Updated at 5:45 p.m. Eastern Time after additional launch delays were announced.
KENNEDY SPACE CENTER, Florida — A last-minute problem delayed the launch of Boeing’s CST-100 Starliner atop Atlas 5 on its first crewed flight June 1, delaying the mission by at least four days.
Ground computers halted the countdown 3 minutes and 50 seconds before the scheduled 12:25 a.m. Eastern launch of the Crew Flight Test (CFT) mission, with NASA astronauts Butch Wilmore and Suni Williams aboard. Because Starliner has an immediate launch window, the hold aborted the launch attempt.
In a briefing a few hours after the scrub, United Launch Alliance Chief Executive Tory Bruno said a card in one of three redundant ground control computers known as the launch sequencer came in slower than the other two when coming out of the T-4 minute hold. “That tripped a red line and triggered an automatic hold,” he said.
He said technicians have not yet been able to access the computer located near the launch pad while the vehicle’s propellants are being unloaded. He estimated it would take at least a few hours to examine the computer and see if any cards or other hardware are faulty and need to be replaced.
“If it’s as simple as changing a card, we have spares for everything,” he said. He concluded that the job would be simple enough to be completed in time for the June 2 launch attempt. “If it’s more involved than that or just takes longer to get it all done, then we’ll move to a backup date of the 5th.” There is also another launch opportunity on June 6.
In a statement about two hours after the briefing, NASA said the launch attempt on June 2 would not be made to give teams more time to study the problem. An update on the next launch attempt is expected on June 2.
NASA, Boeing and United Launch Alliance worked to troubleshoot other minor problems during the countdown. About two hours before the scheduled launch, launch controllers reported a problem with valves controlling the flow of liquid oxygen and liquid hydrogen to the Centaur upper stage so its tanks could be filled.
Bruno said at the briefing that one of the three computer racks was not ordering the valves to open, so controllers switched to a different rack. He said it was the same rack that later triggered the hold, but it contained a different card. He said those cards have generally been reliable, though he added that switching cards is “not unique.”
Less than 20 minutes before liftoff, spacecraft controllers noticed a problem with the fans that circulate air in the pressure suits worn by Wilmore and Williams. A few minutes later, the fans started working again. A change in voltage when the spacecraft switches on internal power caused the fans to stop, and spacecraft controllers turned them back on, Mark Nappe, Boeing vice president and commercial crew program manager, said at the briefing.
The helium leak detected after the previous launch attempt on May 6 was not a problem in this launch attempt. Controllers reported that the leak rate was acceptable and, in fact, had decreased.
Officials acknowledged the last-minute work was frustrating. “It’s natural to be a little disappointed,” said Steve Stich, NASA’s commercial crew program manager. “What happened, and what I saw in the control room and heard the loops in Houston, was that everybody was very professional and they were used to it.”
Any delay beyond June 6 could cause significant delays. Stich said in a pre-launch briefing on May 31 that ULA would need time to replace batteries in the rocket if it did not launch by June 6. Gary Wentz, vice president of government and commercial programs at ULA, said the battery replacement would take about 10 days.
NASA officials said earlier this year that they must complete certification of Starliner by November or December so that the first operational mission, Starliner-1, could launch in early 2025 as currently planned. At a prelaunch briefing on May 31, Stich declined to say whether that schedule would remain despite the delay in launching the CFT.
“That will be something we will work on after the flight,” he said of certification. “The path for Starliner-1 is obviously through the Crew Flight Test. That’s the most important thing for certification.”
Nappi said May 31 that 80% of the certification plan is already complete and will be completed by November, but the remaining work will depend on what happens during the CFT mission, including in-flight anomalies that need to be resolved.
“The longer it takes to fly the CFT, the less time we have to review that data,” he said. “Whenever we fly, it’s important to complete the certification review as quickly as possible.”
