by Critical tests are on tap this weekend to confirm Boeing Starliner capsules safety can be carried his team of two returned to Earth despite problems that arose early in the mission, officials said Thursday.
Unexpected helium leak and degraded maneuvering thrusters, found during the ship’s rendezvous with the International Space Station in early June, prompted weeks of testing and analysis that extended the ship’s first pilot test flight from just over one week to nearly two months.
Steve Stich, manager of NASA’s Commercial Crew Program, said Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williamsboth veterans of earlier visits to space stations, have tackled the extended mission and are enjoying their bonus time in orbit.
As for when they might be cleared to return to Earth, Stich told reporters “we don’t have a big announcement today about a return date. We’re making great progress, but we’re not quite ready to do that . “
“A series of very important tests” for Starliner
Two technical hurdles remain: tests this weekend to “hot fire” the 27 maneuvering thrusters in the Starliner service module to ensure they will function as expected between launch and re-entry; and parallel testing to confirm five known helium leaks in the propulsion pressurization system that have not deteriorated.
Pressurized helium is used to push propellants to the flippers for ignition. The thrusters, in turn, are needed to reorient the Starliner as needed after unlocking it and keep it steady when rockets double up to release the ship from orbit for re-entry and landing.
“We’re going to fire all those thrusters through several pulses, but to make sure before we deploy, the whole system functions the way we expected it to and the way it did the last time we checked it,” a Stich said. “We’ll also get a chance to look at the helium system.
“It’s been six weeks since we last checked that helium system, which was on June 15. So we’ll pressurize the manifold, and then we’ll fire up the thrusters, and then we’ll have a chance to look at the helium leak rates. and verify that the system is stable.”
Overall, “it’s a very important series of tests that we will do over the weekend,” he said.
Assuming there are no major surprises, a NASA flight readiness review will be conducted to outline the problems to senior management, along with the “flight rationale,” that is, that the problems are understood in the analysis and that there is no credible threat to safety. there.
“There is some significant education on the leadership heading into the agency’s flight readiness review,” Stich said. “It’s difficult for us to explain everything that’s going on, and I apologize for that. This is a very complicated matter.”
The Starliner was launched on its first pilot test flight on June 5. During the subsequent rendezvous with the International Space Station, multiple helium leaks were detected – one was known before launch – and five forward maneuvering thrusters failed to work as the flight software expected. .
Four were subsequently successfully tested and one was declared a failure.
The thrusters were exposed to direct sunlight for long periods of time, causing them to operate at higher than normal temperatures. That, along with the rapid-fire sequence of the burns during the rendezvous, likely contributed to the observed performance.
To find out, Boeing took a flight thruster from another Starliner to NASA’s test facility in White Sands, New Mexico, and ran it through two sets of rendezvous to replicate what the Starliner experienced in orbit as well as five back to to Earth, or “downhill,” cases.
Similar thrust degradation was observed and when engineers disassembled the test thruster, it was found that the Teflon seal was slightly deformed, probably due to exposure to one of the propellants, nitrogen tetroxide.
“The team … is looking at that thruster to see if that particular seal could survive the rest of the flight,” Stich said. “If you look at what we did on that thruster, it shows that we can survive up to five feet downhill. So we’re making sure that seal stays intact.”
Regarding the helium leaks, Stich said that flight controllers had pressurized the system for tests earlier in orbit and that the known leaks had not worsened; all were within acceptable limits.
“We’re going to check this weekend on the helium leak case, and then right before undock, we’ll repressurize the system and check the helium leaks. … We’re making sure everything is covered.”
When the Starliner took off, its batteries were rated for 45 days in space. Based on their actual performance in orbit, Stich said that limit has been extended to 90 days. Thursday was the ship’s 50th day in space and Stich said Wilmore and Williams could return to Earth by the end of August.
“I’m very confident that we have a good vehicle to bring the crew back with,” said Mark Nappi, Boeing Starliner program manager. “We need to take the next steps to show that information to everyone else, and that’s the result of the agency’s review, and that’s what we’re going to do next week.”
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