The CST-100 Starliner, with veteran astronauts Barry "Butch" Wilmore and Sunita "Suni" Williams aboard, launched to space on Wednesday from Florida for a much-delayed test flight aimed at demonstrating the spacecraft's flightworthiness and sharpening Boeing's competition with Elon Musk's SpaceX.
Launched atop an Atlas V rocket furnished and flown by the Boeing-Lockheed Martin (LMT.N) joint venture United Launch Alliance (ULA), the reusable gumdrop-shaped capsule has been in space for its one-day journey to the ISS, where it is scheduled to dock autonomously at around 12:15 p.m. ET (1615 GMT).
During the flight, helium leaks were detected on Starliner's propulsion system, rendering unusable some of its 28 thrusters used to maneuver in space. The astronauts remain safe and the spacecraft has backup thrusters to compensate for the loss, according to NASA and Boeing.
Starliner uses helium to add pressure to the propellant for its thrusters. NASA and Boeing did not specify the location of the downed thrusters or how quickly the helium was leaking.
NASA mission managers on Thursday morning gave Boeing the green light to proceed with Starliner's docking to the ISS as the agency's space station office monitors the leak rate, NASA said.
Once securely coupled to the space laboratory, Wilmore and Williams would conduct a series of standard procedures, such as checking for airlock leaks and pressurizing the passage between the capsule and ISS, before opening the entry hatches.
They would be welcomed aboard by the outpost's current seven resident crew members - four fellow U.S. astronauts and three Russian cosmonauts.
Plans call for Wilmore and Williams to remain aboard the station for about eight days, then depart on a return flight that will take Starliner on a fiery re-entry back through Earths' atmosphere and end with a parachute and airbag-assisted landing in the U.S. Desert Southwest, a first for a crewed NASA mission.
The Starliner launch on Wednesday followed years of technical problems, various delays and a first successful 2022 test mission to the orbital laboratory without astronauts aboard.
Last-minute issues had nixed the Starliner's first two crewed launch attempts, including a helium leak found on the capsule's propulsion system that officials later determined was not serious enough to warrant a mechanical fix.
NASA and Boeing officials at the time pointed to a faulty seal on one thruster component that was failing to keep the helium inside.
Boeing built Starliner under contract with NASA to compete with SpaceX's Crew Dragon capsule, which since 2020 has been the U.S. space agency's only vehicle for sending ISS crew members to orbit from U.S. soil. The current mission marks Starliner's first test flight with astronauts aboard, a requirement before NASA can certify the capsule for routine astronaut missions.
Selected as crew for the pivotal flight were two NASA veterans who have previously logged 500 days in space between them - Wilmore, 61, a retired U.S. Navy captain and fighter pilot, and Williams, 58, a former Navy helicopter test pilot with experience flying more than 30 different aircraft.
Getting Starliner to this point has been a fraught process for Boeing under its $4.2 billion fixed-priced contract with NASA, which wants the redundancy of two different U.S. rides to the ISS. The Starliner is several years behind schedule and more than $1.5 billion over budget. Meanwhile, Boeing's commercial airplane manufacturing operations have been rocked by a series of crises involving its 737 MAX jetliners.
