April 29, 2011 | 1
KENNEDY SPACE CENTER—The shuttle Endeavour suffered a minor but potentially troublesome electrical failure that delayed its launch from Friday to Monday at the earliest. Technicians won’t know for sure until they drain the external fuel tank and get access to the errant unit, a process that will take 24 hours. By Sunday noontime, NASA officials say they should know how bad things are and how long a fix will take.
At a press conference this afternoon, launch integration manager Mike Moses and launch director Mike Leinbach described the problem. It occurred in one of Endeavour‘s three auxiliary power units (APUs), which provide hydraulic pressure for adjusting the rocket nozzles and moving the ailerons and other aerodynamic control surfaces. These units have caused trouble in the past: two caught fire during Columbia‘s landing in December 1983. This time, an electric heater in APU No. 1 failed, which could have caused the hydrazine fuel to freeze once in orbit and burst the fuel line. Leaking hydrazine would then have ignited when the orbiter re-entered the atmosphere. In practice, Moses said that if the launch had gone ahead, engineers would have shut the unit down, purged it, and relied on the other two.
Launch controllers noticed the problem about 9 a.m. Friday when a thermostat didn’t turn the heater on when it should have. Technicians went into the cockpit and flipped a switch to change the heating power source, in case that was the issue. It wasn’t. Although the shuttle could have gotten by with only a single APU, the team decided to play it safe. "You don’t like lifting off without redundancy," explained Leinbach. Controllers scrubbed at 12:16 p.m., by which time the astronauts had just left for the launch pad.
After technicians drain the tank, they will need to enter the aft of the orbiter on the left side to access the heater. The fix may be as simple as swapping in a new thermostat, in which case Endeavour could refuel straight away and fly on Monday. But the problem may also lie in a switch box known as the load control assembly (LCA), which is harder to get at. Because the LCA affects several different systems, any replacement would have to undergo two days of extensive testing. Such an extensive delay could run into scheduling conflicts with an Air Force rocket launch planned for next week or a Russian Soyuz undocking from International Space Station—Endeavour‘s destination.
The drama of the day adds to what has already been something of an emotional rollercoaster. Yesterday, the storm front that proved so deadly elsewhere in the South hit Florida. Thunderstorms drenched Kennedy Space Center and spidery lighting bolts raced across the sky. The bad weather delayed the opening of the gantry by five hours, yet the launch team worked overtime and kept the launch on schedule—the longest such delay they’ve ever been able to make up for. The weather cleared and would have been fine by launch time, had the electrical problem not struck—an irony that Moses called "salt in the wound."
Delays are not exactly a novelty in the shuttle program, but this one has been particularly visible because Endeavour‘s final flight is so historic. Those few diehard space reporters who have stuck with the program through thick and thin keep exclaiming about how many journalists (hundreds) have shown up to see Endeavour off. It’s the second-to-last shuttle mission and arguably the last to really do anything significant, including the final spacewalks of the shuttle program, completion of the U.S. portion of the space station, and installation of the station’s most important scientific instrument, the Alpha Magnetic Spectrometer. Needless to say, the human drama was heightened by the shooting of Gaby Giffords, whose husband Mark Kelly is the mission commander, as well as her presence at Kennedy to observe the launch privately with other crew family members and possibly President Obama. The President and his family planned to attend the launch and went ahead with their visit despite the scrub. They spoke with astronauts, visited the control center and walked under the belly of the Atlantis orbiter, currently being prepped for the ultimate shuttle flight in late June.
Image: Launch officials at Friday press conference at Kennedy Space Center; credit: Rob v. Mackelenbergh