Chandra X-Ray Observatory (CXO)

Launch data: Designation 25867 / 99040B Launch date 23 Jul 1999 Launch site  KSC, LC-39B Launch vehicle Shuttle STS-93 with IUS-27 Mission Scientific: X-ray astronomy Deep Highly Exxentric Earth orbit: Perigee / Apogee  9999 x 138825 km Eccentricity  7.97E-01 Inclination  28.5 deg Period  3808.92 min Deep Highly Exxentric Earth orbit on Febr. 2019: Perigee / Apogee  17315 x 131541 km Eccentricity   Inclination  69.1 deg Period  3809.5 min

Specifications:

Description:

• 10 m focal length telescope
  ACIS: camera with 10 X-ray CCD imagers based on Astro D technology
  HRC: camera similar to Rosattechnology

Mission details:

• Designed to observe X-rays from high energy regions of the universe, such as hot gas in the remnants of exploded stars.
• The launch was delayed several time, including in Jan 1999 when TRW reported conductivity problems on multi-layered circuit boards.
  
• Chandra/IUS-27 was deployed from Columbia at 1147 UTC Jul 23. At 1248 UTC the IUS-27 SRM-1 motor fired for 125s to enter a 226 x 13841 km x 28.5 deg orbit. The SRM-1 then separated (it appears that a second object may also be being tracked in this orbit) and SRM-2 fired at 1251 UTC for 117 seconds. Chandra then deployed its solar arrays at 1322 UTC, and SRM-2 separated from Chandra at 1350 UTC. Chandra was placed in a 330 x 72030 km x 28.45 deg orbit. This was about 900 km lower than planned, the IUS underperformed slightly, but Chandra's own IPS propulsion system will make up most of the difference. The ACIS and HRC cameras have been switched on and both are operating well.
• At 0111 UTC on Jul 25 the IPS engines were fired for 5 minutes to raise perigee to 1192 km. The burn went well and the vehicle was extremely stable.
  TRW's IPS propulsion system is a dual-mode system, with O2/hydrazine for the four main 450N IPS engines, and mono hydrazine for the RCS system. There's also a small momentum dumping hydrazine system that is used throughout the mission for attitude control when the momentum wheels get saturated. Any extra hydrazine left over when the O2 runs out will be transferred to that system.
• Chandra is the heaviest Shuttle payload yet.
• The IPS-3 burn to raise apogee to 140000 km was carried out at 22:32 UTC on Jul 31, 1999. DSN tracking indicates the orbit is now 3482 x 139384 km x 28.5 deg. A further IPS-4 burn on Aug 4 raised perigee to around 5700 km, and another perigee raise burn is planned for Aug 7.
  The Integral Propulsion System on Chandra uses four TR-308 bipropellant thrusters for orbit changes. The thrusters use N2O4 (nitrogen tetroxide) oxidizer and N2H4 (hydrazine) fuel. They have a thrust of 472N and a specific impulse of 322.3s; the TR-308 is an upgrade of the TR-306 that was used on three Lockheed Martin Series 5000 satellites. The same fuel tanks also feed Marquardt 89N monopropellant hydrazine RCS thrusters. In addition to the IPS, the MUPS (Momentum Unloading Propulsion System) uses 0.9N hydrazine thrusters to unload momentum from the gyro systems used to point Chandra. (Thanks to the TRW propulsion experts for the info). Thrusters LAE-1 and LAE-3 were used for the first three burns; LAE-2 and LAE-4 were used for IPS-4 and will be used for the remaining burns.
• On Jul 6, 2011 Chandra entered its first unplanned safemode since 2000. As of Jul 12, the spacecraft has been recovered to normal operation and the science program has resumed. The safemode was caused when unusually strong gravity gradient torques coincided with the end of a slew, and this combined with a complexity in the software confused Chandra into incorrectly thinking that it was out of control, when in fact it was actually pointing stably. It took a couple of days to figure out exactly what happened, but the hardware is now fully exonerated: as it prepares to complete 12 years in orbit Chandra is still in excellent health.
• On Oct 10, 2018 the Chandra X-ray Observatory also entered safemode due to three seconds of bad data from one of the gyroscopes. Chandra has had very few incidents during its so-far-19-year-long mission; it has now returned to normal pointing mode and is expected to resume science observations in the coming week or two following some ground-commanded onboard reconfiguration and tests.

External links:

• Satellite tracking (n2ya.com): Real time satellite tracking