The USA Experiment
The USA Experiment is an X-ray timing experiment with large collecting area and microsecond time resolution capable of conducting a broad program of studies of galactic X-ray binaries.
USA is one of nine experiments aboard the Advanced Research and Global Observation Satellite shown here at the February 23, 1999 launch. USA operated from May 1, 1999 through November 16, 2000.
USA is a collimated proportional counter X-ray telescope with about 1000 cm^2 of effective area per detector with two detectors sensitive to photons in the energy range 1-15 keV. A unique feature of USA is that photon events are time tagged by reference to an onboard GPS receiver allowing precise absolute time and location determination.
USA also has a number of applied objectives, including development of techniques for X-ray navigation and timekeeping, studies of the upper atmosphere and aurorae, and a side-by-side test of a rad-hard processor vs. a commercial off-the-shelf computer in the space environment.