While NASA is discussing the Safety of Boeing’s Starliner spacecraft After numerous helium leaks and engine problems, the agency is taking a backup plan to rescue the ship’s two crew members “increasingly seriously” Back to Earth aboard a SpaceX Crew Dragon, officials said Wednesday.
In this case – and there are no final decisions yet – Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williams remain on board the International Space Station for another six months and land with a Crew Dragon scheduled for launch on September 24 to bring long-term crew members to the outpost.
NASA
Two of the four “Crew 9” astronauts already assigned to the Crew Dragon flight would be removed from the mission and the ship would launch with two empty seats. Wilmore and Williams would then return to Earth with the two Crew 9 astronauts in February of next year.
Shortly before the Crew Dragon’s launch, the Starliner would undock from the station’s forward port and return to Earth under computer control without astronauts on board. The Crew Dragon would then dock at the vacated forward port.
Two previous test flights of the Starliner were conducted without crew and both landed successfully. The current Starliner’s computer system would need to be updated with new data files and flight controllers would need to brush up on procedures, but that work can be done in time to allow for a mid-September return.
If that scenario occurs, Wilmore and Williams would ultimately spend 268 days – 9.7 months – in space, instead of the roughly week-long stay they had planned when they launched aboard a United Launch Alliance Atlas 5 rocket on June 5.
Because of the uncertainty about the exact cause of the engine problems, “I would say our chances of an unmanned return of the Starliner have increased a little bit, given how things have unfolded over the last week or two,” said Ken Bowersox, NASA director of space operations.
“That’s why we’re looking at this option more closely to make sure we can handle it.”
However, he cautioned that no final decision would be made on when and how the Starliner crew would be brought home until the agency completes a high-level review of its flight readiness.
No date has been set yet, but it could happen late next week or the week after.
“Our first choice is to bring Butch and Suni back on Starliner,” said Steve Stich, NASA’s Commercial Crew Program manager. “However, we have done the necessary planning to ensure that we have other options open to us. We have worked with SpaceX to ensure that they are prepared to bring Butch and Suni back on Crew 9 if we need that.”
“Well, we haven’t approved that plan (yet). We’ve done all the work necessary to make sure that plan is in place … but we haven’t officially put it into effect yet. We wanted to make sure we had all that flexibility.”
Before the Starliner’s launch, NASA and Boeing engineers knew of 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.
NASA
However, the day after launch, four more helium leaks occurred and five rear-facing maneuvering thrusters failed to function as expected. Since then, NASA and Boeing have been conducting data reviews and ground tests to determine the exact cause of these two problems.
Starliner uses pressurized helium to fuel the thrusters, which are critical to keeping the spacecraft correctly oriented. This is especially important during the deorbit braking process, which uses larger rocket engines to slow the craft for reentry and a pinpoint landing.
To clear the Starliner for a manned return to Earth, engineers must develop an acceptable “flight logic” based on test data and analysis that provides confidence that the spacecraft can survive re-entry and landing with the required safety.
“The Boeing team is very confident, given the uncertainty we have, that the vehicle could bring the crew home,” Bowersox said. “But we have other people who are probably a little more conservative. They’re concerned that we don’t know for sure, so they think the risk is higher and would recommend that we don’t come home (with Starliner) because we have another option.”
“So that’s part of the discussion we’re having right now. But I think both views are reasonable given the uncertainty we have, and that’s why we’re trying to reduce that uncertainty.”
Boeing is adamant that the Crew Dragon backup plan is not necessary. Tests and analysis of helium leaks in the Starliner’s propulsion system and initial problems with the maneuvering thrusters showed that the spacecraft had more than enough room to return Wilmore and Williams safely to Earth.
Boeing says the helium leaks are known, they have not worsened, and there is more than enough pressurized gas on board to fuel the engines needed to maneuver and stabilize the spacecraft during the critical braking phase for deorbiting, reentry and landing.
In addition, engineers now believe they understand why some of the rear-facing maneuvering thrusters overheated during rendezvous with the space station and fired with less thrust than expected, causing the Starliner’s flight computer to shut them down during approach.
Ground tests of a new Starliner engine, which was fired hundreds of times under conditions mimicking those on board the spacecraft, reproduced the overheating symptom, likely caused by multiple firings during tests of the capsule’s manual control system in prolonged direct sunlight.
The greater-than-expected heating likely caused small seals in the engine valve “cups” to deform and expand, the analysis shows, reducing fuel flow. The engines aboard the Starliner were tested in space under more normal conditions and all worked fine, suggesting the seals had taken on a less disruptive shape.
New procedures are designed to prevent the overheating that occurred during the rendezvous. Additional manual test firings have been ruled out, no prolonged exposure to sunlight is planned, and fewer firings will be required when leaving the station than during the rendezvous.
William Harwood/CBS News
In a statement Wednesday, Boeing said: “We continue to believe in the capabilities and flightworthiness of Starliner. Should NASA decide to change the mission, we will take the necessary steps to configure Starliner for an unmanned return.”
The helium lines and thrusters are housed in the Starliner’s service module, which will be jettisoned to burn up in the atmosphere before the crew capsule re-enters the atmosphere for landing. As a result, engineers will never be able to examine the hardware firsthand and prove with certainty what went wrong.
At this point, this uncertainty seems to favor bringing Wilmore and Williams back to Earth aboard the Crew Dragon. But it is not certain yet.
“If we could recreate the physics in some offline testing to understand why that valve heats up and pushes out and then why it contracts, that would give us additional confidence to go ahead and bring Butch and Sonny back on this vehicle,” Stich said.
“That’s what the team is really trying to do: We want to look through all the data and see if we can get a good physical explanation for what’s happening.”
In the meantime, the wait for a decision in one direction or the other drags on.
“In the end, someone – a specific person – who makes the decision has to come to a conclusion,” Wayne Hale, a former shuttle flight director and program manager, wrote in a blog post earlier this week.
“The engineers will always, always, always demand more testing, more analysis, more time to get more information and be more confident in their conclusions. The decision maker must also decide when enough has been done. The problem with all of this … is that human lives are always at stake.”
Hale concluded his post by saying, “I don’t envy today’s decision makers who are weighing the reasons for a flight. My only advice is to listen carefully, ask pointed questions and request more data if necessary. But when the time comes, a decision must be made.”
