NASA and Boeing officials are preparing for a second launch attempt on the first crewed test flight of the Starliner spacecraft on Saturday from the Cape Canaveral Space Station in Florida.
Liftoff of Boeing’s Starliner enclosed on a United Launch Alliance Atlas V rocket is scheduled for 12:25 p.m. EDT (4:25 p.m. UTC). NASA Commander Butch Wilmore and Pilot Suni Williams, both experienced astronauts, will lead the Starliner spacecraft on its first crewed trip into low Earth orbit.
The first flight of a crew on a new spacecraft is not an everyday event. Starliner is the sixth crewed orbiter-class spacecraft in the history of the US space program, following Mercury, Gemini, Apollo, the space shuttle and SpaceX’s Crew Dragon. In 2014, NASA signed a $4.2 billion contract with Boeing to develop the Starliner, but the project is years behind schedule and has cost Boeing nearly $1.5 billion in cost overruns. SpaceX, meanwhile, was awarded the contract at the same time as Boeing and began launching astronauts on Crew Dragon four years ago this week.
Now it’s finally the 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 leaves the ground on Saturday, the spacecraft is due to dock at the ISS on Sunday at 13:50 EDT (17:50 UTC) 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 leave the station and return to Earth for a parachute landing. If the mission takes off on Saturday, the earliest nominal landing date would be Monday, June 10.
Wilmore and Williams were already here. On May 6, the astronauts were strapped into their seats in the cockpit of the Starliner awaiting liftoff on 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 the Starliner’s service module that delayed the mission until this weekend.
Flying as it is
After weeks of review and analysis, managers determined that the Starliner was safe to fly as it was with the leak. The spacecraft uses helium gas to pressurize its propulsion system and propel hydrazine and nitrogen tetroxide propellants from internal tanks to the capsule’s maneuvering thrusters.
“When we looked at this issue, it didn’t come down to trade,” said Mark Nappi, Boeing vice president and program manager for the Starliner. “It came down to the question: is it safe or not? It’s 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 capsules around the perimeter of the Starliner spacecraft’s service module. In the worst case scenario, if the condition worsened during flight, ground controllers could isolate it by closing the leaky manifold. If the leak doesn’t get any worse, engineers are confident they can fix it without much impact on the mission.
“We really looked carefully at what our options were with this particular flange,” said Steve Stich, NASA’s commercial crew program manager, who oversees the agency’s contract with Boeing. The flange has a helium tube and lines for the spacecraft’s toxic fuel and oxidizer, making the repair “problematic,” Stich said.
To safely repair the leak, which officials believe was likely caused by a faulty seal, ground teams would have to detach the capsule from the Atlas V rocket, take it back to the hangar, empty its fuel tanks. This would likely delay the long-delayed Starliner test flight until later this year.
But the leakage is relatively small and stable. “That’s about half a pound a day out of 50 pounds of total capacity in the tank,” Stich said.
“In our case, we have a margin in the helium tank, and we’ve tried very hard to understand that margin and understand the worst cases, and we’ve taken the time to go through that data,” Stich said. “We really think we can manage this leak, so we look at it before launch, and then if it increases during the flight, we can deal with it.”