NICMOS 2 observations are crucial for constraining distances to most of the existing sample of z > 1 SNe Ia. Unlike conventional calibration programs, these observations involve long exposure times and low count rates. Reciprocity failure is known to exist in HgCdTe devices and a correction for this effect has already been implemented for high and medium count rates. However, observations at faint count rates rely on extrapolations. Here instead, we provide a new zero-point calibration directly applicable to faint sources. This is obtained via inter-calibration of NIC2 F110W/F160W with the Wide Field Camera 3 (WFC3) in the low count-rate regime using z similar to 1 elliptical galaxies as tertiary calibrators. These objects have relatively simple near-IR spectral energy distributions, uniform colors, and their extended nature gives a superior signal-to-noise ratio at the same count rate than would stars. The use of extended objects also allows greater tolerances on point-spread function profiles. We find space telescope magnitude zero points (after the installation of the NICMOS cooling system, NCS) of 25.296 +/- 0.022 for F110W and 25.803 +/- 0.023 for F160W, both in agreement with the calibration extrapolated from count rates greater than or similar to 1000 times larger (25.262 and 25.799). Before the installation of the NCS, we find 24.843 +/- 0.025 for F110W and 25.498 +/- 0.021 for F160W, also in agreement with the high-count-rate calibration (24.815 and 25.470). We also check the standard bandpasses of WFC3 and NICMOS 2 using a range of stars and galaxies at different colors and find mild tension for WFC3, limiting the accuracy of the zero points. To avoid human bias, our cross-calibration was "blinded" in that the fitted zero-point differences were hidden until the analysis was finalized.

Using the sample of Type Ia supernovae (SNe Ia) discovered by the Hubble Space Telescope (HST) Cluster Supernova Survey and augmented with HST-observed SNe Ia in the GOODS fields, we search for correlations between the properties of SNe and their host galaxies at high redshift. We use galaxy color and quantitative morphology to determine the red sequence in 25 clusters and develop a model to distinguish passively evolving early-type galaxies from star-forming galaxies in both clusters and the field. With this approach, we identify six SN Ia hosts that are early-type cluster members and eleven SN Ia hosts that are early-type field galaxies. We confirm for the first time at z>0.9 that SNe Ia hosted by early-type galaxies brighten and fade more quickly than SNe Ia hosted by late-type galaxies. We also show that the two samples of hosts produce SNe Ia with similar color distributions. The relatively simple spectral energy distributions (SEDs) expected for passive galaxies enable us to measure stellar masses of early-type SN hosts. In combination with stellar mass estimates of late-type GOODS SN hosts from Thomson Chary (2011), we investigate the correlation of host mass with Hubble residual observed at lower redshifts. Although the sample is small and the uncertainties are large, a hint of this relation is found at z>0.9. By simultaneously fitting the average cluster galaxy formation history and dust content to the red-sequence scatters, we show that the reddening of early-type cluster SN hosts is likely E(B-V) < 0.06. The similarity of the field and cluster early-type host samples suggests that field early-type galaxies that lie on the red sequence may also be minimally affected by dust. Hence, the early-type hosted SNe Ia studied here occupy a more favorable environment to use as well-characterized high-redshift standard candles than other SNe Ia.

We present Advanced Camera for Surveys, NICMOS, and Keck adaptive-optics-assisted photometry of 20 Type Ia supernovae (SNe Ia) from the Hubble Space Telescope (HST) Cluster Supernova Survey. The SNe Ia were discovered over the redshift interval 0.623 < z < 1.415. Of these SNe Ia, 14 pass our strict selection cuts and are used in combination with the world's sample of SNe Ia to derive the best current constraints on dark energy. Of our new SNe Ia, 10 are beyond redshift z = 1, thereby nearly doubling the statistical weight of HST-discovered SNe Ia beyond this redshift. Our detailed analysis corrects for the recently identified correlation between SN Ia luminosity and host galaxy mass and corrects the NICMOS zero point at the count rates appropriate for very distant SNe Ia. Adding these SNe improves the best combined constraint on dark-energy density, ρDE(z), at redshifts 1.0 < z < 1.6 by 18% (including systematic errors). For a flat ΛCDM universe, we find ΩΛ = 0.729 ± 0.014 (68% confidence level (CL) including systematic errors). For a flat wCDM model, we measure a constant dark-energy equation-of-state parameter w = −1.013+0.068−0.073 (68% CL). Curvature is constrained to ∼0.7% in the owCDM model and to ∼2% in a model in which dark energy is allowed to vary with parameters w0 and wa. Further tightening the constraints on the time evolution of dark energy will require several improvements, including high-quality multi-passband photometry of a sample of several dozen z > 1 SNe Ia. We describe how such a sample could be efficiently obtained by targeting cluster fields with WFC3 on board HST. The updated supernova Union2.1 compilation of 580 SNe is available at http://supernova.lbl.gov/Union.

We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.90.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology.

B. Abbott, M. Abolins, V. Abramov, B.S. Acharya, I. Adam, D.L. Adams, M. Adams, S. Ahn, H. Aihara, G.A. Alves, N. Amos, E.W. Anderson, R. Astur, M.M. Baarmand, V.V. Babintsev, L. Babukhadia, A. Baden, V. Balamurali, B. Baldin, S. Banerjee, J. Bantly, E. Barberis, P. Baringer, J.F. Bartlett, A. Belyaev, S.B. Beri, I. Bertram, V.A. Bezzubov, P.C. Bhat, V. Bhatnagar, M. Bhattacharjee, N. Biswas, G. Blazey, S. Blessing, P. Bloom, A. Boehnlein, N.I. Bojko, F. Borcherding, C. Boswell, A. Brandt, R. Breedon, R. Brock, A. Bross, D. Buchholz, V.S. Burtovoi, J.M. Butler, W. Carvalho, D. Casey, Z. Casilum, H. Castilla-Valdez, D. Chakraborty, S.-M. Chang, S.V. Chekulaev, L.-P. Chen, W. Chen, S. Choi, S. Chopra, B.C. Choudhary, J.H. Christenson, M. Chung, D. Claes, A.R. Clark, W.G. Cobau, J. Cochran, L. Coney, W.E. Cooper, C. Cretsinger, D. Cullen-Vidal, M.A.C. Cummings, D. Cutts, O.I. Dahl, K. Davis, K. De, K. Del Signore, M. Demarteau, D. Denisov, S.P. Denisov, H.T. Diehl, M. Diesburg, G. Di Loreto, P. Draper, Y. Ducros, L.V. Dudko, S.R. Dugad, A. Dyshkant, D. Edmunds, J. Ellison, V.D. Elvira, R. Engelmann, S. Eno, G. Eppley, P. Ermolov, O.V. Eroshin, V.N. Evdokimov, T. Fahland, M.K. Fatyga, S. Feher, D. Fein, T. Ferbel, G. Finocchiaro, H.E. Fisk, Y. Fisyak, E. Flattum, G.E. Forden, M. Fortner, K.C. Frame, S. Fuess, E. Gallas, A.N. Galyaev, P. Gartung, V. Gavrilov, T.L. Geld, R.J. Genik II, K. Genser, C.E. Gerber, Y. Gershtein, B. Gibbard, B. Gobbi, B. Gómez, G. Gómez, P.I. Goncharov, J.L. González Soĺıs, H. Gordon, L.T. Goss, K. Gounder, A. Goussiou, N. Graf, P.D. Grannis, D.R. Green, H. Greenlee, S. Grinstein, P. Grudberg, S. Grünendahl, G. Guglielmo, J.A. Guida, J.M. Guida, A. Gupta, S.N. Gurzhiev, G. Gutierrez, P. Gutierrez, N.J. Hadley, H. Haggerty, S. Hagopian, V. Hagopian, K.S. Hahn, R.E. Hall, P. Hanlet, S. Hansen, J.M. Hauptman, D. Hedin, A.P. Heinson, U. Heintz, R. Hernández-Montoya, T. Heuring, R. Hirosky, J.D. Hobbs, B. Hoeneisen, J.S. Hoftun, F. Hsieh, Ting Hu, Tong Hu, T. Huehn, A.S. Ito, E. James, J. Jaques, S.A. Jerger, R. Jesik, T. Joffe-Minor, K. Johns, M. Johnson, A. Jonckheere, M. Jones, H. Jöstlein, S.Y. Jun, C.K. Jung, S. Kahn, G. Kalbfleisch, D. Karmanov, D. Karmgard, R. Kehoe, M.L. Kelly, S.K. Kim, B. Klima, C. Klopfenstein, W. Ko, J.M. Kohli, D. Koltick, A.V. Kostritskiy, J. Kotcher, A.V. Kotwal, A.V. Kozelov, E.A. Kozlovsky, J. Krane, M.R. Krishnaswamy, S. Krzywdzinski, S. Kuleshov, S. Kunori, F. Landry, G. Landsberg, B. Lauer, A. Leflat, J. Li, Q.Z. Li-Demarteau, J.G.R. Lima, D. Lincoln, S.L. Linn, J. Linnemann, R. Lipton, F. Lobkowicz, S.C. Loken, A. Lucotte, L. Lueking, A.L. Lyon, A.K.A. Maciel, R.J. Madaras, R. Madden, L. Magaña-Mendoza, V. Manankov, S. Mani, H.S. Mao, R. Markeloff, T. Marshall, M.I. Martin, K.M. Mauritz, B. May, A.A. Mayorov, R. McCarthy, J. McDonald, T. McKibben, J. McKinley, T. McMahon, H.L. Melanson, M. Merkin, K.W. Merritt, C. Miao, H. Miettinen, A. Mincer, C.S. Mishra, N. Mokhov, N.K. Mondal, H.E. Montgomery, P. Mooney, M. Mostafa, H. da Motta, C. Murphy, F. Nang, M. Narain, V.S. Narasimham, A. Narayanan, H.A. Neal, J.P. Negret, P. Nemethy, D. Norman, L. Oesch, V. Oguri, E. Oliveira, E. Oltman, N. Oshima, D. Owen, P. Padley, A. Para, Y.M. Park, R. Partridge, N. Parua, M. Paterno, B. Pawlik, J. Perkins, M. Peters, R. Piegaia, H. Piekarz, Y. Pischalnikov, B.G. Pope, H.B. Prosper, S. Protopopescu, J. Qian, P.Z. Quintas, R. Raja, S. Rajagopalan, O. Ramirez, S. Reucroft, M. Rijssenbeek, T. Rockwell, M. Roco, P. Rubinov, R. Ruchti, J. Rutherfoord, A. Sánchez-Hernández, A. Santoro, L. Sawyer, R.D. Schamberger, H. Schellman, J. Sculli, E. Shabalina, C. Shaffer, H.C. Shankar, R.K. Shivpuri, M. Shupe, H. Singh, J.B. Singh, V. Sirotenko, E. Smith, R.P. Smith, R. Snihur, G.R. Snow, J. Snow, S. Snyder, J. Solomon, M. Sosebee, N. Sotnikova, M. Souza, A.L. Spadafora, G. Steinbrück, R.W. Stephens, M.L. Stevenson, D. Stewart, F. Stichelbaut, D. Stoker, V. Stolin, D.A. Stoyanova, M. Strauss, K. Streets, M. Strovink, A. Sznajder, P. Tamburello, J. Tarazi, M. Tartaglia, T.L.T. Thomas, J. Thompson, T.G. Trippe, P.M. Tuts, V. Vaniev, N. Varelas, E.W. Varnes, D. Vititoe, A.A. Volkov, A.P. Vorobiev, H.D. Wahl, G. Wang, J. Warchol, G. Watts, M. Wayne, H. Weerts, A. White, J.T. White, J.A. Wightman, S. Willis, S.J. Wimpenny, J.V.D. Wirjawan, J. Womersley, E. Won, D.R. Wood, Z. Wu, H. Xu, R. Yamada, P. Yamin, T. Yasuda, P. Yepes, K. Yip, C. Yoshikawa, S. Youssef, J. Yu, Y. Yu, B. Zhang, Y. Zhou, Z. Zhou, Z.H. Zhu, M. Zielinski, D. Zieminska, A. Zieminski, E.G. Zverev, and A. Zylberstejn

J. Albert, G. Aldering, S. Allam, W. Althouse, R. Amanullah, J. Annis, P. Astier, M. Aumeunier, S. Bailey, C. Baltay, E. Barrelet, S. Basa, C. Bebek, L. Bergström, G. Bernstein, M. Bester, B. Besuner, B. Bigelow, R. Blandford, R. Bohlin, A. Bonissent, C. Bower, M. Brown, M. Campbell, W. Carithers, D. Cole, E. Commins, W. Craig, T. Davis, K. Dawson, C. Day, M. DeHarveng, F. DeJongh, S. Deustua, H. Diehl, T. Dobson, S. Dodelson, A. Ealet, R. Ellis, W. Emmet, D. Figer, D. Fouchez, M. Frerking, J. Frieman, A. Fruchter, D. Gerdes, L. Gladney, G. Goldhaber, A. Goobar, D. Groom, H. Heetderks, M. Hoff, S. Holland, M. Huffer, L. Hui, D. Huterer, B. Jain, P. Jelinsky, C. Juramy, A. Karcher, S. Kent, S. Kahn, A. Kim, W. Kolbe, B. Krieger, G. Kushner, N. Kuznetsova, R. Lafever, J. Lamoureux, M. Lampton, O. Le Fèvre, V. Lebrun, M. Levi, P. Limon, H. Lin, E. Linder, S. Loken, W. Lorenzon, R. Malina, L. Marian, J. Marriner, P. Marshall, R. Massey, A. Mazure, B. McGinnis, T. McKay, S. McKee, R. Miquel, B. Mobasher, N. Morgan, E. Mörtsell, N. Mostek, S. Mufson, J. Musser, R. Nakajima, P. Nugent, H. Olus.eyi , R. Pain, N. Palaio, D. Pankow, J. Peoples, S. Perlmutter, D. Peterson, E. Prieto, D. Rabinowitz, A. Refregier, J. Rhodes, N. Roe, D. Rusin, V. Scarpine, M. Schubnell, M. Seiffert, M. Sholl, H. Shukla, G. Smadja, R. M. Smith, G. Smoot, J. Snyder, A. Spadafora, F. Stabenau, A. Stebbins, C. Stoughton, A. Szymkowiak, G. Tarlé, K. Taylor, A. Tilquin, A. Tomasch, D. Tucker, D. Vincent, H. von der Lippe, J-P. Walder, G. Wang, A. Weinstein, W. Wester, M. White

The Supernova/Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled astrophysical measurements. We here describe a self-consistent reference mission design that can accomplish this goal with the two leading measurement approaches being the Type Ia supernova Hubble diagram and a wide-area weak gravitational lensing survey. This design has been optimized to first order and is now under study for further modification and optimization. A 2-m three-mirror anastigmat wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The instrumentation suite provides simultaneous discovery and light-curve measurements of supernovae and then can target individual objects for detailed spectral characterization. The SNAP mission will discover thousands of Type Ia supernovae out to z = 3 and will obtain high-signal-to-noise calibrated light-curves and spectra for a subset of > 2000 supernovae at redshifts between z = 0.1 and 1.7 in a northern field and in a southern field. A wide-field survey covering one thousand square degrees in both northern and southern fields resolves {approx} 100 galaxies per square arcminute, or a total of more than 300 million galaxies. With the PSF stability afforded by a space observatory, SNAP will provide precise and accurate measurements of gravitational lensing. The high-quality data available in space, combined with the large sample of supernovae, will enable stringent control of systematic uncertainties. The resulting data set will be used to determine the energy density of dark energy and parameters that describe its dynamical behavior. The data also provide a direct test of theoretical models for the dark energy, including discrimination of vacuum energy due to the cosmological constant and various classes of dynamical scalar fields. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy or equation of state w(z) can be similarly measured to 5% for the present value w{sub 0} and {approx} 0.1 for the time variation w' {triple_bond} dw/d ln a|{sub z=1}. For a fiducial SUGRA-inspired universe, w{sub 0} and w' can be measured to an even tighter uncertainty of 0.03 and 0.06 respectively. Note that no external priors are needed. As more accurate theoretical predictions for the small-scale weak-lensing shear develop, the conservative estimates adopted here for space-based systematics should improve, allowing even tighter constraints. While the survey strategy is tailored for supernova and weak gravitational lensing observations, the large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs.

A wide field space-based imaging telescope is necessary to fully exploit the technique of observing dark matter via weak gravitational lensing. This first paper in a three part series outlines the survey strategies and relevant instrumental parameters for such a mission. As a concrete example of hardware design, we consider the proposed Supernova/Acceleration Probe (SNAP). Using SNAP engineering models, we quantify the major contributions to this telescope's Point Spread Function (PSF). These PSF contributions are relevant to any similar wide field space telescope. We further show that the PSF of SNAP or a similar telescope will be smaller than current ground-based PSFs, and more isotropic and stable over time than the PSF of the Hubble Space Telescope. We outline survey strategies for two different regimes - a “wide” 300 square degree survey and a “deep” 15 square degree survey that will accomplish various weak lensing goals including statistical studies and dark matter mapping.

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

The SuperNova/Acceleration Probe (SNAP) will measure precisely the cosmological expansion history over both the acceleration and deceleration epochs and thereby constrain the nature of the dark energy that dominates our universe today. The SNAP focal plane contains equal areas of optical CCDs and NIR sensors and an integral field spectrograph. Having over 150 million pixels and a field-of-view of 0.34 square degrees, the SNAP NIR system will be the largest yet constructed. With sensitivity in the range 0.9-1.7 microns, it will detect Type Ia supernovae between z = 1 and 1.7 and will provide follow-up precision photometry for all supernovae. HgCdTe technology, with a cut-off tuned to 1.7 microns, will permit passive cooling at 140 K while maintaining noise below zodiacal levels. By dithering to remove the effects of intrapixel variations and by careful attention to other instrumental effects, we expect to control relative photometric accuracy below a few hundredths of a magnitude. Because SNAP continuously revisits the same fields we will be able to achieve outstanding statistical precision on the photometry of reference stars in these fields, allowing precise monitoring of our detectors. The capabilities of the NIR system for broadening the science reach of SNAP are discussed.

A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Ia supernovae and to standardize the magnitude of each candidate by determining explosion parameters. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have very high efficiency and low spectral resolution (R 100), constant through the wavelength range (0.35-1.7 microns), adapted to the scientific goals of the mission.

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 in the visible and near-infrared wavelength regime. The requirements for the instrument suite and the present configuration of the focal plane concept are presented. A two year R&D phase, largely supported by the Department of Energy, is just beginning. We describe the development activities that are taking place to advance our preparedness for mission proposal in the areas of detectors and electronics.

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.

We present the baseline telescope design for the telescope for the SuperNova/Acceleration Probe (SNAP) space mission. SNAP’s purpose is to determine expansion history of the Universe by measuring the redshifts, magnitudes, and spectral classifications of thousands of supernovae with unprecedented accuracy. Discovering and measuring these supernovae demand both a wide optical field and a high sensitivity throughout the visible and near IR wavebands. We have adopted the annular-field three-mirror anastigmat (TMA) telescope configuration, whose classical aberrations (including chromatic) are zero. We show a preliminary optmechanical design that includes important features for stray light control and on-orbit adjustment and alignment of the optics. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of the design tasks being carried out during the current SNAP research and development phase.

The SuperNova/Acceleration Probe (SNAP) mission will require a two-meter class telescope delivering diffraction limited images spanning a one degree field in the visible and near infrared wavelength regime. This requirement, equivalent to nearly one billion pixel resolution, places stringent demands on its optical system in terms of field flatness, image quality, and freedom from chromatic aberration. We discuss the advantages of annular-field three-mirror anastigmat (TMA) telescopes for applications such as SNAP, and describe the features of the specific optical configuration that we have baselined for the SNAP mission. We discuss the mechanical design and choice of materials for the telescope. Then we present detailed ray traces and diffraction calculations for our baseline optical design. We briefly discuss stray light and tolerance issues, and present a preliminary wavefront error budget for the SNAP Telescope. We conclude by describing some of tasks to be carried out during the upcoming SNAP research and development phase.

The Supernova/Acceleration Probe (SNAP) is a proposed space-borne observatory that will survey the sky with a wide-field optical/near-infrared (NIR) imager. The images produced by SNAP will have an unprecedented combination of depth, solid-angle, angular resolution, and temporal sampling. For 16 months each, two 7.5 square-degree fields will be observed every four days to a magnitude depth of AB=27.7 in each of the SNAP filters, spanning 3500-17000Å. Co-adding images over all epochs will give AB=30.3 per filter. In addition, a 300 square-degree field will be surveyed to AB=28 per filter, with no repeated temporal sampling. Although the survey strategy is tailored for supernova and weak gravitational lensing observations, the resulting data will support a broad range of auxiliary science programs.

The SuperNova/Acceleration Probe (SNAP) will measure precisely the cosmological expansion history over both the acceleration and deceleration epochs and thereby constrain the nature of the dark energy that dominates our universe today. The SNAP focal plane contains equal areas of optical CCDs and NIR sensors and an integral field spectrograph. Having over 150 million pixels and a field-of-view of 0.34 square degrees, the SNAP NIR system will be the largest yet constructed. With sensitivity in the range 0.9–1.7 μm, it will detect Type Ia supernovæ between z = 1 and 1.7 and will provide follow-up precision photometry for all supernovæ. HgCdTe technology, with a cut-off tuned to 1.7 μm, will permit passive cooling at 140 K while maintaining noise below zodiacal levels. By dithering to remove the effects of intrapixel variations and by careful attention to other instrumental effects, we expect to control relative photometric accuracy below a few hundredths of a magnitude. Because SNAP continuously revisits the same fields we will be able to achieve outstanding statistical precision on the Further author information: (Send correspondence to G.T.) G.T.: E-mail: gtarle@umich.edu, Telephone: 1 734 763 1489 photometry of reference stars in these fields, allowing precise monitoring of our detectors. The capabilities of the NIR system for broadening the science reach of SNAP are discussed.

The Supernova / Acceleration Probe (SNAP) is a proposed space-borne observatory that will survey the sky with a wide-field optical/near-infrared (NIR) imager. The images produced by SNAP will have an unprecedented combination of depth, solid-angle, angular resolution, and temporal sampling. For 16 months each, two 7.5 square-degree fields will be observed every four days to a magnitude depth of AB = 27.7 in each of the SNAP filters, spanning 3500–17000Å. Co-adding images over all epochs will give AB = 30.3 per filter. In addition, a 300 square-degree field will be surveyed to AB = 28 per filter, with no repeated temporal sampling. Although the survey strategy is tailored for supernova and weak gravitational lensing observations, the resulting data will support a broad range of auxiliary science programs.

The SuperNova / Acceleration Probe (SNAP) is a space-based e xperiment to measure the expansion history of the Universe and study both its dark energy and the dark matter. The e xp riment is motivated by the startling discovery that the expansion of the Universe is accelerating. A 0.7 squaredegree imager comprised of 36 large format fully-depleted n-type CCD’s sharing a focal plane with 36 HgCdTe detectors fo rms the heart of SNAP, allowing discovery and lightcurve measurements simultaneously for many supernovae. The imag er and a high-efficiency low-resolution integral field spectrograph are coupled to a 2-m three mirror anastigmat wide-fi eld telescope, which will be placed in a high-earth orbit. The SNAP mission can obtain high-signal-to-noise calibrat ed light-curves and spectra for over 2000 Type Ia supernovae at redshifts between z = 0.1 and 1.7. The resulting data set can not only determine the amo unt of dark energy with high precision, but test the nature of the dark energy by exam ining its equation of state. In particular, dark energy due t o a cosmological constant can be differentiated from alterna tives such as “quintessence”, by measuring the dark energy’ s equation of state to an accuracy of ±0.05, and by studying its time dependence.

The SuperNova / Acceleration Probe (SNAP) is a space-based experiment to measure the expansion history of the Universe and study both its dark energy and the dark matter. The experiment is motivated by the startling discovery that the expansion of the Universe is accelerating. A 0.7 square-degree imager comprised of 36 large format fully-depleted n-type CCD's sharing a focal plane with 36 HgCdTe detectors forms the heart of SNAP, allowing discovery and lightcurve measurements simultaneously for many supernovae. The imager and a high-efficiency low-resolution integral field spectrograph are coupled to a 2-m three mirror anastigmat wide-field telescope, which will be placed in a high-earth orbit. The SNAP mission can obtain high-signal-to-noise calibrated light-curves and spectra for over 2000 Type Ia supernovae at redshifts between z=0.1 and 1.7. The resulting data set can not only determine the amount of dark energy with high precision, but test the nature of the dark energy by examining its equation of state. In particular, dark energy due to a cosmological constant can be differentiated from alternatives such as "quintessence", by measuring the dark energy's equation of state to an accuracy of +/-0.05, and by studying its time dependence.