June 6 (Reuters) - Boeing's ( BA ) new Starliner capsule

and its inaugural two-member NASA crew were set to approach the

International Space Station for docking on Thursday after helium

leaks detected on the spacecraft showed fresh problems in the

crucial test mission.

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 ( BA ) competition with Elon Musk's SpaceX.

Launched atop an Atlas V rocket furnished and flown by the

Boeing-Lockheed Martin 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 ( BA ).

Starliner uses helium to add pressure to the propellant for

its thrusters. NASA and Boeing ( BA ) did not specify the location of

the downed thrusters or how quickly the helium was leaking.

NASA mission managers on Thursday morning gave Boeing ( BA ) 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 ( BA ) officials at the time pointed to a faulty

seal on one thruster component that was failing to keep the

helium inside.

Boeing ( BA ) 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 ( BA ) 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 ( BA ) commercial

airplane manufacturing operations have been rocked by a series

of crises involving its 737 MAX jetliners.