NASA managers have extended their hold on the space shuttle Atlantis' launch until at least Friday, due to a problem in the shuttle's electrical power system.
The problem cropped up early Wednesday, just before NASA was to start filling the shuttle's external fuel tank for launch to the international space station. Mission managers met throughout the afternoon, engaged in a "spirited discussion" over what to do, said shuttle program manager Wayne Hale.
On Wednesday evening, Hale said the managers decided to pass up a launch opportunity on Thursday but leave open the possibility of a Friday launch at 11:40 a.m. ET.
The problem has to do with erratic readings from a coolant pump that chills one of the shuttle's three electricity-generating fuel cells. Hale noted that the problem did not technically violate any of NASA's launch constraints.
"The fuel cell works fine on two phases ... and there is certainly the possibility that it will work fine for the duration of the entire mission," Hale told reporters at NASA's Kennedy Space Center in Florida.
However, the erratic readings indicated that "there’s something funny going on in that fuel cell," Hale said, and sparked concern that the cell could fail. NASA rules say all three fuel cells must be working to launch, and if one fails in orbit, the shuttle must come home promptly.
Engineers will continue gathering data to make sure they fully understand the factors behind the erratic readings — then managers will decide whether to give the go-ahead for a launch attempt as is, or forget about launching this week and have the fuel cell replaced. Hale said the decision was shaping up as a "50-50" proposition.
"If you want high drama, this is about as good as it gets," he said.
NASA has said Friday is the last day that Atlantis can get off the ground before interfering with the planned launch of a Russian Soyuz vehicle on a trip to the space station later in the month. During Wednesday's briefing, Hale acknowledged that Atlantis could conceivably be launched on Saturday and perform a shortened mission.
"If we scrub Friday, for whatever reason, we will have that discussion," Hale said.
If Atlantis does not lift off this week, the space agency may have to wait until late October — or relax daylight launching rules instituted after the 2003 Columbia accident and try again at the end of September. NASA's current rules say shuttles have to be launched in daylight so that the big external fuel tank can be photographed for evidence of any broken-off pieces of foam of the sort that doomed Columbia.
Atlantis and its six astronauts plan to haul 17.5 tons of girders and solar panels into orbit and resume construction of the international space station, which has been on hold since even before the Columbia disaster three and a half years ago. Astronauts will make three spacewalks to put the pieces together.
The shuttle was originally supposed to lift off on Aug. 27 — but launch was delayed, first by a lightning bolt that hit the launch pad, then by Tropical Storm Ernesto, then by the electrical problem.
As the managers continued to study the problem, astronauts on the ground and in orbit waited. The three-man crew of the international space station kept asking if Atlantis is visiting them soon.
“We’re trying like heck to preserve the options for launching this week, but there’s a lot to consider,” astronaut Stephen Robinson told the space station from Mission Control in Houston.
Slideshow 12 photos
Month in Space: January 2014
Instead of donning their orange spacesuits for liftoff, Atlantis’ six astronauts visited the launch pad to take photographs.
NASA is caught in a schedule squeeze. The space agency made an agreement with the Russians not to attempt a launch after Friday because Russia is sending a three-person Soyuz capsule to the space station on Sept. 18. If Atlantis blasts off after Friday for its full-duration mission, there would be a traffic jam at the space station.
Once the Soyuz comes back, NASA may attempt a launch in late September even though it would be in the dark, spokesman Allard Beutel said.
If NASA doesn’t ease its rules, the next launch attempt after Friday would be Oct. 26 and 27.
NASA has to squeeze 15 shuttle launches into the next four years to finish the construction of the half-built space station.
This report includes information from The Associated Press and MSNBC.com.