Over the last two weeks, the 45-foot-long Chandra has used five "burns" of its Integral Propulsion System (IPS) to propel itself from a temporary "transfer orbit", where it was placed by an Inertial Upper Stage (IUS), to a highly elliptical Earth orbit that extends more than one-third the distance to the moon.

The final burn, which lasted about 8 minutes, was completed on August 7 at 1:46 a.m. EDT. It placed Chandra in an orbit that measures approximately 6,000 miles by 86,300 miles, a variation of less than 1 percent from its target orbit. The observatory will now orbit the Earth about once every 63.5 hours.

Over the next five years, Chandra will use the world's most powerful X-ray telescope to probe the mysteries of a universe that cannot be seen by the human eye or conventional optical telescopes.

Its array of exquisitely polished and aligned mirrors will allow X-ray astronomers to produce previously unattainable images of celestial phenomena such as quasars, black holes, remnants of exploding stars, and clouds of multi-million degree gas that comprise clusters of galaxies.

"The successful delivery of Chandra to orbit by our new dual-mode Integral Propulsion System, or IPS, marks another milestone in TRW's history of fulfilling customers' requirements with superior systems engineering," said Joanne Maguire, vice president and general manager, TRW Space & Laser Programs Division.

"The development and use of the IPS allowed us to place Chandra in a high altitude orbit that will maximize its viewing time and yield of high-quality X-ray science data. And its dual-mode design helped reduce the size, cost and weight of the Chandra spacecraft, which allowed us to fly a larger, more capable science payload," said Maguire.

The successful orbital insertion, added Maguire, also validated TRW's IPS design decision to use multiple, modest thrust engines to perform a series of gradual orbit adjustment burns rather than relying on one large engine to make a single orbit adjustment.

"The IPS' redundant and robust design allowed NASA and the TRW-led flight operations team controlling the satellite to readily address a minor performance issue with one of the IPS engines and still deliver the observatory safely and accurately to its proper orbit," she said.

Chandra's IPS includes four (two primary, two back-up) of TRW's new 105-pound thrust, bipropellant Advanced Columbium Liquid Apogee Engines (ACLAE), and eight (four primary, four back-up) 20-pound-thrust, monopropellant reaction control system (RCS) thrusters.

Opposing pairs of ACLAEs provided the thrust for the major orbit adjustment burns while the RCS thrusters provided attitude control for Chandra during the major burns.

The system is called dual-mode because it uses a common supply of hydrazine fuel to support both the bipropellant operation of the ACLAEs, using nitrogen tetroxide as the oxidizer, and the monopropellant operation of the RCS thrusters.

This design approach eliminated the need for two dedicated fuel systems, which reduced the spacecraft size and weight. TRW further reduced the IPS' weight by using aluminum-lined, graphite composite overwrapped propellant tanks.

The IPS' dual-mode design provides Chandra with another unique feature. Any "leftover" hydrazine not consumed during the initial orbit insertion process can be transferred, via an actuated valve, to the hydrazine tank that fuels Chandra's eight small on-orbit attitude control thrusters, thereby extending the mission life.

NASA's Chandra X-ray Observatory is the first spacecraft to fly TRW's new ACLAE. With a specific impulse of 322.5 seconds, it is one of the world's most efficient bipropellant rocket engines.

Specific impulse is a measure of the amount of thrust produced by an engine per pound of fuel consumed. TRW is currently developing Rhenium-based engines that will be even more efficient.

Although Chandra is now in its final orbit, the work of TRW's flight operations team at the Chandra Operations Control Center, Cambridge, Mass. is far from over.

Over the next few weeks, the team will continue to activate and check out Chandra's two science instruments. Chandra is expected to be ready to begin its science operations by late August.

Chandra, the third in NASA's family of Great Observatories that includes the Hubble Space Telescope and the TRW-built Compton Gamma Ray Observatory, was launched from Kennedy Space Center aboard the Space Shuttle Columbia at 12:31 a.m. EDT on July 23.

Approximately seven hours after launch, it was deployed from the Shuttle approximately 146 miles above the Earth attached to the IUS. After two burns of the IUS, which placed it in an orbit measuring approximately 206 miles by 45000 miles, Chandra deployed its 64-foot-span solar panels, then separated successfully from the IUS.

TRW has been designing and producing spacecraft for NASA's most challenging space science missions for more than 40 years. In addition to Chandra, the company is currently developing designs and technologies for several of NASA's future space astronomy missions, including the Space Interferometry Mission, the Next Generation Space Telescope, which are both part of NASA's Origins program, and Constellation-X, the successor mission to Chandra.

Space Science - SpaceDaily Special Report

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