The booster's first Shuttle use in April 1983 had been less-than-spectacular, delivering the first TDRS payload into a lower-than-intended orbit. This embarrassing failure led to a number of other missions being either cancelled or repeatedly postponed. Although the system certainly matured with age, it was still prone to technical problems; one of which conspired to push back the already-delayed Chandra launch. On 9 April 1999, a Titan IV rocket carried a top-secret missile early warning satellite into orbit; the first and second stages of its attached IUS failed to separate properly and the $250 million payload was lost.
Ordinarily, NASA would have watched the resultant investigation with interest and incorporated its findings into its own plans to prepare Chandra's IUS for launch. That was complicated, however, by the fact that the investigation itself was top-secret. Moreover, said Scott Higginbotham, the KSC engineer overseeing Chandra's pre-launch processing, the IUS assigned to STS-93 was impounded as part of the investigative process! Columbia's launch, by then scheduled for 9 July, came under review and the impounded IUS had a domino-like effect on the training of the crew and ground staff.
''We were planning a two-day-long sim[ulation], starting 14 April, that would involve all the different control centres; a joint integrated simulation with everybody,'' said Lead Flight Director Bryan Austin. ''That was going to be a big deal. That has been postponed because the Sunnyvale [IUS control centre in California] Air Force folks and Boeing IUS people were going to be taken away initially to be part of the investigation. That exercise has been put on hold. That kind of put a wrench in things in terms of our sim schedule.''
The Chandra launch was also particularly critical because it was the Shuttle's first IUS launch since July 1995 and, pointed out Austin, ''there's been a lot of change in the expertise level, collectively. For the most part, IUS deploy procedures are the same, but something that to me has been a struggle for this flight with some of our IUS friends is to get them to realise that the payload on the other end of the IUS is not the typical thing the Shuttle has been doing.''
He was referring to the fact that, as soon as the Chandra/IUS transitioned to internal battery power, just minutes before deployment, the observatory would be on its own. On previous missions, if something went awry at the last moment, the IUS and its payload could be retracted for another try or brought back to Earth. However, mainly due to power and temperature constraints, mission controllers had just one shot at a successful Chandra deployment. ''It's either going to be orbiting space trash,'' said Austin, ''or it's going to go out and do its mission.''
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