NASA clear voltage spike issue

by Chris Bergin

NASA managers – who had been meeting on Wednesday to evaluate the over-volt condition that occurred just after the start of the countdown this week – have cleared Discovery for flight. The concern over the Solid Rocket Booster adhesive has also been cleared.

The spike (see image below) was “small” and only for 0.434 seconds, caused by Ground Support – namely the Mobile Launch Platform. Managers also used historical records from STS-87 to aid their evaluations.

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STS-87 in 1997 suffered a very similar situation with Shuttle Columbia. She was eventually cleared for flight, which raised hopes that Discovery would also be cleared.

One area of interest is the Point Sensor Box (PSB), which was active at the time of the spike. Recent ECO (Engine Cut Off) sensor discussions have headed back to the PSB as a potential culprit for recent erratic behaviour by the ECO sensors.

Those sensors themselves have also been targeted as the reason for erratic readings during tanking, leading to recent sensors being ‘hand picked’ – supported by a reduced LCC (Launch Commit Criteria) allowing a single ECO to fail ‘wet’ in the countdown.

However, it is the size and length of time of the spike that are raising hopes that no problems will be found from the over-volt. That was confirmed by the evaluations that took place at the T-1 MMT (Management Mission Team) meeting today.

Image of the spike – full size image and supporting documentation available on L2

‘We discovered the over-volt problem right after we got into the countdown,’ noted NASA Test Director Jeff Spaulding earlier on Wednesday.

‘When we start the checkouts at the beginning of the countdown, we do flight controller testing and a lot of other things that we do, but we did get an over volt indication.

‘We went back and traced it to one of our ground support supplies and we did change that out. These are large power supplies, 800lb power supplies, so it’s not a small task.

‘We re-tested and didn’t have any issues, but we’re going through the systems to check that there aren’t any issues with what we saw. But it was small and for a very short period of time.’

Meanwhile, weather concerns have continued to point to the launch being moved back from Thursday, with 60 percent weather constriants being forecast for launch day, worsening for the following couple of days.

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