Seemingly crossed stars Boeing Starliner — within minutes of its long-delayed launch on the spacecraft’s first manned test flight — was grounded again Saturday when one of the three redundant computers managing the countdown from the base of the launch pad encountered a problem and initiated a last-minute cleanup.
Engineers were initially told to prepare for another launch attempt at 12:03 a.m. EDT Sunday, assuming the problem could be resolved in time. However, NASA later announced that the team would miss Sunday’s launch and try to give engineers more time to assess the computer problem.
The Starliner test flight includes rendezvous and docking with the International Space Station. Based on the station’s orbit and Starliner’s ability to catch up, the next two launch opportunities after Sunday are Wednesday at 10:52 a.m. EDT and Thursday at 10:29 a.m. NASA said the agency will provide an update on Sunday.
The Starliner crew, Commander Barry “Butch” Wilmore and co-pilot Sunita Williams, arrived within about two hours of takeoff on May 6, but were derailed due to difficulties. with pressure relief valve in their Atlas 5 aa rocket helium leak in the capsule propulsion module.
Those issues were resolved, and after a few minor hiccups on Saturday, the countdown appeared to be running smoothly toward the scheduled 12:25 p.m. EDT start. But 10 seconds after the countdown came out of its scheduled stop at the T-minus 4-minute mark, the clock suddenly stopped ticking.
Launches to the International Space Station are timed for when the Earth’s rotation brings the pad into alignment with the space station’s orbit, a requirement when trying to rendezvous with a target moving at nearly 5 miles per second. An unscheduled suspension of the countdown for such missions will immediately trigger a minimum 24-hour launch delay.
NASA
Tory Bruno, CEO of United Launch Alliance, builder of the Atlas 5 rocket, said the problem Saturday involved one of three interconnected computer racks in a building near the base of the launch pad. Each rack contains several systems, including identical circuit boards, that work together as a “ground start sequencer” that controls the final steps in the countdown.
The GLS computers control events such as the retracting of the umbilicals and the firing of the explosive bolts that release the rocket from the launch pad, and all three must be in perfect alignment for the countdown to continue.
During Saturday’s launch attempt, the countdown dropped to T-minus 4 minutes before entering a scheduled four-hour suspension. As the countdown continued to four minutes before launch, one of the three GLS circuit boards took longer than expected to synchronize with the other two. That was enough to trigger an automatic pause at T-minus 3 minutes and 50 seconds.
NASA
Engineers planned to begin troubleshooting after they had jettisoned Atlas 5’s liquid hydrogen and oxygen propellants and gained access to the computer room. Deciding how to proceed depended on isolating the problem and replacing and testing any suspect components.
The launch team, while disappointed, took the latest delay in stride.
“You know when you make a play and you get a bad call, at first you’re a little irritated or a little frustrated, but you immediately focus on the next pitch and that’s what our teams do. We’re focused on the next pitch,” said Mark Nappi, Boeing’s Starliner project manager.
“As we entered the launch cleanup and launch turnaround, I looked into the control room and everyone had their heads down and were working on procedures to prepare for the next attempt tomorrow.
Bruno said, “The disappointment lasts about three seconds. And then you just get busy right away and do your job. We’ll be back.”
Whenever it takes off, the long-awaited flight will be the first manned launch of Atlas 5 and the first for the Atlas family of rockets since astronaut Gordon Cooper launched just a few miles away on the last flight of the Mercury program 61 years ago. .
It will also be the first manned flight of the Starliner, Boeing’s answer to the SpaceX Crew Dragon, an already operational, lower-cost spacecraft that has carried 50 astronauts, cosmonauts and civilians into orbit in 13 flights, including 12 to the space station, since the first manned test flight in May 2020.
NASA funded the development of both spacecraft to ensure that the agency would be able to launch crews to the base even if one company’s shuttle was grounded for whatever reason.
NASA had for years delayed the plan due to budget shortfalls and a series of technical problems that cost Boeing about $1.4 billion to fix, and had hoped to get the Starliner into orbit on May 6. But the launch was thwarted when United Launch Alliance engineers discovered problems with a pressure relief valve in the upper stage of the Centaur rocket.
Atlas 5 was pulled off the pad and back to ULA’s Vertical Integration Facility, where the Centaur valve was quickly replaced. But following the launch scrub, Boeing engineers saw signs of a small helium leak in the Starliner’s propulsion system.
The leak was traced to a flange in a pipe that supplied pressurized helium to power one specific reaction control system nozzle in the Starliner’s service module. The leak was characterized as “very small”, but engineers needed to show that it would not drastically deteriorate in flight and cause problems for other jets.
After extensive analysis and testing, mission managers concluded that the spacecraft could be safely launched as is, with the understanding that even if the escape velocity were hundreds of times worse than previously observed, it would not pose a risk to the crew or the mission. As it turned out, the leakage rate remained within acceptable limits on Saturday.