Lesson Plans

Lesson Plan #5 - Adjoined Article

Note: We recommend that you print this article and distribute it to your students.

Fuel leak wasn't shuttle's only flaw
By Brahm Rosensweig, Jul. 26, 1999, Discovery Channel website http://www.exn.ca

The present shuttle mission, which launched at just after midnight Friday night, boasts a couple of firsts. It's the first U.S. spacecraft to be commanded by a woman, Air Force Col. Eileen Collins. And the mission has successfully delivered that world's largest X-ray telescope, the Chandra telescope, to space. But it also flirted with another first, this one a bit less desirable than the others – to be the first shuttle mission to be forced into an emergency landing. The reason: a suspected, insidious hydrogen fuel leakage before, during and into liftoff.

In a harmless but uncomfortable event, the engines of the Columbia turned themselves off a second or two early during the 8 ½-minute climb to orbit, leaving the shuttle some 11 kilometres lower than its anticipated position. Flight managers think they know what caused the shortfall, and have pictures to back it up.

These images, taken seconds after liftoff, show a small illuminated jet coming out of an unexpected place beside the main thrust of the engine. This could indicate that a minute leak of liquid hydrogen fuel was depleting the shuttle's fuel supply before it even launched. The engines shut down because Columbia's external tank ran out of oxygen earlier than planned, and this would be consistent with a hydrogen leak -- the main engine would attempt to compensate by using more oxygen to provide thrust. According to NASA spokesmen, temperatures in the engine's turbines rose three or four degrees higher than predicted, which would be consistent with a hydrogen leak. Engineers suspect that as much as 11,000 kg of hydrogen may have leaked out, though they stress that this is still purely hypothetical – Columbia's engines are in for a full inspection after landing on Tuesday, and they won't know until then.

The leak would have occurred in one or several cooling tubes that pass over the bell-shaped nozzle of the shuttle engine, possibly beginning one or two seconds before liftoff. Over 1,000 of these slender steel tubes are used to carry the supercooled hydrogen over the hot nozzle, serving the dual function of cooling the nozzle while preheating the hydrogen as it heads towards the combustion chamber. This is not the first time a shuttle launch has suffered from a small leak in these tubes, but this is certainly the most severe. If the fuel loss had been greater, it might conceivably have forced the craft into an emergency landing, either near Florida or over West Africa.

The fuel leak was not the only minor mishap to mar the shuttle's ascent –- there was also an electrical failure that was noticed by commander Collins at liftoff. A short circuit lasting about a second knocked out computers that controlled two of the shuttle's three engines. Backup computers kept the engines working, and NASA said that the loss of power should have no impact on the mission. Redundancy in the shuttle's design helps lessen the effects of both the electrical as well as the fuel malfunction.

Luckily, these events has not deterred the mission's main objective, which is to bring into orbit the Chandra X-ray Observatory. The worlds largest X ray telescope, which will focus on X-rays undetectable on Earth emitted by black holes, exploding stars and colliding galaxies, was released into space without a hitch on Friday shortly before 8a.m. EDT. The first test data from the $1.5-billion, 22,680-kilogram telescope are due to arrive in three to four weeks.


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