September 7, 2024
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Starliner spacecraft returns safely to Earth without astronauts on board
Starliner’s first manned test flight landed successfully, with the two astronauts still in orbit awaiting another return flight.
Boeing’s Starliner spacecraft approaches the International Space Station (ISS) in early June 2024. The spacecraft’s crew, NASA astronauts Butch Wilmore and Suni Williams, are scheduled to remain at the ISS until February 2025.
After three ordeals in space, the orbital mission, originally scheduled to last just over a week, ended with an autonomous landing, slowed by parachutes and cushioned by airbags, at NASA’s White Sands Spaceport in New Mexico just after midnight EDT.
Starliner, the Boeing-built spacecraft that launched a trouble-ridden test flight to the International Space Station (ISS) in June, has finally returned to Earth. The same can’t be said for its crew, however. NASA astronauts Butch Wilmore and Suni Williams remain on the ISS. Citing safety concerns, NASA officials last month decided to return them in February 2025 on the proven Dragon spacecraft built and operated by Boeing’s aerospace competitor, SpaceX. To accommodate the change, two other NASA astronauts, Zena Cardman and Stephanie Wilson, had to be removed from SpaceX’s next scheduled Dragon flight to the ISS, the Crew 9 mission, scheduled to launch later this month. This will leave two seats open for Wilmore and Williams when Dragon returns to Earth in February of next year.
“This was a great day to bring Starliner home, and we’re very pleased to have successfully undocked, deorbited, and landed the spacecraft,” Steve Stich, program manager for NASA’s Commercial Crew Program, said at a press conference after the landing, summing up the spacecraft’s “near flawless” performance. “I’m thrilled for the Boeing team, and all of my colleagues across the country, both at NASA and at Boeing, who worked on this mission. We owe them a debt of gratitude that we were able to bring the spacecraft home today.”
Chasing the Dragon
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Starliner’s third successful landing means Boeing’s program will survive for another flight, but what happens next is still largely up in the air.
The test flight was supposed to be the final step in certifying Starliner as ready to carry astronauts to the ISS once a year. However, if the spacecraft fails to return with a crew on board, NASA may require additional test flights before granting certification, the costs of which would be borne by Boeing. When NASA selected Boeing and SpaceX to develop a crewed spacecraft in 2014, the companies signed a “fixed price” contract, meaning that they, not NASA, would cover any cost overruns. Furthermore, payments from NASA were contingent on each company meeting certain targets. NASA allocated a total of $2.6 billion to SpaceX and $4.2 billion to Boeing. SpaceX flew its first crewed Dragon to the ISS in May 2020 and has been fulfilling its contractual obligations with NASA ever since. In contrast, Boeing’s Starliner program has been plagued by technical failures and delays, and the company has lost $1.6 billion so far on the effort, according to a quarterly report in late June.
At a press conference last month announcing the switch to Dragon as the return vehicle for Wilmore and Williams, NASA Administrator Bill Nelson said he was “100 percent” confident Starliner would fly with crew again, and noted he had recently spoken with Boeing’s new CEO, Kelly Ortberg. “He has expressed to me our intention to continue resolving any issues once Starliner has returned safely,” Nelson said.
It’s still unclear when and how Starliner will return to crewed flight, or what assurances other space-faring nations partnering with NASA on the ISS will require before flying their own personnel on Boeing’s spacecraft. But one thing is certain: Time is running out for the company to meet its obligations to NASA. NASA plans to deorbit the ISS in 2031, and recently announced that it has hired SpaceX to perform that mission using a heavily modified Dragon.
On December 22, 2019, at the end of NASA’s orbital flight test, the unmanned Starliner spacecraft landed under an inflated parachute in White Sands, New Mexico.
A long goodbye
Wilmore and Williams closed the Starliner’s hatches at 1:29 p.m. EDT Thursday in preparation for the unmanned departure. Calypso— It detached from the ISS at 6:04 p.m. EDT on Friday, leaving the astronauts behind as the station passed over central China. Immediately after detachment, the spacecraft performed a “breakout burn,” a sequence of 12 pulses from its secondary thrusters to rise away from the ISS to avoid crashing into any orbiting habitats. Calypso After shrinking to a speck barely visible through the ISS’s viewport, Williams radioed mission controllers with a simple, almost plaintive declaration: “She’s on her way home.”
Over the next few hours, the spacecraft underwent a series of diagnostic tests while drifting 90 kilometers from the ISS. Then, at 11:17 p.m. EDT, Calypso It began its deorbit burn, used its secondary thrusters to set its trajectory, and then fired its more powerful primary thrusters to enter Earth’s atmosphere. During its descent, another burn from the secondary thrusters CalypsoThe empty crew module separated from the service module, and the service module burned up at high altitude as planned.
The burning edge of the Service Module, which was necessary to expose the protective heat shield during Starliner’s return, was a fundamental obstacle to resolving the spacecraft’s most worrisome malfunction. The expendable module is equipped with 28 auxiliary thrusters, five of which failed during Starliner’s approach to the ISS and rendezvous on June 6. Starliner also experienced repeated small leaks of helium (an inert gas used to pump propellant into the thrusters) from here. However, since the failed hardware was destined to be destroyed at high altitude rather than retrieved and studied, the only option was to analyze it from afar and gather as much data as possible to try to find the cause and a remedy before the Service Module burned up above Earth.
In the doghouse
From these remote investigations and ground tests of the same thrusters, NASA and Boeing engineers traced the failure of the five Service Module thrusters to overheating during operation. Investigators determined that the Service Module’s secondary thrusters are housed in four propulsion pods known as “doghouses,” which retained more heat than expected during thruster firing, exacerbating the problem. Overheating likely caused Teflon seals to expand, restricting propellant flow and ultimately leading to failure. In a worst-case scenario, such a failure could result in a catastrophic crash into the ISS, destroying it, or disintegrating in a fireball during re-entry into the atmosphere.
Though engineers identified the cause of the thruster problems, uncertainties remained. For example, four of Starliner’s five failed thrusters have since been restored, but no one could fully explain how they worked. In discussions with NASA, Boeing officials insisted that it was still safe to return two astronauts on the spacecraft—a key objective that, if not achieved, would require future crewed test flights that would likely be significantly over budget. But with no way to thoroughly test the thrusters in orbit to verify their performance, NASA ultimately decided it would be safer to return Starliner without Wilmore and Williams.
“There was tension in the room” during the final meetings on the issue, Stich acknowledged during a pre-departure press conference Wednesday. “Boeing believed in a model that they had built that tried to predict the degradation of the thrusters over the remainder of the flight. … The NASA team looked at that model and saw some limitations. It really had to do with, ‘Can we be confident in the thrusters? And how well can we predict that degradation from undocking to the deorbit burn?’ And (we) weren’t comfortable with that.”
Still, Stich insisted at a press conference on Wednesday that “we have confidence in the vehicle. Starliner has already made two successful (unmanned) landings so far, and we expect another successful one on Friday.”
With a near-perfect (but not entirely successful) re-entry and landing now in the books, Boeing is expected to redouble its efforts to bounce back from the spaceflight fiasco and repair Starliner’s tarnished reputation. But whether NASA or anyone else should still have confidence in those efforts is another matter entirely.
