Atlantis is cleared for liftoff
08 September, 2006
CAPE CANAVERAL - NASA will try to launch Atlantis and six astronauts today despite a power generator problem that could cut short a critical mission to resume construction of the half-built International Space Station.
Pending the results of a final engineering analysis early today, NASA aimed to launch Atlantis at 11:41 a.m., starting the first station assembly flight since seven astronauts were killed in the 2003 Columbia accident.
The decision to press ahead came despite recommendations from the generator manufacturer and NASA's own safety office.
Both urged mission managers to delay the launch until the suspect fuel cell could be replaced.
Managers said they are confident the power generator will operate without problems.
They said the chances of a failure are low, and that a failure would not endanger the Atlantis astronauts.
Manufacturer UTC Power of South Windsor, Conn., "did not consider it a safety issue. They concurred on the fact that the fuel cell is not going to blow up, explode, catch fire -- any of those kind of things," NASA shuttle program manager Wayne Hale said.
Hale added, though, that NASA was accepting the risk that a power generator failure might force the Atlantis astronauts to return to Earth without completing their mission.
"There is some risk. That is undeniable," he said.
"The risk is that we may be wrong and we get on orbit and this fuel cell will not function properly. And at that point, we're going to have a discussion about how much of the mission can be accomplished," Hale said. "I am comfortable that that is a very low risk."
Added Steve Poulos, manager of NASA's Orbiter Projects Office at Johnson Space Center in Houston: "I don't have any concern that we are going to lose this fuel cell on the way uphill or during the mission."
Risk of explosion
Shuttles are equipped with three fuel cells that combine liquid hydrogen and liquid oxygen to generate electricity to run spaceship systems. An electrical short was detected in a coolant pump connected to one of the generators, prompting NASA to call off a planned launch Wednesday.
The short reduced from three to two the number of circuits operating the pump. The loss of a second would prompt a pump shutdown, and the fuel cell could overheat. A mechanical breakdown could follow and, in a worst-case scenario, liquid hydrogen and liquid oxygen could come into contact without the proper cooling. A fire or explosion could result.
The suspect generator last flew on a July 1999 flight. Five seconds after liftoff, a short circuit crashed two engine computers, leaving five astronauts one failure away from a risky and unprecedented emergency-landing attempt. The failure ultimately was blamed on faulty wiring.
NASA flight rules require all three fuel cells to be operating before clearing a shuttle for launch. The suspect generator on Atlantis is operating, but on two circuits rather than three.
Hale and Poulos noted that none of the 30 fuel cell coolant pumps in NASA's inventory has ever failed in flight -- despite the fact they were built 30 years ago.
"I wish my car was that good," Hale said.
The Atlantis crew aims to outfit the station with a 17.5-ton truss segment equipped with a new set of solar wings that will double the amount of power available at the outpost.
The flight is the first of 15 required to finish the international station before a September 2010 deadline set by President Bush.
The launch attempt today might be the last before the Atlantis mission would slip back behind a previously planned crew rotation at the station. In that case, the launch would be delayed until late September at the earliest.
The deadline, however, might be extended a day if minor technical problems or bad weather force a delay. A launch attempt at 11:15 a.m. Saturday then would be an option.