By 1990, Ali AbuTaha made the dynamic-overshoot error known in the USA and abroad in lectures, courses and official documents. NASA and others began to take notice. Bob Sieck, Shuttle launch director, commenting on an earlier scrubbed launch at the STS45/Atlantis post-launch press conference on 24 March, 1992, said: "We scrubbed because of...transient leaks" during loading of the ET. "This was a transient-leak condition due to the thermal environment of the plate changing temperature during the first few minutes of the loading procedure," he added.

Analysing previous liquid-oxygen-tank loading, Sieck commented:"We expected to see the transients again, and we did." Loading of liquid hydrogen, using a different procedure where there is a longer cold-soak, resulted in "no leakage".

He was asked whether the "thermal transient" had occurred before. "When you really look at the data with a magnifying glass," he replied, the thermal transient "...had been there before on a number of missions".

Sieck says that the loading of the STS 45 ET had included loading the hydrogen " a slow fill...but we got the transient on the oxygen". Sieck was asked how much the thermal transient was. "The amplitude of the spike...was probably 100% more" than recognised before and he agreed that it had an effect on the "wear and tear" of parts.

This example of the dynamic overshoot is mirrored in sudden changes in temperature, pressure and voltage in aircraft, industrial and nuclear reactors - and the electrical industry.

Asked why fuses were being changed on the Hubble Space Telescope, a NASA spokesman explains that the agency had discovered that the original 3A fuses were inadequate and were replaced with 5A fuses.

When pressed, he says that, when the circuits were turned on, the current went up to 5A because of transient conditions before settling down at 3A - a 70% overshoot on the Hubble.

The Hubble launch was delayed for two weeks specifically while AbuTaha's claims were being analysed up to vice-presidential level, but NASA made the launch on the assumption that dynamic overshoot was understood. What else on the Hubble was designed without regard to a 70% overshoot?


Source: Flight International