SpaceX capsule explosion means it probably won’t fly astronauts until 2020

A leaky valve in the propulsion system of a SpaceX Crew Dragon astronaut capsule is probably what caused the spacecraft to explode during a test three months ago, a company official said Monday, and he acknowledged that the accident could delay the company’s first human flight until 2020.

No astronauts were in the capsule during April’s accident, and the explosion did not injure anyone.

“Overall, it’s something the components should not have done,” Hans Koenigsmann, SpaceX vice president of build and flight reliability, said Monday during a joint news conference with NASA. “But at the same time, we learned a very valuable lesson … that makes the Crew Dragon a safer vehicle.”

SpaceX plans to use its Crew Dragon capsule to transport NASA astronauts to the International Space Station and back to Earth. The Hawthorne company and Boeing Co. have been awarded a combined total of $6.8 billion in NASA contracts to build crew capsules for the missions.

Before the accident, SpaceX had planned to use the capsule to fly astronauts to the space station possibly as early as this month. Now, doing so by the end of the year looks “increasingly difficult,” Koenigsmann said.

The explosion occurred April 20, while SpaceX was conducting a series of engine tests on the capsule.

Two separate, five-second test firings of the capsule’s Draco thrusters — which help the spacecraft maneuver in space — were successful. The accident occurred about 100 milliseconds before the final test, which was supposed to involve firing the capsule’s SuperDraco escape-system thrusters, Koenigsmann told reporters in May.

He said Monday that the explosion occurred while the spacecraft’s propulsion systems were being pressurized in preparation for that final test.

A leaky valve in the propulsion system allowed a propellant — nitrogen tetroxide — to cross over into the helium tubes in the capsule’s pressurization system. Known as a check valve, it was made of titanium and designed to let material through in only one direction.

Then, when the system was pressurized, high-pressure helium rushed through the tubes, probably driving the liquid back through the valve with “significant force” and destroying it, Koenigsmann said. A reaction involving the titanium caused the valve to ignite, resulting in the explosion, SpaceX said.

Koenigsmann said the company’s accident investigation team — which includes officials from NASA, the Federal Aviation Administration and the National Transportation Safety Board — found burn marks within the valve, as well as data and video evidence supporting this scenario. SpaceX also performed tests of similar conditions at its facility in McGregor, Texas, which were able to re-create the explosion.

The company did not expect that the driving of nitrogen tetroxide into a titanium component would cause “such a violent reaction,” Koenigsmann said. SpaceX said in a statement that titanium has been used safely in many other spacecraft over the years.

To fix the problem, SpaceX has replaced the check valves on its other Crew Dragon capsules with “burst disks,” which seal completely until they are opened by high pressure, Koenigsmann said. He said that is the type of functionality used for the SuperDraco launch escape system, and he described the new component as “pretty reliable.”

“Complete separation of the systems” is the best solution in this case, he said. “The burst disk we have now is definitely the safer approach overall.… We didn’t really expect this to be a problem prior to that, but that’s what you learn when you test.”

SpaceX initially described the situation as an “anomaly,” but a leaked video of the test showed the capsule exploding. A photograph taken by a Florida Today journalist shortly after the April incident showed a plume of orange smoke rising above Cape Canaveral Air Force Station, where the test occurred — a sign, experts said at the time, that nitrogen tetroxide was probably involved. The capsule’s destruction was later confirmed in May by Koenigsmann.

The April accident “was, in a lot of ways, a gift for us because it was a test on the ground,” said Kathy Lueders, who is in charge of NASA’s commercial crew program. “Through this process ... we will continue to learn things that will help us to fly safer.”

The Crew Dragon capsule that was destroyed in the explosion had been used in March on a test flight to the space station, with no people aboard. The capsule was launched atop a SpaceX Falcon 9 rocket, then successfully docked autonomously with the space station and stayed there for about five days before returning to Earth.

SpaceX had planned to use the same capsule for an in-flight abort test originally scheduled for this summer, which would have tested its emergency escape system. But the company has other capsules in production that will be used for this and future tests.

Koenigsmann said Monday that the company had finished about 80% of its investigation and was in the process of checking the entire system for any other potential vulnerabilities. He and Lueders declined to give a new specific date for SpaceX’s first test flight with astronauts aboard.

Lueders noted that SpaceX still needs to work through other, previously scheduled tests of the capsule before flying a crew. “I hope it’s this year, but we’re going to fly when it’s the right time and when we know we’ll be flying our crew safely,” she said.

Boeing, which is building its own Starliner capsule to transport NASA astronauts, has also seen development problems. A part of its test capsule suffered what the company also described as an “anomaly” last year during a test fire of the spacecraft’s launch-abort engines.

In May, Boeing said it completed tests of the capsule’s in-space maneuvering thrusters, as well as its launch-abort engines.

Boeing is scheduled to launch its capsule on its first, uncrewed flight to the space station in August.