Redeployment Of Spartan

The success of USMP-4 had, however, been tempered by the botched deployment of Spartan-201, although flight controllers hoped that all might not be lost. On 29 November, Kregel performed a status check of the satellite to gather data on its health in anticipation of a possible redeployment towards the end of the mission. Six to 20 hours of free-flying solar observations might still be possible, as opposed to the 50 originally planned, but ultimately the option was called off because of concerns about available propellant reserves in Columbia's RCS tanks.

Propellant for only one rendezvous - not two - had been budgeted by mission planners when they calculated the amount of manoeuvring fuel the Shuttle would require to support the Spartan deployment and retrieval activities. Unfortunately, most of that propellant had been used by Kregel during the manual rescue on 24 November and the Mission Management Team determined that the crew would not be able to conserve enough fuel in Columbia's tanks to ensure a successful recapture. Moreover, if a similar problem was encountered while attempting to grapple the satellite, or additional station-keeping time was needed, propellant margins would run dangerously low.

"Right now,'' said Lee Briscoe of Mission Operations on 28 November, "we have about 115-120 lb [of propellant] in the forward [tanks]. We're looking for something like 200 lb to be able to go do [a second rendezvous]. We're short a little bit. If we can [conserve] propellant and things go very well, then we can see what we've got. In the next two days, we'll be watching that, see what our propellant situation will be in the forward [tanks], before we will be able to tell managers what we have the ability to do.''

However, during all satellite-deployment missions, flight controllers ensure that enough fuel is on board to guarantee success, even if critical systems fail during the rendezvous and force the Commander to expend more propellant than intended. For example, if Columbia's Ku-band radar had failed during the final approach to Spartan, Kregel would not have been able to make a high-precision rendezvous and would have had to use more fuel. "In computing our margins for this case,'' said Lee Briscoe of Mission Operations, "we just didn't have that kind of propellant. The things we were looking at here were doing strictly a 'mean' rendezvous: we were not protecting the Ku-band failure case [and] then we were having to allow for some bit of flyaround and station-keeping gas. That's not necessarily an easy thing to do and, if you were deploying a brand-new, fresh spacecraft, you wouldn't do it in those circumstances." This was a pity, particularly as Kregel performed a status check on Spartan on 29 November and found it to be in excellent health. This forced managers into a quandary and they deferred their final decision until the 30th.

Two possible options were explored: releasing the satellite on 1 December and picking it up the following day, or setting it free on the 2nd and retrieving it about 20 hours later. Both would require a one-day extension of the mission to 17 days. Ultimately, the risks proved just too high. Not only could Columbia probably not support a full rendezvous, taking into account the potential failures, but there was a chance the $10-million Spartan might be lost and the complex deployment and retrieval procedures would adversely impact the high-priority last few days of USMP-4 operations.

"Here's a case where we have the Spartan in the [payload] bay. We have it: it's a healthy spacecraft [and] we can bring it back,'' Briscoe rationalised. "If you were to deploy it under these kinds of propellant margins, you could stand a 40 or 50% chance of not bringing it back if you had dispersions or failures as you tried to rerendezvous with it. Based on that, the management team decided we would go ahead and forgo another deploy and retrieval. The flight control team wasn't comfortable with the amount of propellant that we had.''

Nor could Spartan conduct its solar observations while attached to the end of the RMS; although Columbia could be oriented with great precision, it was not good enough to aim the instruments with sufficient accuracy. By 30 November, it was official: there would be no redeployment, the crew would return to Earth as planned on 5 December and Spartan would be impounded as part of an investigation into what went wrong. Already, some members of the media were pointing fingers at Chawla for having botched the deployment and many were not afraid to question the crew during space-to-ground news conferences.

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