The launch of a United Launch Alliance Atlas 5 rocket carrying Boeing’s Starliner capsule has been pushed back four more days, from Friday to next Tuesday, to give engineers time to make sure that a helium leak in the ship’s propulsion system on crew was cleared, officials said Tuesday.
Liftoff from Pad 41 of the Space Force Station at Cape Canaveral is now targeted for May 21 at 4:43 PM EDT, with docking at the International Space Station established the following afternoon. The flight is expected to end with a landing in White Sands, New Mexico, around May 30.
Mission Commander Barry “Butch” Wilmore and co-pilot Sunita Williams had hoped to take off on the first manned flight of the Starliner last Monday. They were in the process of connecting when the countdown was aborted due to a problem with an oxygen pressure relief valve in the Centaur rocket’s upper stage.
Two days later, Atlas 5 was removed from the launch pad and moved back to the nearby ULA Vertical Integration Facility, where the suspect valve was replaced. The tests confirmed that the rocket was suitable for another launch attempt.
An unrelated helium leak in the Starliner’s propellant pressurization system was noted during last week’s countdown, but remained within safe limits for flight. After Atlas 5 and Starliner were returned to VIF for oxygen valve replacement, managers decided to take a closer look at the helium problem.
The leak was discovered in the plumbing forming a helium manifold inside one of the four “doghouse” modules located around the outside of the Starliner’s drum-shaped service module. Each doghouse features four Orbital Maneuvering and Attitude Control thrusters—OMACs—and four small reaction control system maneuvering nozzles.
Pressurized helium gas is used to push propellants to the rocket engines in each doghouse, as well as four powerful engines at the base of the spacecraft, which will be used during in-flight downtime to propel the capsule away from a malfunctioning booster. The leak was traced to a flange on one RCS thruster.
The bolts have been re-tightened and engineers believe the system is ready for flight. But managers decided to pressurize the helium lines throughout the spacecraft so engineers could monitor them over time to make sure the lines were actually leak-free or within acceptable limits.
“As part of the testing, Boeing will bring the propulsion system to flight pressurization, just as it does before launch, and then allow the helium system to vent naturally to confirm existing data and improve flight justification,” the company said in a statement.
“Mission teams have also completed a thorough review of data from the May 6 launch attempt and are not tracking any other issues.”
Wilmore and Williams, both veteran Navy test pilots and astronauts with four flights to the station between them, flew back to Johnson Space Center in Houston last Friday for additional simulator training. They are expected to fly back to Florida later this week to prepare for another launch attempt.
The Starliner is one of two commercial crewed shuttles ordered by NASA since the shuttle was retired in 2011. SpaceX won a $2.6 billion contract to develop the company’s Crew Dragon spacecraft, and Boeing received $4.2 billion for the development of the Starliner.
The goal was to stimulate the development of independent, commercially operated spacecraft capable of transporting astronauts to and from the International Space Station. Ordering spacecraft from multiple suppliers will allow NASA to continue sending crews to the space station even if a problem shuts down one company’s shuttle.
SpaceX launched its first two-person crew in 2020. Since then, the company has launched eight NASA-sponsored crew rotation flights to the station, three commercial research missions to the lab, and a privately funded two-man, two-woman trip to low Earth orbit. A total of 50 people have flown into space aboard Crew Dragons.
Wilmore and Williams will be the first astronauts to fly aboard the Starliner after a series of technical problems that included major software problems during an initial unmanned test flight in December 2019 and corroded propulsion system valves that delayed the second test unmanned mission for May 2022
The second test flight, paid for by Boeing, was successful, but engineers faced further questions about the parachute harness connectors and the protective tape wrapped around the cables, which posed a fire risk if shorted. Work to fix these issues and others delayed the first pilot launch until this month.
The Atlas 5 oxygen valve problem was the responsibility of United Launch Alliance. The helium leak responsible for the latest delay is on the Starliner list, but was thought to be a relatively minor problem. However, managers leave no stone unturned to ensure flight safety.
