Weekend testing of the removed ET-125 LH2 Feed-through connector resulted in “circuit instability” on two ECO (Engine Cut Off) sensors during LH2 test runs at the Marshall Space Flight Center (MSFC).
While testing will continue, these opening results add confidence to the initial data that pointed to the “External Plug / Feed Through Receptacle Pin Contacts” as the cause of the ECO system anomalies during the two STS-122 launch attempts and subsequent tanking test.
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MSFC Test Results:
The LH2 Feed-through connector from ET-125 was removed from the tank before Christmas, before being shipped off to MSFC. Further tests – from visual to X-ray – were conducted, prior to its installation into a test area (Test Stand 300).
Over the weekend – while its replacement was being installed into ET-125 – engineers tested the removed connector in a simulation of the conditions of cryogenic tanking.
The hope was to find similar issues with the ECO data readouts that caused the scrub of the launch attempts late last year, so as to confirm the removed external feed-through hardware is the culprit. This exercise appears to have been successful.
‘Re-create the open circuit anomaly seen on STS-122 at ET-125 Feed-through with LH2, results: Helium Cryo Test: Circuit #2 showed signs of instability – 10mv upward excursion,’ noted test result documentation, acquired by L2.
‘LH2 Test #1: Circuit #4 showed signs of instability – Max around 250mv for 5 Minutes, around 9 minutes into Chill-down profile (-416 F). Max around 270mv for 45 minutes, and around 2 hours into Warm-up profile (-200 F): Isolated to circuit 4 excitation pin 35.
‘LH2 Test #2: Circuit #4 showing signs of instability – Max around 270mv for around 9 minutes into Chill-down profile (-416 F) Has not recovered (during test). Isolated to circuit 4 excitation pin 35. Circuit transitioned back during Warm-up.
‘Circuit #2 showing signs of instability. Max around 50mv, around 1 hour at stable temps (-416 F) Has not recovered (during test). Isolated to circuit 2 excitation pin 4. Circuit transitioned back during Warm-up
‘LH2 Test #3: Circuit #4 intermittently opened shortly after cryo-shock. Open was controlled to Cryostat pressure (40 to 5 psig pressure cycles). TDR was monitoring circuit and captured open. Isolated to circuit 4 excitation pin 35.’
More data will be gained from the results, likely to focus on the root cause, currently believed to be caused by the “relative motion possible between socket and pin contacts”. This issue should not occur with the replacement connector now inside ET-125, following a procedure to solder the pins in place.
The test schedule remains on track to support the re-aligned launch date target of NET (No Earlier Than) February 7, with the latest schedules on both testing and ET-125 repair, showing completion dates of January 28.
‘Splice/Channelize Pigtails to W01 Harness was completed on Friday afternoon. Work continued throughout the weekend with Internal Connector mate to New Feedthru Assembly, Confidence Test being successfully performed,’ noted processing information on Monday.
‘Feedthru Plate and Seal Leak Checks passing nominally and the ET LH2 Tank being repressurized. Fairing and Strut Cover installation will begin this morning. PDL Pour of Penetrations and subsequent cure will follow.’
Allowing for the process of returning the vehicle into a launch posture, engineers have some flexibility, should the repair – such as cure time – suffer any related delays.
L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.
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