 The Principal Investigator (PI) was Prof. Laurence E. Peterson of UCSD.Also in the wheel was a cosmic gamma-ray (>50 MeV) sky survey instrument contributed by MIT, with PI Prof. William L. Kraushaar.OSO-3 obtained extensive hard X-ray observations of solar flares, the cosmic diffuse X-ray background, and multiple observations of Scorpius X-1, the first observation of an extrasolar X-ray source by an observatory satellite.