Active wavefront correction of a space telescope provides a technology path for extremely high contrast imaging astronomy at levels well beyond the capabilities of current telescope systems. A precision deformable mirror technology intended specifically for wavefront correction in a visible/near-infrared space telescope has been developed at Xinetics and extensively tested at JPL over the past several years. Active wavefront phase correction has been demonstrated to 1 Angstrom rms over the spatial frequency range accessible to a mirror with an array of actuators on a 1 mm pitch. It is based on a modular electroceramic design that is scalable to 1000s of actuator elements coupled to the surface of a thin mirror facesheet. It is controlled by a low-power multiplexed driver system. Demonstrated surface figure control, high actuator density, and low power dissipation are described. Performance specifications are discussed in the context of the Eclipse point design for a coronagraphic space telescope.

The German Instrument for Multi-channel Photometry and Astrometry (DIVA), dedicated to the German (DLR) small extraterrestrial satellite program, is intended as a kind of technology precursor mission to GAIA. DIVA is scheduled for launch in 2004 and shall perform a sky survey to measure within 2 years life time the positions, parallaxes, magnitudes, etc. of about 35 million stars. The main instrument, covering the spectral range of 400-1000nm, observes 2 fields of view (0.6° x 0.77°) by a single Focal Plane Assembly (FPA). The focal length is 11200mm. The DIVA Optomechanics is based on a high precision Three Mirror Anastigmat (TMA) concept with 8 mirrors, 5 of them flat. An extremely high short term stability (torsion tolerance) of 0.3 mas over 10h only has to be realized only by passive means to achieve the astrometrical performance requirements. The paper describes the phase B2 design activities wrt. the optomechanical and thermal design of the main instrument. Special emphasis is given to an exhausting, but very pragmatic thermomechanical and optical performance trade off between a cost effective athermal design concept, applying mirrors and an optical bench made from a specially treated isotropic aluminum alloy, and a thermally stable hybrid material concept based on a Carbon Fiber Reinforced Plastics (CFRP) sandwich structure and Zerodur mirrors. The selection of the final baseline design solution shall be reported. According to the very high long and short scale surface properties of the candidate aluminum mirrors a sophisticated manufacturing procedure was established based on conventional and ion beam polishing techniques. The representative breadboard mirror test results will be given.

During the course of performing space flight qualification testing of composite mirrors at NASA GSFC, a serendipitious event was observed which, in retrospect, should have been obvious. Investigation of this phenomenon leads to a promising avenue towards the fabrication of large aperture precision spherical mirrors with very long radius of curvature (>f/100). Such mirrors are required for future missions such as the Stellar Imager. We report on the observation and analysis of the event, optical measurements, and the development of associated active figure control systems.

The Ultra-Violet Italian Sky Surveyor (UVISS) is a small SiC far- and near-UV telescope under study by the Italian Space Agency to be installed on an available Express Pallet (ExPa) of the International Space Station (ISS). UVISS has two focal plane instruments: an ultraviolet imaging camera and a far ultraviolet spectrograph. This paper summarizes the conclusions of the study about the optical configuration of the spectrograph. This instrument has to cover the 91-130 nm spectral region with a moderately low resolving power (greater than 300 at 100 nm), a spatial resolution of 4 arcsec on-axis and minimization of spatial aberrations over arcmin's long entrance slit. Many problems had to be faced in the design of this instrument: from the very small available room, to the rather short visibility time of a single target on the sky, to the intrinsic pointing instability of the ISS. The adopted configuration of the spectrograph foresees the use of a spherical grating with parallel variable line spacing in the Harada mounting. The theoretical performance of this instrument obtained by ray-tracing simulation is given, showing that the optical requirements can be satisfied. Also, several efforts have been done in order to study the possibility of reconstructing the target spectra by means of a photon recentering technique to compensate the pointing instabilities due to the ISS environment. The details of this analysis are described, showing that the system optical performance can essentially be maintained also with a carrier so unstable as the ISS.

An overview of silicon carbide (SiC) materials is provided, focusing on reaction bonded (RB) SiC and its properties. The Miniature Infrared Camera and Spectrometer (MICAS) and Advanced Land Imager (ALI) SiC space instruments produced by SSGPO and flown under NASA's New Millennium Program are described, and some of the mission requirements associated with UV and extreme UV (EUV) applications are reviewed. Manufacturing options associated with SiC reflectors are reviewed and the optical performance demonstrated with these materials is presented. In order to review the suitability of these materials to UV and EUV missions microroughness and surface scatter results are shown.

The Hubble Space Telescope (HST) has provided superb imaging and spectroscopic capability for studying galaxies, stars, and nebulae in the ultraviolet and visible (UVIS) wavelength regions, as well as in the near infrared. The HST is a 2.4-meter telescope with imaging, spectroscopic, and limited coronagraphic instrumentation. NASA plans to discontinue its operations in 2010. Next generation ultraviolet and visible telescope capability to replace HST is currently under discussion. The new facility would include a very large aperture collector, ultra wide field of view (WFOV) imagery, precise wavefront control, and high UVIS efficiency. Such a facility would combine ultra wide FOV imagery that is diffraction-limited at Lyman-α (λ = 122 nm) with efficient broad spectral coverage. The design must also provide spectroscopic, and possibly coronagraphic, capability in addition to imagery. This paper will discuss design trades for such capabilities and present design configurations. The paper will also identify key technologies needed to support the implementation of the new facility.

We describe a novel process to improve the extreme ultraviolet (EUV) reflection efficiency of multilayer-coated replica gratings through an intermediate CN_X overcoat. Au-coated and uncoated (SiO₂ surface) Hitachi replica gratings (20 x 20 mm, 4800 g/mm, 13° blaze angle), designed to provide peak efficiencies at 304 Å in 3rd order, were measured using an AFM prior to and after the CN$_X coating. The CN_X coating produced substantially smoother grating facets without significantly degrading the grating groove profile. The gratings were then overcoated with a 10 layer Mo/Si stack optimized for near normal reflectivity at 304 Å. Reflectivity measurements in 3rd order demonstrated an enhancement in absolute grating efficiency by a factor of 4 over the Mo/Si + Au-coated grating. The results of this simple experiment suggest that, with further improvements, the CN_X overcoating process may provide a useful and relatively inexpensive alternative to the use of ion-etched blazed gratings in the EUV for some applications.

Rosetta is one of the cornerstone missions of the European Space Agency for having a roundez-vous with the periodic comet P/Wirtanen in 2011. One of the imaging instruments on board the satellite is the Wide Angle Camera, a cooperation among several European institutes. This camera adopts an all reflecting, unvignetted unobstructed two mirror configuration which allows to cover a 12° X 12° Field of View with an F/5.6 aperture and an optical quality better than 80% geometrical ensquared energy inside approximately 20 arcsec. The flight model of this camera has been successfully integrated and tested in our laboratories and finally has been integrated on the satellite. In this paper we are going to describe the optical characteristics of the camera, and to summarize the results so far obtained with the preliminary calibration data. The analysis of the optical performance of this model shows a good agreement between theoretical performance and experimental results.

We report on the design and fabrication of a long-slit imaging dual order spectrograph to be launched on a sounding rocket-borne telescope. The instrument's purpose is to investigate faint emissions of extended astronomical regions near bright objects on intermediate angular scales (3 - 300") and with moderate spectral resolution (≈3 Å) in the 900 - 1650 Å bandpass. The design relies upon a toroidally figured holographically ruled grating to provide astigmatism correction in both orders and an intrinsically low scattered light level. The use of both orders doubles the collection efficiency, nearing that achievable with a blazed grating, while simultaneously providing a system redundancy that is desirable in the high risk environment of space-based astronomy missions. We will discuss the predicted instrument performance and present preliminary pre-flight calibration data.

UVISS is a small telescope of 50 cm aperture designed for accommodation on the International Space Station, and it will employ multilayer coatings for imaging in the near UV (130 - 260 nm) and possibly also far UV (90 - 115 nm) bands. Near UV filters have been designed using MgF₂, BaF₂, Al₂O₃, SiO₂, Y₂O₃, and the far UV filter has been designed using LiF and Y₂O₃. Tests are in progress on some of these coatings, including trade-off's between multilayers and Indium filters short-wards of Lyα. The first results are encouraging, since they show that the technique appears to be feasible.

A new method is presented for amplitude and phase control using two liquid crystal spatial light modulators in conjunction with a white light Michelson interferometer. Preliminary proof-of-concept measurements are given showing the prospect of using this method for correction of amplitude errors in telescopes.

We present the design for a high resolution broad band Self Compensating All Reflective Interferometric Echelle Space Telescope spectrometer (SCARIEST). Because of its all reflective design, the system works throughout the UV. We discuss the system's design, capabilities, and limitations as well as possible applications.

The WAC is a telescope developed by University of Padova for the OSIRIS experiment, mainly composed by two instruments, Narrow Angle Camera and Wide Angle Camera, and the related electronics. The payload will fly on board of the Rosetta ESA scientific mission, that will be flown to encounter Comet Wirtanen after about 10 years of flight in 2013. WAC main scientific objectives are to follow structure evolution in the coma and monitor their dynamics. To fulfill scientific requirements, the optical characteristics of the WAC telescope may be summarized as follows: wide field of view of 12° X 12°, focal length of 140 mm, operate in the wave-length range 240-1000nm after 10 years in space, Encircled Energy greater than 70% over the entire FoV, contrast ratio of 10^-4 to detect coma activities against a bright nucleus, minimum exposure time of 10 msec with a repeatability better than 1/500, scattered light rejection for sources inside and outside FoV. This paper deals with the design optimization of critical parts and acceptance test campaign performed to validate the thermo-structural behavior of the WAC. The functional and performance tests carried out at experiment and system level demonstrated the overall capability of the telescope to satisfy the system and scientific requirements.

The design and development of an optical bench (OB) for Wide Field Camera 3 (WFC3), a next generation science instrument for the Hubble Space Telescope (HST) has proven a challenging task. WFC3 will replace Wide Field Planetary Camera 2 (WF/PC 2) during the next servicing mission of the HST in 2004. The WFC3 program is re-using much of the hardware from WF/PC 1, returned from the First Servicing Mission, which has added complexity to the program. This posed some significant packaging challenges, further complicated by WFC3 utilizing two, separate optical channels. The WF/PC 1 optical bench could not house the additional optical components, so a new bench was developed. The new bench had to be designed to accommodate the sometimes-conflicting requirements of the two channels, which operate over a wavelength range of 200nm to 1800nm, from Near Ultraviolet to Near Infrared. In addition, the bench had to interface to the reused WF/PC 1 hardware, which was not optimized for this mission. To aid in the design of the bench, the team used software tools to merge structural, thermal and optical models to obtain performance (STOP) of the optical systems in operation. Several iterations of this performance analysis were needed during the design process to verify the bench would meet requirements. The fabrication effort included a rigorous material characterization program and significant tooling. After assembly, the optical bench underwent an extensive qualification program to prove the design and manufacturing processes. This paper provides the details of the design and development process of this highly optimized optical bench.

Recording methods for making aberration corrected holographic gratings are drastically simplified by using a multimode deformable mirror (MDM). For this, the plane MDM acts upon one of the two recording beams. The MDM design is derived from a vase form having a constant rigidity on its clear aperture and a perimeter ring of higher rigidity linked to several external radial arms. It is shown that MDM compensators provide easily the superposition of many interesting active optics modes that we have named Clebsch-Zernike modes. These modes belong to a sub-class of the triangle aberration mode matrix. They are generated by only applying a uniform loading onto the rear side of the clear aperture and/or axial forces and radial moments onto the outer ring. In addition the spherical aberration provided by a uniform loading, the Clebsch-Zernike modes are distributed along the two lower diagonals of the triangle matrix. Several six-arm MDMs, and twelve-arm MDMs have been built and experienced. Due to the huge simplification for the design of optical systems as compensators, such a recording method is to be considered as a universal one. As an example of the method, the recording of three concave holographic gratings of the HST Cosmic Origins Spectrograph has been investigated. The result is that much higher order aberrations can simultaneously be corrected. Compared to the design of the COS team, the residual blur of monochromatic images along the spectra occupy areas in average 30 times smaller -- as well in term of pixel number -- decomposing as follows: (1) gain of 10 times in spectral resolution and, in the orthogonal direction, (2) gain of 1 -1.2 in limiting magnitude.

We describe the development of optics for the SPEAR space-mission to map the far ultraviolet (900-1750 Å) sky. The SPEAR spectrometers contain unusual reflective optics to optimize sensitivity to diffuse emission. We describe the manufacture, test and performance of the collecting mirrors: Pyrex parabolic cylinders with a 90 degree off-axis angle. We also describe the development of the diffraction gratings: ellipses of rotation that are holographically-ruled with constant spacing and blazed with ion-beam ablation.

CHIPS is a NASA UNEX mission designed for diffuse background spectroscopy in the EUV bandpass from 90-260Å. The spectrometer is optimized for peak resolution near 170 Å, in order to study diffuse emissions from cooling million degree plasma. Details of local bubble thermal pressure, spatial distribution, and ionization history are the goals of CHIPS observations. We discuss the opto-mechanical design adopted to meet the throughput, signal to noise, and spectral resolution requirements within the mass, volume, and budgetary constraints of a UNEX Delta-II secondary payload. Mechanical tolerance requirements for the six spectrometer channels are discussed, along with details of the lightweight mounting scheme for CHIPS diffraction gratings, front cover slit mechanisms and thermal design. Finally, visible light and vacuum alignment techniques are discussed, as well as with methods employed to minimize stray light.

We present the optical design and predicted performance of the Extreme Ultraviolet Spectrometer (EUVS) developed for the Jupiter Magnetospheric Explorer (JMEX) mission. JMEX was proposed as small explorer (SMEX) mission designed to observe the Jovian system to study the dynamical relationship between Jupiter's magnetosphere and Io, the primary source of material for the Io plasma torus. NASA selected JMEX as one of six SMEX missions for detailed technical study. While JMEX was ultimately not selected for flight, the EUVS instrument design has a unique set of performance characteristics that may be useful for other applications, such as a multi-object spectrometer, a push-broom spectrometer for diffuse objects, or an imaging spectrometer with high spatial resolution. The EUVS is an imaging spectrograph originally designed to observe the Io plasma torus. EUVS provides moderate resolution (~0.1 nm) spectra between 64 to 114 nm over +/- 260" with 2" spatial resolution. The optical design is based on an off-axis Gregorian telescope, where the secondary mirror is replaced with an aberration-corrected holographic grating. The grating diffracts and focuses the UV light onto a cross-delay line microchannel plate detector with a potassium bromide photocathode. The primary mirror and grating are coated with boron carbide to maximize the normal incidence reflectivity at the shortest wavelengths. This high throughput, two-element design provides a compact instrument suitable for a small spacecraft while maintaining an efficient optical path that provides 7-12 cm² of effective area.

The Cosmic Origins Spectrograph (COS) is a new instrument for the Hubble Space Telescope that will be installed during servicing mission 4, currently scheduled for March 2004. The primary science objectives of the mission are the study of the origins of large scale structure in the universe, the formation, and evolution of galaxies, the origin of stellar and planetary systems and the cold interstellar medium. As such, COS has been designed for the highest possible sensitivity on point sources, while maintaining moderate (λ/Δλ = 20,000) spectral resolution. In this paper, the instrument design and predicted performance is summarized, as well as summary of the instrument flight and prototype component performance to date.

We present an overview of the ACS on-orbit performance based on the calibration observations taken during the first three months of ACS operations. The ACS meets or exceeds all of its important performance specifications. The WFC and HRC FWHM and 50% encircled energy diameters at 555 nm are 0.088" and 0.14", and 0.050" and 0.10". The average rms WFC and HRC read noises are 5.0 e^- and 4.7 e^-. The WFC and HRC average dark currents are ~ 7.5 and ~ 9.1 e^-/pixel/hour at their operating temperatures of - 76°C and - 80°C. The SBC + HST throughput is 0.0476 and 0.0292 through the F125LP and F150LP filters. The lower than expected SBC operating temperature of 15 to 27°C gives a dark current of 0.038 e^-/pix/hour. The SBC just misses its image specification with an observed 50% encircled energy diameter of 0.24" at 121.6 nm. The ACS HRC coronagraph provides a 6 to 16 direct reduction of a stellar PSF, and a ~1000 to ~9000 PSF-subtracted reduction, depending on the size of the coronagraphic spot and the wavelength. The ACS grism has a position dependent dispersion with an average value of 3.95 nm/pixel. The average resolution λ/Δλ for stellar sources is 65, 87, and 78 at wavelengths of 594 nm, 802 nm, and 978 nm.

The Advanced Camera for Surveys (ACS), installed in HST in SM3B, is fitted with a grism and three prisms for slitless spectrometry. The Wide Field Camera (WFC), with a field of 3.4x3.4' and 0.05" pixels, allows slitless grism spectrometry at a dispersion of 40Å per pixel over the range 0.55 to 1.05 μm. The High Resolution Camera (HRC) provides optimally sampled imaging above 0.6μm over a field of 26x29" (0.026" pixels), uses the same grism for slitless spectrometry at 24ÅA/pixel, and a prism covering the 1600-3300Å range with a 4maximum dispersion of 5Å/pixel. The Solar Blind Channel (SBC), with pixels of 0.030x0.034" (field size 31x35"), also has two prisms giving a maximum dispersion of about 2Å/pixel and covering the 1200-1800Å range; one prism excludes the geocoronal Lyman-α for lower background. The ground and in-flight calibration and astrophysical use of the grism and prism modes of ACS is described. Particular problems for slitless spectrometry include the dependence of spectral resolution on image size, determination of wavelength zero points and removal of flat field. The in-flight calibrations have been derived to extend and strengthen the ground calibrations taken using line and continuum lamps which will not be available in orbit. A software package is available to extract ACS spectra, based on a catalogue of images in a direct image, and has been extensively tested with a dedicated simulator. The wide range of astrophysical programs, for which the ACS spectral modes are well suited, will be outlined, with examples from accepted programs.

We present an overview of the Advanced Camera for Surveys (ACS) CCD detectors performance based on the ground testing and the calibration observations taken during the first four months of ACS operation. ACS has been installed into the Hubble Space Telescope in March 2002 and consists of three different cameras. Two of them employ CCD detectors: the Wide Field Camera a mosaic of two 4096 x 2048 CCDs and the High Resolution Camera a single 1024 x 1024 chip. A review of the on-orbit performance is presented here and also comparison is made with the instrument specifications, published performance expectation and ground test results.

The off-axis location of the Advanced Camera for Surveys causes strong geometric distortion in all detectors -- the Wide Field Camera (WFC), High Resolution Camera (HRC), and Solar Blind Camera (SBC). Dithered observations of rich star cluster fields are used to calibrate the distortion. We describe the observations obtained, the algorithms used to perform the calibrations and the accuracy achieved. We present our best current calibration of the geometric distortion of each of the detectors.

COS has two distinct ultraviolet channels covering the spectral range from 1150Å to 3200Å. The NUV channel covers the range from 1700Å to 3200Å and uses the Hubble Space Telescope's STIS spare MAMA. The FUV channel uses a micro channel plate detector with a cross-delay line readout system to cover the range from 1150Å to 1900Å. Due to the analog nature of the readout electronics of the FUV detector, this system is sensitive to temperature variations and has non-uniform pixel size across its sensitive area. We present a step-by-step description of the calibration process required to transform raw data from the COS into fully corrected and calibrated spectra ready for scientific analysis. Initial simulated raw COS data is used to demonstrate the calibration process.

The flight microchannel plate detectors to be used in the Cosmic Origins Spectrograph, a fourth generation instrument for the Hubble Space Telescope, have been calibrated in the laboratory before being integrated into the spectrograph. This paper presents additional findings following a second scrub that became necessary when a fault was found with the quantum efficiency enhancement grid.

The Advanced Camera for Surveys (ACS), installed in the Hubble Space Telescope in March 2002, has significantly extended HST's imaging capabilities. We describe the on-orbit optical alignment procedures and results, detailing the excellent image quality performance achieved. Comparison is made with the instrument specifications, ground test results and published performance expectations. The residual aberration content over the field of each channel is described and compared with the optical model, and various other performance measures, including sharpness and encircled energy are treated. The effects of the telescope focus oscillations due to thermal variations ("breathing") and image positional stability are also discussed.

Recent advances in deformable mirror technology for correcting wavefront errors and in pupil shapes and masks for coronagraphic suppression of diffracted starlight enable a powerful approach to detecting extrasolar planets in reflected (scattered) starlight at visible wavelengths. We discuss the planet-finding performance of Hubble-like telescopes using these technical advances. A telescope of aperture of at least 4 meters could accomplish the goals of the Terrestrial Planet Finder (TPF) mission. The '4mTPF' detects an Earth around a Sun at five parsecs in about one hour of integration time. It finds molecular oxygen, ozone, water vapor, the 'red edge' of chlorophyll-containing land-plant leaves, and the total atmospheric column density -- all in forty hours or less. The 4mTPF has a strong science program of discovery and characterization of extrasolar planets and planetary systems, including other worlds like Earth. With other astronomical instruments sharing the focal plane, the 4mTPF could also continue and expand the general program of astronomical research of the Hubble Space Telescope.

Visible light coronagraphy from space is a promising technique for extrasolar planet detection and characterization. However, technology development in several areas is needed before a search for terrestrial planets is feasible with a coronagraph. The most challenging technologies appear to be: construction of 10 m scale, precision lightweight optics; millikelvin level control of temperature changes; and achieving reflectivity uniformity of 10^-4 across all mirrors. Additional technical challenges include: wavefront sensing to the sub-angstrom level; precise, stable deformable mirrors; and construction of coronagraphic masks with accurate shape or transmission profile. The current status and suggested development path of these technologies will be discussed.

Eclipse is a proposed Discovery-class mission to perform a sensitive imaging survey of nearby planetary systems, including a complete survey for Jupiter-sized planets orbiting 5 AU from all stars of spectral types A-K to distances of 15 pc. Eclipse is a coronagraphic space telescope concept designed for high-contrast visible wavelength imaging and spectrophotometry. Its optical design incorporates essential elements: a telescope with an unobscured aperture of 1.8 meters and optical surfaces optimized for smoothness at critical spatial frequencies, a coronagraphic camera for suppression of diffracted light, and precision active optical correction for suppression of light scattered by residual mirror surface irregularities. For reference, Eclipse is predicted to reduce diffracted and scattered starlight between 0.25 and 2.0 arcseconds from the star by at least three orders of magnitude compared to any HST instrument. The Eclipse mission offers precursor science explorations and critical technology validation in support of coronagraphic concepts for NASA's Terrestrial Planet Finder (TPF). A baseline three-year science mission would provide a survey of the nearby stars accessible to TPF before the end of this decade, promising fundamental new insights into the nature and evolution of possibly diverse planetary systems associated with our Sun's nearest neighbors.

The ECLIPSE mission will carry out the first sensitive imaging survey of nearby planetary systems, including the detection and characterization of Jovian planets, exozodiacal dust disks and cool brown dwarfs in the solar neighborhood. This survey will be performed with a 1.8 meter optical telescope and a coronagraphic camera, with active wavefront control, designed to achieve contrast levels of 10^-9 for bright objects centered on the coronagraph's occulting spot with an accuracy of 2 arcseconds (1σ) and a stability of 0.01 arcseconds (1σ). These requirements impose a number of significant challenges, including the need to: (1) Sense pointing errors to the 1 milli-arcsecond (mas) accuracy level, (2) Keep satellite jitter below 3 mas, (3) Design an attitude control system to meet the stringent pointing and pointing stability requirements, and (4) Avoid exciting satellite vibrational modes. Drawing on our experience with large space telescopes such as the Chandra X-ray Observatory, the Space Interferometry Mission and the Next Generation Space Telescope, we have designed an attitude control system for ECLIPSE that successfully meets these challenging requirements. This paper describes the trades and analyses that led up to our design, and its predicted performance.

Detecting life-bearing Earth-like planets (ELPs) is one of NASA's highest priority goals. In this paper we derive the wave-front requirements for optical detection of ELPs with an 8-m space telescope and coronagraph. We will present detailed simulations that show that an 8-m coronagraphic space telescope can detect Earth-sized planets around nearby stars, provided that the wavefront at the detector is corrected to an RMS error of ~λ/3000. We use the derived wavefront error to set requirements for a deformable mirror based on micro-electro-mechanical systems technology.

NASA's Kepler Mission is designed to determine the frequency of Earth-size and larger planets in the habitable zone of solar-like stars. It uses transit photometry from space to determine planet size relative to its star and orbital period. From these measurements, and those of complementary ground-based observations of planet-hosting stars, and from Kepler's third law, the actual size of the planet, its position relative to the habitable zone, and the presence of other planets can be deduced. The Kepler photometer is designed around a 0.95 m aperture wide field-of-view (FOV) Schmidt type telescope with a large array of CCD detectors to continuously monitor 100,000 stars in a single FOV for four years. To detect terrestrial planets, the photometer uses differential relative photometry to obtain a precision of 20 ppm for 12th magnitude stars. The combination of the number of stars that must be monitored to get a statistically significant estimate of the frequency of Earth-size planets, the size of Earth with respect to the Sun, the minimum number of photoelectrons required to recognize the transit signal while maintaining a low false-alarm rate, and the areal density of target stars of differing brightness are all critical to the photometer design.

The Galactic Exoplanet Survey Telescope (GEST) will observe a 2 square degree field in the Galactic bulge to search for extra-solar planets using a gravitational lensing technique. This gravitational lensing technique is the only method employing currently available technology that can detect Earth-mass planets at high signal-to-noise, and can measure the abundance of terrestrial planets as a function of Galactic position. GEST's sensitivity extends down to the mass of Mars, and it can detect hundreds of terrestrial planets with semi-major axes ranging from 0.7 AU to infinity. GEST will be the first truly comprehensive survey of the Galaxy for planets like those in our own Solar System.

The COROT small satellite project is a space mission dedicated to stellar seismology and search for telluric extra-solar planets. For the two programs a very high photometric precision is needed. The COROT seismology program will measure periodic variations with amplitude of 2.10^-6 of the photon flux emitted by bright stars. COROT will also be able to detect the presence of exoplanets when they pass between the satellite and their parent star. Modifying both the integration time and the focus conditions, it allows to detect photons flux variations about 7.10^-4 in one hour integration, compatible with an occultation detection on a very large number of stars (magnitude between 12 and 15.5). Between 10 and 40 telluric planets in the "habitable zone" and several hundreds of hot Jupiters should be detected depending on hypotheses about planets existence. To reach the required performances a stringent instrument stability is necessary. The satellite Preliminary Design Review will be held in November 2002 while the instrument is already in development phase for a delivery of the flight model in 2004. The launch is scheduled late 2005, by the first SOYUZ launcher to fly from the Guyana Space Center. The project activities are currently focused on the instrument and system engineering. Straylight rejection, pointing, thermal stability are the main critical points of the mission, on a LEO at 826 kms, for which cost-effective compromises have been found to 1mit their effects. This paper recalls the scientific program s, the main characteristics of the mission, describes the impact of the three main perturbators on the photometric precision and the technical solutions which reduce their contribution at an acceptable level.

We demonstrate solar spectra from a novel interferometric method for compact broadband high-resolution spectroscopy. The spectral interferometer (SI) is a hybrid instrument that uses a spectrometer to externally disperse the output of a fixed-delay interferometer. It also has been called an externally dispersed interferometer (EDI). The interferometer can be used with linear spectrometers for imaging spectroscopy or with echelle spectrometers for very broad-band coverage. EDI's heterodyning technique enhances the spectrometer's response to high spectral-density features, increasing the effective resolution by factors of several while retaining its bandwidth. The method is extremely robust to instrumental insults such as focal spot size or displacement. The EDI uses no moving parts, such as purely interferometric FTS spectrometers, and can cover a much wider simultaneous bandpass than other internally dispersed interferometers (e.g. HHS or SHS).

The primary goal of Kepler, a recently selected Discovery mission, is to search for terrestrial size planets orbiting other stars using the transit method. To accomplish this goal, a space-based photometer is being developed that employs a 0.95-meter Schmidt camera incorporating a large focal plane array (FPA). The FPA is populated with 42 large format custom CCD detectors with integral field flattening optics covering a 100 square degree field of view. The FPA will measure the precise relative intensity of approximately 100,000 main sequence stars nearly continuously over the mission's 4-year lifetime to search for the small changes caused by planetary transits. All critical electronics are housed immediately behind the FPA, which yields a low noise compact design that is both robust and fault tolerant. The design and development of the FPA, its detectors, its main systems issues, and their relationship to photometric precision will be discussed along with results from detailed performance models.

Advances in photocathodes (GaN, Diamond, GaAs), microchannel plates (Silicon MCP's), and readouts (Cross strip) are poised to make a significant impact on the capabilities of future space instruments. Alkali halide cathode efficiencies have been improved and GaN photocathodes have achieved >30% DQE in the UV with a bandpass limit of ~400nm. In addition diamond photocathodes have been made with 40% DQE and bandpass up to 200nm, and GaAs photocathodes with ~50% DQE in the visible have been made. This offers the potential for efficient photon counting from 10 - 900nm. Silicon MCP's of 25mm format with ~7μm pores, have been made, achieving gain of nearly 10⁴ for a single Si MCP. The quantum detection efficiency for Si MCP's is the same as glass MCP's, but the background is as low as ~ 0.02 events sec^-1 cm^-2, the best for any MCP. Flat fields are free of any periodic modulation, and the gain uniformity is good. Silicon MCP's have low stopping power for X, gamma and cosmic rays, are stable at high temperatures (>800°C), and chemically compatible with many photocathodes. The cross delay line and cross strip anodes are based on multi-layer metal and ceramic cross strip patterns. Event positions are encoded by the difference of signal arrival times at the anode contacts (delay line) or by direct sensing of the charge on each strip (cross strip) and determination of the charge cloud centroid for each event. The spatial resolution (<5μm) achieved is sufficient to resolve 7μm microchannel plate pores while using low MCP gain (≈2 x 10⁶). Image linearity is good enough to see distortions in the microchannel plate pore alignment, and the low MCP gain will enhance the overall lifetime of MCP detector systems.

Microchannel plate (MCP) photon counting detectors using image readout devices such as the Vernier and Cross-strip anodes can now achieve spatial resolutions limited by the pore geometry of commercially available MCPs. We describe progress in the development of a new readout system, part of our program to achieve MCP limited spatial resolution and larger format sizes using the small pore MCPs. We discuss the limitations of charge division devices that require high precision charge measurement and present a readout technique using charge comparison, with the potential to achieve large format readouts at high count rates. This scheme use a technique whereby the position coordinate of an event is represented by the order of amplitudes of a set of electrodes. Each coordinate is identified by a unique permutation of electrodes and is determined by comparing the charge collected on the electrodes. One of the major advantages offered by this scheme is a much lower signal-to-noise requirement. This will allow the detector to operate at substantially lower gain, raising the MCP limited count rate threshold. We present a simple and practical readout design to implement the charge comparison scheme, which uses the image charge technique to enhance performance in the areas of spatial resolution, linearity and image stability. The high count rate capability of the new design is augmented by an ability to capture events in parallel without the requirement for excessive numbers of electronic channels. We describe an electronics scheme specifically for the charge comparison readout and discuss how it can provide enhanced spatial resolution by using a charge centroiding technique based on pulse timing information. We support this with timing measurements obtained from a breadboarded electronic channel.

We describe a novel readout system for photon-counting microchannel plate detectors, based on a custom-designed event-driven CMOS Active Pixel Sensor (APS). The event-driven APS device is fiber-optically coupled to the microchannel plate intensifier in a configuration analogous to that employed in intensified CCDs (ICCDs). APS technology permits the incorporation of comparator circuitry within each pixel. When coupled with suitable CMOS logic outside the array area, the comparators can be used to trigger the readout of small sub-array windows only when and where intensified photon events have been detected. The event-driven APS readout thus completely eliminates the local dynamic range limitation of ICCDs, while achieving a high global count rate capability and delivering high (MCP-limited) spatial resolution (through sub-pixel centroiding of the event splashes, performed off-chip). We elaborate on this concept and the design of the event-driven APS below.

We present our latest results in the development of Silicon micromachined microchannel plates, which open completely new possibilities in the detector technologies. For the first time Z-stacks of Si microchannel plates with pore bias of 5-8 degrees were tested in a high gain photon counting imaging detector without any post-amplification stage with conventional glass MCP's. The gain of Z-stacks of Si (40:1 L/D, 6 μm pores on 8 μm centers, 18-25 mm in diameter) MCP's was found to be as high as ~10⁶ with peaked pulse height distribution. The full-field illumination images appeared to be quite uniform, with relatively small (~±10%) gain variation. Quantum efficiency of opaque diamond photocathode deposited on Si MCP was measured in reflection mode and compared with the performance of flat-substrate diamond photocathodes. We also present the results of our study of long-term gain stability of Si MCP's: variation of Si MCP gain as a function of extracted charge was investigated.

The basic requirement for an imaging low-light level system (one capable of single photon counting) is that the device has low dark current. Photocathode based devices have the advantage over solid state devices in this regard as the dark current is inherently low. A further requirement for UV detectors is the necessity to suppress the sensitivity in the red, and wide-band gap semi-conductors fill this role well. For nitride based semi-conductors, there is still the issue of making p-type material and making alloys with Al or In to move the red cutoff to the blue (Al) or red (In). Regardless of the material (e.g. another choice is diamond) coupling the resulting photocathode to a device such as a micro-channel plate (MCP) is necessary to produce imaging. Based on advances we have made both in the production of p-type GaN photocathodes, diamond photocathodes, and read-outs of Si MCPs, we are on the verge of making high quality UV imaging systems for astronomy and other low-light level applications. However, the outstanding question is how to optimize the photo-cathode performance. In this paper we discuss this question in the context of our progress in making GaN-based photo-cathodes.

The Wide Field Camera 3 (WFC3) is an instrument which is being developed for the Hubble Space Telescope. It will have a UV/VIS channel which will include two 2051 X 4096 pixel, thin, backside illuminated CCDs. These CCDs produce interference fringes in narrow band or monochromatic light images taken in the 700 nm to 1000 nm wavelength range. We have obtained 146 monochromatic images for each of the four flight candidate CCDs. These images can be used to model the physical structure of the CCD, which are described by a set of parameters deduced by solving the Fresnel equations for the absorption within the CCD as a function of wavelength. We have used the formalism developed to model the Space Telescope Imaging Spectrograph's CCD by Malumuth et. al. to determine the free parameters for a large portion of one of the WFC3 flight candidate CCDs. From these fits we are able to evaluate the ability to fit the fringing of real data by comparing a model fringe flat to an observed fringe flat. We find that we should be able to reduce the observed fringe amplitude by a factor of five or better. Finally we show that for a certain class of object (extended emission line object with a variety of radial velocities) this model is an excellent method for removing the effect of fringing.

Physical surface changes due to a wet chemical method to increase the extreme ultraviolet (EUV) quantum detection efficiency (QDE) of microchannel plate (MCP) detectors is examined. We show evidence that enhanced channel surface roughness and the creation of a low density surface layer combine to increase the secondary electron emission coefficient, which inturn, increases the quantum detection efficiency of the input MCP. The use of the wet chemical method to enhance the MCP EUV QDE by five different space flight programs is also discussed.

We report on the progress of the activity, started one year ago, to obtain a photon counting, MCP-based detector, optimized for high count-rate. A new electronic board, hosting both the APS and the electronics processing unit, has been developed. The new architecture of the system, designed to drive the detector, to acquire the images and compute the photon event centers, is described in detail in this paper. We also report the functional tests carried out on the sub-parts of the detector along with a preliminary characterization of the system.

The primary goal of the Spectroscopy and Photometry of the IGM's Diffuse Radiation (SPIDR) Mission is to detect and map the huge filamentary structures, the "cosmic web", predicted to be present in the IGM. The SPIDR instrument comprises six imaging spectrographs providing 8° x 8° and 2.5° x 2.5° high-resolution spatial maps of IGM features in the OVI and CIV wavelength bands. For simplicity and economy all six spectrographs utilize virtually identical detector systems. Each detector records a two-dimensional image whose axes represent spectral and one-dimensional spatial information, the second spatial axis being obtained by tomographic reconstruction. We describe the design of the prototype detector built for the SPIDR mission. The detector uses a conventional microchannel plate (MCP) arrangement with a charge division readout anode used in the image charge configuration. The image charge technique provides enhanced resolution, linearity and stability in a more compact mechanical design. The predictable distribution of the induced image charge footprint has allowed us to accurately simulate the readout performance in software. The conservative requirements of the SPIDR spectrograph allow the use of a conventional wedge and strip anode which benefits from the design improvements generated using our software simulation. Redesign of the boundary electrodes has enabled us to improve overall linearity and increase useful imaging area. We describe the integrated electronics system for the SPIDR prototype, designed for low mass and power consumption. A single printed circuit board is used to house analog signal processing, digital processing, and power systems.

We describe the performance results for the Galaxy Evolution Explorer (GALEX) far ultraviolet (FUV) and near ultraviolet (NUV) detectors. The detectors were delivered to JPL/Caltech starting in the fall of 2000 and have undergone approximately 1000 hours of pre-flight system-level testing to date. The GALEX detectors are sealed tube micro-channel plate (MCP) delay line readout detectors. They have a 65 mm diameter active area, which will be the largest format on orbit. The FUV detector has a spectral bandpass from 115 - 180 nm and the NUV detector has a bandpass from 165 - 300 nm. We report here on the performance of the detectors before and after integration into the instrument. Characteristics measured include the background count rate and distribution, gain vs. applied high voltage, spatial resolution and linearity, flat fields, and quantum efficiency.

The SPEAR (Spectroscopy of Plasma Evolution from Astrophysical Radiation) mission to map the far ultraviolet sky uses micro-channel plate (MCP) detectors with a crossed delay line anode to record photon arrival events. SPEAR has two MCP detectors, each with a ~25mm x 25 mm active area. The unconventional anode design allows for the use of a single set of position encoding electronics for both detector fields. The centroid position of the charge cloud, generated by the photon-stimulated MCP, is determined by measuring the arrival times at both ends of the anode following amplification and external delay. The temporal response of the detector electronics system determines the readout's positional resolution for the charge centroid. High temporal resolution (< 35ps x 75ps FWHM) and low power consumption (<6W) are required for the SPEAR detector electronics system. We describe the development and performance of the detector electronics system for the SPEAR mission.

The Far Ultraviolet Spectroscopic Explorer satellite (FUSE) is a NASA Origins mission launched on 1999 June 24 and operated from the Johns Hopkins University Homewood campus in Baltimore, MD. FUSE consists of four aligned telescopes feeding twin far-ultraviolet spectrographs that achieve a spectral resolution of R=20,000 over the 905-1187 Å spectral region. This makes FUSE complementary to the Hubble Space Telescope and of broad general interest to the astronomical community. FUSE is operated as a general-purpose observatory with proposals evaluated and selected by NASA. The FUSE mission concept evolved dramatically over time. The version of FUSE that was built and flown was born out of the "faster, better, cheaper" era, which drove not only the mission development but also plans for operations. Fixed price contracts, a commercial spacecraft, and operations in the University environment were all parts of the low cost strategy. The satellite performs most functions autonomously, with ground contacts limited typically to seven 12-minute contacts per day through a dedicated ground station. All support functions are managed by a staff of 40 scientists and engineers located at Johns Hopkins. In this configuration, we have been able to achieve close to 30% average on-target science efficiency. In short, FUSE is a successful example of the "faster, better, cheaper" philosophy.

This paper presents new families of geocentric orbits in the Sun-Earth spatial elliptic three-body problem (ER3BP) useful for deep space science missions such as planet finding and characterization. The main driver for this study is the need to find practical geocentric orbits that remain within a bounded distance from Earth, thus allowing high data-rate communication while ensuring safe operational environment far from thermal perturbations and visual occultations as well as Earth's magnetic and radiation fields, yet free of the stability and stationkeeping concerns associated with libration point missions or Halo orbits. The orbit characterization procedure is performed using a novel approach. Optimal initial conditions are found using niching genetic algorithms, which render global optimization while permitting several optimal or sub-optimal solutions to co-exist. This approach yields diverse families of orbits, both planar and three-dimensional, including out-of-ecliptic orbits that greatly reduce the impact of the local zodiacal cloud. Stability of the orbits is determined using the notion of practical stability. The effect of solar radiation pressure and the Moon's gravitational perturbation are simulated, showing that the orbits are not significantly affected. This feature implies that no station-keeping is required. Optimal direct transfer trajectories from Low Earth orbit are briefly presented, showing that insertion into the characterized orbits may be performed using modest energetic requirements.

We discuss technologies for micro-arcsec echo mapping of black hole accretion flows in Active Galactic Nuclei (AGN). Echo mapping employs time delays, Doppler shifts, and photoionization physics to map the geometry, kinematics, and physical conditions in the reprocessing region close to a compact time-variable source of ionizing radiation. Time delay maps are derived from detailed analysis of variations in lightcurves at different wavelengths. Echo mapping is a maturing technology at a stage of development similar to that of radio inteferometry just before the VLA. The first important results are in, confirming the basic assumptions of the method, measuring the sizs of AGN emission line regions, delivering dozens of black hole masses, and showing the promise of the technique. Resolution limits with existing AGN monitoring datasets are typically approximately 5 - 10 light days. This should improve down to 1 - 2 light days in the next-generation echo mapping experiments, using facilities like Kronos and Robonet that are designed for and dedicated to sustained spectroscopic monitoring. A light day is 0.4 micro-arcsec at a redshift of 0.1, thus echo mapping probes regions 10³ times smaller than with VLBI, and 10⁵ times smaller than with HST.

Kronos is a multiwavelength observatory designed to map the accretion disks and environments of supermassive black holes in various environments using the natural intrinsic variability of the accretion-driven sources. Kronos is envisaged as a Medium Explorer mission to NASA Office of Space Science under the Structure and Evolution of the Universe theme. We will achieve the Kronos science objectives by developing cost-effective techniques for obtaining and assimilating data from the research spacecraft and its subsequent work on the ground. The science operations assumptions for the mission are: (1 Need for flexible scheduling due to the variable nature of targets, (2) Large data volumes but minimal ground station contact, (3) Very small staff for operations. Our first assumption implies that we will have to consider an effective strategy to dynamically reprioritize the observing schedule to maximize science data acquisition. The flexibility we seek greatly increases the science return of the mission, because variability events can be properly captured. Our second assumption implies that we will have to develop some basic on-board analysis strategies to determine which data get downloaded. The small size of the operations staff implies that we need to "automate" as many routine processes of science operations as possible. In this paper we will discuss the various solutions that we are considering to optimize our operations and maximize science returns on the observatory.

The FUSE (Far Ultraviolet Spectroscopic Explorer) instrument includes two large-format microchannel plate detectors with double delay line anodes. The generally good detector performance has permitted the collection of scientific data with high spectral resolving power, and has enabled the observation of fainter objects than could be easily observed with previous missions in this wavelength range. As with any complex instrumentation, however, there have been numerous challenges which have arisen during the mission. We discuss the on-orbit performance of the FUSE detectors since launch, and describe some of the lessons learned. This includes a discussion of their operation on orbit and the effects that detector performance has had on the scientific data collected. The strategies taken to minimize the impact of detector anomalies on the data will also be discussed.

The Far Ultraviolet Spectroscopic Explorer is a NASA Origins mission launched in June 1999 to obtain high-resolution spectra of astronomical sources at far-ultraviolet wavelengths. The science objectives require the satellite to provide inertial pointing at arbitrary positions on the sky with sub-arcsecond accuracy and stability. The requirements were met using a combination of ring-laser gyroscopes, three-axis magnetometers, and a fine error sensor for attitude knowledge, and reaction wheels for attitude control. Magnetic torquer bars are used for momentum management of the reaction wheels, and coarse sun sensors for safe mode pointing. The gyroscopes are packaged as two coaligned inertial reference units of three orthogonal gyroscopes each. There are four reaction wheels: three oriented along orthogonal axes, the fourth skewed at equal angles (54.7°) with respect to the others. Early in the mission the gyroscopes began showing signs of aging more rapidly than expected, and one failed after two years of operation. In addition, two of the orthogonal wheels failed in late 2001. The flight software has been modified to employ the torquer bars in conjunction with the two remaining wheels to provide fine pointing control. Additional new flight software is under development to provide attitude control if both gyroscopes fail on one or more axes. Simulations indicate that the pointing requirements will still be met, though with some decrease in observing efficiency. We will describe the new attitude control system, compare performance characteristics before and after the reaction wheel failures, and present predicted performance without gyroscopes.

The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5 km. It is designed to image stars and binaries with sufficient resolution to enable long-term studies of stellar magnetic activity patterns, for comparison with those on the sun. It will also support asteroseismology (acoustic imaging) to probe stellar internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of the magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars. The ultimate goal of the mission is to achieve the best-possible forecasting of solar activity as a driver of climate and space weather on time scales ranging from months up to decades, and an understanding of the impact of stellar magnetic activity on life in the Universe. In this paper we describe the scientific goals of the mission, the performance requirements needed to address these goals, the "enabling technology" development efforts being pursued, and the design concepts now under study for the full mission and a possible pathfinder mission.

The Full-sky Astrometric Mapping Explorer (FAME) space mission will perform an all sky astrometric survey with unprecedented accuracy. FAME will produce an astrometric catalog of 40 million stars between 5th and 15th visual magnitude. For the bright stars (5th to 9th magnitude), FAME will determine the positions and parallaxes to better than 50 μas, with proper motion errors of 70 μas per year. For the fainter stars (between l0th and 15th magnitude), FAME will determine positions and parallaxes accurate to better than 500 μas with proper motions errors less than 500 μas per year. FAME will also collect photometric data on the 40 million stars. The accuracy of a single observation of a 9th magnitude star will be 1 mmag. The FAME mission will impact almost all areas of astrophysics. It will find planets revolving around nearby stars, further studies of stellar evolution, determine the location of dark matter in the Milky Way galaxy, and measure the size and age of the universe. It will also establish a celestial reference frame with an accuracy better than a microarcsecond.

Kronos is a multiwavelength observatory proposed as a NASA Medium Explorer. Kronos is designed to make use of the natural variability of accreting sources to create microarcsecond-resolution maps of the environments of supermassive black holes in active galaxies and stellar-size black holes in binary systems and to characterize accretion processes in Galactic compact binaries. Kronos will obtain broad energy range spectroscopic data with co-aligned X-ray, ultraviolet, and optical spectrometers. The high-Earth orbit of Kronos enables well-sampled, high time-resolution observations, critical for the innovative and sophisticated methods that are used to understand the accretion flows, mass outflows, jets, and other phenomena found in accreting sources. By utilizing reverberation mapping analysis techniques, Kronos produces advanced high-resolution maps of unprecedented resolution of the extreme environment in the inner cores of active galaxies. Similarly, Doppler tomography and eclipse mapping techniques characterize and map Galactic binary systems, revealing the details of the physics of accretion processes in black hole, neutron star, and white dwarf binary systems. The Kronos instrument complement, sensitivity, and orbital environment make it suitable to aggressively address time variable phenomena in a wide range of astronomical objects from nearby flare stars to distant galaxies.

We present the instrument design, the image motion correction algorithm, and the predicted performance of the Ultraviolet Imager (UVI) proposed for the Jupiter Magnetospheric Explorer (JMEX) mission. The JMEX mission is a small explorer mission (SMEX) designed to observe the Jovian system and to study the dynamical relationship between Jupiter's magnetosphere and Io, the primary source for the Io plasma torus. JMEX was selected as one of six SMEX missions for review by NASA following additional design and analysis. While not selected for flight, the design includes several innovative design features which permit 0.25" imaging on a SMEX class spacecraft which are of general interest. The UVI consists of the Ultraviolet Telescope (UVT) and the Ultraviolet Imager Instrument Package (UVIIP). The UVT is a 50 cm Cassegrain telescope, and the UVIIP consists of an elliptical tertiary mirror, an eight position filter/prism wheel, a cross-delay line microchannel plate detector and a visible light image motion sensor. The integrated system will provide 0.25" imaging over a 100" field of view between 115 and 200nm.

We present a status report on CHIPS, the Cosmic Hot Interstellar Plasma Spectrometer. CHIPS is the first NASA University-Class Explorer (UNEX) project. CHIPS was selected in 1998 and is now scheduled for launch in December of 2002. The grazing incidence CHIPS spectrograph will survey the sky and record spectra of diffuse emission in the comparatively unexplored wavelength band between 90 and 260 Å. These data will provide important new constraints on the temperature, ionization state, and emission measure of hot plasma in the "local bubble" of the interstellar medium.

The evolution of hot interstellar medium (ISM) in galaxies is fundamental to the evolution of our cosmos. The Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) mission will study the hot ISM, providing pointed observations and the first all-sky spectral maps in the Far (FUV) Ultraviolet. The FUV bandpass contains the primary cooling lines of abundant elements in a variety of ionization states. SPEAR's broad bandpass (λλ 900 - 1750 Å), spectral resolution (λ/δλ ~ 700) and imaging resolution (5' - 10') has been chosen to determine independently the quantity, temperature, depletion, and ionization of hot galactic gas. These SPEAR data will allow us to study the hot ISM on both large and small scales and to discriminate among models of the large-scale creation, distribution, and evolution of hot gas in the Galactic disk and halo.

The proposed SuperNova/Acceleration Probe (SNAP) mission will have a two-meter class telescope delivering diffraction-limited images to an instrumented 0.7 square-degree field sensitive in the visible and near-infrared wavelength regime. We describe the requirements for the instrument suite and the evolution of the focal plane design to the present concept in which all the instrumentation -- visible and near-infrared imagers, spectrograph, and star guiders -- share one common focal plane.

EUVE and the ROSAT WFC have left a tremendous legacy in astrophysics at EUV wavelengths. More recently, Chandra and XMM-Newton have demonstrated at X-ray wavelengths the power of high-resolution astronomical spectroscopy, which allows the identification of weak emission lines, the measurement of Doppler shifts and line profiles, and the detection of narrow absorption features. This leads to a thorough understanding of the density, temperature, abundance, magnetic, and dynamic structure of astrophysical plasmas. However, the termination of the EUVE mission has left a gap in spectral coverage at crucial EUV wavelengths (~100-300 Å), where hot (10⁵ - 10⁸ K) plasmas radiate most strongly and produce critical spectral diagnostics. CHIPS will fill this hole only partially as it is optimized for diffuse emission and has only moderate resolution (R~150). For discrete sources, we have successfully flown a follow-on instrument to the EUVE spectrometer (A_eff ~ 1 cm², R ~ 400), the high-resolution spectrometer J-PEX (A_eff ~ 3 cm², R ~ 3000). Here we build on the J-PEX prototype and present a strawman design for an orbiting spectroscopic observatory, APEX, a SMEX-class instrument containing a suite of 8 spectrometers that together achieve both high effective area (A_eff > 10 cm²) and high spectral resolution (R ~ 10,000) over the range 100-300 Å. We also discuss alternate configurations for shorter and longer wavelengths.

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit m_AB~20-21) to an ultra-deep survey of 4 square degrees (limit m_AB~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (m_AB~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

The Far Ultraviolet Spectroscopic Explorer (FUSE) has been a great success, and has addressed many critical scientific questions (Moos, et al, 2000). However, it has also highlighted the need for even more powerful instrumentation in the 900-1200 Å regime. In particular, significantly increased effective area will permit the pursuit of additional scientific programs currently impractical or impossible with FUSE. It is unlikely that FUSE will last more than a few more years. Nor is it likely that any large scale UV-optical follow-on to HST (such as SUVO) will include the 900-1200 Å bandpass. However, FUSE remains well oversubscribed and continues to perform excellent science. Therefore, a MIDEX class mission in the next 4-6 years that could significantly improve on the FUSE capabilities would be a powerful scientific tool that would be of great utility to the astronomical community. It would open up new scientific programs if it can improve on the sensitivity of FUSE by an order of magnitude. We have identified a powerful technique for efficient, high-resolution spectroscopy in the FUV (and possibly the EUV) that may provide exactly what is needed for such a mission. To achieve a factor of 10 improvement in effective area, we propose using a large (meter class), low-cost, grazing incidence metal optics. This would produced in a manner similar to the EUVE mirrors (Green, et al, 1986), using diamond turning to create the optical figure followed by uncontrolled polishing to achieve a high quality surface. This process will introduce significant figure errors that will degrade the image quality. However, if a holographic grating is employed, which has utilized the actual telescope in the recording geometry, all wavefront errors will be automatically corrected in the end-to-end spectrometer, and high quality spectroscopy will be possible with low quality (and low-cost) optics. In this way a MIDEX class FUSE can be proposed with 10 times the effective area of the current instrument.

The SPIDR mission is designed to test predictions of cosmological models of the structure of the universe. In addition, SPIDR will provide new information about hot gas in a variety of Galactic environments. These diagnostics will bo obtained through spectral imaging of selected astrophysical fields in the 100 - 160 nm band. In this paper we will provide an overview of the SPIDR mission and its observational approach.

The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibility, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS. The WSO, as presently conceived, will be constructed and operated with the same distributed philosophy. This will allow as many groups and countries to participate, each contributing as much as feasible but allowing multi-national participation. Although designed originally with a conservative approach, the WSO embodies some innovative ideas and will allow a world-class mission to be realized with a moderate budget.

We report on the successful sounding rocket flight of the high resolution (R=3000-4000) J-PEX EUV spectrometer. J-PEX is a novel normal incidence instrument, which combines the focusing and dispersive elements of the spectrometer into a single optical element, a multilayer-coated grating. The high spectral resolution achieved has had to be matched by unprecedented high spatial resolution in the imaging microchannel plate detector used to record the data. We illustrate the performance of the complete instrument through an analysis of the 220-245Å spectrum of the white dwarf G191-B2B obtained with a 300 second exposure. The high resolution allows us to detect a low-density ionized helium component along the line of sight to the star and individual absorption lines from heavier elements in the photosphere.

The SPEAR micro-satellite payload consists of dual imaging spectrographs optimized for detection of the faint, diffuse FUV (900-1750 Å) radiation emitted from interstellar gas. The instrument provides spectral resolution, R~750, and long slit imaging of <10' over a large (8°x5') field of view. We enhance the sensitivity by using shutters and filters for removal of background noise. Each spectrograph channel uses identically figured optics: a parabolic-cylinder entrance mirror and a constant-ruled ellipsoidal grating. Two microchannel plate photon-counting detectors share a single delay-line encoding system. A payload electronics system conditions data and controls the instrument. We will describe the design and predicted performance of the SPEAR instrument system and its elements.

Ultraviolet astronomy is an important tool for the study of the interplanetary medium and diffuse, angularly extended emissions in planetary/comet atmospheres and their near space environments. We describe a new technique for high étendue observations of emission lines at R > 10⁵ with an all-reflective spatial heterodyne spectrometer and polarmetric sampling of these lines with an ultraviolet optimized waveplate-Brewster mirror combination. The resulting system is themo-mechanically stable, has light collecting power substantially greater than HST for extended emissions, despite having a volume of several x 10^-3 m³. This makes the SHS polarimeter ideal for spacecraft applications. We describe the SHS and polarmetric optical techniques and provide a discussion of its planned development for studies of interplanetary hydrogen.

The ACS solar blind channel (SBC) is a photon-counting MAMA detector capable of producing two-dimensional imaging in the UV at wavelengths 1150-1700 Angstroms, with a field of view (FOV) of 31" × 35". We describe the on-orbit performance of the ACS/SBC from an analysis of data obtained from the service mission observatory verification (SMOV) programs. Our summary includes assessment of the point-source image quality and point spread function (PSF) over the SBC FOV, the dark current measurements, the characteristics of the flat fields, fold analysis, throughput, and the UV sensitivity monitor to check for contamination. Where appropriate, a comparison with pre-launch calibration data will also be made.