For the second time in a month, the first crewed launch of Boeing’s Starliner space capsule was called off while the crew members were in their seats, waiting for liftoff.
The hold was called by the computer that monitors systems on Starliner’s launch vehicle, United Launch Alliance’s Atlas V rocket, during the final minutes of the countdown at Cape Canaveral Space Force Station in Florida.
The ground launch sequencer triggered an end to today’s countdown with just three minutes and 50 seconds remaining. Mission managers started investigating what triggered the alarm, even as the launch pad team began the process of helping NASA astronauts Butch Wilmore and Sunita Williams out of the capsule.
The next opportunities for launch come on Sunday, Wednesday, and Thursday, but the timing for the next launch attempt depends on the issue that caused the hold and how quickly it can be resolved.
Starliner is due to transport Wilmore and Williams on a shakedown cruise to the International Space Station — a trip that’s also meant to deliver supplies and a replacement pump for the station’s urine-recycling system. The gumdrop-shaped capsule has been through two uncrewed test flights, but this mission will mark the first time Starliner carries astronauts to orbit.
Today’s scrub marked the latest setback for a development and testing effort that has already been through years of delays — and more than $1 billion in cost overruns that Boeing has had to cover.
Starliner’s first uncrewed flight test fell short of full success in 2019, forcing a second uncrewed test that met its objectives in 2022.
A fresh set of problems cropped up during the first attempt to launch the crewed flight test on May 6. Mission managers called off that countdown two hours before launch, due to a balky oxygen relief valve on the rocket’s Centaur upper stage. In the course of resolving that issue, engineers detected a small helium leak that was traced to a flange on one of the Starliner service module’s thrusters.
NASA and Boeing spent days assessing the leak’s potential impact, and the team decided the safest course of action was to live with the leak and work around it.
“It’s a really, really small leak, and it’s well within the margin that we have,” said Steve Stich, program manager for NASA’s Commercial Crew Program.
During a pre-launch briefing, Stich said the flange was at a spot in the thruster system where the lines for fuel, oxidizer, and helium for pressurization come together. “It makes it almost unsafe to work on,” he said.
Engineers also learned of a potential design vulnerability in Starliner’s propulsion system — an issue that could hamper the capsule’s ability to execute a deorbit burn if two of the four thruster units known as “doghouses” were to fail at the same time.
The mission team developed a work-around for the crewed flight test. After that mission is complete, NASA and Boeing will take a closer look at the propulsion system design, and at the leaky helium pressurization system.
Yet another concern came to light at the end of a crewed suborbital space mission that was conducted by Jeff Bezos’ Blue Origin space venture on May 19. When the New Shepard crew capsule descended toward touchdown, one of its three parachutes failed to open completely. Starliner’s parachute system uses a similar design, so NASA and Boeing worked with Blue Origin to make sure the problem wouldn’t crop up during the orbital test mission.
Stich said Blue Origin traced the parachute problem to a reefing line that’s designed to keep the parachute from opening prematurely. There’s a mechanism that’s supposed to cut the line at the proper moment, but Stich said “the cutters, for some reason, did not cut that line.”
“We use a very similar cutter to what Blue Origin uses, so it was important for us to look at that data,” Stich said. “We went back and looked at all of our test data.”
Stich said the Starliner system’s cutters had been successfully tested 160 times, which reassured the team that the parachutes were good to go.
NASA made a last-minute switch in the payloads for Starliner’s flight test: The pump for the space station’s urine-recycling system failed unexpectedly, forcing the crew to store their urine in bags and tanks. NASA decided to provide some relief, so to speak, by sending up a 150-pound replacement tank in Boeing’s capsule.
To keep Starliner’s mass distribution in balance, two suitcases containing clothing and personal hygiene items for Wilmore and Williams were removed from the payload manifest.
“They’ll just use our generic supplies that we have on board,” said Dana Weigel, who manages NASA’s International Space Station Program. “The reason why we have them there is for cases like this.”
If everything goes according to plan, Wilmore and Williams will spend about eight days on the space station. At the end of their space station stay, the duo will ride Starliner back down for a parachute-aided, airbag-cushioned landing in the western U.S., at a site to be determined based on the weather and the timing of the return.
Boeing will use the data gathered during the test flight to fine-tune its spacecraft design. Those refinements should clear the way for Starliner to take its place alongside SpaceX’s Crew Dragon as a commercial “space taxi” that’s capable of ferrying astronauts to and from orbit.
That’s assuming, of course, that everything goes according to plan.
This report has been updated with news developments during the countdown.
