(Reuters) -Boeing's new Starliner capsule and an inaugural two-member NASA crew safely docked with the International Space Station on Thursday, meeting a key test in proving the vessel's flight-worthiness and sharpening Boeing's competition with Elon Musk's SpaceX.

The rendezvous was achieved despite an earlier loss of several guidance-control jet thrusters, some of them due to a helium propulsion leak, which NASA and Boeing said should not compromise the mission.

The CST-100 Starliner, with veteran astronauts Barry "Butch" Wilmore and Sunita "Suni" Williams aboard, arrived at the orbiting platform after a flight of nearly 27 hours following its launch from Cape Canaveral Space Force Station in Florida.

The reusable, gumdrop-shaped capsule, dubbed "Calypso" by its crew, was lofted into space on Wednesday atop an Atlas V rocket furnished and flown by Boeing-Lockheed Martin's United Launch Alliance joint venture.

It autonomously docked with the ISS while both were orbiting some 250 miles (400 km) over the southern Indian Ocean at 1:34 p.m. EDT (1734 GMT), as the two vehicles soared around the globe in tandem at about 17,500 miles (28,160 km) per hour.

The spacecraft's final approach to the ISS and docking, following a brief interval when Wilmore manually controlled the capsule, was shown on a NASA webcast.

"Nice to be attached to the big city in the sky," Wilmore radioed to mission control in Houston shortly after docking.

Once securely coupled to the space laboratory with a series of 12 hooks, Wilmore and Williams must conduct a series of standard procedures, such as checking for airlock leaks and pressurizing the passage between the capsule and the ISS, before opening the entry hatches.

That process was expected to take about two hours.

They were to 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 reentry back through Earth's atmosphere and end with a parachute and airbag-assisted landing in the U.S. Desert Southwest, a first for a crewed NASA mission.

On its voyage to the ISS, helium leaks were detected on Starliner's propulsion system, knocking out some of the 28 thrusters used by the capsule to make precision maneuvers in space. However, the spacecraft still had enough functioning thrusters to compensate for the loss, according to NASA and Boeing. An additional thruster was disabled by mission control just before final approach.

YEARS OF TECHNICAL PROBLEMS

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 glitches 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 American 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 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.