In late 2019, Boeing appeared to have a good chance at beating SpaceX to become the first private U.S. company to take astronauts to orbit.
In the four and a half years since, a lot has gone wrong. Here’s a timeline of the setbacks that caused Boeing to fall so far behind SpaceX in providing American astronauts a ride to low Earth orbit.
December 2019: A ‘high-visibility close call.’
On Dec. 20, 2019, Boeing looked to be in the homestretch.
A Starliner capsule — the same spacecraft that is to take the NASA astronauts Butch Wilmore and Suni Williams to the space station on Saturday — was on the launchpad atop an Atlas V rocket.
The test flight to the space station had no astronauts on board, and its mission was to assess the spacecraft’s navigation, propulsion and docking systems. If the flight were to pass this last technical hurdle, a trip with astronauts aboard could take place within months.
The Atlas V rocket launched flawlessly, releasing Starliner.
And then the mission immediately went awry.
The spacecraft’s clock was set to the wrong time, making Starliner think it was in the wrong location. The capsule fired its thrusters to try to get to where it thought it should be. At the same time, a communications glitch thwarted efforts by flight controllers at mission control to diagnose and fix the problem.
The Starliner spacecraft used up too much propellant, and the planned docking at the space station was called off.
During the troubleshooting, Boeing engineers discovered another software error that would have fired the wrong thrusters during a maneuver leading up to re-entry. NASA labeled the incident a “high-visibility close call” that could have destroyed the spacecraft if the errors had not been patched from the ground during the flight.
An investigation revealed multiple failures in Boeing’s processes that should have caught the mistakes before the launch. An exhaustive audit reviewed one million lines of software code.
NASA officials admitted that maybe they had placed too much trust in Boeing, which had decades of experience working with NASA.
Summer 2021: Corrosion on the launchpad.
NASA and the company decided that a second uncrewed test was needed before a flight with astronauts aboard. The spacecraft was rolled out onto the launchpad in July, but a problem aboard the space station prompted a delay to early August. Then ahead of an Aug. 4 launch attempt, mission managers discovered corroded propellant valves on Starliner that would not open. The test flight was called off and another lengthy round of troubleshooting followed.
May 2022: Another launch, more problems.
The second uncrewed test finally launched on May 19, 2022.
During a maneuver to put Starliner in a stable orbit, two thrusters failed, but the spacecraft was able to compensate. It proceeded to dock at the space station and returned to Earth successfully.
July 2023: Parachutes and tape.
Before the test flight with astronauts aboard, then scheduled for July 2023, two more issues emerged. Protective tape that was wrapped around wiring insulation turned out to be flammable, and a key component in the parachute system was weaker than designed and could break if Starliner’s three parachutes did not deploy properly.
About a mile of the tape was replaced, and the parachute design was upgraded and strengthened, and then retested.
May 2024: Still not ready to fly.
“We’ve been taking our time to go through everything methodically because it is a test flight, and we want it to go well,” Steve Stich, program manager for NASA’s commercial crew program, said during a news conference on May 3.
Mark Nappi, the program manager at Boeing for Starliner, said: “We are ready to perform the test flight. And I’ve never felt readier on any mission that I’ve ever participated in.”
But Starliner was still not quite ready.
The countdown on May 6 was proceeding smoothly until a balky valve on the second stage of the Atlas V rocket — unrelated to Starliner — started acting up, vibrating audibly at about 40 times a second.
The launch was called off, and the rocket needed to be taken off the launchpad for the valve to be replaced. That work was completed within a few days.
But a thornier issue emerged.
As the propellants were drained from the tanks of the Atlas V rocket, engineers discovered a small helium leak in the Starliner’s propulsion system.
Helium, an inert gas, is used to push propellants to the thrusters, and if too much helium is lost, the thrusters may not work properly.
The leak was traced to a seal on a helium line leading to one of 28 small thrusters known as reaction control system engines.
“Much like you would have on any piece of your plumbing at home, a faucet or anything like that,” Mr. Stich said during a telephone news conference on May 24. “There’s a seal that keeps that interface tight.”
Tests showed no leaks in the seals leading to the other 27 reaction control system engines, and engineers were confident that the single leak was manageable. There are no plans to replace the seal, which would require pulling Starliner off the Atlas V rocket and would lead to an even lengthier delay for the flight.
“We could handle this particular leak if that leak rate were to grow even up to 100 times,” Mr. Stich said.
The helium leak led NASA and Boeing to take a wider look at the Starliner’s propulsion system, which revealed a “design vulnerability,” Mr. Stich said. If a series of unlikely failures occurred, the spacecraft might not be able to bring the astronauts safely back to Earth.
If there were problems with the larger engines intended to be fired for a maneuver to drop the spacecraft out of orbit, one of the backup plans was to use eight of the smaller thrusters. However, the analysis showed that an additional failure might mean there would be only four of the smaller thrusters available.
The engineers then developed another backup plan to bring Starliner out of orbit with only the four thrusters. NASA and Boeing officials said that after weeks of studying the problem, they were confident they could manage problems that might arise from the leak.
And on Saturday, finally, maybe, Mr. Wilmore and Ms. Williams will fly on Starliner.