NASA Considers Several Ways To Fix Space Shuttle Leak on Pad
CAPE CANAVERAL, Fla. (AP) _ Taking a cue from heart surgeons, engineers are considering a thin tube with an expandable balloon on the end to plug a leak that threatens a long delay of the next space shuttle mission.
To work, the device would have to follow a ″tortuous path″ 20 feet through a one-half inch line that contains six sharp bends.
It would be something like a medical procedure known as an angioplasty, but instead of opening a clogged artery, it would close off the leaking line.
This approach is just one of several being weighed to fix the small leak on the launch pad and avoid rolling Discovery back to a hangar for repairs, which could delay the planned early September launch by as much as two months.
A decision on moving Discovery is not expected until after a test-firing of the shuttle’s three main engines on the pad. That test is set for July 28, but officials said Thursday preparations were behind schedule and it might have to be postponed a day or two.
The leak of nitrogen tetroxide gas is in a fitting on an engine compartment vent line leading to an oxidizer tank. It is six feet from the nearest access panel and thus inaccessible for normal repairs.
″We’ve got people looking at the prudent and safe thing to do,″ said Forrest S. McCartney, director of the Kennedy Space Center. The odds, he said, are 50-50 on a rollback of Discovery.
The three main NASA centers involved with the shuttle are working on different approaches to fixing the leak on the pad.
At the Johnson Space Center in Houston, the focus is on entering the shuttle’s cargo bay and cutting holes through both the rear of the bay and the engine compartment to reach the leak, then plug it by some method, including encapsulating it with a clamshell-like device filled with a sealant.
The Kennedy Space Center is considering ways of reaching and sealing off the leak through the engine compartment access panel.
At the Marshall Space Flight Center in Huntsville, Ala., the materials and processing lab is devising a mockup of the 20-foot line to test the ″angioplasty″ approach.
Lab director Bob Schwinghamer said two heads are being developed for the ″snake.″
″The snake with the balloon on the end would have to run through this tortuous path like an angioplasty procedure,″ he said. ″The balloon would be filled with an epoxy and when it reached the leak it would be expanded. We would leave pressure on the line until the expoxy cured. Then we could extract the snake or leave it there.″
He said leaving the snake-tube would cause no problem because the line is no longer needed. It’s sole purpose is to vent excess air when the nitrogen tetroxide oxidizer tank is being filled. The tank already has been filled and the tiny leak has allowed only a small amount of the gas to escape.
Schwinghamer said the balloon material would have to be something like teflon or allrez to be compatible with the leaking nitrogen tetroxide gas. The escaped gas can cause a problem if it mixes with moisture in the air, forming corrosive nitric acid.
Schwinghamer said a second approach would be to fit the head of the tube with a tiny string of beads to ease its course through the vent line. ″At the appropriate location, we would inject a sealant through the hollow tube,″ he said.
Engineers hope to be able to start testing all suggested approaches by this weekend.
Discovery, with a crew of five astronauts, is to make the first shuttle flight since Challenger exploded on Jan. 28, 1986, killing the crew of seven.