NASA recently confirmed that Boeing’s CST-100 Starliner capsule suffered a fifth helium leak in its propulsion system. Engineers are currently working to prepare the vehicle for its return to Earth, scheduled for next week. This new loss, although smaller than previous ones, represents a significant challenge for the mission team.
In a statement released on June 10, 2024, NASA said spacecraft teams are examining “what impacts, if any, five small leaks in the Service Module’s helium collectors might have on the remainder of the mission.” This was the first reference to the presence of five leaks; Previously, NASA mentioned four losses during a briefing shortly after the spacecraft docked with the International Space Station (ISS) on June 6.
NASA was aware of a leak at the time of Starliner’s June 5 launch, detected shortly after a canceled launch attempt on May 6. At the time of launch, NASA and Boeing officials considered the problem an isolated case, likely caused by a sealing defect. However, a few hours after launch, controllers detected two more leaks, one of them relatively large at 395 psi per minute, Steve Stich, NASA’s commercial crew program manager, explained during the briefing.
Corrective measures and future operations
A fourth leak was discovered after docking, although it was much smaller at 7.5 psi per minute. “Over the next few days, we need to look at the loss rate and figure out what to do as it relates to the rest of the mission,” Stich said.
After docking, NASA closed the helium collectors in the propulsion system to stop leaks, although they will need to be reopened to use the spacecraft’s thrusters during undocking and deorbiting maneuvers. NASA said June 10 that engineers estimate Starliner has enough helium to support 70 hours of flight operations, while only seven is needed for return to Earth.
In addition to the helium leaks, engineers are investigating a reaction control system (RCS) thruster that shut down during the spacecraft’s flight to the ISS. Four other thrusters were deactivated by the flight software but later reactivated. Additionally, an RCS oxidizer isolation valve in the Starliner service module did not close properly.
Changes to the return program
NASA had initially scheduled the Starliner undocking for June 14, but on June 9 announced the postponement to no earlier than June 18. This delay was decided to avoid a conflict with a spacewalk scheduled for June 13 by NASA astronauts Tracy Dyson and Matt Dominick.
The two NASA astronauts who flew Starliner to the ISS, Butch Wilmore and Suni Williams, are currently busy both conducting tests on the spacecraft and carrying out other tasks, such as scientific experiments.
