NASA has decided how to fix a burst fuel line weld that caused a hydrogen fuel leak and prevented the space shuttle Atlantis mission departing for the International Space Station (ISS) on Thursday. Engineers will repair the weld using a two-piece 鈥渃lam鈥� component and the launch will now be on Sunday at the earliest.
Plumes of hydrogen were spotted at the launch pad at Kennedy Space Center in Florida while Atlantis was being prepared for take-off. Launch was scheduled to take place between 1900 GMT and 2300 GMT.
NASA will decide on Friday whether to push the launch back beyond Sunday. NASA鈥檚 new security policy means that a precise take-off time will not be provided until 24-hours before take-off.
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The leak occurred at a point connecting two aluminium pipes carrying excess hydrogen fuel away from the shuttle鈥檚 external fuel tank. Engineers believe a crack in the join between the pipes was caused by sudden temperature decrease and accumulated wear and tear.
Cryogenic shock
鈥淭here was a cryogenic shock to a weld that had been in place for some time,鈥� a Kennedy Space Center spokesperson told New Scientist. 鈥淲elds do fail.鈥�
Engineers plan to clamp a two-piece clamshell-like component over the crack and weld it together. This will provide a more durable solution than simply welding the two pipes themselves back together, according to the NASA spokesman.
The fuel lines are cooled prior to full fuelling with small amounts of hydrogen and oxygen gas. The shuttle鈥檚 external tank then is filled 1.9 million litres of liquid hydrogen and liquid oxygen for launch.
The NASA spokesman adds that engineers do not intend to inspect or replace the welds on other launch platforms because it is not thought to be the result of a design flaw. The spokesman also dismissed suggestions that the leak reflects the deterioration of infrastructure at Kennedy Space Center, a charge made in a recent NASA Aerospace Safety Advisory Panel report.
Construction work
The Atlantis shuttle mission will involve major construction work at the ISS. The shuttle will carry a hexagonal frame known as the S-Zero truss that will form the backbone of a 100-metre long solar array.
The S-Zero truss also features a set of rails that will be used to transport the station鈥檚 robot arm. This will make further construction work outside the station possible.
The truss will be put in place during the four spacewalks planned for the 11-day mission.