ECO sensor fails – Atlantis SCRUB

by Chris Bergin

A LH2 ECO (Engine Cut Off) #3 sensor failed during tanking, but External Tank managers have decided recommend that NASA proceeds with the launch of Shuttle Atlantis on STS-115. However, ONE dissenting voice has seen the launch scrubbed, with a 24 hour turnaround.

Troubleshooting since around 4:30am EDT on an issue believed to be related to the Point Sensor Box. The problem is now understood to be more related to the circuits between the PSB and the ECOs, rather than the sensors themselves.

**L2 STS-115 Coverage: L-2 and L-1 MMT Notes. ALL related handbooks, from Final Flight Plan to EVA Presentations (550mb of 115 presentations downloadable)**

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KEY EVENTS: (Colour code: Red ‘No Go’ – Green: ‘Go’)
External Tank Weather Orbiter Range.

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Key Points/Newsflashes: Meetings taking place: 4:28am EDT: LH2 ECO sensor failure. Troubleshoot. Tyvek cover loss on F3L. 5AM EDT Workers off to the pad during replenish. 5:20am EDT: NASA internal memos speaking of a potential 24 hour scrub being called, pending troubleshooting. 6:00am EDT: LCC GNC-74 violated. 6:30am EDT: Management push to proceed with launch with 3/4 ECOs today. 7:25am EDT: ET – Go for launch. MMT decision – Go for launch. SCRUB.

Refer to live update thread for up to the second updates.

Main Article

Two options were on the table for the Mission Management Team (MMT). One was to proceed with 3/4 ECO sensors, the other to scrub for 24 hours and attempt to launch on Saturday. ET have noted they are go for launch, which will be a critical element for the evaluations.

As per Launch Commit Criteria (LLC) rules, newly expanded on at a recent PRCB meeting that was chaired by Shuttle manager Wayne Hale, the correct procedure should be to scrub for 24 hours.

However, it is now believed that the ECOs are not specifically at fault, with sources noting it is more likely to be an indication that the Point Sensor Box (PSB) on the orbiter – and more so the circuits inbetween – are at fault.

When it came down to the poll of all centers, the MMT showed a majority wanted to fly today.

‘Flight Crew systems was the one decenting vote,’ noted a NASA memo describing the decision.

‘However MPS integration of JSC engineering did not want to accept the LCC waiver, hence they were no-go.

‘Subsequent to the poll, the MMT chairman opted to detank and try again tomorrow.’

Early reactions to the scrub have been positive, noting the obvious lack of ‘go fever’ which NASA has been accused off in the past.

The decision to comply with LCC launch rules has been applauded.

A number of other issues have been noted this morning, refer to the live update thread for information.

One such issue includes the Tyvek cover on thruster F3L, with the concern being if any water gets into the thruster, it could freeze and block.

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