The second D-5B satellite reached orbit in 1975 and was named Castor.
The 76 kg polyhedron was 0.72m long and 0.8m in diameter. Its primary payload was the CACTUS accelerometer which could measure tiny accelerations. It was used for aeronomy and geodesy, and even for registering micrometeoroid impacts. The surface of the D-5B satellite was covered with solar cells and laser reflectors.
| Castor | |||
| Date | Time | Event | Orbit |
|---|---|---|---|
| 1975 May 17 | 1032 | Launch by Diamant B P.4 | CSG ELD |
| 1039:13 | P.06 shutdown, orbit insertion | ||
| 1044 | Despin weights released | ||
| 1044:30 | P.06 sep from Castor/Pollux, | ||
| releasing clamps 39D, 39E | |||
| 1045:02 | Pollux sep, releasing clamps 39F,G | ||
| 100.1 272 x 1268 x 30.0 | |||
| 1975 May 31 | 100.24 273 x 1266 x 30.0 | ||
| 1976 Feb 25 | 99.48 271 x 1195 x 30.0 | ||
| 1978 Dec 2 | 92.79 244 x 578 x 30.0 | ||