In late 2019, Boeing seemed to have a good chance of beating SpaceX and becoming the first private U.S. company to put astronauts into orbit.
In the four and a half years since then, a lot has gone wrong. Here’s a timeline of the setbacks that caused Boeing to fall so far behind SpaceX in offering American astronauts a ride to low Earth orbit.
December 2019: A ‘high-visibility close call’.
On December 20, 2019, Boeing seemed to be on its way back.
A Starliner capsule — the same spacecraft that will carry NASA astronauts Butch Wilmore and Suni Williams to the space station on Saturday — was on the launch pad atop an Atlas V rocket.
The test flight to the space station did not carry any astronauts and the mission was to assess the spacecraft’s navigation, propulsion and docking systems. If the flight were to pass this final technical hurdle, a voyage with astronauts on board could take place within months.
The Atlas V rocket launched flawlessly, releasing Starliner.
And then the mission immediately went wrong.
The spacecraft’s clock was set to the wrong time, causing Starliner to believe it was in the wrong location. The capsule fired its thrusters in an attempt to reach where it thought it should be. At the same time, a communications problem thwarted efforts by flight controllers at mission control to diagnose and resolve the problem.
The Starliner spacecraft consumed too much propellant and the planned docking with the space station was aborted.
While troubleshooting, Boeing engineers discovered another software glitch that could have fired the wrong thrusters during a pre-reentry maneuver. NASA labeled the incident a “high-visibility close call” that could have destroyed the spacecraft if the errors had not been corrected from the ground during the flight.
An investigation revealed multiple flaws in Boeing’s processes that should have caught the errors before launch. One million lines of software code were assessed during an extensive audit.
NASA officials admitted they may have placed too much trust in Boeing, which had decades of experience working with NASA.
Summer 2021: Corrosion on the launch pad.
NASA and the company decided that a second unmanned test was needed before a flight with astronauts on board. The spacecraft was rolled out to the launch pad in July, but a problem aboard the space station forced a delay until early August. Before a launch attempt on August 4, mission managers discovered corroded propellant valves on Starliner that would not open. The test flight was canceled and another long round of troubleshooting followed.
May 2022: Another launch, more problems.
The second uncrewed test was finally launched on May 19, 2022.
During a maneuver to put Starliner into a stable orbit, two thrusters failed, but the spacecraft was able to compensate. It then landed at the space station and successfully returned to Earth.
July 2023: Parachutes and tape.
Before the test flight with astronauts on board, which was then scheduled for July 2023, two more problems emerged. Protective tape wrapped around the wiring insulation was found to be flammable, and a key part of the parachute system was weaker than designed and could break if Starliner’s three parachutes failed to deploy properly.
About a mile of the tape was replaced and the parachute design was upgraded and strengthened, then retested.
May 2024: Still not ready to fly.
“We’ve taken the time to go through everything methodically because it’s a test flight and we want it to go well,” Steve Stich, program manager for NASA’s commercial crew program, said during a May 3 news conference.
Mark Nappi, Boeing program manager for Starliner, said: “We are ready to conduct the test flight. And I have never felt more prepared for any mission I have ever participated in.”
But Starliner still wasn’t quite ready.
The countdown on May 6 was going smoothly until a clunky valve on the Atlas V rocket’s second stage – unrelated to Starliner – started functioning and vibrated audibly at a rate of about 40 times per second.
The launch was aborted and the rocket had to be removed from the launch pad to replace the valve. That work was completed within a few days.
But a thornier problem emerged.
While the propellants were being drained from the Atlas V rocket’s tanks, 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.
“Just like you would have at home on any part of the sewer system, a tap or something like that,” Mr. Stich said during a telephone news conference on May 24. “There is a seal that holds that interface securely.”
Tests showed that there was no leakage in the seals leading to the other 27 engines of the reaction control system, and engineers were confident that the single leak was controllable. There are no plans to replace the seal, which would require Starliner to be pulled from the Atlas V rocket and lead to an even longer flight delay.
“We could address this particular leak if the leak rate increased even up to 100 times,” Mr. Stich said.
The helium leak prompted NASA and Boeing to take a broader look at the Starliner’s propulsion system, which revealed a “design vulnerability,” Mr. Stich said. If a series of unlikely failures were to occur, the spacecraft might not be able to return the astronauts safely to Earth.
If there were problems with the larger engines intended to be fired for a maneuver to drop the spacecraft from orbit, one of the backup plans was to use eight of the smaller thrusters. However, the analysis found that an additional failure could mean only four of the smaller thrusters would be available.
The engineers then developed another backup plan to deorbit Starliner using only the four thrusters. NASA and Boeing officials said that after weeks of studying the problem, they were confident they could address the problems that could arise from the leak.
And on Saturday, Mr. Wilmore and Mrs. Williams may finally fly Starliner.