Suspicions fall on fuel tank
By
MALCOLM BROWNE,
of the New York Times News Service (through NZPA) Cape Canaveral Suspicions have focused on the shuttle Challenger’s huge external fuel tank, a potential bomb that carried more than 1,457,000 litres of liquid hydrogen and more than 529,000 litres of liquid oxygen at lift-off. The most logical explanation is that a large leak must have occurred either in the tank or in the pipeline and pumping system that carried liquid hydrogen to the orbiter’s three main engines.
Barbara Schwartz, a spokesperson for the space agency’s Johnson Space Centre, acknowledged that pure liquid or gaseous hydrogen cannot burn; only if the pure hydrogen carried in the rear section of the shuttle’s tank were allowed to come into contact with air, or with the liquid oxygen in the tank’s nose section, could it have burned or exploded. But what might have started the leak, and what could have ignited the explosion that followed? Parallel questions, never fully answered, were raised after the fire that destroyed the German airship Hindenburg as it was landing at Lakehurst, New Jersey, on May 6, 1937. The shuttle Challenger, like the Hindenburg, had been releas-
ing hydrogen gas into the air shortly before the disaster, and some of the gas might have remained aboard the craft, mixed with air and ready to detonate if exposed to the smallest spark.
Neither the National Aeronautics and Space Administration nor Martin Marietta Aerospace, the external fuel tank’s maker, would comment on possible causes of the disaster.
But the geometry of the shuttle’s external fuel tank, as described by official manuals from N.A.S.A. and the Rockwell International Corporation, a shuttle contractor, suggest one potential dangerpoint in particular: the "intertank,” or midsection of the structure, which separates the liquid oxygen tank from the liquid hydrogen tank. The bulk of the hydrogen fuel is closest to the liquid oxygen at this point, and a rupture or leak in the plumbing or walls of the intertank could have flooded the two fluids together to create a gigantic bomb.
Suggestions that the unseasonably cold weather at Cape Canaveral might have played a role in the accident were discounted by a N.A.S.A. official. Liquid hydrogen and liquid oxygen are far colder than any winter air, as are all the tanks, plumbing and equipment with which they come into
contact. Liquid hydrogen must be kept at —217 deg. and liquid oxygen at —147 deg.; at higher temperatures they boil away. During the period between the fuelling of a shuttle and its lift-off, a time that may last many hours, great quantities of liquid hydrogen and oxygen boil away and are constantly replenished up to a few minutes before the beginning of each mission.
The intertank is a key player in this transaction of liquids and gases. It houses an umbilical plate, various controls, detection instruments, and the valving and purging systems used before lift-off to get rid of gaseous hydrogen as it boils away from the fuel tank. Could a leak or valve malfunction in the intertank have created an explosive mixture?
The pipelines that carry frigid liquid hydrogen and liquid oxygen, 43cm in diameter, are designed to be robust enough to contain pressures exceeding 34 pounds a square inch and flow rates bf more than one tonne of liquid a second. But might a weld or a flange have given way? Certainly, the external fuel tank was being subjected to great mechanical stresses at the instant it blew up; the explosion occurred several seconds after the shuttle’s main engines were boosted to full power. One set of the stresses resulting from the move to full power centered on points at both sides of the Intertank, to which the solid-fuel booster rockets were attached. Another stress point concerning, the intertank is the forward attachment point
connecting the tank to the nose of the orbiter. If any of these three attachment points had somehow failed or ripped loose, catastrophic damage to the tank might have resulted.
Another critical part of the external fuel tank is its tail, at which an attachment point joins the rear of the tank to the orbiter. Through this point pass the propellant feed lines, pressurisation lines and electrical circuits that connect the shuttle with the tank — connections designed to be severed instantly once the fuel is consumed and the tank is jettisoned.
Reconstruction of the causes of an aircraft disaster is usually difficult and time-consuming. Finding the detailed reasons for the destruction of the shuttle Challenger may prove impossible.
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Press, 30 January 1986, Page 3
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754Suspicions fall on fuel tank Press, 30 January 1986, Page 3
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