It seems Boeing’s Starliner Spacecraft can’t quite get away from various complications on its first crewed mission. Earlier today and not too long after the additional helium leaks were found, the decision was made to call off the initial docking as five of the spacecraft’s thrusters failed. As a result, NASA and Boeing decided to push the docking back a few hours as they dealt with the problem and ensured everything was safe to proceed.
Thankfully this eventually resulted in a successful docking with the ISS, marking the first crewed flight on Starliner to reach the orbiting laboratory. It does however beg questions about whats to come in the next few days. Here I will go more in-depth into Starliner’s initial approach, the loss of thrusters, what to expect in the near future, and more.
Thruster Failure
Yesterday on the 5th Starliner launched successfully and soon began its 24-hour journey in orbit to rendezvous with the International Space Station. About 6 hours after the launch additional helium leaks were found however the agency determined they were not a threat to the mission or the crew and they proceeded on practically as normal. This included the crew of two going into their planned sleep period.
Early this morning they woke up and began work to prepare for the docking originally scheduled to happen at 12:15 pm EST. Around that time NASA said in a statement, “Following in-flight reviews of the mission and helium leaks, the Starliner and International Space Station mission management teams are “go” to proceed with space station arrival. The flight control team will continue to monitor the leak rates in Starliner’s propulsion system. After docking, all of Starliner’s manifolds will be closed per normal plans. All other Starliner systems are functioning normally” they said.
Unfortunately, that soon would not necessarily be the case. As the vehicle got closer to the station in preparation for its final approach, issues were detected with multiple of the vehicles RCS thrusters. Specifically, in a NASA statement they were quoted saying, “As Starliner began its approach to the space station, five reaction control system thrusters failed off during flight.” These are the small thrusters the spacecraft uses for minute adjustments on orbit such as docking to the ISS. When the issue was found they decided to hold the spacecraft and run some tests. Officially they waited at the 200 meter hold point near the station.
The tests consisted of hot firing the affected thrusters. This managed to re-enable four of the five thrusters while the crew manually piloted the spacecraft at the station’s 200-meter hold. During the NASA livestream one of the commentators was quoted saying, “Teams on the ground hot fired 4 of the reaction control system thrusters, these are located on the service module. The crew was able to report they were able to hear all but one of those hot fires. Thankfully for the crew, the fix allowed them to continue on with their mission. In another NASA statement released soon after the docking they pointed out, “After re-selecting four of the thrusters, Starliner had the fault tolerance required to approach the space station for docking. At the 10-meter hold point, the mission team completed system readiness evaluations and proceeded with docking” they said.
The docking occurred right around 1:30 pm or about an hour and 15 minutes after the original goal. Since then, this is about all the information NASA and Boeing have released on the thrusters and helium leaks. They had stressed before that the helium leaks were an isolated problem and didn’t affect other systems. Obviously, the loss of the thrusters brings some concern as to whether or not that was 100% the case. Ideally, they will get even more information now that the spacecraft is docked to the station and ensure everything is in order for an eventual departure and reentry.
Mark Nappi, Boeing’s Starliner program manager was quoted saying, “We have two problems on this vehicle right now: the helium leak and figuring out how to fine-tune these thrusters so that they’re not selected off. Those are pretty small, really, issues to go deal with, and we’ll figure them out for the next mission. So I don’t see these as significant at all” he said.
On the bright side, the docking was eventually successful, and about two hours later the hatch was opened. Here you could see both Butch and Suni exit the spacecraft and greet all the other astronauts on the station. The current mission plan calls for the crew to work on the station and conduct tests for the next week or so before they attempt reentry and complete the mission. In the coming days, we can expect more information and updates from the company.
Problems In the Past
Looking back at Starliner’s history actually reveals another instance of thruster issues on a previous test flight. In this case, back in 2022, Boeing launched the uncrewed OFT 2 test flight. It carried a test dummy suited in the blue Boeing inflight spacesuit. Here, two Orbital Maneuvering and Attitude Control System (OMACS) thrusters failed during the orbital insertion burn, but the spacecraft was able to compensate using the remaining OMACS thrusters with the addition of the Reaction Control System (RCS) thrusters. Not only that but a couple of RCS thrusters used to maneuver Starliner also failed during docking due to low chamber pressure. In other words, the same thrusters at practically the same time in the mission experienced similar issues.
Whether or not the helium leaks are to blame is not clear but they have suggested otherwise. When they first tested all 8 of Starliner’s helium manifolds, they found that the leak was isolated to one flange in one of the spacecraft’s 28 RCS thrusters or Reaction Control System Thrusters.
Before the launch, they conducted a relevant test and said in a company statement, “Pressure testing performed on May 15 on the spacecraft’s helium system showed the leak in the flange is stable and would not pose a risk at that level during the flight. The testing also indicated the rest of the thruster system is sealed effectively across the entire service module. Boeing teams are working to develop operational procedures to ensure the system retains sufficient performance capability and appropriate redundancy during the flight. they said”
At the time they also talked about a possibility that was unlikely but could result from certain thruster failures. Here Steve Stich said engineers performed a review of the rest of the propulsion system just to make sure they didn’t have any other things that they should be concerned about. However, that review did actually turn up something he called a “design vulnerability” with Starliner’s propulsion system where, in a rare circumstance, the spacecraft would not be able to perform a deorbit burn if two adjacent “doghouses” that contain RCS and larger orbital maneuvering and attitude control (OMAC) thrusters failed. That failure, he said, would knock out enough OMAC and RCS thrusters to prevent existing backup plans for carrying out a deorbit burn from being implemented. To solve this issue in a timely manner, engineers developed a different deorbit reentry mode that would alter the burns from the RCS. They highlighted that this outcome would be highly unlikely but something they want to prepare for just in case.
At Starliner’s current state, it seems they were able to get 4 of the 5 thrusters working again meaning the vast majority of RCS thrusters are available. In a comment earlier today from Stich, he said, “We don’t necessarily understand exactly why we lost the jets. The software sees something that is doesn’t like about that thruster, maybe a little less thrust or the thrust rise rate doesn’t come up exactly the way that the software is looking for. And so what the software does, it says, I won’t use that thruster anymore.”
Mark Nappi had similar comments talking about the software and it unselecting the thrusters. What’s most important now is preparing for the rest of the mission as some of the final milestones are extremely important. After undocking, the next flight test objective will assess manual piloting of Starliner before switching back to autonomous operations. The crew will spend approximately six hours in the spacecraft from undocking until its first landing opportunity. You then have reentry which is a challenge in itself. During re-entry to Earth’s atmosphere, the spacecraft will begin to slow down from orbital velocity and the crew could feel loads up to 3.5 g. The spacecraft’s forward heat shield will be jettisoned after re-entry, having completed its work protecting the parachute system, and two drogue and three main parachutes will further slow Starliner’s descent. If all that works as planned, the base heat shield will deploy, exposing the dual airbag system. The six primary airbags will deploy at the base of the capsule, cushioning its landing at approximately 4 mph in the western United States.
Following a landing and successful recovery, NASA will complete work to certify the spacecraft as an operational crew system for long-duration rotation missions to the space station, beginning with NASA’s Boeing Starliner-1 expected to launch in 2025. The plan would then be to start launching humans on Starliner consistently and much more frequently.
Conclusion
So far, Boeing has kept running into complications during its first crewed flight test of Starliner. Thankfully they have determined that the crew is in no danger and they docked with the ISS earlier today. They now have the second half of the mission ahead of them. We will have to wait and see how it progresses and the impact it has on the space industry.