WASHINGTON – NASA has confirmed that Boeing’s CST-100 Starliner spacecraft has suffered a fifth, albeit small, helium leak in its propulsion system, as engineers work to prepare the vehicle for its return to Earth next week.
In a June 10 statement, NASA said spacecraft teams were investigating “what impact, if any, five small leaks in the service module helium manifolds would have on the remainder of the mission.” That was the first reference to five leaks in the spacecraft; NASA had said there were four during a briefing hours after the spacecraft docked with the International Space Station on June 6.
In a June 11 statement to SpaceNews, NASA spokesman Josh Finch said the fifth leak was discovered around the time of that post-dock briefing. “The leak is significantly smaller than the others and is recorded at 1.7 psi [pounds per square inch] per minute,” he said.
NASA was aware of one leak at the time of Starliner’s June 5 launch, having discovered it shortly after a scrapped launch attempt on May 6. At the time of the launch, NASA and Boeing officials believed it was a one-time problem, likely caused by a defect in a seal. Hours after launch, however, controllers said they discovered two more leaks, one of which was relatively large at 395 psi per minute, Steve Stich, NASA’s commercial crew program manager, said during the briefing.
After docking, a fourth leak was found, although it was much smaller at 7.5 psi per minute. “What we need to do in the next few days is look at the leak rate there and figure out what we’re going to do compared to the rest of the mission,” Stich said during the briefing.
NASA closed the helium manifolds in the propulsion system after docking to stop the leaks, although they will have to be opened to use the spacecraft’s thrusters for docking and deorbit maneuvers. NASA said on June 10 that engineers estimate Starliner has enough helium to support 70 hours of flight operations, while Starliner will need only seven hours to return to Earth.
In addition to the helium leaks, engineers are also studying a reaction control system (RCS) thruster that shut down during the spacecraft’s flight to the ISS. Four other thrusters were disabled by flight software, but later enabled again. An RCS oxidation isolation valve in the Starliner service module is also not closed properly.
“We have all integrated the commercial crew program, Boeing and ISS teams, and are working very well together to come up with a future plan to put us in the best position for disengagement and re-entry,” said Dina Contella, deputy program manager of the NASA ISS. , said during a June 11 briefing about a series of upcoming spacewalks at the ISS. “Teams are still figuring out the best ways to test and prepare for disconnection and re-entry.”
These teams have some time to complete that work. NASA had initially scheduled a June 14 Starliner disengagement, but NASA said on June 9 it was delaying the disengagement until no earlier than June 18. That delay was intended to avoid a conflict with a June 13 ISS spacewalk, or EVA, by NASA astronauts Tracy Dyson. and Matt Dominick.
“To have it back to back, where we had an EVA followed by disconnection, was not the most convenient,” Contella said. Every few days there are opportunities to disconnect, determined by the orbital mechanics that establish a landing in the southwestern United States.
The two NASA astronauts who flew Starliner to the ISS, Butch Wilmore and Suni Williams, have been busy conducting tests of Starliner while on the station, while also doing other work such as science experiments. “Butch and Suni are an extra set of hands,” she said, especially as other ISS crew members prepare for upcoming spacewalks. “Having Butch and Suni available to do some important critical science has been excellent.”
Wilmore and Williams have publicly praised the spacecraft’s performance. “The spacecraft was more accurate than I expected. We could stop on a dime, so to speak,” Wilmore said during a June 10 phone call with NASA leadership discussing how the spacecraft maneuvered.
“Our experienced test pilots have been overwhelmingly positive about their Starliner flights, and we can’t wait to learn more from them and the flight data to further improve the vehicle,” said Mark Nappi, Boeing vice president and Commercial Crew Program Manager. from the astronauts in a June 11 statement.