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.