Their high-stakes mission was supposed to last about a week — but 56 days later, two NASA astronauts are still aboard the International Space Station, waiting as teams on the ground try to figure out how to bring them home safely in the Boeing spaceship they rode to orbit.
The beleaguered Starliner capsule has two problems: its propulsion system is leaking helium and five of its thrusters malfunctioned as it was docking with the space station. Mission managers were aware of the leaks before the vehicle lifted off but had said they were unlikely to affect the flight or the astronauts’ safety.
Over the weekend, NASA and Boeing engineers conducted a key test of the Starliner, which launched veteran astronauts Sunita Williams and Butch Wilmore on the vehicle’s first crewed flight on June 5.
The “hot fire test,” as it is known, was the second such test of the Starliner’s thrusters while it has been docked at the space station. It involved firing 27 of the capsule’s 28 jets for bursts of no longer than 1.2 seconds. Engineers on the ground evaluated the thrusters’ performance one at a time and also checked the status of the helium leaks.
In a blog post published Tuesday, NASA said preliminary results were encouraging, with all of the tested thrusters performing well.
“Both teams were very happy with the results,” Chloe Mehring, NASA’s flight director for the Starliner mission, said in a statement.
The agency also said it had verified that the Starliner’s propulsion system was stable and that helium leak rates had not increased in a way that might jeopardize a return trip to Earth. The helium system will be checked again before the Starliner capsule undocks from the space station, according to NASA.Wilmore and Williams were seated inside the Starliner capsule during the hot fire test as part of their return preparations, NASA said.
The thrusters are crucial for maneuvering the spacecraft in orbit, such as when the capsule approaches the space station and when it backs away from the outpost during the undocking process.
The capsule’s reaction control thrusters are also used to guide it into proper position before a different set of engines is fired to begin the journey out of orbit.
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The in-orbit Starliner tests came after weeks of work on the ground using a test engine at NASA’s White Sands Test Facility in New Mexico. Teams subjected that engine and thrusters — which were developed for future Starliner flights — to conditions similar to those that the capsule experienced on its way to the space station. Engineers also replicated conditions that the Starliner will experience as it undocks and prepares to re-enter the atmosphere.In the coming days, NASA and Boeing officials will assess data from all the tests to date and may conduct a formal review to discuss when to bring the capsule and its astronaut crew home.
NASA has not set a target landing date for the mission, but has said there are opportunities throughout August.
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Initially, NASA had set a 45-day time limit for Wilmore and Williams to stay at the space station because of constraints with the Starliner capsule’s batteries. But agency officials said this month that the batteries were being recharged while the spacecraft is docked, thus lowering the risk of extending the capsule’s time in orbit.With this mission, Boeing was hoping to prove that its Starliner capsule could safely ferry astronauts to and from the International Space Station — a key step before NASA can authorize the company to conduct routine flights to the orbiting outpost. Rival company SpaceX has been transporting NASA astronauts since 2020.
Starliner’s first uncrewed test flight, in 2019, also encountered problems and was cut short after software glitches prevented the capsule from attempting to dock at the space station. Subsequent fuel valve issues caused several delays before the vehicle succeeded in docking at the space station without a crew in 2022.
Then in the spring, the NASA astronauts’ launch was delayed twice before they finally lifted off.
Wilmore and Williams’ lengthy stay on the space station makes the orbiting outpost more crowded, but mission managers have said there are enough supplies and resources aboard to accommodate them.
As they await their return to Earth, Williams and Wilmore have been conducting science experiments and assisting with various space station duties alongside the seven crew members — four NASA astronauts and three Russian cosmonauts — who were already stationed there.
“This is a tough business that we’re in,” Wilmore said this month in a news briefing from the space station. “Human spaceflight is not easy in any regime, and there have been multiple issues with any spacecraft that’s ever been designed, and that’s the nature of what we do.”
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