The first real problem with Endeavour – during pad processing for STS-118 – is being worked by engineers at 39A, after a leak was observed in the orbiter’s crew cabin.
The leak, observed at more than 10 times greater than the allowable rate of pressure decay, was first spotted on Saturday, and elevated as a problem during Sunday.
UPDATE: Leak Issue Resolved! See latest article on site.
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According to information and memos acquired by the L2 section of NASASpaceflight.com, the leak was observed by ECL/ECLSS (Environmental Control & Life Support Systems) engineers during the Crew Module with Spacehab Leak Test – part of the scheduled pad flow ahead of Endeavour’s targeted opening launch attempt on August 7.
Engineers noticed a decay in the crew cabin’s pressure at a rate of 0.06 psi (pounds per square inch) over a one hour period. The maximum allowable rate is 0.022 psi over a four hour period. This led to the issue being raised to an IPR (Interim Problem Report).
Troubleshooting was immediate, as engineers checked the Ground Support Equipment (GSE) – which has suffered a number of leaks during the pad flow – along with the opening of the side hatch and the venting of the vehicle.
Following the evaluation of related systems, the hatch on the orbiter was closed and the cabin re-pressurized. Unfortunately, the decay in pressure remained at a rate of 0.06 psi.
As part of the process to locate the area of the leak, engineers carried out the process of venting the vehicle again, before re-pressurizing only the crew cabin, only to find that the decay rate had increased to nearly 0.089 psi per hour. The crew cabin was once again vented for continued troubleshooting.
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Engineers on Sunday reviewed forward plans for the troubleshooting effort, as pad processing continued in tandem with the lowering of the APU (Auxiliary Power Unit) carts from the 135ft level of the launch complex – which requires the removal of all non-essential workers from the pad.
At present, engineers are unsure as to why the orbiter’s cabin is leaking, following a successful leak check on the orbiter whilst she was inside her OPF (Orbiter Processing Facility). That test was conducted on May 15.
After the APU carts were lowered and moved to Launch Pad 39B, engineers returned to the orbiter to work on isolating the location of the leak, placing tape over various valves and locations related to the crew cabin.
Endeavour has once again been powered up, as she awaits another leak check once her hatch has been closed. This time engineers will utilize an ultrasonic leak detector to aid their efforts to find the source of the leak.
‘If the leak still exists, we should take the option to power up, go to remote, and clear the crew cabin, close the I/E hatch and perform a cabin leak check removing the probe, installing the cap, and performing the leak check using the cabin press xdcr,’ noted an Environmental Control engineering memo.
‘Given the latest leak rate we saw (0.0886 psi/hr) we will need to use cabin press (0.08 psi/bit), and monitor for 4 hours.’
Efforts to isolate the leak will continue after this process.
Meanwhile, an important milestone for STS-118’s LON (Launch On Need) was achieved on Sunday, following the arrival of ET-120 at the Kennedy Space Center.
The tank is required to fly with Discovery as a rescue mission, should Endeavour suffer a serious problem on orbit. Discovery’s primary mission – STS-120 – is due to launch in October.
The Pegasus barge containing ET-120 left the Michoud Assembly Facility (MAF) in New Orleans early last week. The tank is due to be transferred to the Vehicle Assembly Building (VAB), first shift Monday.
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