Within minutes of its long-delayed launch on the spacecraft’s first test flight, the star-crossed Boeing Starliner was forced to land again Saturday when one of three redundant computers managing the countdown from the base of the launch pad experienced a problem, forcing a last-minute recall.
Engineers were initially told to prepare for another launch attempt at 12:03 a.m. Eastern Time on Sunday, assuming the problem would be resolved in time. But NASA later announced the team would skip Sunday’s opportunity to give engineers more time to assess the computer problem.
Starliner’s test flight includes rendezvous and docking with the International Space Station. Depending on the lab’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. EDT. NASA said the agency will provide an update on Sunday.
The Starliner crew, commander Barry “Butch” Wilmore and co-pilot Sunita Williams, derailed their Atlas 5 rocket about two hours after launch on May 6 because of a problem with a pressure relief valve and a helium leak in the capsule’s propulsion module.
Those problems were resolved and, after a few minor interruptions on Saturday, the countdown appeared to be moving smoothly toward the planned launch at 12:25 p.m. EDT. But 10 seconds after the countdown exited its planned pause at the T-minus 4-minute mark, the clocks suddenly stopped running.
Space station launches are timed for the moment when Earth’s rotation aligns the pad with the space station’s orbit, a necessity when trying to rendezvous with a target moving at about 5 miles per second. An unplanned halt in the countdown for such missions immediately triggers a minimum 24-hour launch delay.
Tory Bruno, CEO of United Launch Alliance, the maker of the Atlas 5 rocket, said Saturday that the problem was tied to one of three networked computer racks in a building at the base of the launch pad. Each rack contains multiple systems, including identical circuit boards that together work as a “ground launch sequencer,” managing the final steps in the countdown.
The GLS computers manage events such as the retraction of the umbilical cord and the firing of the explosive bolts that release the rocket from the pad for flight, and all three must be in absolute unison to begin the countdown.
During Saturday’s launch attempt, the countdown lasted until T-minus 4 minutes and then entered a planned four-hour pause. When the countdown resumed four minutes before blastoff, one of the three GLS circuit boards took longer than expected to sync up with the other two. This was enough to trigger an automatic pause at the T-minus 3 minute 50 second mark.
Engineers planned to begin troubleshooting after draining the liquid hydrogen and oxygen propellants from the Atlas 5 and accessing the computer room. The decision on how to proceed depended on isolating the problem, replacing and testing any suspect components.
The launch team, while disappointed, took the latest delay in stride.
“You know when you’re playing a game and you get a wrong decision, you might get a little annoyed or a little frustrated at first, but you quickly refocus on the next pitch and that’s what our teams do, they focus on the next pitch,” said Mark Nappi, Boeing’s Starliner project manager.
“As we went into launch scrub and launch turnaround, I looked into the control room and saw everyone with their heads down working on procedures to get ready for another attempt tomorrow.”
Bruno said: “The frustration lasts about three seconds. And then you get back to work and do your job. We’ll be back.”
Whenever it flies, this long-awaited flight will be the first piloted flight of the Atlas 5 and also a first for the Atlas rocket family since astronaut Gordon Cooper flew just a few miles away on the Mercury program’s final flight 61 years ago.
Likewise, this will be the first piloted flight of Starliner, Boeing’s answer to SpaceX’s Crew Dragon, an already operational, less expensive spacecraft that has carried 50 astronauts, cosmonauts and civilians to orbit on 13 flights since its initial pilot test flight in May 2020, 12 of them to the space station.
NASA funded the development of both spacecraft to ensure that if one company’s ship was grounded for some reason, the agency would still be able to send a crew to the outpost.
NASA had hoped to deliver the Starliner to orbit on May 6, years behind schedule because of budget shortfalls and a variety of technical problems that cost Boeing $1.4 billion to fix. But the launch was canceled when United Launch Alliance engineers discovered a problem with a pressure-relief valve on the rocket’s Centaur upper stage.
The Atlas 5 was rolled off the pad and back to ULA’s Vertical Integration Facility, where the Centaur valve was promptly replaced. But after the launch scrub, Boeing engineers noticed signs of a small helium leak in the Starliner’s propulsion system.
The leak was traced to a flange in the pipeline that delivers pressurized helium to power a specific reaction control system jet in Starliner’s service module. The leak was described as “very small,” but engineers needed to show it wouldn’t get too bad in flight and cause problems for other thrusters.
After extensive analysis and testing, mission managers concluded that the spacecraft could be launched safely, saying that even if the leak rate was 100 times higher than the rate seen so far, it would pose no threat to the crew or the mission. As it turned out, the leak rate on Saturday remained within acceptable limits.
