On 19 May 1975 the satellite's 96.46-minute orbit had an apogee of 611 kilometres (380 mi) and a perigee of 568 kilometres (353 mi), at an inclination of 50.6 degrees. It was built to conduct experiments in X-ray astronomy, aeronomics, and solar physics. The spacecraft was a 26-sided polyhedron 1.4 metres (4.6 ft) in diameter. All faces (except the top and bottom) were covered with solar cells. A power failure halted experiments after four days in orbit with all signals from the spacecraft lost after five days of operation. The satellite reentered the Earth's atmosphere on 11 February 1992.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Manned flights are indicated in bold text. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).