Plans for the first balloon flight of the gamma-ray polarimeter experiment (GRAPE)

We have developed a design for a hard X-ray Compton polarimeter operating in the energy range from 50 to 500 keV, which we refer to as GRAPE (Gamma-Ray Polarimeter Experiment). We are currently preparing a balloon payload for a flight from Ft. Sumner, NM in the fall of 2011. Using a large (16-element) array of detector modules, this payload is being designed to search for polarization from known point sources of radiation, namely the Crab and Cygnus X-1. This first flight will not only provide a scientific demonstration of the GRAPE design (by measuring polarization from the Crab nebula), it will also lay the foundation for subsequent long duration balloon flights that will be designed for studying polarization from gamma-ray bursts and solar flares. Here we shall present data from calibration of the first flight module detectors and review the latest payload design.