NASA and Boeing officials are ready for a second attempt to launch the first crew test flight on the Starliner spacecraft from Cape Canaveral Space Force Station, Florida, on Saturday.
Boeing’s Starliner, atop a United Launch Alliance Atlas V rocket, is scheduled to launch at 12:25 PM EDT (4:25 PM UTC). NASA Commander Butch Wilmore and pilot Suni Williams, both experienced astronauts, will take the Starliner spacecraft on its maiden voyage to low Earth orbit with a crew on board.
The first crew flight on a new spacecraft is not an everyday occurrence. Starliner is the sixth orbital-class spacecraft in the history of the U.S. space program, following Mercury, Gemini, Apollo, the space shuttle and SpaceX’s Crew Dragon. NASA signed a $4.2 billion contract with Boeing in 2014 to develop Starliner, but the project is years behind schedule and has cost Boeing nearly $1.5 billion in cost overruns. SpaceX, meanwhile, won a contract at the same time as Boeing and started launching astronauts on the Crew Dragon four years ago this week.
Now it’s finally Starliner’s turn. A successful crew test flight would set the stage for six operational Starliner flights to transport astronauts to and from the International Space Station (ISS).
Assuming the test flight lifts off Saturday, the spacecraft should 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 of its planned test objectives, and pending good weather conditions in the Starliner landing zone in the western United States, the spacecraft will depart the station and return to Earth for a landing with parachutes. If the mission departs on Saturday, the earliest nominal landing date would be Monday, June 10.
Wilmore and Williams have been here before. On May 6, the astronauts were strapped into their seats in the Starliner cockpit, awaiting liftoff for a flight to the International Space Station. A valve failure on the Atlas V rocket prevented launch that day, and officials subsequently discovered a helium leak in Starliner’s service module, delaying the mission until this weekend.
Flying as it is
After weeks of assessments and analysis, managers determined that Starliner can fly safely as is with the leak. The spacecraft uses helium gas to pressurize its propulsion system, pushing hydrazine and nitrogen tetroxide propellants from its internal tanks to the capsule’s thrusters.
“When we looked at this problem, it didn’t come down to transactions,” said Mark Nappi, vice president and Starliner program manager at Boeing. “It came down to: Is it safe or not? And it is safe, and that’s why we decided we can fly with what we have.”
Ground teams traced the leak to a flange on one of four doghouse-shaped propulsion pods around the perimeter of the Starliner spacecraft’s service module. In the worst case, if the condition worsened during the flight, ground controllers could isolate it by closing the manifold feeding the leak. If the leak does not worsen, engineers are confident they can resolve the problem without major impact on the mission.
“We looked very carefully at what our options were with this particular flange,” said Steve Stich, manager of NASA’s commercial crew program, which oversees the agency’s contract with Boeing. The flange has a helium line and lines for the spacecraft’s toxic fuel and oxidizer, making a repair “problematic,” Stich said.
To safely repair the leak, which officials believe is likely caused by a faulty seal, ground teams would have to disconnect the capsule from the Atlas V rocket, return it to a hangar and empty its fuel tanks. This would likely delay the long-delayed Starliner test flight until the end of this year.
But the leak is relatively small and stable. “It’s about half a pound per day out of a total capacity of 50 pounds in the tank,” Stich said.
“In our case, we have margin in the helium tank, and we looked very hard to understand that margin and to understand the worst cases, and we took the time to go through that data,” Stich said. “We really think we can control this leak, by looking at it before launch, and if it gets bigger during the flight, we can control it too.”