COS B [ESA]

TheCOS B (Celestial Observation Satellite B) scientific satellite was developed by theEuropean Space Agency (ESA) to study extraterrestrial gamma radiation in the 25 MeV to1 GeV energy range from a highly elliptical orbit of roughly 100,000 km apogee, 350 kmperigee, and near-polar inclination.

NASA provided, on a fully reimbursable basis, theDelta launch vehicle and the associated launch services. The COS B spacecraft wascylindrical with a diameter of 140 cm and a height of 121 cm. Four monopole antennas,protruding 51.2 cm below the bottom of the cylindrical body, gave the spacecraft a totaleffective height of 172.2 cm. The spacecraft obtained orientation of its angular momentumvector with respect to inertial space using data from an earth albedo sensor and a solarsensor. Spacecraft attitude was adjusted by a nitrogen cold-gas attitude control system(ACS). The ACS included two spin-rate-adjust nozzles to maintain the spin rate at 10 rpmand two precession nozzles to adjust the momentum vector. The spacecraft had a pcm/psk/pmtelemetry system with 6.5-W real-time-only transmitter providing a switchable bit rate of160 and 320 bps and a pcm/psk/pm, up-link/down-link, range-tone command system. Power wassupplied by 9480 solar cells mounted on 12 subpanels on the cylindrical body of thespacecraft. Communications, command, and control of the COS-B satellite in orbit wereprovided by the ESA Estrack network.

COS-B carried a single large experiment the design and provision of which have been theresponsibility of a group of research laboratories known as the Caravane Collaboration.The characteristics of the instrument are described below. The Gamma-Ray Telescopeperformed well throughout the mission: the only complication being the occasional erraticperformance of the spark-chamber and the inevitable reduction in performance as the sparkchamber gas aged. This aging was, however, minimized by means of a gas-replenishmentsystem that permitted emptying and refilling of the spark chamber. As the rate of gasdeterioration decreased with time, it became possible to increase the interval betweenflushing from its initial value of once every 6 weeks to about once every 36 weeks beforethe final flushing in November 1981. The spark chamber was still performing creditably atthe end of the mission in April 1982.

COS B was initially planned to be launched on theEuropa-2 launch vehicle, but due to the unavailability after several launch failures, it was finally launched on an americanDelta-2913 rocket instead. It operated for 6 years and 8 months until it was switched off on 25 April 1982.

A repeat flight modelCOS B2 was considered as a payload of the secondAriane-1 development flight, but was cancelled.

Launch Sites:

• Ko =   Centre Spatial Guyanais (CSG), Kourou, French Guiana, France   
• Va =   Vandenberg Air Force Base, California, USA   

References:

• ESA:COS-B

• COS A
• COS B

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