Shuttle Stop

One of Murphy's laws goes "Given an intermittant malfunction, the malfunction will return soon after the obviously defective part has been replaced." That's funny, if safety isn't involved.

Many highly automated or mechanized systems go down because a safety device, or other sensing device, is inappropriately showing a fault. The normal course of business is to by-pass the device. If there are layers of safety devices or systems, the process can be run successfully in the face of the degraded protection. That is, until enough layers have been removed that a single fault causes a catastrophic failure. For industrial systems, frequently the fault is invisible once by-passed, and no one gets around to fixing it.

Think of the pressure on the launch team - everyone gathered waiting for takeoff. But, think of the embarassment if the article crashed? Even if the fault they could have by passed was immaterial to the failure, they would have been fried. Probably, if you were flying commercial, they would have by passed it an gone on relying on redundent protections.

The two shuttle catastrophes arose from failure of mechanical components, the O-rings and the tiles. Neither was metal. Probably there are pretty good methods of measuring or predicting metal failure. Neither system had a back up.

The o-rings were used under a measurable condition [temperature] outside the range of testing and certification. It's unclear to BrooklynDodger whether the tiles were tested under the range of foreseeable impact, or whether the foreseeable impacts had been investigated.


Jul 14, 7:46 AM EDT
NASA Eyeing Cause of Fuel-Gauge Problem

CAPE CANAVERAL, Fla. (AP) -- NASA technicians are hoping to get a better idea Thursday about whether they'll be able to fix a sensor problem at the pad or have to return the space shuttle Discovery to the hangar for more extensive repairs.

The problem with a fuel sensor forced managers to scrub Wednesday's planned launch, just 2 1/2 hours left in the countdown and further delaying NASA's return to space travel after the 2003 Columbia disaster.

Thousands of people had descended on Florida's Kennedy Space Center for the launch, including families of the seven astronauts killed when Columbia disintegrated.

Similar fuel-gauge problems had cropped up during tests in April but technicians and officials thought they had been fixed.

Shuttle managers had no idea whether Wednesday's trouble was in the gauge at the bottom of Discovery's fuel tank, a stretch of cabling and wiring, an electronics box inside the shuttle or something else entirely.