AXAF Credit - NASA

The Chandra Advanced X-ray Astrophysics Facility was designed to study the composition and nature of galaxies, stellar objects and interstellar phenomena as well as basic issues in theoretical physics using the most sensitive X-ray telescope ever built.

The Chandra Advanced X-ray Astrophysics Facility was one of the four Great Observatories (along with HST, GRO, and SIRTF). International participants include the UK, Germany, and the Netherlands. Originally consisting of 2 separate spacecraft, the AXAF program was reduced to a single spacecraft in 1993 due to fiscal constraints. Satellite operations would be conducted by MSFC using NASA's Deep Space Network.

The spacecraft: had a light weight composite structure, and was 3-axis stabilized, using a zero momentum biased control system. Solar arrays generated over 2 kW and recharged three 40 AHr nickel hydrogen batteries. Six reaction wheels provided attitude control, with the control system fed by four 2-degree-of-freedom dry tuned rotor gyros. Two 1.8 Gbit solid state recorders could store 18.8 hours of data per recorder. The Integral Propulsion System on Chandra used four TR-308 bipropellant thrusters for orbit changes. The thrusters used N2O4 (nitrogen tetroxide) oxidizer and N2H4 (hydrazine) fuel. They had a thrust of 472 N and a specific impulse of 322.3s; the TR-308 was an upgrade of the TR-306 that was used on three Lockheed Martin Series 5000 satellites. The same fuel tanks also fed Marquardt 89 N monopropellant hydrazine RCS thrusters. In addition to the IPS, the MUPS (Momentum Unloading Propulsion System) used 0.9 N hydrazine thrusters to unload momentum from the gyro systems used to point Chandra.

The X-ray telescope consisted of four pairs of nearly cylindrical mirrors, ranging from 1.4 meters in diameter to 0.68 meters in diameter. These mirrors focused X-ray energy over a 10 m focal length onto two of the four science instruments, the High Resolution Camera (HRC) and the AXAF CCD Imaging Spectrometer (ACIS). Also carried were two non-focal plane instruments, the High-Energy Transmission Grating (HETG), and Low-Energy Transmission Grating (LETG).

Design Life: 5 years. Typical orbit: 10,000 km x 40,000 km, incl. = 28.5 deg. Length: 12.20 m (40.00 ft). Span: 18.90 m (62.00 ft). Associated Launch Vehicle: Shuttle.

• 1999 July 23 - Chandra - Launch Site: Cape Canaveral. Launch Vehicle: Shuttle. Perigee: 20,046 km (12,455 mi). Apogee: 128,769 km (80,013 mi). Inclination: 45.10 deg. Period: 3,808.60 min.

  The Chandra Advanced X-ray Astrophysics Facility was one of NASA’s four Great Observatories (along with Hubble Space Telescope, Compton Gamma Ray Observatory, and the SIRTF). Chandra will study the composition and nature of galaxies, stellar objects and interstellar phenomena as well as basic issues in theoretical physics using the most sensitive X-ray telescope ever built. The IUS under-performed and placed Chandra in an orbit about 900 km lower than planned. Therefore Chandra's own IPS propulsion system had to be used to make up the difference. The first such manoeuvre was at 01:11 GMT on July 25 when the IPS engines fired for 5 minutes to raise perigee to 1192 km. Further perigee burns on July 31, August 4, and August 7 raised the orbit to its final 10,000 km x 140.000 km.Additional Details: Chandra (12534).

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