Uncertainties cloud shuttle schedule

Discovery's domino effect
The Atlantis delay has implications for Discovery as well: Like last year’s mission, the upcoming mission must provide a "safe haven" option for the crew, in case astronauts spot potentially fatal damage to the shuttle's heat shield during on-orbit inspections. That option calls for the shuttle crew to take shelter aboard the international space station and wait for another shuttle to pick them up.

The current "safe haven" plan calls for Atlantis to be launched on a rescue mission as early as Aug. 4. That implies that the shuttle's seven crew members would have to hunker down with the station's two long-term residents for almost three months. NASA says that option is workable because the station has more stocks of food and water, and more reliable life support hardware, than it did last year.

The shuttle fleet's third surviving vehicle, Endeavour, had been due to follow Atlantis on the flight rotation in December. However, that mission has now been switched to Discovery. Whether there will be a flight-ready tank on hand by the end of the year remains in doubt.

The bottom line is that the benefits of flying the next mission in May are evaporating, and the slips in the follow-on flight schedule are putting greater strains on the contingency planning for the May launch. Because of this domino effect, a delay of two months makes sense, some space workers have told MSNBC.com.

Issues mount up
The concerns over verifying the safety of the tank modifications are far from the only issues being juggled by the NASA shuttle team. It's normal to encounter such issues during launch preparations, and they are often resolved by assigning extra resources, but this time some officials fear there may be just too many of them to resolve in time for a May liftoff.

Mechanical checks have revealed potential problems with the overhead windows in the crew cabin; with pressure seals and possible contamination in the main engines; and with a leaky hydraulic power unit that was thought to have been fixed. Tile replacement, and in particular the installation of "gap fillers," has lagged behind planned schedules.

Echoes of past problems are also being heard. Some engineers interpret sketchy data from last year's launch as suggesting there really was a debris impact on Discovery's left-wing leading edge, the same location where Columbia suffered its mortal wound in January 2003. In addition, one of the low-level sensors in the fuel tank is showing similar symptoms to an equivalent sensor in Discovery’s flight last year, a problem that led to a significant last-minute delay.

Currently, Discovery's preparations are at condition "yellow," meaning that significant effort will be required to meet the schedule. Officials are hoping to roll Discovery from the Orbiter Processing Facility to the Vehicle Assembly Building on April 6, so that it can be mated to the tank and solid-rocket boosters and rolled out to the pad about April 13.

Dates drive discussions
John Muratore, NASA’s manager for shuttle systems and integration, reportedly concluded Thursday's meeting by acknowledging that a “tremendous amount of engineering work” was being laid out. He wanted everyone to understand that the launch date will be driven by the completion of this required engineering work, and that setting a date was intended to provide a target for concerns to be aimed at.

“We should not be thinking that if we put a launch date out, that means that we will compromise the engineering work to make that launch date,” he insisted, according to another attendee. The purpose, rather, is “to force a discussion about what work there is, that needs to be done – and drive those issues out of the woodwork.”

So far that process has been working, and engineers have clearly been vigorously bringing their concerns forward. If, as a result, there turns out to be too much work to get done before May — and that prospect is widely accepted as likely— then the mission will wait for a July flight with all the safety concerns properly addressed.

Worse things could happen. In the past, when the rough-and-tumble exchanges that now characterize NASA’s meetings was suppressed, worse things did happen. So none of these issues, and no amount of time needed to get it right, should be considered bad news.

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