Launch slip likely for shuttle Atlantis

NASA charted a course Thursday for fixing shuttle Atlantis, but a mission to deliver a new science lab to the International Space Station likely will be pushed back a few days if not weeks, an official said.

A suspect plug and electrical connector first must be removed from the shuttle's external tank and sent to an Alabama testing facility for troubleshooting and repairs, and its unclear how long the work will take.

"This is going to probably not allow us to fly on Jan. 10. We are probably going to be a little bit after that," NASA shuttle program manager Wayne Hale said.

"Frankly, at this point, schedule is not paramount in my mind. We know we have a plan to go forward and it's going to take as long as it takes," he added. "I would say this is not a long-term problem on the order of months but on the order of days to perhaps a couple of weeks."

An apparent problem with low-level fuel sensors in the 15-story tank forced NASA to scrap plans to launch Atlantis and seven astronauts with the European Space Agency's Columbus science laboratory earlier this month.

The sensors provide a back-up means for shutting down the shuttle's three main engines after a nine-minute climb to orbit. Their failure could trigger a catastrophic explosion in flight or an unprecedented emergency landing attempt.

Engineers subsequently determined that the problem most likely is in an electrical connector and plug that routes wires through the wall of the tank to the sensors, which are located near the bottom of the bullet-shaped fuel reservoir.

The go-forward plan approved Thursday calls for technicians to remove the suspect connector and plug from the tank at Kennedy Space Center's launch pad 39A by Saturday.

The hardware then will be shipped to NASA's Marshall Space Flight Center in Huntsville, Ala., for bench tests and repairs. The repair scheme now envisioned calls for wires within the connector and plug to be soldered solid before the equipment is reinstalled at the launch pad.

Should NASA determine the problem lies within an associated connector on the inside of the tank, Atlantis would have to be rolled back to the KSC Vehicle Assembly Building for repairs, a move that would trigger a more significant launch delay.

Engineers now think the wires contract when exposed to supercold temperatures when liquid hydrogen stored at Minus 423 degrees Fahrenheit is pumped into the tank. The theory is that freezing condensate then forms a barrier that interrupts electrical signals on an intermittent basis and causes, in effect, an open circuit.

Atlas rocket manufacturer Lockheed Martin had similar trouble with low-level sensors in its Centaur upper stage about a decade ago, and the company solved the problem by soldering wires within associated plugs and connectors.

The build-up of the tank and booster stack for a station assembly mission set for launch on Endeavour on Feb. 14 is on hold until at least Jan. 2. It's unlikely the assembly work will be completed in time to support the mid-February launch date.

Hale said a new launch date for Atlantis will be established once the root cause of the problem can be verified and the soldering work can be completed and certified.

Hale said he remains confident that NASA will be able to complete construction of the international outpost before a presidential deadline on Sept. 30, 2010.