  SNAP is a candidate for the Joint Dark Energy Mission (JDEM) that seeks to
place constraints on the dark energy using two distinct methods. The first,
Type Ia SN, is discussed in a companion white paper. The second method is weak
gravitational lensing, which relies on the coherent distortions in the shapes
of background galaxies by foreground mass structures. The excellent spatial
resolution and photometric accuracy afforded by a 2-meter space-based
observatory are crucial for achieving the high surface density of resolved
galaxies, the tight control of systematic errors in the telescope's Point
Spread Function (PSF), and the exquisite redshift accuracy and depth required
by this project. These are achieved by the elimination of atmospheric
distortion and much of the thermal and gravity loads on the telescope. The SN
and WL methods for probing dark energy are highly complementary and the error
contours from the two methods are largely orthogonal.
