The SNAP sat project  first science goal is the exploration of dark energy (see below) and the accelerating univesse using supernova type Ia as cosmological probes.
However there are significantly more interesting and exciting science that can be accomplished with sucha  a satellie.
Consider, in particular, gravitational lensing potential of SNAP sat.

    Recent measurements carried out by the Supernova Cosmology Project (SCP) and the High-Z Supernova team have made the startling discovery that the expansion of the universe is accelerating. This result is based on the Hubble diagram for type Ia supernovae, and has been corroborated by results from several experiments, both similar and complementary. Einstein's General Theory of Relativity requires that some mechanism must drive this expansion rate either through a new form of energy, such as a new vacuum energy density (cosmological constant), or a yet unknown kind of particle or field fundamental to the creation and formation of the universe. The source of this acceleration is more powerful than the gravitation from all seen and unseen forms of matter and known energy. Theorists are unable to explain the observed effect and follow-up measurements would have a tremendous impact on the field of fundamental physics. The Supernova / Acceleration Probe (SNAP) Mission is expected to provide a understanding of the mechanism driving the acceleration of the universe. The satellite observatory is capable of measuring up to 2,000 distant supernovae each year of the three-year mission lifetime. These measurements will map out in detail the expansion rate of the universe at epochs varying from the present to 10 billion years in the past. SNAP will determine the spatial curvature of the universe thus providing a fundamental test of the theory of inflation - the theoretical mechanism that drove the initial formation of the universe, and a measure of the key cosmological parameters Omega_m and Omega_L. This sensitive experiment uses type Ia supernovae as an astronomical standard candle to provide a distance scale, which, combined with the redshift obtained from the spectral lines from the supernova and its host galaxy determine the cosmological parameters and ultimately the nature of the "missing energy" in the universe. Type II supernovae are also expected to provide an independent precision measurement of cosmological parameters using the blackbody emission from the hot type II photosphere to obtain a luminosity-distance scale.

Please note that SNAP  is still in the proposal stage and that many features of the satellite are being designed and revised.  Therefore, technical specifications of the satellite are subject to change and all images should be considered artistic interpretations of what SNAP might look like in the future.