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On July 26, NASA (NASA)andBoeingInvestigation of the Starliner continuesspaceshipAppeared in spaceThrusterFailure and helium leak problems. According to a press release on July 25, the spacecraft plans to conduct a 28-thrust reaction control system (RCS) ignition test on the International Space Station this Saturday (July 27) or Sunday (July 28). Since one of the thrusters has been judged unsuitable for return flight due to a failure, this test will only use the remaining 27 thrusters.

Although the ground will issue operational instructions, NASA, which performs the manned flight test (CFT) mission, has a special interest and a background as a Navy test pilot.astronautButch Wilmore and Suni Williams are also expected to participate in the test.

"We're going to do several pulse tests on all of these thrusters to make sure that the entire system is functioning as we expected and as we did last time before we leave the International Space Station," Steve Stich, director of NASA's Commercial Crew Program, said at the launch event.

“We will also be checking the helium system. It has been six weeks since the last check on June 15. We will pressure test the cylinders one by one, then fire the thrusters and check the helium leak rate to confirm the stability of the system,” Stich added.

The Starliner was launched on June 5 and was originally planned to have a mission of about 10 days. But before it could successfully dock with the International Space Station, it encountered thruster and helium leak problems, so the mission was extended indefinitely so that engineers could troubleshoot and resolve these problems.

Ground tests at the White Sands Proving Ground in New Mexico in early July gave engineers a deeper understanding of the problems during the docking process. For example, recent ground tests found that the valve system of an MR-104J test thruster produced by Rocketdyne Aerospace, similar to the one used on the Starliner, was severely degraded due to three years of storage and exposure to nitrogen dioxide vapor; the seal swelled and restricted the flow of propellant. Engineers also found stuck Teflon in the downstream filter, indicating that the seal had eroded under high temperature conditions, Stich noted.

Stich noted that the performance of the Starliner's RCS thrusters in orbit is consistent with ground-based observations. He explained at the press conference that this thruster has been used in other space programs of Rocketdyne Aerospace, but has been modified for the needs of the Starliner service module.

"This mission is allowing us to begin to better understand how the guidance, navigation and control system and the flight control system command thruster firing in flight, which we cannot fully understand through ground testing and analysis alone," Stich explained.

Each set of RCS thrusters is surrounded by protective structures called "dog houses", which not only provide insulation but also protect the thrusters from the severe cold of space. There are four such "dog houses" in the service module. Studies have shown that during the continuous operation of the Orbit Maneuvering and Attitude Control System (OMAC), if multiple RCS thrusters are frequently activated in a short period of time, the temperature of the thrusters will increase more than expected.

Stich said that it may not be necessary to change the design, but to adjust the way the thrusters are used in flight to solve this problem, such as reducing the frequency of ignition. He stressed that relevant discussions are ongoing; NASA plans to conduct an agency-level review of the manned flight mission as early as next week and will invite the Aerospace Safety Advisory Group to participate.

Mark Nappi, Boeing's commercial crew missions program manager, added that Rocketdyne worked closely with Boeing throughout the mission to explore solutions, which could include new seals, a different flight trajectory for future missions, or different thermal protection inside the doghouse.

Missions like manned flight tests often encounter unexpected situations, and the Starliner has been certified to be able to safely leave the International Space Station in an emergency. In June of this year, the astronauts on the CFT mission were reassigned to perform maintenance tasks on the International Space Station after participating in on-orbit troubleshooting. Their mission has lasted 50 days and is still continuing.

NASA also extended the CFT's initial stay in space from 45 days because the battery performance on orbit was better than expected. Stich noted in a briefing on Thursday that the mission has now been officially extended to 90 days, until September 3, although the exact landing date has not yet been determined.

Understanding the root cause of the thruster and helium leaks in the RCS system is critical to future Starliner missions, which are scheduled to take place as early as 2025 and are expected to carry at least three astronauts for a six-month stay at the International Space Station.

Starliner joins SpaceX's Crew Dragon as the two privately operated spacecraft that have transported astronauts to the International Space Station. The Crew Dragon has flown multiple missions since May 2020 and is based on the SpaceX cargo Dragon spacecraft that has flown multiple times since 2012. As a new spacecraft, Starliner faced development challenges after its first space flight.

In December 2019, Starliner's first unmanned mission failed to reach the International Space Station after a computer problem put it into the wrong orbit. After the COVID-19 pandemic hit, dozens of corrections were made, and the unmanned mission in May 2022 successfully reached its destination, although it also had thruster problems that NASA believes have been resolved for the manned mission.

The manned flight test was originally planned for 2023, but the mission was delayed due to the discovery of flammable tape in the spacecraft's wiring and the parachute load was less than expected. A few months later, the mission looked like it was about to launch as planned on May 6. But a few hours before launch, the astronauts were pulled out of the spacecraft due to a vibration problem found in a valve on the United Launch Alliance (ULA) Atlas V rocket.

The spacecraft stayed on hold for a month because a valve needed to be replaced and a tiny helium leak was discovered in one of the RCS thrusters. While extensive testing and modeling on the ground did not reveal the expected problems with the CFT mission, analysis revealed a potential safety hazard: Under certain circumstances, if enough RCS thrusters failed in adjacent containments, it could affect one reentry option. After a series of engineering and simulation tests, NASA and Boeing certified a new reentry mode that requires fewer RCS thrusters to fire simultaneously.

Ultimately, the CFT mission was launched on June 5, although the launch encountered delays during the countdown phase due to a ground equipment failure affecting the Atlas V rocket. In addition to the problems encountered when docking with the International Space Station, both NASA and Boeing emphasized that the performance of the "Starliner" in space was stable and the spacecraft was operating well. As former US Navy test pilots, Williams and Wilmore are accustomed to long-term missions and participation in development projects.

Boeing and SpaceX each received billions of dollars to transport astronauts under contracts signed with NASA's Commercial Crew Program in 2014. Since SpaceX launched its first crewed test mission in May 2020, it has flown 11 crews to the International Space Station, eight for NASA and three for short-term missions for Axiom Space.

SpaceX's mission is currently on hold due to a problem with the second stage of the Falcon 9 rocket that was launched earlier this month while launching Starlink satellites. Although the Falcon 9 rocket has completed a static fire test, the Federal Aviation Administration (FAA) has not yet responded to SpaceX's request to restart the mission; SpaceX argues that there was no risk to the public during the launch because only the second stage of the rocket in space was affected.

SpaceX is expected to launch two missions to the International Space Station in August, subject to FAA approval and NASA's independent review. The two missions are Northrop Grumman's Cygnus cargo spacecraft and the Crew-9 mission's four astronauts aboard the manned Dragon spacecraft to the International Space Station. (Chenchen)