Shuttle Endeavour cabin leak being investigated
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: July 31, 2007
Engineers readying the shuttle Endeavour for the start of its countdown Saturday and launch next Tuesday on a space station assembly mission are wrestling with an apparent crew cabin leak that is proving difficult to isolate.
On Saturday, engineers carried out a standard crew module-airlock leak test and were surprised to note a pressure decay rate of 0.06 pounds per square inch in one hour. The allowable limit is 0.022 psi over four hours. After opening the crew cabin hatch and verifying the position of numerous valves, additional checks were carried out with similar results.
Troubleshooting continued Sunday and by Monday, engineers believed they had isolated the problem to a loose fitting in ground equipment. But tests Monday night to confirm that were not successful and engineers now suspect a real leak. Endeavour passed a similar leak test on May 15, before the shuttle was moved to the launch pad, and it's not clear what might have changed.
Endeavour is carrying a pressurized logistics module in its cargo bay that is connected to the shuttle's external airlock by a short tunnel. The airlock, in turn, is attached to the aft bulkhead of the crew module and there are multiple hatches, valves and seals where a leak could occur. Engineers suspect possible problems with a pressure relief valve located behind the back wall of the shuttle's toilet.
Troubleshooting is not yet complete and it's not yet clear what impact work to replace the valve, if required, might have on Endeavour's launch date. Such work would be invasive, however, and time is short.
The Endeavour astronauts - commander Scott Kelly, pilot Charles Hobaugh, Tracy Caldwell, Rick Mastracchio, Dave Williams, educator-astronaut Barbara Morgan and Al Drew - plan to fly to the Kennedy Space Center on Friday. The countdown is scheduled to begin at 9 p.m. Saturday for a launch at 7:02 p.m. Tuesday.
A wild card in the shuttle's ground processing flow is the planned launch of the Mars Phoenix lander atop a Delta 2 rocket from the Cape Canaveral Air Force Station. Liftoff had been targeted for 5:35:18 a.m. Friday, but the high-priority flight has slipped 24 hours, to 5:26:31 a.m. Saturday, because of anticipated bad weather today.
Phoenix could launch as late as Sunday morning, at 5:17:23 a.m., and not impact NASA's plans to launch Endeavour on Tuesday. But bad weather or additional problems with the Mars mission could have an impact on the shuttle.
The $414 million mission has a limited 22-day launch window that won't reopen for another two years. NASA managers have said Phoenix likely would be given additional launch tries, if necessary.