A problem with two Engine Cut Off (ECO) sensors has led to the scrub of STS-122’s launch attempt on Thursday.
The launch date has moved to NET (No Earlier Than) Saturday, with evaluations to take place on if they can fly with two faulty sensors. Due to the complexity of the problem, engineers require further evaluations to pinpoint the cause of the sensor issues.
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Scrub and troubleshooting latest:
‘ET LH2 Low level liquid sensors 3, and 4 failed wet when SIM dry commands were sent,’ noted exclusive L2 MMT level live coverage. ‘This is a scrub condition. Must have 3 of 4. Recommend SCRUB.’ (8:30am)
Launch attempt is now scrubbed (ET recommendation via LCC rules around 9am, to MMT – concured). It was later noted on the loop – and then through PAO, before the turn of the hour (9:57am). Engineers will monitor the sensors during detanking to learn more data on the two sensors.
Troubleshooting may include engineers entering the aft, demating and remating the monoball electrical connections, in order to see if there are bad electrical paths between the ECO sensors and electronics.
‘(Appears it could be an) open circuit somewhere between the monoball producion break and the Point Sensor Box,’ was an initial finding, as per L2.
During the LH2 tank drain, the 5 percent sensor remained WET, even when the tank was empty. 10 minutes later, both the 5 percent sensor and ECO #4 went DRY. The ECO #3 was still indicating WET some time afterwards, before re-setting.
Engineers are still trying to find the cause, which now appears to be downstream of the monoball area – which contains multiple connectors that channel data and power from the orbiter over to the tank and SRBs.
Evaluations include the possibility of taking the option to enter the aft to check connections and wiring, which involves rollback of the RSS, door opening, platform installation, troubleshooting, PRSD tank refill etc. That decision remains fluid, and may be decided on Friday.
If that was called, engineers would then perform ‘wiggle’ tests on certain connections in the aft of Atlantis. However, it is not certain if the issue is on the orbiter or ET side.
That process would mean at least three or four days of standdown.
At around 3:15pm local, LH2 ECO #1 suddenly went WET. An hour later, the sensor registered DRY on its own accord. This was a seperate event, with the ET empty at the time.
MMT have debated the possibility of a tanking test on Friday (which appears unlikely) with the launch date moving to no earlier than Saturday. The MMT will meet at 2pm Friday to evaluate if the launch needs to be delayed yet further, due to the complexity of the problem.
Currently, the MMT are trying to find rationale on flying as-is with a 2/4 LCC scenario. This will be discussed more on Friday.
A new article on status will published later today.
Preparations for launch have proceeded smoothly, with Fuel Cell loading completed on Wednesday. Engineers also repaired a leak detector sensor problem in the pad’s GSE (Ground Support Equipment) – caused by a dirty connector.
The OWP on the -Y side of the Pad/Mobile Launch Platform (MLP) gave engineers some additional work ahead of RSS retract, before being bypassed for repair after launch.
Pad workers were two hours down on the timeline earlier in the proceedings – caused by a longer than scheduled pad closure. However, this was caught up by the time a floodlit Atlantis was revealed by RSS retract last night.
MLP interior securing, and TSM closeout are complete, with Fuel Cell calibration in work. In total, five GSE issues have been reported during the countdown, but none are a constraint to launch.
Go for tanking was given, with a chilldown and slowfill of the External Tank on the timeline at just after 7am local time. Chilldown has been completed, with slowfill operations beginging (7:43am). Issue noted on SIM test of ECO sensors (see newsflash at the top of the article).
One issue is being troubleshooted, with communications between MILA and the Johnson Space Center – which tracks the Shuttle radio transmissions during the first 7.5 minutes of launch. The primary system (1) is suffering from ‘dropouts’ – LCC (Launch Commit Criteria) allows launch with one working system, though redundancy is preferred.
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STS-122 FRR Summary:
Shuttle management rounded up the points of interest at the Agency-wide (Level 1/SOMD) FRR (Flight Readiness Review), which was conducted last week. Items of interest included the ‘spalling’ issue with the RCC panels, and the mitigation of glove damage during STS-122’s EVAs.
‘It is widely recognized that the glove cuts seen in the last year on ISS are a hazard we do not yet understand, thus there is great concern for any planned EVA tasks without the overglove as a protection for this unknown problem,’ noted JSC/MOD shuttle manager Paul Hill.
‘In particular, the wording of an exception to doff gloves to prevent going late in the EVA timeline left some with the impression that there was not sufficient rigor in the criteria for using the overgloves.
‘MOD confirmed that we recognize the potentially catastrophic risks of glove cuts, have planned and will conduct EVAs with a bias towards wearing the overgloves as much as practical. The EVA Office was given an action to coordinate criteria for donning the gloves in response to glove RTV loss during an EVA.’
The concern with the RCC panels, noted by NASA Engineering and Safety Center (NESC) ahead of STS-120, was again deemed as no threat to safe flight at the STS-122 FRR, although Hill noted they will take a closer look at three panels on Atlantis, after her return to Earth.
‘RCC panels 9R, 12L and 13R are being flown with thermographic IR responses in the range of concern to analysts. The NESC expressed concern with the damage growth model and the subsequent burn through analysis that was discussed in deciding to fly these panels as-is,’ added Hill.
‘Thus, the locations of interest on 9R, 12L and 13R are not burn through concerns for STS-122 entry, although they could present issues for the next flight of this vehicle (these panels) depending on post-flight thermography.’
This article will be updated during the countdown.
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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