While NASA is debating about safety of the Boeing Starliner spacecraft due to multiple helium leaks and thruster problems, the agency is “increasingly serious” about its backup plan to carry two crew members. return to Earth aboard the SpaceX Crew Dragon, officials said Wednesday.
In that case – and no final decision – Starliner commander Barry “Butch” Wilmore and co-pilot Sunita Williams will remain in the International Space Station for another six months and come down on the Crew Dragon that has been scheduled to launch on September 24 to carry long-duration crew members to the outpost.
NASA
Two of the four “Crew 9” astronauts already assigned to the Crew Dragon spacecraft will be bumped from the mission and the ship will launch with two empty seats. Wilmore and Williams will then return to Earth next February with two Crew 9 astronauts.
Shortly before Crew Dragon’s launch, Starliner will launch from the station’s forward port and return to Earth under computer control, with no astronauts on board. Crew Dragon will then dock in the empty forward port.
Two previous Starliner test flights were flown without a crew and both landed successfully. The Starliner’s computer system now needs to be updated with fresh data files, and flight controllers need to follow these procedures, but the work can be done in time to support the mid-September return.
If that scenario plays out, Wilmore and Williams will spend 268 days — 8.8 months — in space instead of the week or so planned when they blast off on a United Launch Alliance Atlas 5 rocket on June 5.
Based on the uncertainty about the exact cause of the thruster problem, “I would say that the likelihood that we will return an unclaimed Starliner is greatly reduced based on what has happened in the last week or two,” said Ken Bowersox, director of NASA. space operation.
“That’s why we’re taking a closer look at those options to make sure we can address them.”
But he cautioned that no final decision will be made on when — or how — to bring the Starliner crew home until the agency completes its highest-level flight readiness review.
No date has been set, but it could happen at the end of next week or the week after.
“Our primary option is to get Butch and Suni back on the Starliner,” said Steve Stich, manager of NASA’s Commercial Crew Program. “However, we’ve done the necessary planning to make sure we have other options open. We’ve been working with SpaceX to make sure they’re ready to (return) Butch and Suni on Crew 9 if we need them.
“At the moment, we have not approved this plan (yet). We have done all the work to make sure that this plan is there … but we have not officially activated it. in place.”
Before Starliner launched, NASA and Boeing engineers became aware of a small helium leak in the spacecraft’s propulsion system. After ground tests and analysis, the team concluded the ship could be launched safely.
NASA
However, a day after launch, four more helium leaks developed and the five aft-facing maneuvering thrusters failed to operate as expected. Since then, NASA and Boeing have conducted data reviews and ground tests to find out what caused the problem.
The Starliner uses pressurized helium to propel propellant into the thrusters, which are essential to keeping the spacecraft moving properly. That is especially important when “burning” the de-orbit brake using a larger rocket engine to slow the ship down for re-entry and landing on the target.
To clear the Starliner for return to Earth, engineers must develop an acceptable “flight rationale” based on test data and analysis that provides confidence that the craft can re-enter and land with the required level of safety.
“The Boeing team is (firmly) confident that the vehicle can get the crew home now with all the uncertainty,” Bowersox said. “But we have other people who are maybe a little more conservative. They’re worried that we don’t know for sure, so they think the risk is higher and they advise us not to go home (on the Starliner) because we have other options.
“So that’s part of the discussion we’re having now. But again, I think both views are reasonable with the band of uncertainty that we have, so our efforts are trying to reduce that uncertainty.”
Boeing emphatically said that the Crew Dragon backup plan was not needed and that testing and analysis of helium leaks in the Starliner propulsion system and early problems with the maneuvering thrusters showed that the spacecraft had enough margins to bring Wilmore and Williams safely back to Earth.
The helium leak is understood, says Boeing, they are not getting worse and more than enough pressurized gas on board to push the propellant to the thrusters needed to maneuver and stabilize the spacecraft through the critical de-orbit brake burn to release. orbit for re-entry and landing.
In addition, engineers believe they now know what caused some of the rearward-facing maneuvering jets to overheat and fire at lower than expected thrust during rendezvous with the space station, causing the Starliner flight computer to shut down on approach.
A ground test of the new Starliner thruster, fired several times in conditions that mimic what people experience on board the spacecraft, mimics signs of overheating, which may have been caused by multiple firings during tests of the capsule’s manual control system in direct sunlight. .
The higher-than-expected heating could have caused the small seals on the thruster valve “poppets” to deform and expand, the analysis showed, which reduced propellant flow. The thrusters on the Starliner were test fired in space under more normal conditions and everything was working properly, showing the seals had returned to a less intrusive form.
There is a new procedure to prevent overheating that occurs during rendezvous. Additional manual test shooting has been rejected, no sunlight is planned and less frequent firing is required for station departures compared to rendezvous.
William Harwood/CBS News
In a statement Wednesday, Boeing said, “We still believe in the Starliner’s capabilities and the reason for the flight. If NASA decides to change the mission, we will take the necessary actions to arrange the Starliner to return uncrewed.”
The helium tubes and thrusters are attached to the Starliner service module, which will be ejected to burn up in the atmosphere before the crew capsule re-enters for landing. So, engineers won’t be able to examine the hardware first to prove, with certainty, what’s wrong.
At this point, uncertainty seems to favor bringing Wilmore and Williams back to Earth aboard the Crew Dragon. But it is not a certainty yet.
“If we can replicate the physics in some offline testing to understand why this poppet is heating and extruding and then whether it’s contracting, that will give us additional confidence to move forward, to get Butch and Sonny back in this vehicle,” said Stich.
“That’s what the team is doing, to try to look at all the data and see if they can come up with a good physical explanation for what’s going on.”
In the meantime, waiting for a decision, one way or another, drags on.
“At the end of the day, someone — a few people — is appointed to be the decision maker, that person has to draw the conclusions,” Wayne Hale, a former flight director and program manager, wrote in a blog post earlier this week.
“The engineers always ask for more tests, more analysis, more time to get more information to be more confident about their conclusions. The decision-maker also has to decide when it’s done. All these formulas… it always involves a risk to human life. “
Hale concluded the post by saying: “I do not envy the decision makers today, who are considering the reasons for flight. My advice is to listen carefully, ask questions effectively, ask for more data if necessary. But when the time comes, a decision must be made. “
