NASA managers decided Saturday to delay the shuttle Discovery’s launch an additional day to Wednesday to give engineers enough time to complete replacement and retest of leaky quick-disconnect fittings in the ship’s right-side orbital maneuvering system rocket pod.
If all goes well, Discovery’s countdown will begin at 2 p.m. EDT Sunday (1800 GMT), setting up a launch attempt at 3:52:13 p.m. Wednesday, roughly the moment Earth’s rotation carries launch pad 39A into the plane of the space station’s orbit. The forecast calls for a 70 percent chance of acceptable weather Wednesday and Thursday, improving to 80 percent “go” on Friday.
NASA Test Director Jeffrey Spaulding said engineers are “really confident” they can finish the work in time to start the countdown Sunday.
“The team has done an excellent job overnight, it’s been a lot of hard work,” he said. “I think they’ve done a great job and I look forward to getting the call to stations tomorrow (to start the countdown).”
The primary goals of Discovery’s 39th and final mission are to deliver a loaded cargo storage module to the International Space Station, along with a spare set of cooling system radiators that will be mounted on the lab’s main power truss.
Assuming an on-time launch, Discovery would dock with the space station at 12:36 p.m. Friday. Two spacewalks are planned, on Nov. 7 and 9, with undocking on tap Nov. 12 at 5:02 a.m. and landing back at the Kennedy Space Center at 9:59 a.m. Nov. 14.
Launch had been targeted for Monday, but engineers ran into problems overnight Thursday with leaking nitrogen and helium quick-disconnect couplings used by Discovery’s right-side OMS pod. The nitrogen gas is used to open and close a variety of valves while the helium is used to pressurize propellant tanks in the rocket pod.
Engineers decided early Friday to replace the fittings, delaying the start of Discovery’s countdown to Saturday and pushing launch from Monday to Tuesday.
The repair work required engineers to vent high-pressure helium tanks in the OMS pod before swapping out the couplings. The replacement work was completed early Saturday and engineers began a series of leak tests to make sure the new fittings were tight before re-pressurizing the helium system.
Because the tanks were fully vented for the repair work, engineers had to first carry out an intermediate repressurization, a process expected to take about six hours to complete, followed by a 16-hour procedure to bring the system up to flight pressure.
To make a Tuesday launch target, NASA had to start Discovery’s countdown by 2 p.m. (1800 GMT) Saturday. But after a management review earlier Saturday, it was clear more time was needed and the decision was made to push the launch back one more day to Wednesday.
“The plan as we knew it yesterday was to vent down the tank and replace some parts we thought were faulty on an air-half coupling on our right-hand OMS maneuvering system pod and then do some leak checks,” Spaulding said. “As we went through the day, we learned there was some additional work we needed to do … from a leak check perspective and some of the venting operations that needed to be done.
“We did remove and replace the air-half coupling and the ground-half coupling that we talked about yesterday, the parts that were faulty, and we’ve done some initial leak checks on those and also some moisture samples. And all of those came back good.”
Spaulding said engineers expect to complete the helium re-pressurization procedure early Sunday, well before the planned start of the countdown.
The shuttle’s current launch period extends through Nov. 7. Spaulding said NASA managers planned to follow normal procedures, making two attempts in a row, if necessary, before standing down a day to give the launch team a chance to rest. Another two launch attempts then would be possible on Nov. 6 and 7 if necessary.
“Launching on Wednesday, we still have up to and including Sunday, so that gives us … our normal four (launch attempts) in five-day capability we like to preserve,” Spaulding said.
The next launch window opens Dec. 1.