ATLAST: Advanced Technology Large-Aperture Space Telescope Marc Postman STScI Pathways 2009, Barcelona, Spain A NASA Astrophysics Strategic Mission Concept Study of the Science Cases & Technology Developments needed to build an AFFORDABLE 8m - 16m UV/Optical Filled-Aperture Space Telescope
Ball Aerospace: Vic Argabright Teri Hanson Paul Atcheson Leela Hill Morley Blouke Steve Kilston Dennis Ebbets Goddard Space Flight Center: David Aronstein Rick Lyon Lisa Callahan Gary Mosier Mark Clampin Bill Oegerle David Content Bert Pasquale Qian Gong George Sonneborn Ted Gull Richard Wesenberg Tupper Hyde Jennifer Wiseman Dave Leckrone Bruce Woodgate Advanced Technology Large-Aperture Space Telescope (ATLAST) Concept Study Team JPL: Peter Eisenhardt Dave Redding Greg Hickey Karl Stapelfeldt Bob Korechoff Wes Traub John Krist Steve Unwin Jeff Booth Michael Werner Johnson Space Flight Center: John Grunsfeld Marshall Space Flight Center: Bill Arnold Phil Stahl Randall Hopkins Gary Thronton John Hraba Scott Smith Northrop Grumman: Dean Dailey Chuck Lillie Cecelia Penera Ron Polidan Rolf Danner Amy Lo Princeton University: Jeremy Kasdin Robert Vanderbei David Spergel STScI: Tom Brown Marc Postman, P.I. Rodger Doxsey Neill Reid Andrew Fruchter Kailash Sahu Ian Jordan Babak Saif Anton Koekemoer Ken Sembach Peter McCullough Jeff Valenti Matt Mountain Bob Brown University of Colorado: Webster Cash Mike Shull Jim Green University of Massachusetts: Daniela Calzetti Mauro Giavalisco
Is There Life Elsewhere in the Galaxy? Need to multiply these values by Earth x fB to get the number of potentially life-bearing planets detected by a space telescope. Earth = fraction of stars with Earth-mass planets in HZ fB = fraction of the Earth-mass planets that have detectable biosignatures Why is a large UVOIR space telescope required to answer this question? Habitable Zones (HZ) of nearby stars subtend very small angles (<200 mas) Earth-mass planets within these HZ will be very faint (>29 AB mag) Requires high-contrast (10-10) imaging to see planet. Cannot achieve this from the ground. Number of nearby stars capable of hosting potentially habitable planets is not large (e.g., non-binary, solar type or later). Sample size D3 Planets with detectable biosignatures may be rare. May need to search many systems to find even a handful. Sample size D3 Number of FGK stars for which SNR=10, R=70 spectrum of Earth-twin could be obtained in <500 ksec If: EarthxfB ~1 then DTel ~ 4m EarthxfB< 1 then DTel ~ 8m EarthxfB << 1 then DTel ~ 16m To maximize the chance for a successful search for life in the solar neighborhood requires a space telescope with an aperture of at least 8-meters Green bars show the number of FGK stars that could be observed 3x each in a 5-year mission without exceeding 20% of total observing time available to community.
45 pc 40 B-V Color < 0.4 30 0.4 - 0.6 0.6 - 0.8 20 0.8 - 1.2 10 > 1.2 5 2-meter 4-meter 3 FGK stars 21 FGK stars 8-meter 16-meter 144 FGK stars 1,010 FGK stars F,G,K type stars whose HZ can be resolved by a telescope of the indicated aperture & for which a R=70 exoplanet spectrum can be obtained in <500 ksec.
SNR=10 @ 760 nm Rayleigh Scattering H2O H2O H2O H2O H2O O2() O2(B) O2(A) H2O O2(A) Detail: @ 750 nm R=100 ATLAST Spectrum of 1 Earth-mass Terrestrial Exoplanet at 10 pc Exposure: 45.6 ksec on 8-m 7.8 ksec on 16-m Bkgd: 3 zodi Contrast: 10-10 Reflectance (Planet Mass)2/3 5 Earth-mass: 15.6 ksec on 8-m
SNR=10 @ 760 nm Rayleigh Scattering H2O H2O H2O H2O O2() O2(B) H2O H2O O2(A) O2(A) Detail: @ 750 nm R=500 ATLAST Spectrum of 1 Earth-mass Terrestrial Exoplanet at 10 pc Exposure: 503 ksec on 8-m 56 ksec on 16-m Bkgd: 3 zodi Contrast: 10-10 Reflectance (Planet Mass)2/3 5 Earth-mass: 172 ksec on 8-m
Earth at 10 pc Earth at 20 pc 16-m 8-m 4-m ~9 days 16-m 8-m 4-m Detecting Photometric Variability in Exoplanets Ford et al. 2003: Model of broadband photometric temporal variability of Earth Require S/N ~ 20 (5% photometry) to detect ~20% temporal variations in reflectivity. Need to achieve a single observation at this S/N in < 0.25 day of exposure time in order to sample the variability with at least 4 independent observations per rotation period.
Transit Spectroscopy Simulations of Super Earthsby Clampin & LindlerAssume: M2 Star with K-mag = 6. Instrumental Effects have been modeled assuming JWST-like spectrograph 8-m ATLAST 16-m ATLAST Intermediate super-earth R = 150 20 transits (P ~ 22 days) Intermediate super-earth R = 150 20 transits Able to retain substantial H2 in atmosphere Super Earths have mass up to 10 x Earth 8-m ATLAST 16-m ATLAST Intermediate super-earth R = 150 100 transits Hydrogen-rich super-earth R = 500 20 transits
ATLAST Concepts 8-m Monolithic Primary (shown with on-axis SM configuration) 9.2-m Segmented Telescope 36 1.3-m hexagonal mirror segments 16.8-m Segmented Telescope 36 2.4-m hexagonal mirror segments
Monolithic Primary On and off-axis secondary mirror concepts investigated. Off-axis concept optimal for exoplanet observations with internal coronagraph but adds complexity to construction and SM alignment. Uses existing ground-based mirror materials. This is enabled by large lift capacity of Ares V cargo launch vehicle (~55 mT). Massive mirror (~20 mT) has ~7 nm rms surface. Total observatory mass ~44 mT. Segmented Primary Only studied designs with an on-axis secondary. Requires use of (relatively) lightweight mirror materials (15 - 25 kg/m2) & efficient fabrication. 9.2m observatory has a total mass of ~14 mT (16.8-m has a total mass of ~35 mT). 9.2-m observatory can fly in EELV: Does not require Ares V. Requires active WFS&C system. Studying two architectures: 8-m monolithic and (9.2-m, 16.8-m) segmented mirror telescopes
Advanced Technology Large-Aperture Space Telescope (ATLAST) 16.8-m in Ares V fairing (with extended height) Ares V Notional 10 m Shroud Delta IV H+ EELV meters 8-m Primary installed in its fully deployed configuration at launch. 8-m Monolithic Telescope 9.2-m Segmented Telescope 16.8-m Segmented Telescope Observatory dry mass = 44 mT Observatory dry mass = 14 mT Observatory dry mass = ~35 mT
On-axis Cass Focus for UV & Exoplanet Instr. Three Mirror Anastigmat (TMA) Focii for Wide Field Instr. Common Features for all Designs • Diffraction limited @ 500 nm • Designed for SE-L2 environment • Non-cryogenic OTA at ~280o K • Thermal control system stabilizes PM temperature to ± 0.1o K • OTA provides two simultaneously available foci - narrow FOV Cassegrain (2 bounce) for Exoplanet & UV instruments and wide FOV TMA channel for Gigapixel imager and MOS • Designed to permit (but not require) on-orbit instrument replacement and propellant replenishment (enables a 20+ year mission lifetime)
Summary of the ATLAST Concepts Assumes a ~$200M technology development program in 2011-2017
Starlight Suppression • Characterizing terrestrial-like exoplanets (<10 Mearth) is a prime ATLAST scientific objective. • Challenge: how do we enable a compelling terrestrial exoplanet characterization program without: • making the optical performance requirements technically unachievable for a viable cost (learn from TPF-C) and • seriously compromising other key scientific capabilities (e.g., UV throughput).
4m 10m 16m Earth 0.25 MEARTH Exoplanet Super-Earth (3x MEARTH) Starlight Suppression Options: External Occulter: “Starshade” ATLAST-9m with 55-m Starshade: 2.0 Zodi 2.0 Zodi 2.0 Zodi 0.4 Zodi Images courtesy of Phil Oakley & Web Cash 2008, 2009 Simulations of exosolar planetary systems at a distance of 10 pc observed with an external occulter and a telescope with the indicated aperture size. Planet detection and characterization become increasingly easier as telescope aperture increases.The challenges of deploying and maneuvering the star shade, however, also increase with increasing telescope aperture. ATLAST Starshade Parameters: 8m - 9.2m telescope: IWA = 58 mas, 55m shade @ ~80,000 km IWA = 40 mas, 75m shade @ ~155,000 km 16m telescope: IWA = 40 mas, 90m shade @ ~185,000 km 3.0 Zodi
1.8m telescope, contrast 1E-9 with IWA of 0.25 arcsec. W. Traub et al. Coronagraph & Wavefront Correction Both Needed Pasquale, Stahl, et al. 2009 ATLAST 8m x 6m Off-axis design Starlight Suppression Options: Internal Coronagraphs • JPL’s High-Contrast Imaging (HCI) Test-Bed has demonstrated sustained contrast levels of < 10-9 using internal, actively corrected coronagraph. Require monolithic mirror and, usually, an off-axis optical design. • Segmented optics introduce additional diffracted light. Visible Nulling Coronagraph (VNC) can, in principle, work with segmented telescope to achieve 10-10 contrast. VNC chosen as starlight suppression method for TMT as well as for EPIC and DAVINCI mission concepts. Transmission VNC Sky Transmission Pattern with 64 x 64 DM at 0.68 - 0.88 microns . Credit: J. Krist, JPL
8-m Starlight Suppression Options: Monolithic On-Axis 8-m Telescope With relay pupil aperture masking, it is possible to place an internal coronagraph behind each sub-aperture. Analysis of performance is TBD. Preliminary dynamic analysis indicates that the double arch spiders have a 7.5 Hz first mode versus the conventional 4-arm spider, which has a 10.5 Hz first mode. The double arch spider meets the Ares V launch requirement. 3m X 6m 3m X 6m Double-arch Spider for 8-m on-axis telescope
For more info on ATLAST:http://www.stsci.edu/institute/atlast Large UVOIR telescopes are required for many other astrophysics research areas • Star formation & evolution; resolved stellar populations • Galaxy formation & evolution; supermassive black hole evolution • Formation of structure in the universe; dark matter kinematics • Origin and nature of objects in the outer solar system A “life finder” telescope will clearly be a multi-billion dollar facility - support by a broad community will be needed if it is to be built. ATLAST can characterize a large sample of potentially habitable worlds AND do a wide range of pioneering astrophysics.