As engineers complete their examination of thruster issues and helium leaks on the crewed spacecraft, NASA and Boeing have once more extended the CST-100 Starliner’s stay at the International Space Station.
NASA said during a briefing on June 18 that the Crew Flight Test (CFT) mission, which was originally scheduled to bring Starliner back to Earth on June 22, has been rescheduled a second time. As of right now, Starliner is expected to disembark from the station on June 25 at 10:10 p.m. Eastern and land at White Sands, New Mexico, on June 26 at 4:51 a.m. Eastern.
During the briefing, representatives from NASA and Boeing stated that the prolonged stay at the station will allow them more time to investigate two major problems the spacecraft had on its journey to the station almost two weeks ago: thruster failures and helium leaks in the spacecraft’s propulsion system.
Several aft-facing reaction control system (RCS) thrusters were briefly activated during that task; however, when Starliner got closer to the station, the spacecraft’s computer shut off five of the thrusters. Controllers repaired four of the thrusters so that the docking could continue.
Steve Stich, the manager of NASA’s commercial crew program, stated that the one thruster that was not repaired prior to docking displayed a “strange signature” and produced virtually no thrust. The spaceship will no longer use the thruster for undocking and deorbiting operations.
During a short burn lasting a quarter of a second, the other thrusters—those that behaved normally and those that malfunctioned during the approach—exhibited the expected profile of chamber pressures. During a longer burn of 1.2 seconds apiece, the thrusters also performed as planned, as determined by the controllers’ testing of the flight control system of the station.
“Coming out of that, we feel very confident in the thrusters and the team is just making sure to go look at the thrusters in detail across the whole flight,” the speaker stated. This involves contrasting their performance with that of the unmanned test flight, known as OFT-2, which took place in May 2022 and during which two thrusters failed during approach but were fixed before the mission’s conclusion.
According to Stich, engineers are investigating the reason behind the thrusters being offline during the approach, which could be related to frequent use. “We have some theories about what’s going on inside the thruster where the thruster gets very hot,” he said, citing the possibility that high temperatures hinder the appropriate blending of oxidizer and fuel.
The thruster test was another tool used by engineers to monitor the five helium leaks they found in the propulsion system. He claimed that leak rates had decreased in each instance, in one case by 50%.
Regarding the helium leaks, “it seems to be related to the activity of the thrusters,” he stated. Heat from the thrusters or sliding surfaces that erode seals could be the cause of that. He pointed out that while two of the lesser leaks might be comparable to leaks observed on the OFT-2 mission, the three larger leaks most certainly had similar origins.
Stich stated that similar to the thruster testing, the decreased helium losses give him hope that the spacecraft would be able to operate as planned while undocking and deorbiting. He claimed that in the later stages of flight, “the demand on the thrusters is much, much less.”
According to him, the failing thrusters and the helium leaks are occurring in different “doghouses” on the service module. But he did say that the thruster failures and helium leaks might have been caused by the “dynamic operations” that Starliner carried out as it approached the station.
Up until June 22, NASA and Boeing engineers will keep analyzing Starliner. After that, they will concentrate on getting ready to undock and head back to Earth. The decision to prolong Starliner’s stay at the station took that work into consideration. According to Mark Nappi, vice president and program manager for commercial crew at Boeing, “we don’t get the service module back, so this is an opportunity to fully understand the system’s performance without the pressure of schedule.” “We have the time.”
He stated that 77 of the 87 flight test objectives that were laid forth prior to launch have been accomplished by the CFT mission; the remaining objectives have to deal with undocking and landing. To make the most of their extra time at the station, engineers added an unknown number of extra test objectives, such as recording Starliner’s hatch operations and gathering more data on cabin air temperature.
After being questioned repeatedly during the briefing, Stich and Nappi both reiterated that they thought Starliner was safe for NASA astronauts Butch Wilmore and Suni Williams to use on their way back to Earth. According to Stich, the additional time gives engineers more opportunity to examine how the vehicle performs, especially while it is powered down—a feature that will be useful for upcoming extended stays at the station.
He also mentioned that NASA had given the go-ahead for Starliner to be used in an emergency to return Wilmore and Williams. “We’re taking a little extra time to review all the data and also learn as much as we can while we have the service module in orbit.”
Spacewalk modifications
Williams and Wilmore have been hard at work at the station assisting with Starliner system testing. Stich remarked, “They love Starliner, and they’re so happy to be a part of the mission,”
Additionally, the two have been lending a hand at the station. NASA ISS program manager Dana Weigel stated, “We’ve taken advantage of some of their extra time and extra helping hands,” including for research.
The two supported NASA astronauts Tracy C. Dyson and Matt Dominick during their scheduled spacewalk on June 13. However, NASA reported that there was a “spacesuit discomfort issue,” which resulted to the cancellation of that spacewalk shortly before it was supposed to begin.
Weigel stated that Dominick was the astronaut who felt uncomfortable in the suit, but he did not go into detail about the particular problem that caused the postponement. That day, we were unable to find a solution, she stated.
Since then, NASA has changed its schedule for upcoming spacewalks. Dyson and Mike Barratt are now expected to carry out a spacewalk on June 24. This spacewalk will accomplish the same goals as the one that was postponed on June 13: it will retrieve a malfunctioning electronics box and gather samples from the outside of the station that will be used to identify any microorganisms.
Barratt already had a suit ready and was scheduled to conduct a spacewalk in the near future, according to Weigel. “We decided it just made sense to use Tracy and Mike,” she stated.
NASA will not assign astronauts to the July 2 spacewalk until after the June 24 spacewalk, but it will take place in order to do extra station maintenance. Weigel stated that due to oxygen consumed in preparation for the cancelled spacewalk on June 13, the agency’s original three spacewalk schedule will now only consist of two spacewalks.