Leak issue resolved – Endeavour back on track for August 7

by Chris Bergin

Engineers have managed to resolve a crew cabin leak on Endeavour, which had threatened the August 7 launch attempt of STS-118.

Working late into Sunday, engineers carried out several leak checks to find the source of the leak, which in the worst case scenario would have led to the rollback of the vehicle. In the end, the source of the leak was a loose nut on the Probe Assembly related to the Ingress/Egress Hatch, which simply required a half turn to stop the leak.

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The issue came to light on Saturday, during the standard leak tests on the crew cabin and Spacehab module. 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.

Several more leak checks were conducted, as the effort to find the source of the leak – a process which could have taken a large amount of time – took place, including the use of an ultrasonic leak detector.

The leak was identified as specific to the crew cabin, with one leak check showing the pressure decay rate had increased to nearly 0.089 psi per hour.

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‘IPR (Interim Problem Report) opened when the leak checks failed for the crew module and Spacehab. Troubleshooting with D-hatch closed exonerated Spacehab as the leak source,’ noted troubleshooting information.

In the end, leak detectors weren’t required, as due diligence from United Space Alliance engineers found, prior to pressurizing the Crew Module, that the b-nut on the Probe Assembly – which feeds the cables and the pressurized breathing air into the Ingress/Egress Hatch – was loose.

The nut was tightened hand-tight with approximately 180 degrees rotation by an engineer, and the leak test was performed with nominal results at approximately 0.001 psi/hr.

‘Additional troubleshooting on Sunday revealed that the nut on the probe flex hose hookup assembly, which connects to the fitting on the hatch, rotated 180 degrees CW – it appeared that the nut was not on fully hand tight,’ noted processing information on Monday.

‘Nut was tightened and leak check tests were performed successfully and with no issues. IPR disposition is in work.’

Another leak test will be conducted on Tuesday, to ensure the issue has been resolved. As per usual, a final leak check will take place after the hatch is closed for launch. 

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