SNAP is a proposed orbiting optical/near-IR imaging and spectrographic telescope dedicated to dark-energy investigations. As suggested by the name, the initial approach was to use highredshift Type Ia supernovae to map the expansion history of the Universe to high precision. The resultant design—an approximately 2-meter aperture, diffraction-limited telescope with maximal field of view tiled with visible and near-IR detectors—is in fact nearly optimal for the measurement of weak gravitational lensing as well. With substantial guidance from Penn faculty, the SNAP program has evolved to include a substantial WL survey along with SNe measurements. These two approaches now combine to make SNAP a leading candidate for the NASA-DOE JDEM.

The University of Pennsylvania has been an institutional member of the SNAP collaboration since 2003. While Penn personnel have been involved in many aspects of the design, optimization, and forecasting for SNAP, our activities in the past 4 years have centered on two areas: first, the development and use of a flexible and reliable simulation system, SNAPsim; second, the definition of the weak lensing dark energy investigation. Some of this work is very basic and general, e.g., devising means by which WL can be used to measure dark energy, understanding the fundamental limitations of the WL method and estimating the optimal redshift distribution to minimize statistical and systematic errors on dark energy parameters from SNe luminosity distance measurements. Other work has been more practical, e.g., devising data-reduction techniques that minimize WL systematic errors. Some is very specific to SNAP, e.g., the development of SNe and WL-derived science requirements for the project.