffraction limited (lambda/20) telescope optics suppression of the starlight to ~1e-10 would be possible.

Amplitude apodization of a telescope's pupil can be used to reduce the diffraction rings (Airy rings) in the PSF to allow high contrast imaging. Rather than achieving this apodization by selectively removing light at the edges of the pupil, we propose to produce the desired apodized pupil by redistributing the pupil's light. This lossless apodization concept can yield a high contrast PSF which allows the efficient detection of Earth-sized planets around stars at ~10pc with a 2m visible telescope in space. We review the current status of a JPL-funded study of this concept for the Terrestrial Planet Finder (TPF) mission, including a lab experiment and extensive computer simulations.

This paper summarizes our work designing optimal shaped pupils for high-contrast imaging. We show how any effective apodization can be created using shaped pupils and present a variety of both one-dimensional and azimuthally symmetric pupil shapes. Each pupil has its own performance advantage and we discuss the tradeoffs among various designs. Optimizations are typically performed by maximizing a measure of system throughput under constraints on contrast and inner working angle. We mention the question of sensitivity to aberrations. Controlling aberrations will be critical for any implementation of a planet-finding coronagraph. Finally, we present our first laboratory results testing a shaped pupil coronagraph.

In this work we study vector electromagnetic wave propagation in a visible-light coronagraph for applications to the design and analysis of Terrestrial Planet Finder (TPF). A visible light coronagraph in TPF requires detection of a terrestrial planet which is ~1010 dimmer than the central stellar source. Consequently, any theory used to design and analyze TPF requires accuracy better than 10-10 in intensity or 10-5 in electric field. Current coronagraphic approaches to TPF have relied on scalar diffraction theory. However, the vector nature of light requires a vector approach to the problem. In this study we employ a time-harmonic vector theory to study the electromagnetic field propagation through metallic focal plane occulting mask on dielectric substrate. We use parallelized edge-based vector finite element model to compute the wave propagation in a three-dimensional tetrahedral grid representing the geometry of the coronagraph. The edge-based finite element method overcomes the problem of modal propagation and rigorously enforces the field divergence to be zero. The reflectivity and transmittivity in the geometry are computed through the gold metal in various shapes using a planar incident beam. Subsequently, the near-field beam diffraction around the mask is investigated.

Predictions of contrast performance for the Eclipse coronagraphic telescope are based on computational models that are tested and validated with laboratory experience. We review recent laboratory work in the key technology areas for an actively-corrected space telescope designed for extremely high contrast imaging of nearby planetary systems. These include apodized coronagraphic masks, precision deformable mirrors, and coronagraphic algorithms for wavefront sensing and correction, as integrated in the high contrast imaging testbed at JPL. Future work will focus on requirements for the Terrestrial Planet Finder coronagraph mission.

To find evidence of life in the Universe outside our solar system is one of the most compelling and visionary adventures of the 21st century. The technologies to create the telescopes and instruments that will enable this discovery are now within the grasp of mankind. Direct imaging of a very faint planet around a neighboring bright star requires high contrast or a hypercontrast optical imaging system capable of controlling unwanted radiation within the system to one part in ten to the 11th. This paper identifies several physical phenomena that affect image quality in high contrast imaging systems. Polarization induced at curved metallic surfaces and by anisotropy in the deposition process (Smith-Purcell effect) along with beam shifts introduced by the Goos-Hachen effect are discussed. A typical configuration is analyzed, and technical risk mitigation concepts are discussed.

The telescope for a Terrestrial Planet Finder (TPF) coronagraph has exceedingly stringent phase and amplitude requirements, especially for the large, monolithic primary mirror (possibly as large as 4 meters by 10 meters). The pertinent derived engineering requirements will be summarized based on a described set of science objectives to simulate solar type stars and their companion earth-size planets. We will also present an optical design for a sub-scale coronagraphic testbed as an essential step in examining the system sensitivities. The major subassemblies of the testbed include: 1) a star/planet simulator that affords variation in contrast, adjustable relative separation and angular orientation and 2) a relay optical system representative of a TPF 3-mirror telescope that allows the imposition of known optical perturbations over the desired wavefront spatial frequencies. We will compare these TPF testbed mirror wavefront requirements with levels recently achieved on the Advanced Mirror System Demonstrator and planned for the James Webb Space Telescope (JWST).

Fourier transform imaging spectroscopy can be performed with a segmented-aperture telescope or a multiple-telescope array using the subaperture piston control mechanisms. Spectrum recovery from intensity measurements is analyzed for a general aperture configuration. The spatial transfer functions of the recovered spectral images are shown to vanish necessarily at the DC spatial frequency. This poses an interesting image reconstruction problem as the recovered spectral data is missing low spatial-frequency content. Results of a band-by-band reconstruction of simulated data are presented where the low spatial frequency data is reconstructed by maximizing a sharpness metric based on the spatial derivatives of the object estimate.

The Microlensing Planet Finder (MPF) is a proposed Discovery mission that will complete the first census of extrasolar planets with sensitivity to planets like those in our own solar system. MPF will employ a 1.1m aperture telescope, which images a 1.3 sq. deg. field-of-view in the near-IR, in order to detect extrasolar planets with the gravitational microlensing effect. MPF's sensitivity extends down to planets of 0.1 Earth masses, and MPF can detect Earth-like planets at all separations from 0.7AU to infinity. MPF's extrasolar planet census will provide critical information needed to understand the formation and frequency of extrasolar planetary systems similar to our own.

The atmospheres of planets orbiting other stars may be studied by the technique of transit spectroscopy. This technique needs a very high SNR, so large space telescopes are needed, and bright target stars must be found. This paper uses planetary atmosphere models to discuss the SNR performance required to achieve specific science goals for both giant Jupiter-like planets and for small Earth-like planets. It discusses the space telescopes to survey bright stars to find suitable target stars, and the designs of large space telescopes to perform the transit spectroscopy.

The Extrasolar Planetary Imaging Coronagraph (EPIC) will provide the first direct measurements of a broad range of fundamental physical characteristics of giant planets in other solar systems. These characteristics include orbital inclination, mass, brightness, color, the presence (or absence) of CH4 and H2O, and orbital or rotational-driven variability. EPIC utilizes a 1.5 meter telescope coupled to a Visible Nulling Coronagraph to achieve these science goals. EPIC has been proposed as a Discovery Mission.

Mission requirements, the baseline design, and optical systems budgets for the SuperNova/Acceleration Probe (SNAP) telescope are presented. SNAP is a proposed space-based experiment designed to study dark energy and alternate explanations of the acceleration of the universe’s expansion by performing a series of complementary systematics-controlled astrophysical measurements. The goals of the mission are a Type Ia supernova Hubble diagram and a wide-field weak gravitational lensing survey. A 2m widefield three-mirror telescope feeds a focal plane consisting of 36 CCDs and 36 HgCdTe detectors and a high-efficiency, low resolution integral field spectrograph. Details of the maturing optical system, with emphasis on structural stability during terrestrial testing as well as expected environments during operations at L2 are discussed. The overall stray light mitigation system, including illuminated surfaces and visible objects are also presented.

The Destiny space telescope is a candidate architecture for the NASA-DOE Joint Dark Energy Mission (JDEM). This paper describes some of the scientific and observational issues that will be explored as part of our mission concept study. The Destiny ~1.8-meter near-infrared (NIR) grism-mode space telescope would gather a census of type Ia and type II supernovae (SN) over the redshift range 0.5 < z < 1.7 for measuring the expansion rate of the Universe as a function of time and characterizing the nature of dark energy. The central concept is a wide-field, all-grism NIR survey camera. Grism spectra with 2-pixel resolving power R~70-100 will provide broad-band spectrophotometry, redshifts, SN classification, as well as valuable time-resolved diagnostic data for understanding the SN explosion physics. Spectra from all objects within the 1° x 0.25° FOV will be obtained on a large HgCdTe focal plane array. Our methodology requires only a single mode of operation, a single detector technology, and a single instrument.

The Kepler Mission is a search for terrestrial planets specifically designed to detect Earth-size planets in the habitable zones of solar-like stars. In addition, the mission has a broad detection capability for a wide range of planetary sizes, planetary orbits and spectral types of stars. The mission is in the midst of the developmental phase with good progress leading to the preliminary design review later this year. Long lead procurements are well under way. An overview in all areas is presented including both the flight system (photometer and spacecraft) and the ground system. Launch is on target for 2007 on a Delta II.

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an infrared astronomical satellite with 3.5m cooled telescope which is very powerful in mid- and far-infrared observations and makes complementary role to JWST and Herschel. SPICA will be launched at ambient temperature without any cryogen into the Sun-Earth L2 orbit and cooled down in space to 4.5K with use of efficient radiative cooling and mechanical coolers. The present status of SPICA and the developments of the satellite system are reported.

SAFIR is a large (10 m-class), cold (4-10 K) space telescope for wavelengths between 20 microns and 1 mm. It will provide sensitivity a factor of a hundred or more greater than that of Spitzer and Herschel, leveraging their capabilities and building on their scientific legacies. Covering this scientifically critical wavelength regime, it will complement the expected wavelength performance of the future flagship endeavors JWST and ALMA. This vision mission will probe the origin of stars and galaxies in the early universe, and explore the formation of solar systems around nearby young stars. Endorsed as a priority by the Decadal Study and successive OSS roadmaps, SAFIR represents a huge science need that is matched by promising and innovative technologies that will allow us to satisfy it. In exercising those technologies it will create the path for future infrared missions. This paper reviews the scientific goals of the mission and promising approaches for its architecture, and considers remaining technological hurdles. We review how SAFIR responds to the scientific challenges in the OSS Strategic Plan, and how the observatory can be brought within technological reach.

The far-infrared (FIR) wavelength regime has become of prime importance for astrophysics. Observations of ionic, atomic and molecular lines, many of them present in the FIR, provide important and unique information on the star and planet formation process occurring in interstellar clouds, and on the lifecycle of gas and dust in general. As these regions are heavily obscured by dust, FIR observations are the only means of getting insight in the physical and chemical conditions and their evolution. These investigations require, besides high spectral, also high angular resolution in order to match the small angular sizes of star forming cores and circum-stellar disks. We present here a mission concept, ESPRIT, which will provide both, in a wavelength regime not accessible from ground by ALMA (Atacama Large Millimeter Array), nor with JWST (James Webb Space Telescope).

Ultimately, after the Single Aperture Far-IR (SAFIR) telescope, astrophysicists will need a far-IR observatory that provides angular resolution comparable to that of the Hubble Space Telescope. At such resolution galaxies at high redshift, protostars, and nascent planetary systems will be resolved, and theoretical models for galaxy, star, and planet formation and evolution can be subjected to important observational tests. This paper updates information provided in a 2000 SPIE paper on the scientific motivation and design concepts for interferometric missions SPIRIT (the Space Infrared Interferometric Telescope) and SPECS (the Submillimeter Probe of the Evolution of Cosmic Structure). SPECS is a kilometer baseline far-IR/submillimeter imaging and spectral interferometer that depends on formation flying, and SPIRIT is a highly-capable pathfinder interferometer on a boom with a maximum baseline in the 30 - 50 m range. We describe recent community planning activities, remind readers of the scientific rationale for space-based far-infrared imaging interferometry, present updated design concepts for the SPIRIT and SPECS missions, and describe the main issues currently under study. The engineering and technology requirements for SPIRIT and SPECS, additional design details, recent technology developments, and technology roadmaps are given in a companion paper in the Proceedings of the conference on New Frontiers in Stellar Interferometry.

The Spitzer Space Telescope, the last of the four Great Observatories commissioned by the National Aeronautics and Space Administration, was successfully launched on August 25, 2003 from Kennedy Space Center. The engineering systems for Spitzer were developed by the Jet Propulsion Laboratory, Lockheed Martin Space Systems Company, and Ball Aerospace & Technology Corp. This paper provides an overview of Spitzer, a technical description of all the engineering subsystems, and the associated challenges involved in developing them to satisfy the mission requirements. In addition, this paper describes the performance of the engineering subsystems during the In-Orbit Checkout phase, the Science Verification phase, and the early portions of the Nominal Mission.

The instruments of the Spitzer Space Telescope are cooled directly by liquid helium, while the optical system is cooled by helium vapor. The greater the power dissipation into the liquid helium, the more vapor is produced, and the colder the telescope. Observations at shorter wavelengths do not require telescope temperatures as low as those required at longer wavelengths. By varying the telescope temperature with observing wavelength, we are extending the mission lifetime by an estimated 9%.

The Spitzer Space Telescope is an 85-cm telescope with three cryogenically cooled instruments. Following launch, the observatory was initialized and commissioned for science operations during the in-orbit checkout (IOC) and science verification (SV) phases, carried out over a total of 98.3 days. The execution of the IOC/SV mission plan progressively established Spitzer capabilities taking into consideration thermal, cryogenic, optical, pointing, communications, and operational designs and constraints. The plan was carried out with high efficiency, making effective use of cryogen-limited flight time. One key component to the success of the plan was the pre-launch allocation of schedule reserve in the timeline of IOC/SV activities, and how it was used in flight both to cover activity redesign and growth due to continually improving spacecraft and instrument knowledge, and to recover from anomalies. This paper describes the adaptive system design and evolution, implementation, and lessons learned from IOC/SV operations.

This paper discusses an accurate and efficient method for focal plane survey that was used for the Spitzer Space Telescope. The approach is based on using a high-order 37-state Instrument Pointing Frame (IPF) Kalman filter that combines both engineering parameters and science parameters into a single filter formulation. In this approach, engineering parameters such as pointing alignments, thermomechanical drift and gyro drifts are estimated along with science parameters such as plate scales and optical distortions. This integrated approach has many advantages compared to estimating the engineering and science parameters separately. The resulting focal plane survey approach is applicable to a diverse range of science instruments such as imaging cameras, spectroscopy slits, and scanning-type arrays alike. The paper will summarize results from applying the IPF Kalman filter to calibrating the Spitzer Space Telescope focal plane, containing the MIPS, IRAC, and the IRS science instrument arrays.

The Spitzer Space Telescope was successfully launched on August 25th, 2003. After a 90 day In Orbit Checkout and Science Verification period, Spitzer began its five and one half year mission of science observations at wavelengths ranging from 3.6 to 160 microns. Early results from Spitzer show the observatory performing exceptionally well, meeting performance requirements in all areas. The California Institute of Technology is the home for the Spitzer Science Center (SSC). The SSC is responsible for selecting observing proposals, providing technical support to the science community, performing mission planning and science observation scheduling, instrument calibration and performance monitoring during operations, and production of archival quality data products. This paper will address the performance of the Spitzer science operations for the first nine months of the mission, covering science efficiency, science planning and scheduling metrics, data through-put and processing durations, system improvements, and science community interest. This work was performed at the California Institute of Technology under contract to the National Aeronautics and Space Administration.

We describe the process by which the NASA Spitzer Space Telescope (SST) Cryogenic Telescope Assembly (CTA) was brought into focus after arrival of the spacecraft in orbit. The ground rules of the mission did not allow us to make a conventional focus sweep. A strategy was developed to determine the focus position through a program of passive imaging during the observatory cool-down time period. A number of analytical diagnostic tools were developed to facilitate evaluation of the state of the CTA focus. Initially, these tools were used to establish the in-orbit focus position. These tools were then used to evaluate the effects of an initial small exploratory move that verified the health and calibration of the secondary mirror focus mechanism. A second large move of the secondary mirror was then commanded to bring the telescope into focus. We present images that show the CTA Point Spread Function (PSF) at different channel wavelengths and demonstrate that the telescope achieved diffraction limited performance at a wavelength of 5.5 μm, somewhat better than the level-one requirement.

The first six months of flight data from the Multiband Imaging Photometer for Spitzer (MIPS) were used to test MIPS reduction algorithms based on extensive preflight laboratory data and modeling. The underlying approach for the preflight algorithms has been found to be sound, but some modifications have improved the performance. The main changes are scan mirror dependent flat fields at 24 μm, hand processing to remove the time dependent stim flash latents and fast/slow response variations at 70 μm, and the use of asteroids and other sources instead of stars for flux calibration at 160 μm due to a blue "leak." The photometric accuracy of flux measurements is currently 5%, 10%, and 20% at 24, 70, and 160 μm, respectively. These numbers are expected to improve as more flight data are analyzed and data reduction algorithms refined.

Prior to launch, the Spitzer Space Telescope (SST) secondary focus mechanism was set to a predicted desired in-orbit focus value. This predicted setting, determined from double-pass cold chamber measurements and calculated ground-to-orbit corrections, had an uncertainty greater than the required in-orbit focus accuracy. Because of concern about the potential for failure in a cryogenic mechanism affecting all Spitzer instruments, it was required that any focus correction be made in a set of moves directly from the initial to the desired setting. The task of determining the required focus moves fell to IRAC (Infrared Array Camera), the instrument most affected by and sensitive to defocus. To determine the focus directly from examining images at a fixed focus, we developed two methods, "Simfit" and "Focus Diversity" (W. F. Hoffmann, et. al.1). Simfit finds the focus by obtaining the best match between observed images and families of simulated images at a range of focus settings. Focus Diversity utilizes the focal plane curvature to find the best fit of the varied image blur over the focal plane to a model defocus curve. Observations of a single star at many field locations in each of the four IRAC bands were analyzed before and during the refocus activity. The resulting refocus moves brought the focus close to the specified requirement of within 0.3 mm from the desired IRAC optimum focus. This is less than a "Diffraction Focus Unit" (λx(f/²)) of 0.52 mm at the SST focus at the shortest IRAC band (3.58 microns). The improvement in focus is apparent in both the appearance and the calculated noise-pixels of star images.

This paper gives a description of the mission design, launch, orbit, and navigation results for the Spitzer space telescope mission. The Spitzer telescope was launched by the Delta II Heavy launch vehicle into a heliocentric Earth trailing orbit. This orbit is flown for the first time and will be used by several future astronomical missions such as Kepler, SIM, and LISA. This paper describes the launch strategy for a winter versus a summer launch and how it affects communications. It also describes how the solar orbit affects the design and operations of the Observatory. It describes the actual launch timeline, launch vehicle flight performance, and the long term behavior of the as flown orbit. It also provides the orbit knowledge from in-flight navigation data.

We describe the astronomical observation template (AOT) for the Infrared Array Camera (IRAC) on the Spitzer Space Telescope (formerly SIRTF, hereafter Spitzer). Commissioning of the AOTs was carried out in the first three months of the Spitzer mission. Strategies for observing fixed and moving targets are described, along with the performance of the AOT in flight. We also outline the operation of the IRAC data reduction pipeline at the Spitzer Science Center (SSC) and describe residual effects in the data due to electronic and optical anomalies in the instrument.

The Spitzer Space Telescope Infrared Array Camera (IRAC) is a four-channel camera that uses two pairs of 256 x 256 pixel InSb and Si:As IBC detectors to provide simultaneous images at 3.6, 4.5, 5.8, and 8 microns. IRAC experiences a flux of cosmic rays that produce transient events in images from each of the arrays, with 5-7 pixels per second being affected in an IRAC integration. The vast majority of these transient events can be adequately characterized so they can be effectively detected and flagged by a pipeline software module. However, because of the nature of the arrays and their arrangement in the camera structure, a small fraction of the cosmic ray hits on IRAC produce transients with unusual morphologies which cannot be characterized in a general way. We present nominal cosmic ray rates observed for IRAC on-orbit and rates observed during a period of elevated solar proton flux following a series of X-class solar flares in late 2003. We also present a guide for observers to help identify unusual transient events in their data. We comment on the physical nature of the production of many o9f these unusual transients and how this mechanism differs from the production of "normal" transient events.

The Infrared Array Camera (IRAC) on Spitzer Space Telescope includes four Raytheon Vision Systems focal plane arrays, two with InSb detectors, and two with Si:As detectors. A brief comparison of pre- flight laboratory results vs. in-flight performance is given, including quantum efficiency and noise, as well as a discussion of irregular effects, such as residual image performance, "first frame effect", "banding", "column pull-down" and multiplexer bleed. Anomalies not encountered in pre-flight testing, as well as post-flight laboratory tests on these anomalies at the University of Rochester and at NASA Ames using sister parts to the flight arrays, are emphasized.

The Infrared Array Camera (IRAC) on board the Spitzer Space Telescope uses two dichroic beamsplitters, four interference filters, and four detector arrays to acquire images in four different channels with nominal wavelengths of 3.6, 4.5, 5.8, and 8 μm for channels 1 through 4 respectively. A ray-tracing analysis of the IRAC optical system indicates a distribution of angles that is position-dependent at each optical element and the focal-plane arrays. For the band-pass filters in channels 1 and 2, the angle distribution relative to the filter surface normal is 0-28°, whereas for channels 3 and 4, the distribution is from 30° to 58°. Since these angle variations will cause changes in the center-band wavelengths for these interference filters that needed to be accounted for, we performed spectral performance measurements as a function of the angle of incidence on witness samples corresponding to each of the four filters and the two beamsplitters in the IRAC instrument. These measurements were done in the 2-10 μm wavelength range and at the temperature of 5 K, which is near the operating temperature of IRAC. Based on these filter measurements, we also performed an analysis of the pass-band wavelength distributions as a function of position on the instrument focal-plane array detectors. This information is necessary to attain the highest possible photometric accuracy when using IRAC for astronomical observations.

The pointing calibration and reference sensor (PCRS) of the Spitzer Space Telescope (SST) consists of two 4 by 4 pixel visible band detectors plus associated electronics per redundant side. Located in the cryogenic multi instrument chamber of the science telescope system, these detectors, which have a field of view of 40 by 40 arcsec each, define the telescope coordinate frame. Employing guide stars in the range from 7 to 10 magnitude, the PCRS is used, among other things, for measuring the alignment of the active external autonomous star tracker twice per day. To ensure adequate accuracy, the standard radial position error of the guide stars needs to be less than 120 milliarcsec (mas) out to J2009.5. Initial selection of guide star candidates is performed using the Tycho, Tycho-2, Hipparcos, and Tycho Double Star catalogs. To obtain sufficient depth, the 2MASS PSC, USNO A2.0, 2MASS XSC, and PGC catalogs are used for computing the disturbing effect of neighboring objects. In addition, the DSS is employed for determining the perturbing effect of the sky background for each of the guide star candidates. The paper describes the guide star requirements, the methodology used for computing star position error due to neighboring objects and sky background, and the staged development approach that resulted in a ground-based catalog with 196,087 high-quality guide stars for the PCRS.

A Hubble Space Telescope Wide Field Camera 3 (WFC3) CCD detector was tested for radiation effects while operating at -83C. The goal of the experiment was to evaluate the introduction and annealing rates of hot pixels and to assess the dynamics of that process. The device was irradiated while cold and warmed to +30°C for a 4 hour soak, then cooled back down to -83°C. Hot pixel populations were tracked during warm up and cool down. The results showed that the hot pixels begin to anneal around -40°C and the anneal process was largely completed before the detector reached +30°C. It was also found that, although a large fraction of the hot pixels dropped below the threshold, they remained warmer than the remaining population.

The overall temperature environment of the NICMOS detectors onboard the Hubble Space Telescope (HST) has changed since initial operation in 1997. These changes include an increased detector operating temperature and increases of the temperatures at the aft end of HST and the NICMOS enclosure. The aft shroud of HST is warmer due to on-going degredation of the MultiLayer Insullation (MLI) and increased power from the instruments installed during Servicing Mission 3B (The Advanced Camera for Surveys (ACS) and the NICMOS Cryocooling System (NCS)). This warms the NICMOS fore-optics, affecting the thermal background in long wavelength camera 2 and camera 3 filters. These trends are well described by both direct engineering data from the telescope and thermal emission models which are able to estimate the total thermal contribution to an exposure by knowing the etendue, reflectance, emissivity and temperature of each of the optics. This work reflects the first evidence of spacecraft heating directly affecting science observations onboard HST.

The Wide Field Camera 3 (WFC3) instrument was designed and built to replace the Hubble Space Telescope (HST) instrument Wide Field and Planetary Camera 2 (WF/PC2) and to provide improved ultra-violet through near infrared imaging capability over the extended HST mission. We describe the optical component integration, alignment, and performance testing of the optical bench assembly.

The Wide Field Camera 3 (WFC3) instrument was designed and built to replace the Hubble Space Telescope (HST) instrument Wide Field and Planetary Camera 2 (WFPC2) and to provide improved ultra-violet through near infra-red imaging capability during the extended HST mission. The WFC3 instrument consists of a two-channel instrument providing diffraction-limited imaging across an average 160 arc second square field of view over 200 to 1000 nm on a 4k x 4k Si detector and an average 135 arc second square field of view over 850 to 1700 nm on a 1k x 1k HgCdTe detector. We describe the optical design and predicted performance of WFC3.

The Herschel Space Observatory is a passively cooled 3.5 m telescope (T_mirror < 90 K) scheduled for launch in 2007. One of its three scientific instruments is PACS (Photoconductor Array Camera and Spectrometer) which will carry out astronomical observations in the wavelength range of 57 μm to 210 μm with unprecedented sensitivity and spatial resolution. PACS has two cameras for imaging spectroscopy in two wavelength bands from 57 μm to 130 μm and 130 μm to 210 μm. Both cameras are built up from 25 linear arrays, each with 16 detector pixels consisting of Gallium doped Germanium crystals. By stressing these crystals with a bolt­spring mechanism, the desired cut­-off wavelengths of ~ 127 μm and ~ 205 μm can be reached. The detectors are operated at temperatures of ~ 2 K and read out by cryogenic readout electronics (CRE), featuring pre­amplifiers and multiplexers. Test facilities have been designed and built up at MPIA, Heidelberg, and MPE, Garching, in order to characterize and calibrate the spectrometer cameras before integration into the instrument. Both test facilities have a cryostat cooled by superfluid liquid helium. While the MPE facility uses an internal cold black body to illuminate the camera, the facility at MPIA makes use of an external black body and cold attenuation filters. Tests of the qualification models of the spectrometer cameras show that the detector responsivity is ~ 8 A/W and ~ 40 A/W for the low and high stressed detectors respectively, surpassing the requirements. The NEP is currently limited by CRE readout noise and will be improved with the new generation of FM CREs. Ionizing irradiation significantly increases the detector responsivity, which might make it necessary to operate them with a lower bias voltage. On the other hand, radiation effects can be reliably cured by a combination of bias boosts and infrared flashes.

The SPectral and Photometric Imaging REceiver (SPIRE) will be launched in 2007 as one of three instruments on ESA's sub-millimetric space telescope Herschel. It covers the 200-670 micron spectral range with a three-band, 4'x8' field-of-view (FOV) photometer and a dual-band, 2.6' diameter FOV imaging Fourier transform spectrometer. Alignment verification of the instrument is accomplished optically by means of OGSE based on classical alignment telescopes and specially designed equipment. The main purpose of this process is to make sure the internal instrument cold stop is aligned with the telescope exit pupil, and that it stays aligned as the instrument is taken down to its 4K operating temperature. Optical alignment verification also includes measurement of pupil imaging quality and characterisation of the instrument wavefront error. For the latter, a Hartmann test is implemented, allowing estimation of the main aberration terms and comparison with the ideal instrument. This paper describes the philosophy of the alignment plan and presents the main results obtained during alignment of the structural and thermal model.

The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments on the European Space Agency's Herschel mission. At the start of 2004 the Cryogenic Qualification Model (CQM) of SPIRE was tested with the aim of verifying the instrument system design and evaluating key performance parameters. We present a description of the test facility, an overview of the instrument tests carried out on the CQM, and the first results from the analysis of the test data. Instrument optical efficiency and detector noise levels are close to the values expected from unit-level tests, and the SPIRE instrument system works well, with no degradation in performance from stray light, electromagnetic interference or microphonically induced noise. Some anomalies and imperfections in the instrument performance, test set-up, and test procedures have been identified and will be addressed in the next test campaign.

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESA's Herschel mission. The spectroscopic capabilities of SPIRE are provided by an imaging Fourier transform spectrometer (IFTS). A software simulator of the IFTS has been constructed to predict the instrument performance under operational conditions. We describe in detail the design and integration of the simulator. Examples of simulated data of astronomical targets are presented.

This paper describes the design and implementation of the on-board data compression and reduction software for the HERSCHEL/PACS mission (see also A. Poglitsch et al. in this conference) of the European Space Agency (ESA). Lead by the Max Planck Institute for Extraterrestric Physics (MPE) in Garching, Austrian scientists and software engineers participate in the development of the on-board software for the Photodetector Array Camera and Spectrometer (PACS). The novel detectors' high data rates in addition to the distant spacecraft orbit force us to carry out irreversible reduction steps that are normally done on ground and to use highly specialized compression algorithms for lossless compression of the reduced science and the header data.

SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to be flown on ESA's Herschel Space Observatory. It contains a three-band submillimetre camera and an imaging Fourier transform spectrometer, and uses arrays of feedhorn-coupled bolometric detectors operating at a temperature of 300 mK. Detailed software simulators are being developed for the SPIRE photometer and spectrometer. The photometer simulator is based on an adaptable modular representation of the relevant instrument and telescope subsystems, and is designed to produce highly realistic science and housekeeping data timelines. It will be used for a variety of purposes, including instrument characterisation during ground testing and in orbit, testing and optimisation of operating modes and strategies, evaluation of data reduction software using simulated data streams (derived by "observing" a simulated sky intensity distribution with the simulator), observing time estimation, and diagnostics of instrument systematics. In this paper we present the current status of the photometer simulator and the future development and implementation strategy.

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three instruments on the European Space Agency's Herschel mission. A detailed understanding of the SPIRE instrument is essential for a successful mission. In particular, it is important to characterize both the in-band spectral profile, and any out-of-band spectral leaks, which would severely degrade performance. A test Fourier Transform Spectrometer (TFTS), with its braod spectral coverage and intermediate spectral resolution, was selected for the spectral characterization of SPIRE. The integration of the TFTS with the existing Ground Support Equipment of the Hershel/SPIRE test facility at the Rutherford Appleton Laboratory imposed several mechanical, optical, electrical, and software constraints. In this paper we describe the design and implementation of the TFTS, and present preliminary results from its use in the SPIRE verification and performance tests.

The integration of the SPIRE BSM hardware and its controlling software used the hardware-in-the-loop dSPACE system to enable fast development of the control system and separate site development of the hardware and software. After this separate development, integration of the prototypes at one of the sites was completely successful. Similar development of the SMECm hardware is also described.

We present pre-flight performance of a monolithic Ge:Ga array detector for Far-Infrared Surveyor (FIS) onboard the ASTRO-F satellite. The primary purpose of the ASTRO-F mission is to perform an all-sky survey in four photometric bands form 50-200 um. For shorter half of this spectral range, 50-110 um, we have developed the monolithic Ge:Ga array which is directly connected to a cryogenic readout electronics (CRE) with the indium-bump technology. In order to investigate the point-source detectability in the survey observation, we carry out a simulation experiment. The experiment was done by taking a image of moving pinholes located on the focal plane of the FIS optics. A clear image without any distortion was obtained, but the size of point source image is slightly larger than expected. We estimate the detection limit in the survey observation by taking account of all detector properties including the imaging performance. The results show that the detector sensitivity is sufficiently high to meet the requirement of the ASTRO-F mission.

We have developed the imaging Fourier Transform Spectrometer (FTS) for the FIS (Far-Infrared Surveyor) onboard the ASTRO-F satellite. A Martin-Puplett interferometer is adopted to achieve high optical efficiency in a wide wavelength range. The total optical efficiency of this spectrometer is achieved 40-80% of the ideal value which is 25% of the incident flux. The wavelength range of 50-200μm is covered with two kinds of detector; the monolithic Ge:Ga photoconductor array for short wavelength (50-110μm) and the stressed Ge:Ga photoconductor array for long wavelength (110-200μm). The spectral resolution expected from the maximum optical path difference is 0.18cm^-1. In order to evaluate the spectral resolution of the FTS, we measured absorption lines of H₂O in atmosphere using the optics of the FTS with a bolometer at the room temperature. The measured line widths are consistent with the expected instrumental resolution of 0.18 cm-1. Some spectral measurements at the cryogenic temperature were carried out by using cold blackbody sources whose temperatures are controlled in a range from 20 to 50 K. The derived spectra considering with the spectral response of the system are consistent with expected ones. Spectroscopic observations with the FTS will provide a lot of astronomical information; SED of galaxies detected in the all sky survey and the physical diagnostics of the interstellar matter by using the excited atomic or molecular lines.

MIR-L is a 12-26μm channel of Infrared Camera(IRC) onboard ASTRO-F. The camera employs a refractive optics which consists of 5 lenses (CsI - CsI - KRS-5 - CsI - KRS-5) and a large format Si:As IBC array detector (256 x 256 pixels). The design concept is to realize a wide field of view with a compact size. It has 2 observing modes: a wide field imaging with a field of view of 10.7 x 10.2arcmin² or a pixel resolution of 2.5 x 2.4arcsec²/pixel in 3 bands (12.5-18μm, 14-26μm, 22-26μm), and low resolution spectroscopy with a spectral resolution R = λ/Δλ ≈40 in 2 bands 11-19μm,18-26μm). It also has a small slit to adapt for spectroscopic observations of extended sources. We describe the current design of the optics and the mounting architecture of MIR-L and evaluation of the optical performance at cryogenic temperatures.

We present the latest results of our fast physical optics simulations of the ESA PLANCK HFI beams. The main beams of both polarized and non-polarized channels have been computed with account of broad frequency bands for the final design and positions of the HFI horns. Gaussian fitting parameters of the broadband beams have been presented. Beam polarization characteristics and horn defocusing effects have been studied.

This is a continuation of a series of papers on the integrated modeling activities for the James Webb Space Telescope (JWST). Starting with the linear optical model discussed in part one, and using the optical sensitivities developed in part two, we now assess the optical image motion and wavefront errors from the structural dynamics. This is often referred to as “jitter” analysis. The optical model is combined with the structural model and the control models to create a linear structural/optical/control model. The largest jitter is due to spacecraft reaction wheel assembly disturbances which are harmonic in nature and will excite spacecraft and telescope structural. The structural/optic response causes image quality degradation due to image motion (centroid error) as well as dynamic wavefront error. Jitter analysis results are used to predict imaging performance, improve the structural design, and evaluate the operational impact of the disturbance sources.

The James Web Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2011. This is a continuation of a series of papers on modeling activities for JWST. The structural-thermal-optical, often referred to as "STOP", analysis process is used to predict the effect of thermal distortion on optical performance. The benchmark STOP analysis for JWST assesses the effect of an observatory slew on wavefront error. Temperatures predicted using geometric and thermal math models are mapped to a structural finite element model in order to predict thermally induced deformations. Motions and deformations at optical surfaces are then input to optical models, and optical performance is predicted using either an optical ray trace or a linear optical analysis tool. In addition to baseline performance predictions, a process for performing sensitivity studies to assess modeling uncertainties is described.

The James Webb Space Telescope (JWST) is a large space based astronomical telescope that will operate at cryogenic temperatures, and utilizes a segmented primary mirror with active control. To achieve the science goals for JWST, the image quality over a wide spectral range is necessary. Several metrics related to the quality of the PSF have been used to capture the optical requirement to meet the science goals. We will present the requirements allocation from Point Spread Function Metrics to spatial frequency content in Wave Front Error allocations that reflect the unique forms associated with the active control aspects of the design.

The Canadian contribution to the James Webb Space Telescope (JWST) mission will be the Fine Guidance Sensor (FGS), incorporating a science-observing mode using tunable filters. We describe here the requirements, the opto-mechanical design concept and bread-board test results for the JWST FGS tunable filters. The FGS requires two continuously tunable filters over the wavelength ranges 1.2 - 2.4 microns and 2.4 - 4.8 microns each having a spectral resolution in the range of R~70 to 200. The selected implementation uses dielectric coated Fabry-Perot etalon plates with a small air gaps. The design finesse is ~30 and the filters are used in 3rd order. The operating temperature is ~35K. Current coating designs provide implementations that require only five blocking filters in each wavelength range to suppress unwanted orders. The filters will be scanned via the use of low voltage piezo-electric transducers. We present results from cryogenic tests of coating samples, PZT actuators and a structural model. The PZT actuators were found have a displacement of ~3.3 microns at 30K with an applied voltage of 125V, more than sufficient for the required scan of the Fabry-Perot plate spacing. The prototype etalon coating was found to be very stable cryogenically, having a measured change of transmission of only ~1% at 77K. The same coating on a 12.7 mm thick substrate, similar to that planned for the filter, was found to have a 18 nm peak-to-valley surface figure change when cooled to 30K. These results demonstrate that the development of tunable filters for the JWST FGS is on track to meet the technology readiness requirements of the program.

The James Webb Space Telescope (JWST) is a passively cooled, 6.5m aperture class telescope, optimized for diffraction-limited performance in the near-infrared wavelength region (1 - 5 μm). JWST will be capable of high-resolution imaging and spectroscopy and will carry a scientific payload consisting of three scientific instruments. One of the instruments - NIRSpec - is a near-infrared, multi-object, dispersive spectrograph, which will be provided by ESA. EADS Astrium and its subcontractors have been involved in all ESA instrument studies for JWST. The actual NIRSpec design has evolved during three years of studying of different spectrometer design and performance options. Basic feature of the current design is the all ceramic material concept for the instrument structure and mirror optics; both were successfully tested on component level. This paper presents our NIRSpec design concept and its predicted performance.

The operability requirements of NASA's James Webb Space Telescope (JWST) impose specific challenges on radiation effects mitigation and analysis. For example, the NIRSpec Instrument has the following requirements: •The percentage of pixels defined as operable for target acquisition shall not be less than 97% (TBR) (goal 99%) of the total number of pixels... An inoperable pixel is: ο A dead pixel: a pixel with no radiometric response o A noisy pixel: a pixel with a total noise greater than 21 e-, per Fowler 8 exposure •The percentage of pixels defined as operable for science observations shall not be less than 92% (TBR) (goal 98%) of the total number of pixels... An inoperable pixel is: ο A dead/low-DQE pixel: a pixel deviating by >30% from the DQE mean value ο A noisy pixel: a pixel with a total noise greater than 12 e- (goal 9e-). With these performance requirements and operation in space, the radiation environment from galactic cosmic rays (GCR), energetic solar particles, and activation of spacecraft materials can contribute significantly to the number of inoperable pixels. The two most important issues to date are radiation-induced transient effects and hot pixels. This paper focuses on the methods used to assess the impact of ionizing radiation induced transients on the HgCdTe SCA selected by JWST. Hot pixel effects in these detectors has been previously presented. Both effects are currently under investigation.

The Near-Infrared Spectrograph (NIRSpec) is the James Webb Space Telescope’s primary near-infrared spectrograph. NASA is providing the NIRSpec detector subsystem, which consists of the focal plane array, focal plane electronics, cable harnesses, and software. The focal plane array comprises two closely-butted λ_co ~ 5 μm Rockwell HAWAII-2RG sensor chip assemblies. After briefly describing the NIRSpec instrument, we summarize some of the driving requirements for the detector subsystem, discuss the baseline architecture (and alternatives), and presents some recent detector test results including a description of a newly identified noise component that we have found in some archival JWST test data. We dub this new noise component, which appears to be similar to classical two-state popcorn noise in many aspects, “popcorn mesa noise.” We close with the current status of the detector subsystem development effort.

Knowledge of a spectrograph slit function is necessary to interpret unresolved lines and spectral features in an observed spectrum. In a scanning spectrometer with a single exit slit, the slit function is easily measured by illuminating the entrance slit with a broadband source and scanning the dispersive element. In a fixed grating/or disperser spectrograph, the slit functions have been measured by illuminating the entrance slit with a monochromatic light using a premonochromator or a tunable laser and by varying the wavelength of the incident light. Generally these techniques are very expensive, complex or subject to a poor signal-to-noise ratio so that an accurate measurement is often not possible. Also it would be very laborious and prohibitive to an imaging spectrograph or a multi-object spectrograph that has many sets of entrance and exit slit equivalents. We explore an alternative technique that is manageable for the measurements and where the measurement is not limited by the available signal. In the proposed technique, a Fourier Transform Spectrometer (FTS) is used instead of a pre-monochromator with variable wavelengths in the conventional techniques. This approach can be extended to the visible and ultraviolet (UV) wavelength range and to imaging spectrographs and multi-object spectrograph where multiple entrance slits and multiple exit slit equivalents (detectors) produce numerous different slit functions. In this approach, the advantages of FTS are fully utilized for available signals and the computer-assisted nature of FTS makes the data processing of the measurements manageable.

The James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of galaxy formation in the Universe. The telescope will be launched into orbit about the second Lagrange point and passively cooled to 30-50 K to enable astronomical observations from 0.6 to 28 μm. A group from the NASA Goddard Space Flight Center and the Northrop Grumman Space Technology prime contractor team has developed an optical and mechanical layout for the science instruments within the JWST field of view that satisfies the mission requirements. Four instruments required accommodation within the telescope’s field of view: a Near-Infrared Camera (NIRCam), a Near-Infrared Spectrometer (NIRSpec), a Mid-Infrared Instrument (MIRI) and a Fine Guidance Sensor (FGS) with a tunable filter module. The size and position of each instrument’s field of view allocation were developed through an iterative, concurrent engineering process involving key observatory stakeholders. While some of the system design considerations were those typically encountered during the development of an infrared observatory, others were unique to the deployable and controllable nature of JWST. This paper describes the optical and mechanical issues considered during the field of view layout development, as well as the supporting modeling and analysis activities.

The Fine Guider Sensor (FGS) of the James Webb Space Telescope (JWST) features two tunable filter (R~100) modules covering the 1.2-2.4 μm and 2.4-4.8 μm wavelength ranges, respectively. A set of occulting spots/bars mounted on a small slide located at the edge of the 2.3’x 2.3’ field of view (FOV) along with apodizing masks located in the filter wheel of each channel enable coronagraphic operation. Each coronagraphic field covers a square FOV of 20”x20”. The FGS-TF coronagraph complements the coronagraphic capabilities implemented in NIRCam and MIRI. This paper presents numerical simulations to predict the high-contrast imaging performance of the FGS-TF coronagraph. The combined coronagraphic and differential spectral imaging capabilities of the FGS-TF constitute a powerful tool for detecting and characterizing exoplanets with JWST.

The Integrated Science Instrument Module of the James Webb Space Telescope is described from a systems perspective with emphasis on unique and advanced technology aspects. The major subsystems of this flight element are described including: structure, thermal, command and data handling, and software.

A mechanical slit mask mechanism has been designed for the Near Infrared Spectrograph of the James Webb Space Telescope. This mechanism was successfully tested at a cryogenic temperature of 30K, in vacuum. The reconfigurable mask allows to form 24 optical slits in a 137 x 137 mm² field of view. The slit length is fixed (4.8 mm) and their width can range from 50 μm to 137 mm. The slit positioning accuracy is ± 5 μm and the slit width accuracy is ± 8 μm. The working principle of the mechanism is based on an improved "inch-worm" stepping motion of 48 masking bars forming the optical curtain. Voice coil actuators are used to drive the various clutches and the principal mobile stage. Ratchets which engage in the teeth of a rack machined on the bars allow to cancel the accumulation of motion errors as steps succeed one another. The design makes significant use flexure structures. Cryogenic performance, life and vibration tests have been performed successfully on subassemblies of the mechanism and a full-scale prototype.

We propose to implement an Integral-Field Unit (IFU) mode in the near-infrared spectrograph NIRSpec of the future James Webb Space Telescope (JWST), instrument under the responsibility of the European Space Agency (ESA). The IFU mode will provide unique additional scientific capabilities, complementary to those of the main multi-object mode of NIRSpec. It would cover a 3"x3" field of view with a 0.075" sampling and make use of the R=3000 spectral configurations of NIRSpec, covering the complete 1.0-5.0 microns range in three shots. First performance simulations yield a limiting AB magnitude of 24 for a point-like source. On the technical side, the IFU is based on the advanced image slicer concept and would include a stack of forty 900 μm thick, slicing mirrors. We are currently conducting a prototyping work funded by ESA, aiming at demonstrating a TRL6 readiness level for this technology (see presentation by F. Laurent). We present the optical design of the IFU, the strategy used during its definition (minimum impact on NIRSpec), as well as the proposed implementation within the NIRSpec instrument. We will stress that, this currently optional mode is a unique opportunity to provide JWST with a powerful integral field mode at marginal costs.

Modelling the scientific performance of infrared instruments during the design and definition phase of a project is an essential part of the system design optimisation for both the instrument and the observatory. This is particularly so in the case of space observatories where the opportunities for correcting design errors or omissions following launch are limited. We describe the approach taken to the estimation of the sensitivity of the Mid Infrared Instrument (MIRI) operating from 5 to 28 microns on the NASA/ESA James Webb Space Telescope (JWST) due for launch in 2011. We show how the sensitivity is estimated both for the photometric imager and the integral field spectrometer using a model that includes the effects of background radiation from the telescope and its surroundings; diffraction effects and detector performance and operations.

The spectrometer sub-system of the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) contains four channels which spectrally multiplex the incoming radiation. This incident radiation, spanning a wavelength range from 4.8 to 28.8μm is spectrally divided between the channels using sets of three dichroics combined in series along the optical trains. The four channels, with overlapping wavelengths 4.8-7.8, 7.4-11.9, 11.4-18.3 and 18.3-28.8μm, are in-turn each split into three wavelength ranges to provide the required resolving power with the available detector pixels. This splitting of the wavelengths within each channel is achieved using three separate sets of dichroics and diffraction gratings, mounted on two wheels. This paper describes the design of the dichroics together with a spectral performance model developed to simulate the system spectral throughput for each of the four channels of the MIRI instrument. Details of the spectral design, manufacture, testing and mounting of the dichroics are presented together with the opto-mechanical layout of the instrument.

The MIRI Telescope Simulator (MTS) is part of the Optical Ground Support System (OGSE) for the verification and calibration phase of the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI). The MTS will simulate the optical characteristics of the JWST output beam in an environment similar to the flight conditions. The different functionalities of the MTS are briefly described and its current design, including the illumination and imaging subsystems, is presented.

The James Webb Space Telescope (JWST) is a large space based astronomical telescope that will operate at cryogenic temperatures, and utilize a segmented primary mirror with active control. To achieve the science goals for JWST, the design requires a large collecting aperture to detect distant faint sources, and a large field of view to accommodate multiple large field of view instruments for efficient surveys. We will address the nominal performance and sensitivity of the design for field dependent wave front error, as well as some of the special optical analysis considerations necessary in a system needing remote, on-orbit alignment.

This is the second of a series on the optical modeling activities for the JWST government systems engineering integrated modeling team. Starting with the linear optical model discussed in the first installment, we develop centroid and wavefront error sensitivities for the special case of a segmented optical system such as JWST, where the primary mirror consists of 18 individual segments. Our approach extends standard sensitivity matrix methods used for systems consisting of monolithic optics, where the image motion is approximated by averaging ray coordinates at the image and residual wavefront error is determined with global tip/tilt removed. We develop an exact formulation using the linear optical model, and extend it to cover multiple field points for performance prediction at each instrument aboard JWST. This optical model is then driven by thermal and dynamic structural perturbations in an integrated modeling environment. Results are presented.

NASA’s James Webb Space Telescope (JWST) is a 6.6 m all-reflective on-axis three-mirror anastigmat. The 18-segment and fully actuated primary mirror (PM) presents unique and challenging assembly, integration and alignment requirements. In order to properly integrate the Primary Mirror Segment Assemblies (PMSAs) and align the completed PM, a variety of ground support equipment is used within a tower specifically built for the program. Handling fixtures, gravity offloaders, a variety of optical references, laser scanners, and interferometers are used. This paper outlines the hardware and techniques for integration and alignment of the JWST PM.

The James Webb Space Telescope (JWST) is a large space based astronomical telescope that will operate at cryogenic temperatures, and utilizes a segmented primary mirror with active control. To achieve the science goals for JWST, the image quality over a wide spectral range is necessary. Several metrics related to the quality of the PSF have been used to capture the optical requirement to meet the science goals. We will present the performance predictions for the JWST based on the results of the detailed allocations of the optical requirements.

This paper presents new software (and simulations) that would phase a space based free flyer sparse array telescope. This particular sparse array method uses mirrors that are far enough away for sensors at the focal point module to detect tip tilt by simply using the deflection of the beam from each mirror. Also the large distance allows these circle six array mirrors to be actuated flats. For piston the secondary actuated mirrors (one for each large mirror segment of these widely spaced sparse array mirrors distributed on a parabola) are moved in real time to maximize the Strehle ratio using the light from the star the planet is revolving around since that star usually has an extremely high SNR (Signal to Noise Ratio). There is then no need for a 6DOF spider web of laser interferometric beams and deep dish mirrors (as in the competing Darwin and JPL methods) to accomplish this. Also the distance between the six 3 meter aperture mirrors could be large (kilometer range) guaranteeing a high resolution and also substantial light gathering power (with these 6 large mirrors) for imaging the details on the surface of extrasolar terrestrial type planets. In any case such a multisatellite free flyer concept would then be no more complex than the European cluster which is now operational. This is a viable concept and a compelling way to image surface detail on extra solar earthlike planets. It is the ideal engineering solution to the problem of space based large baseline sparse arrays. Significant details of the software requirements have been recently developed. In this paper the Fortran code needed to both simulate and operate the actuators in the secondary mirror for this type of sparse array is discussed.

The James Webb Space Telescope (JWST) will be a segmented, deployable, infrared-optimized 6.5m space telescope. Its active primary segments will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this fine tuning will come from the analysis of defocussed phase diverse images taken with its near-IR science camera, NIRCam. Here we concentrate on routine maintenance of the JWST primary, as might be expected to occur on a more or less monthly timescale after the telescope is commissioned. We carry out an end-to-end optical and wavefront sensing simulation, starting from the primary mirror figure, calculating a noiseless point-spread function as it would appear on the detector, inject noise sources due to photon statistics, as well as detector and electronics characteristics (as measured in Rockwell HAWAII-2RG detectors in the lab), and reduce the data with a simple scheme to create one realization of a full wavefront sensing operation. We generate JWST point-spread functions for a given OPD map on a JWST pupil with -6, -3, 3, and 6 waves of focus, and simulate three realizations of the same exposure. We start with a mirror figure that provides a point-spread function (PSF) that is just under the acceptable specification for JWST's Strehl ratio, which is 80% at 2 microns in NIRCam. We do not include zodiacal light, diffuse sources, or contamination by other stars in our simulation. Our up-the-ramp exposures include a model of cosmic ray contamination of the data. We calibrate the image to account for dark current and flat field variation, and process the images with an implementation of the Misell-Gerchberg-Saxton algorithm assuming a known pupil support function. Our entire process is described here, to document a tool that helps to verify our intended method of maintaining the JWST PSF within specificatiuons during routine science operations.

The Wavefront Control Testbed (WCT) was created to develop and test wavefront sensing and control algorithms and software for the segmented James Webb Space Telescope (JWST). Last year, we changed the system configuration from three sparse aperture segments to a filled aperture with three pie shaped segments. With this upgrade we have performed experiments on fine phasing with line-of-sight and segment-to-segment jitter, dispersed fringe visibility and grism angle; high dynamic range tilt sensing; coarse phasing with large aberrations, and sampled sub-aperture testing. This paper reviews the results of these experiments.

An analysis is presented that illustrates how the James Webb Space Telescope (JWST) fine-phasing process can be carried out using the Near-Infrared Spectrograph (NIRSpec) data collected at the science focal plane. The analysis considers a multi-plane diffraction model which properly accounts for the microshutter diffractive element placed at the first relay position of the spectrograph. Wavefront sensing results are presented based on data collected from the NASA Goddard Microshutter Optical Testbed.

To achieve and maintain the fine alignment of its segmented primary mirror the James Webb Space Telescope (JWST) plans to use focus-diverse wavefront sensing (WFS) techniques with science camera imagery. The optical requirements for JWST are such that the error contribution from the WFS itself must be limited tp 10nm rms over the controllable degrees of freedom of the telescope. In this paper, we will explore the requirements on the target selection and imaging requirements necessary to achieve the desired level of WFS accuracy. Using Monte Carlo simulations we explore the WFS error as a function of wavefront aberrations level, defocus-diversity level, optical bandwidth and imaging signal-to-noise ratio to establish the key imaging requirements. By taking into account practical integration time limits along with the distribution of the defocused point-spread functions, we establish the bright and faint star magnitude limits suitable for WFS target selection.

The James Webb Space Telescope (JWST) will use image-based wavefront sensing to align the telescope optics and achieve diffraction-limited performance at 2 µm. The Phase Retrieval Camera (PRC) is a high-accuracy, image-based wavefront sensor that was built for the optical characterization of JWST technology-demonstrator mirrors. Recently, experiments with the PRC were performed at the NASA Marshall Space Flight Center to measure the cryogenic surface figure of the beryllium Advanced Mirror System Demonstrator (AMSD). This paper describes the results of these experiments. Using the Modified Gerchberg-Saxton phase retrieval algorithm (JWST’s baseline method for fine-phasing), the PRC measured wavefront aberrations that were as large as 10 waves peak-to-valley (wavefront) in the optical system. A comparison between the PRC results and measurements acquired with an Instantaneous Phase Interferometer will also be presented.

The Northrop-Grumman/Ball/Kodak team is building the JWST observatory that will be launched in 2011. To develop the flight wavefront sensing and control (WFS&C) algorithms and software, Ball is designing and building a 1 meter diameter, functionally accurate version of the JWST optical telescope element (OTE). This testbed telescope (TBT) will incorporate the same optical element control capability as the flight OTE. The secondary mirror will be controlled by a 6 degree of freedom (dof) hexapod and each of the 18 segmented primary mirror assemblies will have 6 dof hexapod control as well as radius of curvature adjustment capability. In addition to the highly adjustable primary and secondary mirrors, the TBT will include a rigid tertiary mirror, 2 fold mirrors (to direct light into the TBT) and a very stable supporting structure. The total telescope system configured residual wavefront error will be better than 175 nm RMS double pass. The primary and secondary mirror hexapod assemblies enable 5 nm piston resolution, 0.0014 arcsec tilt resolution, 100 nm translation resolution, and 0.04497 arcsec clocking resolution. The supporting structure (specifically the secondary mirror support structure) is designed to ensure that the primary mirror segments will not change their despace position relative to the secondary mirror (spaced > 1 meter apart) by greater than 500 nm within a one hour period of ambient clean room operation.

Concerns have been raised in the engineering community about the potentially extremely low levels of structural damping in structures at cryogenic temperatures. Experiments conducted on material coupons have shown that material damping at those temperatures can be orders of magnitude lower than that at room temperature. Whether structural damping in built-up structures at those temperatures can be that low is unknown, but if it was, the telescope resonances could exacerbate microdynamics originating from the structure itself and residual vibrations propagating from the instrument module to the telescope. Since the effect of those vibrations might not be compensated for optically, the observatory might not meet its wavefront and jitter error budgets. The structural damping characteristics of built-up structures in the micrometer to nanometer regime and at cryogenic temperatures are to a large extent unknown. Characterization on structures traceable to future flight designs is therefore necessary to develop an understanding of these characteristics, as well as devise means to mitigate those effects. To address those concerns and to reduce the technical risks in these areas, Lockheed Martin tested the dynamics characteristics of its Single Petal Testbed (SPT) flight-like petal structure at full-scale, from room temperature down to -175C (98K). The SPT was designed by the Lockheed Martin Advanced Technology Center and fabricated by Programmed Composites Inc. Significant changes in dynamics characteristics with temperature were observed, but primarily in mode shapes as opposed to modal frequencies and modal dampings. The modal damping remained fairly constant throughout the temperature range and, to the extent changes could be detected, the trends were more towards an increase than a decrease in damping at 98K, which was highly unexpected. A detailed analysis of these results extracted from dynamics tests conducted during the cool down portion of the last thermal cycle is presented in this report. The levels of damping observed in the built-up petal structure are 10 to 20 times higher than those measured by Marie Levine at JPL on all-composite coupons of the petal panels provided by Lockheed Martin.