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Boeing’s CST-100 Starliner Calypso completed a second star-crossed flight test, touching down in the New Mexico desert with the empty seats and spacesuits of the two NASA astronauts who were pulled from the return trip to Earth due to safety concerns.
Time will tell if the mission was sufficient to proceed with Starliner certification for International Space Station (ISS) crew ferry flights, possibly as early as August 2025.
- More work lies ahead for Boeing Starliner
- The Calypso Flight test ends without crew
- Starliner test pilots transfer to ISS crew
Boeing has spent four years and $1.5 billion more than planned to reach the Starliner Crew Flight Test (CFT) aboard Calypso, one of two spacecraft the company designed and built to fulfill its fixed-price, milestone-based flight service contract with NASA. The agreement, which includes up to six operational ISS crew rotation missions, is currently worth $4.4 billion. Boeing’s total investment in the program has not been disclosed.
Calypso debuted in December 2019 for what was expected to a be a weeklong, uncrewed test run to the ISS. That mission lasted just two days due to software and communications problems that caused the spacecraft to miss its engine burn to reach the ISS. Calypso’s unnamed sistership conducted a follow-up mission in May 2022, paving the way for the CFT.
After additional delays to address a parachute and tape flammability concerns, Calypso was launched again on June 5 with veteran NASA astronauts Barry “Butch” Wilmore and Sunita Wiliams aboard. The spacecraft docked at the station the following day for a planned 7-14-day stay.
Three months later, Calypso departed the ISS—without its crew because of NASA safety concerns about the ship’s propulsion system. Problems surfaced during the spacecraft’s automated approach to the ISS, when five reaction control system (RCS) thrusters were sidelined by the flight computer due to what was later determined to be overheating. All but one of the jets were recovered, and Calypso was able to make an automated docking one orbit later.
The thruster problems followed a series of small helium leaks in the system that pressurizes the Starliner’s RCS jets and larger orbital maneuvering and attitude control (OMAC) system thrusters. Boeing concluded that the leaks resulted from a slight degradation of seals that had been exposed to corrosive propellants. Despite the leaks, the Starliner left the ISS with 10 times more helium than was needed for the return trip to Earth.
“One of the things we’re looking at is a different material on the seal, and maybe a different, slightly enlarged seal to make that seal better so that we can solve the issue with the helium leaks,” Steve Stich, NASA’s Commercial Crew Program manager, told reporters during a pre-landing news conference.
As for the troubled thrusters, engineers suspect the jets overheated because of a manual flying exercise ahead of docking that caused the suspect RCS jets to fire hundreds of times in quick succession while in direct sunlight. Engineers believe the overheating caused Teflon seals in the jets’ poppet valves to swell temporarily, restricting the flow of fuel. Later tests showed that the jets worked as designed, indicating that the seals had returned to normal or near-normal shape.
“We need to understand what kinds of pulses caused that swelling . . . and what temperatures the thruster gets to,” Stich said. “Then, how do we tell the vehicle not to fire the thruster in that manner to cause the extra heating?”
With the clocking ticking for the next ISS crew ferry flight—and Calypso docked in its parking spot—NASA on Aug. 24 announced that it was not fully comfortable with Boeing’s work showing that the Starliner thrusters would perform as planned for the undocking and deorbit maneuvers. The agency transferred Wilmore and Williams to the ISS resident staff, giving both an unexpected third long-duration mission that will last until February 2025.
The astronauts watched as the Starliner departed the station at 6:04 p.m. EDT Sept. 6, marking the end of their roles as test pilots for the spacecraft. “She’s on her way home,” Williams radioed to ground control teams as Calypso passed beyond the station’s safety zone.
Wilmore and Williams will join the upcoming SpaceX Crew-9 crew, replacing two astronauts who had been assigned to the mission since January. Until the Crew-9 Dragon arrives around Sept. 25, Wilmore and Williams’ emergency ride home—should an evacuation be necessary—is the SpaceX Crew-8 Dragon capsule, which has been outfitted with temporary seats on a cargo pallet in the crew cabin’s middeck.
Calypso’s journey back to Earth began with the opening of 12 hooks latching the spacecraft to the forward port of the Harmony module. That allowed springs on the Starliner’s docking ring to push the spacecraft away from the station, a demonstration of the hardware NASA’s Orion crew capsule will employ during Artemis Moon missions.
At 16 ft. from the ISS, sailing 260 mi. over central China, Calypso fired a pair of RCS jets to pick up speed, setting the stage for a dozen short burns over the next 5 min. to move the capsule up, over and behind the ISS. The maneuvers increased the separation between the Starliner and the ISS by 13.7 mi. per orbit.
The so-called “breakout burn” was designed to minimize the number of thruster burns and move the vehicle away from the station about twice as fast as was previously planned with crew onboard.
Unlike Calypso’s June 6 approach to the ISS, the thrusters operated flawlessly during the departure maneuvers, as Boeing predicted. The spacecraft circled the planet in free drift four times, then ignited four OMAC system thrusters at 11:17 p.m. to drop out of orbit.
The 59-sec. burn slowed Calypso by 426 ft./sec., setting up a southwest-to-northeast trajectory over the Pacific Ocean, Mexico’s Baja Peninsula, the Gulf of California, northern Mexico and finally into New Mexico for a landing at NASA’s White Sands Space Harbor at the U.S. Army’s White Sands Missile Range.
During a final test before leaving orbit, 10 of the Starliner’s 28 RCS thrusters on the soon-to-be discarded service module were fired, all successfully. Another 12 RCS thrusters on the returning crew module also were tested, with one failing to fire as commanded, an issue that is under investigation. A second up-firing thruster provided redundancy.
Calypso released its service module as planned at 11:20 p.m. for a destructive reentry in the atmosphere. As the spacecraft neared the end of its plunge through the atmosphere, its guidance, navigation and control (GNC) system failed briefly but then came back online. The spacecraft’s sublimator, or cooling system, functioned satisfactorily during reentry, although it had experienced some difficulty during the capsule’s June 5 launch.
At an altitude of about 24,500 ft., two small drogue parachutes unfurled to slow the Starliner’s descent and stabilize the ship. At about 8,000 ft., a trio of pilot parachutes deployed to pull out the Starliner’s three 104-ft.-dia. main parachutes, slowing the spacecraft’s speed to about 18 mph. About 2,500 ft. above the ground, airbags inflated to mitigate the force of the touchdown, which occurred at 12:01 a.m. EDT Sept. 7 (10:01 p.m. Sept. 6 local time) to bring the three-month CFT mission to a close.
The extra time in orbit gave Boeing a head start on work that will be needed before the Starliner flies again. “I want to recognize the work the Starliner teams did to ensure a successful and safe undocking, deorbit, reentry and landing,” Mark Nappi, vice president and program manager of Boeing’s Commercial Crew Program, said in a statement. “We will review the data and determine the next steps for the program.”
Boeing has declined interview requests and did not attend a CFT post-landing press conference.
“A safe and successful landing was exactly what we wanted,” Joel Montalbano, deputy associate administrator for NASA’s Space Operations Mission Directorate, told reporters after the landing. “We did learn a lot. It’s important to remember this was a test mission.”
“Many parts of the flight went extremely well, and Starliner is a great spacecraft,” Stich told reporters during a pre-landing press conference. “What we really need to go do is look at the things that didn’t perform the way we expected.”
NASA intends to press ahead with a joint evaluation of the spacecraft’s performance while laying out a strategy to forge ahead with any additional development and testing. “We are going to take our time to figure out what we need to do to go fly Starliner-1,” Stich said after Calpyso’s safe return. “I think we will see where we are at in another month or so, and then we will have a little bit better idea of what the overall schedule will be.”
Stich says Boeing has formed teams to look into upgrades to the Starliner, which is to be transported from White Sands to NASA’s Kennedy Space Center for a thorough post-flight evaluation that will be backed up with ground testing.
Among the priorities Stich listed are upgrades to the flanges in the RCS jets to make them more resistant to the hypergolic propellants and possibly also make the flanges larger. NASA and Boeing also are looking to upgrade the thermal control of the “doghouses,” or manifolds that house the RCS and OMAC thrusters. Changes to the spacecraft’s GNC system to manage the thruster firings better are being considered as well to reduce structural stress. “That is really the path to Starliner-1,” Stich said.
“Obviously, there’s some work we need to do on Starliner,” Montalbano added. “Is it slower than we expected? Absolutely . . . but we are making progress. Every time we have a mission, we learn something that gets passed on. We are sharing things across the commercial world.”
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