WASHINGTON — NASA has confirmed that the Boeing CST-100 Starliner spacecraft has suffered a fifth, albeit smaller, leak of helium in its propulsion system as engineers work to prepare the vehicle for its return to Earth next week.
In a statement on June 10, NASA said spacecraft teams were investigating “what effects, if any, the five small leaks in the service module’s helium lines would have on the remainder of the mission.” This was the first mention of five leaks in the spacecraft; NASA mentioned there were four during a brief briefing following the spacecraft’s June 6 landing at the International Space Station.
In a statement to SpaceNews on June 11, NASA spokesman Josh Finch said the fifth leak was discovered around the time of this post-docking briefing. “The leak is significantly less than the others and was recorded at 1.7 psi [pounds per square inch] in a minute,” he said.
NASA was aware of one leak at the time of Starliner’s June 5 launch, which was detected shortly after a clean launch attempt on May 6. At the time of launch, NASA and Boeing officials believed it was a one-time problem, likely caused by a malfunction. in the seal. However, hours after launch controllers said they detected two more leaks, one of which was relatively large at 395 psi per minute, Steve Stich, NASA’s commercial program manager, said at a briefing.
A fourth leak was found after docking, although it was much smaller at 7.5 psi per minute. “What we have to do in the next few days is look at the leak rate there and figure out what we’re going to do relative to the rest of the mission,” Stich said at the briefing.
NASA closed the helium lines in the propulsion system after docking to stop leaks, although they will need to be opened to use the spacecraft’s thrusters for decoupling and deorbit maneuvers. NASA said on June 10 that engineers estimate the Starliner has enough helium for 70 hours of flight, while the Starliner only needs seven hours to return to Earth.
In addition to the helium leaks, engineers are studying one Reaction Control System (RCS) thruster that shut down during the spacecraft’s flight to the ISS. Four other jets were disabled by the flight software but later reactivated. The RCS oxidizer isolation valve in the Starliner service module is also not properly closed.
“We have the commercial crew program, Boeing, the ISS teams, all integrated and working very well together to come up with a plan to get us in the best position for shutdown and return,” Dina Contella, NASA’s ISS deputy program manager. , he said at a June 11 briefing on a series of upcoming ISS spacewalks. “Teams are still working on what are the best ways to test and prepare for disconnection and return.”
These teams have some time to complete this work. NASA originally planned to undock the Starliner on June 14, but NASA said on June 9 that it was pushing back the undocking to June 18 at the earliest. The delay was to avoid a conflict with the ISS spacewalk, or EVA, on June 13 by NASA astronaut Tracy Dyson. and Matt Dominick.
“Having it back to back, if we had an EVA and then an undock, it wasn’t the most comfortable thing,” Contella said. Every few days there are landing opportunities, driven by orbital mechanics, which set up a landing in the southwestern United States.
The two NASA astronauts who flew the Starliner to the ISS, Butch Wilmore and Suni Williams, were busy conducting tests of the Starliner on the station while 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 key critical science was excellent.”
Wilmore and Williams publicly praised the spacecraft’s performance. “The spaceship was accurate, more than I expected. We could stop on a dime, so to speak,” Wilmore said during a June 10 call with NASA management, discussing how the spacecraft maneuvered.
“Our veteran test pilots have been overwhelmingly positive about their flight in the Starliner, and we look forward to learning more from them and the flight data to further improve the vehicle,” said Mark Nappi, Boeing vice president and commercial crew program manager. astronauts in a June 11 statement.