Humid Florida air may have caused valves to stick in Boeing's Starliner space capsule during preparation for a test launch Aug. 3, causing further delay in NASA's astronaut launch program, the company and NASA announced Tuesday.

The capsule, already four years behind schedule at a development cost of $4.6 billion, may not be launched again until early 2022 as the valve investigation continues, NASA officials said in a virtual press conference.

At stake is the competitive nature of NASA's crew launch program that takes astronauts to the International Space Station, as Boeing has a contract to provide an alternative to SpaceX's Crew Dragon capsule.

The Dragon has carried three astronaut crews to the orbiting laboratory, as well as an all-private crew on a three-day orbital journey. Two astronauts selected to fly in the Boeing capsule have been transferred to fly on SpaceX Crew-5 as early as fall 2022.

Despite Boeing's repeated delays, NASA officials say they still have confidence that the aerospace firm will deliver, said Steve Stich, the space agency's manager for the commercial crew program.

"We have every confidence that Boeing will be flying crew soon," Stich said, adding that many Starliner systems performed well during a 2019 test flight.

That flight, however, revealed that Boeing software failed to pick up the mission timeline from the Atlas V rocket that launched it, causing the Starliner capsule to miss a rendezvous with the space station.

NASA found a similar glitch could have destroyed the capsule as it returned to Earth.

Failure of the 2019 test flight prevented NASA from certifying the capsule for astronaut launches.

However, "the guidance and navigation systems, propulsion systems, the thrusters on the service module, life support, avionics -- all performed really well" during that test, Stich said.

Starliner is designed to fly astronauts to the space station much like SpaceX's Crew Dragon spacecraft. NASA intended to have dual domestic providers for the astronaut missions to promote competitive pricing and to ensure that a problem with one company wouldn't create a gap in U.S. launches.

After more than a year of fixes following the 2019 failure, Boeing mounted the capsule on a rocket again in August, but the stuck valves forced launch cancellation.

A substance in Starliner's system that helps initiate a chemical reaction -- known as an oxidizer -- interacted with humidity to corrode at least 13 of 24 valves, said Michelle Parker, Boeing chief engineer for space and launch systems.

"It was a humid time of year, in August," Parker said. "We had looked at the humidity, and we've physically seen some evidence of condensation within the service module."

Tests after the Aug. 3 scrub managed to free nine of those stuck valves using electric pulses or heat, Parker said. But the company still isn't certain of the root cause, and has sent two valves to NASA facilities for further tests.

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