1991-027B
Known simply as GRO (Gamma Ray Observatory) before launch, this spacecraft was renamed the Arthur Holly Compton Gamma Ray Observatory, CGRO, in honor of the American physicist (1892-1962) after whom the Compton Effect of gamma-ray/electron interactions is also named. The spacecraft was built by TRW and operated by GSFC.
CGRO was deployed by Atlantis' RMS arm at 2235 on 1991 Apr 7 into a 93.63 min, 446 x 458 km x 28.5 deg orbit. The most dramatic early results from CGRO were the discovery by EGRET of the gamma-ray loud quasars, and the results from BATSE indicating that gamma ray burst sources were distributed uniformly across the sky.
CGRO had an internal propulsion system to raise its orbit. The GRO propulsion system, built by TRW, had a mass of 281 kg dry and 1920 kg of monopropellant hydrazine, with four thruster modules each with two MRE-5 thrusters. The OAT (Orbit Adjust Thrusters) had some initial pressurization problems just after launch, so it was decided to use a smaller set of thrusters for the orbit adjust. A test firing was carried out on 1993 May 4, and the B-side thrusters were fired twice on 1993 Jun 15, but the second time one thruster did not fire and the burn was aborted. It was decided to go back to using the OATs. Test burns were made on Aug 3, Aug 17 and Sep 7. The first true orbit raising burn was made on Oct 4 around 0500; 6 more burns were made between Oct 6 and 1828 on Oct 14. By Oct 12 the orbit had been raised back to 341 x 446 km x 28.5 deg.
Tape recorder failures limited the amount of data CGRO could send back, so in 1994 the TDRS 1 satellite was moved over a new ground station in Tidbinbilla, Australia to improve data coverage.
| GRO | |||
| Date | Time | Event | Orbit |
|---|---|---|---|
| 1991 Apr 8 | 93.63 446 x 458 x 28.5 | ||
| 1992 Dec 1 | 92.06 372 x 378 x 28.5 | ||
| 1993 Feb 26 | 91.77 357 x 364 x 28.5 | ||
| 1993 May 1 | 91.47 344 x 348 x 28.5 | ||
| 1993 May 13 | 91.55 348 x 352 x 28.5 | ||
| 1993 May 25 | 91.52 347 x 351 x 28.5 | ||
| 1993 Jun 10 | 91.46 344 x 347 x 28.5 | ||
| 1993 Jun 21 | 91.56 347 x 354 x 28.5 | ||
| 1993 Aug 3 | 91.45 341 x 350 x 28.5 | ||
| 1993 Aug 12 | 91.43 340 x 348 x 28.5 | ||
| 1993 Aug 18 | 91.42 338 x 349 x 28.5 | ||
| 1993 Sep 1 | 91.38 336 x 347 x 28.5 | ||
| 1993 Sep 8 | 91.37 336 x 346 x 28.5 | ||
| 1993 Oct 2 | 91.29 333 x 342 x 28.5 | ||
| 1993 Oct 9 | 91.66 340 x 371 x 28.5 | ||
| 1993 Oct 14 | 345 x 409 x 28.4 | ||
| 1993 Oct 21 | 92.44 341 x 446 x 28.5 | ||
| 1997 Mar 24 | ACT engineering test burn | ||
| 1997 Mar 26 | OAT engineering test burn | ||
| 1997 Apr 1 | 1800 | OAT 90s reboost | |
| 1997 Apr 2 | 1900 | OAT 90s reboost | |
| 1997 Apr 3 | 1830 | OAT 90s reboost | |
| 1997 Apr 5 | 1900 | OAT 90s reboost | |
| 1997 Apr 6 | 1700 | OAT 90s reboost | |
| 2000 May 10 | 94.31 482 x 487 x 28.5 | ||
| 2000 May 31 | 0151 | Descent burn 1 23:06 | 92.94 362 x 474 x 28.5 |
| 2000 Jun 1 | 0236 | Burn 2, 26min | 91.62 237 x 471 x 28.5 |
| 2000 Jun 4 | 0356 | Burn 3, 21:39 | |
| 0417 | Burn 3 cutoff | 146 x | |
| 0522:21 | Burn 4, 30 min, 36.8 m/s | ||
| 0552 | Burn 4 cutoff | 27 x | |
| 0609 | Tumble maneuver | ||
| 0610 | loss of contact | ||
| 0613 | Reentry at 50 km | ||
| 0618 | Impact in Pacific SE of Hawaii | ||
Payload:
- OAT Orbit Adjust Thrusters; 4 Rocket Research Corp 445N thrusters, 8 TRW MRE-5 22N thrusters.
- BATSE The Burst and Transient Source Experiment, a NASA-MSFC experiment to detect, locate, and measure the light curves and spectra of gamma ray bursts; 20 keV - 1 MeV
- EGRET The Extreme Gamma ray Event Telescope, to detect gamma ray sources in the 100 MeV range. (20 MeV-30 GeV)
- COMPTEL Imaging Compton Telescope 1-30 MeV
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