Uncertainties cloud shuttle schedule

James Oberg NBC News space analyst

For now, NASA's top shuttle managers are holding firm to a schedule that would launch the shuttle Discovery on its second "return to flight" test mission as early as May 10. However, several senior NASA officials have told NBC News privately that launching in May was at best an iffy proposition.

"We haven't given up on May yet," one official said in an e-mail. However, another source advised against making nonrefundable reservations to see the launch. A third official said there was so much to get done and so little "margin" in the schedule that May was looking more and more unlikely. The sources discussed the situation on condition of anonymity because they were not authorized to speak with the press.

The official view is that NASA is targeting May, rather than shifting to the next launch opportunity in July. During a teleconference on Thursday, NASA officials set May 10 as the earliest date for liftoff, with the launch window extending until May 23. "We are under no thought of delaying launch," shuttle program manager Wayne Hale said, according to accounts from participants.

Fuel tank being shipped
To support a May date for Discovery's launch to the international space station, the shuttle's external fuel tank is being shipped this weekend from the hurricane-battered Michoud Assembly Facility, near New Orleans, to Kennedy Space Center in Florida.

The fuel tank has been a key cause for concern — first of all, because it was foam insulation debris from the tank that dealt a mortal blow to the shuttle Columbia in 2003, leading to the craft's destruction, the loss of the crew and a two-year suspension in shuttle flights. The tanks were redesigned, but debris was seen coming off the tank yet again just after Discovery's launch last July. Fortunately, no serious harm was done.

To resolve the continuing problem, engineers at Michoud removed an aerodynamic protective cover where most of the shedding occurred. The key safety concern, according to numerous space workers who have spoken with MSNBC.com in recent days, is that engineers are far from finishing the analysis and wind tunnel testing to verify that the new configuration is safe to fly.

A widespread fear is that the march toward a defined launch date will put undue pressure on the testing team to come up with the "right" answer and meet the schedule. The "wrong" answer — that the modifications to the external covering of the tank are not provably safe — could require returning the tank to Michoud for rebuilding.

"We would then be screwed out of July, too," one official told MSNBC.com in an e-mail.

Even though Hale said there was "no thought" of delay, he has acknowledged in the past that test results might still rule out a May launch. During an "all-hands" meeting earlier this month, Hale told space workers that he hoped the preliminary analysis would be available in March, but that the definitive tests might take until June. And he promised not to push for May if there were any suspicions that the tank modifications were not safe.

“We are going to have a very interesting review on the external tank,” Hale was quoted as saying during Thursday's teleconference.

Restrictive launch windows
For at least this next mission, NASA planners will stick to the hyper-restrictive launch windows that provide adequate lighting for observing any debris falling from the tank. Combined with other standard constraints, this creates launch windows in May, then from July 1 to 19, then from Aug. 29 to Sept. 14, then two short windows at the end of October and the end of December.

Space officials hope that good results on the next flight will lead to the dropping of these lighting requirements, and the consequent widening of launch windows later in the year. However, even if Discovery launches on time and the requirement for a daytime launch is dropped, there are other potential constraints on future flights — including the schedules for fuel tank delivery, as well as for returning the shuttle Endeavour to flight status after a major overhaul.

For example, the earliest launch date for the mission after Discovery's, involving the shuttle Atlantis, was recently slipped from July 1 to August 28 due to a delay in producing another external fuel tank.

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