(CNN) – Boeing’s Starliner capsule undocked from the International Space Station this Friday night, concluding its nearly three-month stay in space. But it flew with an empty cabin, leaving behind two astronauts who must now remain on the station for another five or six months.
The Starliner left its docking port at the space station shortly after 6 p.m. (Miami time), according to NASA. The capsule spent about six hours flying in free orbit as it slowly descended toward home.
“It’s time to bring Calypso home,” Williams told mission control Friday night. “They can do it. We will cover your back and you will get it done. Bring her back to Earth.”
Near midnight, the capsule reached one of the most important and treacherous stages of its test flight: reentry. The milestone required the Starliner to carefully orient itself as it plunged into the thickest part of Earth’s atmosphere while still traveling at orbital speeds—typically more than 17,000 miles per hour (27,400 kilometers per hour).
As with all spacecraft returning from orbit, the pressure and friction of reentry put enormous strain on the vehicle. The process could have heated the exterior of the craft to more than 3,000 degrees Fahrenheit (1,649 degrees Celsius).
Before the capsule departed, Butch Wilmore and Suni Williams — the two NASA astronauts who took the Starliner to the space station — in June wished the craft, nicknamed “Calypso” by Williams, luck on its journey home. .
The vehicle landed in New Mexico, at the White Sands spaceport, an area within a vast missile field of the same name that was previously used to train NASA space shuttle pilots. The Starliner touched down at 12:01 a.m. ET on Saturday, according to the space agency.
“I want to recognize the work the Starliner teams did to ensure a successful and safe undocking, orbit, reentry and landing,” said Mark Nappi, vice president and program manager of Boeing’s Commercial Crew Program. “We will review the data and determine the next steps for the program.”
During a press conference after the landing, NASA Commercial Crew Program Director Steve Stich said it’s not clear exactly what the path forward is for Starliner – or when the spacecraft might fly again. That “will take a little time,” he said.
However, he added: “We have now landed a capsule on dry land in the United States. The entry, in particular, was almost perfect, which didn’t surprise me, but when I think about the mission, the entry itself was perfect, and the orbit burn was perfect.”
Stich also acknowledged that if the on-the-ground modeling had been perfect, perhaps NASA would have relied on the Starliner to bring Wilmore and Williams home on the vehicle’s return flight.
“If we had a model that would have perfectly predicted what we saw tonight, yes, it seems like an easy decision to say we could have had manned flight, but we didn’t,” Stitch said.
“From a human perspective, we were all happy about the successful landing,” he said. “But there is a part of us, all of us, that wishes it had gone the way we had planned. “We had planned for the mission to land with Butch and Suni on board.”
Hear the “strange noise” coming from the Boeing Starliner that caused the astronauts to alert mission control
Concerns about Starliner’s ability to maintain precise orientation as it re-enters Earth’s atmosphere, given several problems that arose during the first leg of its journey, is one of the reasons NASA opted not to fly the crew. of the Starliner back with the vehicle. Instead, the new plan is for Williams and Wilmore to remain aboard the space station and return home in a SpaceX capsule in February 2025.
At first, NASA officials expressed confidence that they could identify Starliner’s problems and come up with a plan to safely return the vehicle to the crew. But two persistent problems ultimately derailed those plans.
First, a series of helium leaks emerged during the Starliner’s outbound flight in early June. Helium is used to pressurize some of the vehicle’s thrusters, which help the craft stay oriented in space, and problems with some of the helium leaks delayed this manned test mission even before takeoff.
Additionally, five of the Starliner’s 28 “reaction control system” (RCS) thrusters abruptly stopped working en route to the space station. Four were recovered, but at least one will remain out of commission throughout the mission.
NASA and Boeing kept the Starliner in space for weeks as they worked to understand those problems, extending William and Wilmore’s stay from the expected duration of about eight days to months.
At one point, NASA and Boeing said they believed they understood the likely cause of the Starliner’s problems. The “huts,” or structures containing the propulsion equipment, were flying hotter than expected, causing some Teflon seals within the thruster systems to bulge, restricting propellant flow and causing RCS thruster failures. . Separately, officials said the helium leaks could have been caused by seals that degraded from exposure to propellant vapor.
Determining the root cause of a problem on a spacecraft, however, is not an exact science.
And even if the problems were well understood, the Starliner team had to face the fact that it would never be able to inspect the propulsion system on the actual vehicle in space. It was impossible to examine the problem while the Starliner was docked with the space station.
Additionally, the unit housing the problematic RCS thrusters and leaking helium, called the service module, was not intended to survive the return trip. Instead, the service module, which is a cylindrical attachment at the bottom of the crew cabin, is designed to be ejected and discarded on the way back to Earth. And that’s what he will do in this mission.
Ambiguity over what exactly happened to the service module components was a key factor in NASA’s decision to fly the vehicle back without its crew.
“The bottom line regarding bringing back Starliner is that there was too much uncertainty in the thruster prediction,” Steve Stich, manager of NASA’s Commercial Crew Program, said Aug. 24. “It was too much of a risk with the crew, so we decided to go the unmanned route.”
During its dangerous return to Earth, the Starliner has other types of thrusters intended to help the vehicle maintain its orientation while traveling through space.
Alongside the 28 RCS boosters are 20 “Orbital Maneuver and Attitude Control” (OMAC) boosters, each of which has approximately 17 times the thrust of an RCS booster.
But during an earlier news conference, Stich described how problems already identified in the Starliner service module could combine to create a disastrous scenario.
“The worst case would be some failure mechanism built in between the helium leaks and the RCS thrusters,” Stich said. “For a nominal deorbit burn, we fire 10 OMAC thrusters in each of the four deckhouses, and then the RCS jets are there just to maintain orientation.”
During the final descent of the Starliner this Friday, a series of checks carried out by teams on the ground showed that one of the boosters on board the Starliner capsule itself had run out.
The previous thruster failures that worried the Boeing and NASA teams occurred in the Starliner service module, a cylindrical accessory located at the base of the capsule.
During an Aug. 24 press briefing, NASA officials also indicated that Boeing disagreed with some of the space agency’s risk assessments.
There was “just a little disagreement (between NASA and Boeing) in terms of the level of risk,” Stich said. “It depends on how you assess the risk. (…) We did it a little differently with our crew than Boeing.”
But Ken Bowersox, NASA associate administrator for space operations mission management, added that the company left the final decision up to NASA “because of our broader view of all the risks involved.”
Boeing said as recently as Aug. 2 that its “confidence remains high” that the Starliner can return with a crew. But since NASA announced its decision to bring the capsule back without astronauts, the company has said only that it is focused on “executing the mission as determined by NASA, and we are preparing the spacecraft for a safe and successful return without crew,” according to an Aug. 24 statement.
The behavior of the Starliner on its return trip could have broader implications for the future of the Boeing program. The company has already lost more than $1 billion correcting the vehicle’s problems, over years of delays, development setbacks and in-flight errors.
It is not yet clear whether NASA will require Boeing to repeat this test flight, or whether the space agency will consider certifying the spacecraft for regular flights after the mission’s safe landing.
Boeing has already had to repeat one test mission, an uncrewed test flight that took off in 2019. Software problems prevented the vehicle from entering the correct orbit and even reaching the International Space Station, leading NASA to require Boeing to repeat the excursion in 2022.
