Chandra Ready To Open Its Xray Eyes

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It had been one of the most potentially hazardous ascents yet completed and would lead directly to the grounding of the rest of the Shuttle fleet for almost six months. For Eileen Collins' crew, savouring their inaugural moments of weightlessness on the mission, they had other business to take care of: getting their $1.5-billion X-ray observatory ready for deployment. The first few hours were spent checking the health of both Chandra and its IUS, primarily under the direction of Coleman and Tognini, before the stack was tilted up to its deployment angle of 58 degrees.

''Michel and I work as a team,'' Coleman had told an interviewer before launch. ''I put my finger on a switch, he verifies it's the right switch and that is very, very helpful to me. We also have a third person in the background - Steve Hawley -whose job is the big picture of the deploy. It's very human to make a mistake and we cannot afford that. So we're doing everything we can to prevent that.''

If the crew had missed their first deployment window for Chandra, matters would have been complicated somewhat. ''If we have to keep [the observatory and IUS] in the bay overnight, it really constrains things,'' said Bryan Austin. ''If they lose any power to the heaters that keep the [propellant] lines from freezing, it really gets kinda dicey in terms of being able to still possibly even support a mission, because we cannot put them in a warm-enough attitude to keep everything warm without hurting [Chandra].''

Fortunately, all went well on the first attempt. After a critical ''Go/No-Go'' decision by flight controllers in Houston and at the Chandra Operations Control Center (COCC) in Cambridge, Massachusetts, the IUS was switched to internal power and cables routeing electricity to the observatory were severed, which transferred it to its internal batteries. At 12:47 pm, about eight hours after launch, as the Shuttle flew high above Indonesia, Coleman commanded the stack to be spring-ejected from its cradle in the payload bay.

''Houston, we have a good deploy,'' radioed Collins. ''Chandra is ready to open the eyes of X-ray astronomy to the world.'' Added a happy Coleman: ''There are five big smiles in here!'' After the mission, Coleman would tell an interviewer that she was so taken aback by the beauty of the observatory disappearing into the inky blackness on its way to its highly elliptical orbit that she was ''almost too excited to video!'' Shortly after the deployment, Collins and Ashby manoeuvred Columbia into a so-called 'window-protection' orientation, whereby the Shuttle's belly was pointed towards the IUS' nozzle.

An hour later, at 1:47 pm, with Columbia about 50 km 'behind' the Chandra/IUS combination, the first-stage engine fired for just over two minutes. Approximately 60 seconds later, it was jettisoned and the second-stage took over for another couple of minutes. The booster's next job was to keep the observatory properly oriented as its two solar panels unfurled. Shortly before the second-stage separation, after insertion into a preliminary elliptical orbit, at 2:22 pm Chandra's solar panels unfolded perfectly. The separation of the second stage went without incident at 2:49 pm.

By this point, Chandra was in an orbit with an apogee of almost 74,000 km and a perigee of 325 km; this was subsequently adjusted using the observatory's own thrusters over a period of three weeks to achieve a final elliptical path with a high point of 140,000 km and a low point of 10,000 km. After being informed of the successful first firing at 2:16 am on 25 July, Collins replied ''That's good news. There are a lot of cheering people up here on board Columbia.''

The IUS team, needless to say, were also elated. ''We were extremely confident in placing Chandra in its orbit,'' said NASA's IUS representative Rob Kelso after the deployment. ''In addition, this mission culminated in more than three years of training for the IUS flight team at the [US Air Force's] Onizuka Air Station. We couldn't be more pleased.'' Also pleasing - but in a different way - was the discovery of what Wayne Hale called ''our smoking gun'' for the mishap during ascent: Collins found a tripped circuit breaker in Columbia's cockpit for the centre main engine controller.

The tripped breaker persuaded mission managers more than ever before that the controller of the centre engine, or at least its wiring, was responsible for the electrical short. ''Every time you launch, you take a significant risk,'' said Hale, brushing off suggestions that Columbia had flirted with disaster. ''Our job is to manage the risk, to make sure the equipment works the very best it can and that the crew and flight control team are trained to deal with all of the problems.''

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