The Supernova / Acceleration Probe (SNAP) Mission

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to measure the expansion history of the Universe, motivated by the discovery that the expansion is accelerating. It will study both the dark energy and the dark matter, through mapping the distance- redshift relation of Type Ia supernovae and through a wide-area weak gravitational lensing survey. 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 CCD's and near infrared sensors, and a high- efficiency low-resolution integral field spectrograph. The instrumentation suite provides simultaneous discovery and light-curve measurements for many supernovae with the capability to target individual objects for detailed spectral characterization. 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 or various classes of dynamical scalar fields can be differentiated, by measuring the dark energy's equation of state density-to-pressure ratio to an accuracy of ± 0.05, and its time evolution to w' = dw/dz to ± 0.2. Although the survey strategy is tailored for supernova and weak gravitational lensing observations, the large survey area, depth, spatial resolution, time-sampling, and infrared extent of the resulting data will support a broad range of auxiliary science programs.