Technicians scan Discovery's fuel tank for unseen damage. Photo Credit/NASA photo
NASA shuttle managers sounded a cautious note on Wednesday, as they announced further delays in efforts to launch the shuttle Discovery on the senior orbiter’s final flight, an 11-day assembly mission to the International Space Station.
The soonest Discovery could lift off is Dec. 17, the opening of a four-day launch period, though shuttle managers may seek more time to assess unexpected damage to the shuttle’s external fuel tank.
The damage was discovered after a Nov. 5 launch scrub caused by a significant hydrogen leak. A slightly misaligned fuel tank vent line fixture blamed for the hydrogen leak has since been replaced.
Fuel Tank Cracks Worrisome
However, the leak was accompanied by a 20 inch long crack in the insulating foam that covers the 154-foot-long fuel tank. As they removed the damaged foam, technicians at NASA’s Kennedy Space Center found four cracks in adjoining stringers that encircle a region of the tank separating internal oxygen and hydrogen propellant containers.
The cause of the worrisome cracks is still not clear, Bill Gerstenmaier, NASA’s Associate Administrator for Space Operations told a Johnson Space Center news briefing on Wednesday. The news briefing followed the latest in a series of meetings between managers and engineers who are attempting to develop an explanation for the damage and determine whether the cracks represent an added risk to Discovery’s launch.
“We have to understand what our exposure is to that problem recurring somewhere else on this tank,” explained NASA Shuttle Program Manager John Shannon. “So, we are very carefully, very methodically going through it. We’re passing up some launch opportunities to do that. We want to make sure we fully understand the problem before we commit to go fly.”
Prior to Wednesday’s announcement, shuttle managers were considering a launch between Dec. 3rd and 7th.
Soyuz Mission Takes Temporary Precedence
The Dec. 17 launch period extends through Dec. 20. The four-day stretch follows the Dec. 15 launching of a Soyuz spacecraft with U. S., Russian and European astronauts traveling to the space station for a six-month stay. The capsule will dock on Dec. 17 several hours ahead of a possible launching of Discovery at 8:51 p.m., EST.
Since their discovery, the stringer and foam cracks on the shuttle’s fuel tank have been repaired. The damaged areas on the neighboring stringers have been cut away and replaced with structural doublers.
As Gerstenmaier and Shannon explained, they’re still missing explanations for when the cracks formed – in production, in transit to Kennedy or on the launch pad. They’re also missing assurances there is not more unseen damage and the worst case outcome if there is further cracking.
One concern is that the cracks could liberate a chunk of foam that would slam into the spacecraft as the shuttle climbed out of the atmosphere, the event that triggered the 2003 Columbia tragedy.
The assessments are expected to resume Saturday, with another review by managers on Dec. 2.
In Search of Future Launch Dates
The shuttle program has tentatively identified launch opportunities after Dec. 20, though NASA intends to avoid placing the spacecraft in a demanding operational position over New Years’ Eve. The restriction is intended to avoid difficulties with the shuttle flight control system computer clocks during the year end “rollover.”
The space agency will also look at launch opportunities in January, but it could be late February before all of the issues have been addressed.
Discovery’s six astronauts have trained to deliver and equip the station with a new storage compartment and an external platform for spare parts. Discovery is carrying new life support and research equipment as well.