WASHINGTON, May 24 (Reuters) - Boeing ( BA ) and NASA

quelled two technical issues on the company's Starliner

spacecraft, including a "design vulnerability" requiring a

temporary workaround, to get the capsule back on track for its

first mission carrying two astronauts to space, officials said

on Friday.

Starliner's debut crewed mission, a high-stakes test now

planned for June 1, was derailed earlier this month by a small

helium leak detected in its propulsion system hours before it

was due to lift off from Florida. Over two weeks of extra

scrutiny found that the leak poses no major risk to the

astronauts, officials said.

"This is really not a safety of flight issue for ourselves,

and we believe that we have a well-understood condition that we

can manage," Boeing's ( BA ) Starliner boss Mark Nappi told reporters

during a news conference.

Starliner's long-delayed first crewed flight, with NASA

astronauts Suni Williams and Butch Wilmore on board, is a final

test mission before NASA can certify the spacecraft for routine

astronaut trips to and from the International Space Station. It

would become the second U.S. crew capsule alongside SpaceX's

Crew Dragon, which started flying humans in 2020.

Boeing ( BA ) and NASA's probe of the helium leak led engineers to

uncover an additional issue in Starliner's propulsion system

that NASA's commercial crew chief Steve Stich called a "design

vulnerability."

Modeling showed that a cascading, but very unlikely, series

of issues during a mission could eliminate the capsule's backup

thrusters and render it unable to safely return to Earth. A

software fix offered a temporary workaround for the mission, but

Boeing ( BA ) and NASA will discuss whether a deeper redesign is needed

before future flights, officials said.

"It's backed by test data, it's backed by flight data, and

the guidance and navigation modeling have reinforced that this

technique will work," Nappi said, adding the astronauts had

tested the system after the fix.

That broader issue and ad hoc resolution prompted NASA to

call for an additional Flight Readiness Review, an extensive,

day-long meeting among agency officials, Boeing ( BA ) engineers and

independent analysts to justify Starliner is safe for flight.

That meeting is scheduled for Wednesday, three days before

Boeing's ( BA ) target launch time on June 1, 12:25 PM ET. If needed

Starliner also has opportunities to fly June 2, 5 and 6.

Boeing ( BA ), which initially attempted to launch Starliner May 6,

faces pressure to make one of those early June dates.

Anything later than June 6 could trigger weeks or

potentially months of more delays because some perishable items

would need to be replaced on Starliner and its Atlas 5 rocket,

built by the Boeing-Lockheed joint venture United Launch

Alliance (ULA).

That would begin to clash with other scheduled priorities

ULA has on its launch pad, such as Amazon's first launch of its

Kuiper satellites and ULA's second flight of its new Vulcan

rocket, a long-delayed demonstration that would allow it to

start launching Pentagon missions.

Boeing ( BA ) is a longtime NASA contractor that has built modules

for the decades-old International Space Station but has never

before flown humans into space, a feat that persistent struggles

in its Starliner program has made elusive.

Years behind schedule and with $1.5 billion in unplanned

development costs, a success with Starliner is badly needed as

Boeing ( BA ) reels from unrelenting crises in its aviation business.

Starliner in 2019 failed an attempt to reach the ISS,

returning to Earth roughly a week earlier than planned because

of dozens of software, technical and management issues that

reshaped Boeing's ( BA ) relationship with NASA.

The spacecraft succeeded in a re-do flight in 2022 to the

ISS.