We have worked to define the compelling next generation General Astrophysics science that the 4m implementation of the HabEx mission concept might enable. These science drivers have been used to define requirements for a far ultraviolet (FUV) spectrograph design for the telescope design that meets the needs of these programs. We describe both the drivers and the baseline design for the instrument, the modes it might support, and the choices that were made to optimize the performance. The operational performance of the instrument in cooperation with the rest of the telescope design is also discussed.
The HabEx study is defining a concept for a new space telescope with the primary mission of detecting and characterizing planetary systems around nearby stars. The telescope is designed specifically to operate with both a high contrast coronagraph and a starshade, enabling the direct optical detection of exoplanets as close as 70 mas from their star. The telescope will be equipped with cameras for exoplanetary system imaging and with spectrometers capable of characterizing exoplanet atmospheres. Gases such as oxygen, carbon dioxide, water vapor and methane have spectral lines in the visible and near infrared part of the spectrum and may indicate biological activity. In addition to the study of exoplanets, HabEx enables general astrophysics with two dedicated instruments. One instrument is a camera enabling imaging on a 3 arc minute field of view in two bands stretching from the UV to the near infrared. The same instrument can also be operated as a multi-object spectrograph, with resolution of 2000. A second instrument will be a high resolution UV spectrograph operating from 120 nm with up to 60,0000 resolution. We discuss the preliminary designs of the telescope and the optical instruments for the observatory.
The WFIRST Coronagraph Instrument will perform direct imaging of exoplanets via coronagraphy of the host star. It uses both the Hybrid Lyot and Shaped Pupil Coronagraphs to meet the mission requirements. The Phase A optical design fits within the allocated instrument enclosure and accommodates both coronagraphic techniques. It also meets the challenging wavefront error requirements. We present the optical performance including throughput of the imaging and IFS channels, as well as the wavefront errors at the first pupil and the imaging channel. We also present polarization effects from optical coatings and analysis of their impacts on the performance of the Hybrid Lyot coronagraph. We report the results of stray light analysis of our Occulting Mask Coronagraph testbed.
The CubeSat Infrared Atmospheric Sounder (CIRAS) will measure upwelling infrared radiation of the Earth in the MWIR region of the spectrum from space on a CubeSat. The observed radiances have information of potential value to weather forecasting agencies and can be used to retrieve lower tropospheric temperature and water vapor globally for weather and climate science investigations. Multiple units can be flown to improve temporal coverage or in formation to provide new data products including 3D atmospheric motion vector winds. CIRAS incorporates key new instrument technologies including a 2D array of High Operating Temperature Barrier Infrared Detector (HOT-BIRD) material, selected for its high uniformity, low cost, low noise and higher operating temperatures than traditional materials. The detectors are hybridized to a commercial ROIC and commercial camera electronics. The second key technology is an MWIR Grating Spectrometer (MGS) designed to provide imaging spectroscopy for atmospheric sounding in a CubeSat volume. The MGS has no moving parts and includes an immersion grating to reduce the volume and reduce distortion. The third key technology is an infrared blackbody fabricated with black silicon to have very high emissivity in a flat plate construction. JPL will also develop the mechanical, electronic and thermal subsystems for CIRAS, while the spacecraft will be a commercially available CubeSat. The integrated system will be a complete 6U CubeSat capable of measuring temperature and water vapor profiles with good lower tropospheric sensitivity. The CIRAS is the first step towards the development of an Earth Observation Nanosatellite Infrared (EON-IR) capable of operational readiness to mitigate a potential loss of CrIS on JPSS or complement the current observing system with different orbit crossing times.
Scientific consensus from a 2015 pre-Decadal Survey workshop highlighted the essential need for a wide-swath (mapping) low earth orbit (LEO) instrument delivering carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) measurements with global coverage. OCO-2 pioneered space-based CO2 remote sensing, but lacks the CH4, CO and mapping capabilities required for an improved understanding of the global carbon cycle. The Carbon Balance Observatory (CARBO) advances key technologies to enable high-performance, cost-effective solutions for a space-based carbon-climate observing system. CARBO is a compact, modular, 15-30° field of view spectrometer that delivers high-precision CO2, CH4, CO and solar induced chlorophyll fluorescence (SIF) data with weekly global coverage from LEO. CARBO employs innovative immersion grating technologies to achieve diffraction-limited performance with OCO-like spatial (2x2 km2) and spectral (λ/Δλ ≈ 20,000) resolution in a package that is >50% smaller, lighter and more cost-effective. CARBO delivers a 25- to 50-fold increase in spatial coverage compared to OCO-2 with no loss of detection sensitivity. Individual CARBO modules weigh < 20 kg, opening diverse new space-based platform opportunities.
Spacecraft carrying optical communication lasers can be treated as artificial stars, whose relative astrometry to Gaia reference stars provides spacecraft positions in the plane-of-sky for optical navigation. To be comparable to current Deep Space Network delta-Differential One-way Ranging measurements, thus sufficient for navigation, nanoradian optical astrometry is required. Here we describe our error budget, techniques for achieving nanoradian level ground-base astrometry, and preliminary results from a 1 m telescope. We discuss also how these spacecraft may serve as artificial reference stars for adaptive optics, high precision astrometry to detect exoplanets, and tying reference frames defined by radio and optical measurements.
Alignment and Phasing System (APS) is responsible for the optical alignment via starlight of the approximately 12,000 degrees of freedom of the primary, secondary and tertiary mirrors of Thirty Meter Telescope (TMT). APS is based on the successful Phasing Camera System (PCS) used to align the Keck Telescopes. Since the successful APS conceptual design in 2007, work has concentrated on risk mitigation, use case generation, and alignment algorithm development and improvement. Much of the risk mitigation effort has centered around development and testing of prototype APS software which will replace the current PCS software used at Keck. We present an updated APS design, example use cases and discuss, in detail, the risk mitigation efforts.
The most recent concept for the Wide Field Infrared Survey Telescope (WFIRST) Design Reference Mission (DRM) features an instrument that will perform exoplanet detection via coronagraphy of the host star. This observatory is based on the existing Astrophysics Focused Telescope Asset’s (AFTA) 2.4-meter telescope. The WFIRST/AFTA Coronagraph Instrument combines the Hybrid Lyot and Shaped Pupil Coronagraphs to meet the science requirements. The cycle 5 optical design fits the required enclosure and accommodates both coronagraphic architectures. We present the optical performance including throughput of both the imaging and the IFS channels, the wavefront error at the first pupil, and polarization effects from optical coatings.
The WFIRST-AFTA coronagraph instrument takes advantage of AFTAs 2.4-meter aperture to provide novel exoplanet imaging science at approximately the same instrument cost as an Explorer mission. The AFTA coronagraph also matures direct imaging technologies to high TRL for an Exo-Earth Imager in the next decade. The coronagraph Design Reference Mission (DRM) optical design is based on the highly successful High Contrast Imaging Testbed (HCIT), with modifications to accommodate the AFTA telescope design, service-ability, volume constraints, and the addition of an Integral Field Spectrograph (IFS). In order to optimally satisfy the three science objectives of planet imaging, planet spectral characterization and dust debris imaging, the coronagraph is designed to operate in two different modes: Hybrid Lyot Coronagraph or Shaped Pupil Coronagraph. Active mechanisms change pupil masks, focal plane masks, Lyot masks, and bandpass filters to shift between modes. A single optical beam train can thus operate alternatively as two different coronagraph architectures. Structural Thermal Optical Performance (STOP) analysis predicts the instrument contrast with the Low Order Wave Front Control loop closed. The STOP analysis was also used to verify that the optical/structural/thermal design provides the extreme stability required for planet characterization in the presence of thermal disturbances expected in a typical observing scenario. This paper describes the instrument design and the flow down from science requirements to high level engineering requirements.
We evaluate in detail the stability requirements for a band-limited coronagraph with an inner working angle as small as 2
λ/D coupled to an off-axis, 3.8-m diameter telescope. We have updated our methodologies since presenting a stability
error budget for the Terrestrial Planet Finder Coronagraph mission that worked at 4 λ/D and employed an 8th-order
mask to reduce aberration sensitivities. In the previous work, we determined the tolerances relative to the total light
leaking through the coronagraph. Now, we separate the light into a radial component, which is readily separable from a
planet signal, and an azimuthal component, which is easily confused with a planet signal. In the current study,
throughput considerations require a 4th-order coronagraph. This, combined with the more aggressive working angle,
places extraordinarily tight requirements on wavefront stability and opto-mechanical stability. We find that the
requirements are driven mainly by coma that leaks around the coronagraph mask and mimics the localized signal of a
planet, and pointing errors that scatter light into the background, decreasing SNR. We also show how the requirements
would be relaxed if a low-order aberration detection system could be employed.
We are developing the Background-Limited Infrared-Submillimeter Spectrograph (BLISS) for SPICA to provide
a breakthrough capability for far-IR survey spectroscopy. SPICAs large cold aperture allows mid-IR to submm
observations which are limited only by the natural backgrounds, and BLISS is designed to operate near this
fundamental limit. BLISS-SPICA is 6 orders of magnitude faster than the spectrometers on Herschel and
SOFIA in obtaining full-band spectra. It enables spectroscopy of dust-obscured galaxies at all epochs back to
the rst billion years after the Big Bang (redshift 6), and study of all stages of planet formation in circumstellar
BLISS covers 35 - 433 microns range in ve or six wavelength bands, and couples two 2 sky positions simultaneously.
The instrument is cooled to 50 mK for optimal sensitivity with an on-board refrigerators. The detector
package is 4224 silicon-nitride micro-mesh leg-isolated bolometers with superconducting transition-edge-sensed
(TES) thermistors, read out with a cryogenic time-domain multiplexer. All technical elements of BLISS have
heritage in mature scientic instruments, and many have own. We report on our design study in which we are
optimizing performance while accommodating SPICAs constraints, including the stringent cryogenic mass budget.
In particular, we present our progress in the optical design and waveguide spectrometer prototyping. A
companion paper in Conference 7741 (Beyer et al.) discusses in greater detail the progress in the BLISS TES
The Advanced Wavefront Sensing and Control Testbed (AWCT) is built as a versatile facility for developing and
demonstrating, in hardware, the future technologies of wavefront sensing and control algorithms for active optical
systems. The testbed includes a source projector for a broadband point-source and a suite of extended scene targets, a
dispersed fringe sensor, a Shack-Hartmann camera, and an imaging camera capable of phase retrieval wavefront
sensing. The testbed also provides two easily accessible conjugated pupil planes which can accommodate active optical
devices such as fast steering mirror, deformable mirror, and segmented mirrors. In this paper, we describe the testbed
optical design, testbed configurations and capabilities, as well as the initial results from the testbed hardware
integrations and tests.
A technology for establishing best focus of an optical system is described. This technology was recently used to establish best focus of the Orbiting Carbon Observatory spectrometers while the instrument was undergoing thermal-vacuum testing. Three piezo-actuated motors were used to adjust the tip, tilt, and piston of a focal plane assembly relative to the spectrometer's optical system. A set of optical displacement sensors measured tip-tilt-piston throughout the focusing process. With best focus established and confirmed using a pupil-slicing technique, the corresponding sensor measurements were used to specify the geometry and dimensions of a precision-ground shim ring.
The Astrometric Beam Combiner (ABC) is a critical element of the Space Interferometry Mission (SIM) that
performs three key functions: coherently combine starlight from two siderostats; individually detect starlight for
angle tracking; and disperse and detect the interferometric fringes. In addition, the ABC contains: a stimulus,
cornercubes and shutters for in-orbit calibration; several tip/tilt mirror mechanisms for in-orbit alignment; and
internal metrology beam launcher for pathlength monitoring. The detailed design of the brassboard ABC (which
has the form, fit and function of the flight unit) is complete, procurement of long-lead items is underway, and
assembly and testing is expected to be completed in Spring 2009. In this paper, we present the key requirements
for the ABC, details of the completed optical and mechanical design as well as plans for assembly and alignment.
A breadboard is under development to demonstrate the calibration of spectral errors in microarcsecond stellar
interferometers. Analysis shows that thermally and mechanically stable hardware in addition to careful optical design
can reduce the wavelength dependent error to tens of nanometers. Calibration of the hardware can further reduce the
error to the level of picometers. The results of thermal, mechanical and optical analysis supporting the breadboard
design will be shown.