NASA and Boeing officials are gearing up to launch the second of the first crewed test flights of the Starliner spacecraft on Saturday from Cape Canaveral Space Force Station in Florida.
The launch of Boeing’s Starliner aboard a United Launch Alliance Atlas V rocket is scheduled for 12:25 p.m. EDT (16:25 p.m. UTC). Veteran astronauts, NASA Commander Butch Wilmore and pilot Suni Williams, will fly a crewed Starliner spacecraft into low Earth orbit for the first time.
The first crewed flight of a new spacecraft is not an everyday occurrence. Starliner is the sixth orbital-class crewed spacecraft in the history of the U.S. space program, following Mercury, Gemini, Apollo, the Space Shuttle, and SpaceX’s Crew Dragon. NASA awarded Boeing a $4.2 billion contract in 2014 to develop Starliner, but the project has been delayed for years and Boeing has suffered nearly $1.5 billion in cost overruns. Meanwhile, SpaceX was awarded the contract at the same time as Boeing, and began launching astronauts in its Crew Dragon four years ago this week.
Now it’s Starliner’s turn: if the crew test flight is successful, it will set the stage for six operational flights ferrying astronauts to and from the International Space Station (ISS).
Assuming the test flight begins on Saturday, the spacecraft is scheduled to dock with the ISS at 1:50 pm EDT (17:50 UTC) on Sunday to begin a stay of at least eight days. Once managers are satisfied that the mission has achieved all planned test objectives and weather is favorable at the Starliner landing site in the western United States, the spacecraft will leave the station and return to Earth for a parachute landing. If the mission begins on Saturday, the earliest possible landing date would be Monday, June 10.
Wilmore and Williams have found themselves in this situation before: On May 6, astronauts were belted into their seats in the Starliner’s cockpit, waiting to take off for their flight to the International Space Station. A valve failure on an Atlas V rocket canceled that day’s launch, and then a helium leak was discovered in the Starliner’s service module, causing the mission to be postponed until this weekend.
Fly as is
After weeks of review and analysis, managers determined that Starliner was safe to fly with the leak. The spacecraft uses helium gas to pressurize its propulsion system, which pumps hydrazine and nitrogen tetroxide propellants from internal tanks into the capsule’s steering thrusters.
“When we looked at this issue, it wasn’t a question of trade-offs,” said Mark Nappi, Boeing’s vice president and Starliner program manager. “The question was, is it safe? And it is safe, and that’s why we decided we could fly it as is.”
Ground teams have determined that the leak originated from a flange in one of the four doghouse-style propulsion pods around the Starliner spacecraft’s service module. In a worst-case scenario, if the situation worsens during flight, ground controllers can isolate the leak by closing the manifold that’s causing the leak. If the leak doesn’t worsen, engineers are confident they can address it without major impact to the mission.
“We seriously considered what our options were with this flange,” said Steve Stich, NASA’s commercial crew program manager, who oversees the contract with Boeing. The flange holds the helium lines and piping that carry the spacecraft’s toxic fuel and oxidizer, and would be “difficult” to repair, Stich said.
Officials believe the leak is probably due to a faulty seal, but to safely repair it, ground teams would need to detach the capsule from the Atlas V rocket, take it back to a hangar, and drain the fuel tanks, which would likely delay Starliner’s long-delayed test flights until later this year.
But the leak is relatively small and steady: “Of the tank’s total capacity of 50 pounds, the leak is about half a pound per day,” Stich said.
“In our case, we have some headroom in the helium tanks, and we’ve looked hard and spent time looking at that data to understand what that headroom is and what the worst case is,” Stich said. “We think we can really manage this leak by looking at it before launch and also addressing it if it gets bigger during flight.”
