While NASA discusses Boeing’s Starliner spacecraft safety After multiple helium leaks and thruster problems, the agency is getting “more serious” about a backup plan to bring the ship’s two crew members back on board Return to Earth Officials said they were inside the SpaceX Crew Dragon on Wednesday.
In this case – and no final decision has yet been made – Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williams to want Stay on the International Space Station We will be transporting long-term crew members to the outpost with the Crew Dragon, which will remain for another six months and is scheduled to launch on September 24.
Two of the four “Crew 9” astronauts assigned to the Crew Dragon flight would be removed and the ship would launch with two empty seats. Wilmore and Williams would then return to Earth with the two Crew 9 astronauts next February.
Shortly before the Crew Dragon launch, the Starliner would depart the station’s forward dock and return to Earth under computer control with no astronauts on board. The Crew Dragon would then dock in the vacated forward dock.
Two previous Starliner test flights were conducted without crews and both landed successfully. The current Starliner’s computer system will need to be updated with new data files and flight controllers will need to refresh procedures, but that work can be done in time to support a mid-September return.
If that scenario plays out, Wilmore and Williams will spend 268 days (8.8 months) in space when they launch on June 5 aboard a United Launch Alliance Atlas 5 rocket, instead of the week or more they had planned.
“I would say that the chances of an uncrewed Starliner returning have increased slightly based on what’s happened over the last week or two,” said Ken Bowersox, NASA’s director of space operations, considering the exact cause of the thruster problems remains unclear.
“So we’re looking at that option more closely and making sure we can handle it.”
But he warned that a final decision on when and how to bring the Starliner crew home won’t be made until the agency completes its highest-level flight readiness review.
No date has been set yet, but it could happen next weekend or the week after.
“Our primary option is to return Butch and Suni to Starliner,” said Steve Stich, NASA’s Commercial Crew Program manager. “However, we have done the planning necessary to make sure our other options are open. We are working with SpaceX to make sure they are ready to (return) Butch and Suni to Crew 9 if we need to.”
“Now, we haven’t approved that plan (yet). We’ve done all the work to make sure that plan is there… but we haven’t officially launched it. We wanted to make sure that all of that flexibility was in place.”
Before Starliner launched, NASA and Boeing engineers knew there was a small helium leak in the spacecraft’s propulsion system. After ground tests and analysis, the team concluded that the craft could be launched safely as is.
But the day after launch, four more helium leaks occurred and the five rear-facing maneuvering thrusters failed to function as expected. Since then, NASA and Boeing have been conducting data reviews and ground tests to understand exactly what caused both problems.
Starliner uses pressurized helium to push propellants into the thrusters, which is critical for keeping the spacecraft properly oriented. This is especially important during the deorbit braking “burn,” when larger rocket engines are used to slow the craft for re-entry and landing on target.
For Starliner to receive clearance for a piloted return to Earth, engineers must develop an acceptable “flight justification” based on test data and analysis that provides confidence that the craft can perform a re-entry and landing with the required level of safety.
“The Boeing team is very confident that the vehicle can get the crew home with the uncertainty we have right now,” Bowersox said. “But there are others who are probably a little bit more conservative. They are concerned that we don’t know for sure, so they are overestimating the risk and recommending that we avoid returning home (on the Starliner) because we have another option.”
“That’s part of the discussion that we’re having right now. But again, I think both views are reasonable within the range of uncertainty that we have, and so our effort is to reduce that uncertainty.”
Boeing insists that the Crew Dragon backup plan is not necessary and that tests and analysis of helium leaks in Starliner’s thruster system and early problems with its maneuvering thrusters showed the spacecraft had more than enough margin to return Wilmore and Williams safely to Earth.
Boeing says the helium leaks have been contained, are not getting worse and there is more than enough pressurized gas on board to provide propellant for the thrusters needed to maneuver the spacecraft during critical deorbit braking and to deorbit and land.
Similarly, engineers believe they now understand what caused a handful of aft maneuvering jets to overheat and fire with lower thrust than expected during rendezvous with the space station, causing Starliner’s flight computer to shut them down during approach.
Ground tests of a new Starliner thruster fired hundreds of times under conditions similar to those experienced by those aboard the spacecraft replicated the overheating signature, which may have been caused by multiple firings during the tests, resulting from prolonged exposure of the capsule’s manual control system to direct sunlight.
Analysis suggests that higher-than-expected heating likely caused small seals in the thruster valve “poppets” to deform and expand, reducing thruster flow. The thrusters on Starliner were test-fired under more normal conditions in space, and all worked properly, suggesting that the seals had returned to a less intrusive shape.
New procedures are being implemented to prevent overheating during rendezvous. Additional manual test firings have been eliminated, extended exposure to the sun is not planned, and less frequent firings are required for departure from the station compared to rendezvous.
“We remain confident in Starliner’s capability and flight rationale. If NASA decides to modify the mission, we will take the necessary steps to configure Starliner for an uncrewed return,” Boeing said in a statement Wednesday.
The helium plumbing and thrusters are located in the Starliner’s service module, which will be jettisoned to burn up in the atmosphere before the crew capsule re-enters for landing, so engineers won’t be able to examine the hardware firsthand to definitively prove what went wrong.
At this point, that uncertainty seems to support Wilmore and Williams being brought back to Earth aboard the Crew Dragon, but it’s not definitive yet.
“If we can replicate the physics in some offline testing to understand why this poppet heats up and comes out and then contracts, it will give us additional confidence to move forward to get Butch and Sonny back on this vehicle,” Stich said.
“That’s really what the team is trying to do, is look at all the data and try to get a good physical explanation of what’s going on.”
Meanwhile, the wait for a decision is getting longer.
“Ultimately, someone—someone—has to come to a conclusion when the decision is made,” former shuttle flight director and program manager Wayne Hale wrote in a blog post earlier this week.
“Engineers will always, always want more testing, more analysis, more time to learn more and be more confident in their results. The decision maker must also decide when enough is known. The catch in all of this … is that there is always a risk to human life.”
Hale concluded his article by saying, “I do not envy today’s decision makers, those weighing the rationale for flight. My only advice is to listen carefully, ask questions effectively, and ask for more data when necessary. But when the time comes, a decision must be made.”
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