WASHINGTON, June 5 (Reuters) - Boeing's ( BA ) new

Starliner astronaut capsule was launched from Florida on

Wednesday in a much-delayed first test flight carrying a crew, a

milestone in the aerospace giant's ambitions to step up its

competition with Elon Musk's SpaceX.

The CST-100 Starliner, with two astronauts aboard, lifted

off from the Cape Canaveral Space Force Station in Florida,

strapped to an Atlas V rocket furnished and flown by the

Boeing-Lockheed Martin joint venture United Launch

Alliance (ULA).

The gumdrop-shaped capsule and its crew were headed for a

rendezvous with the International Space Station (ISS), two years

after the Starliner completed its first test voyage to the

orbital laboratory without astronauts aboard. Docking maneuvers

with crew will pose another test for Starliner, followed roughly

a week later by the test of returning to Earth.

Boeing ( BA ) intends for Starliner to compete with SpaceX's Crew

Dragon capsule, which since 2020 has been NASA's only vehicle

for sending ISS crew members to orbit from U.S. soil.

Last-minute issues had nixed the Starliner's first two

crewed launch attempts. A May 6 countdown was halted two hours

before liftoff over three issues that required weeks of extra

scrutiny. Another try last Saturday was halted less than four

minutes before liftoff because of a glitch with a launchpad

computer.

On Wednesday, the Atlas V's engines thundered to life in

flaming clouds of exhaust and coolant-water vapor as the

spacecraft roared off its launch pad into the sky from Florida's

Atlantic Coast.

The Atlas V upper stage separated from the rocket's lower

section about four minutes into flight, followed by Starliner's

separation from the second stage. Now on its own in space,

Starliner will ascend deeper into space and fire its onboard

thrusters to plug itself into orbit and kick off its 24-hour

catch-up with the ISS.

The inaugural crew for the seven-seat Starliner includes two

veteran NASA astronauts: Barry "Butch" Wilmore, 61, a retired

U.S. Navy captain and fighter pilot, and Sunita "Suni" Williams,

58, a former Navy helicopter test pilot with experience flying

more than 30 different aircraft.

They have spent a combined 500 days in space over the course

of two ISS missions each. Wilmore is the designated commander

for the flight, with Williams in the pilot seat. They are due to

spend about a week at the ISS before returning to Earth.

BOEING AMBITIONS

Boeing ( BA ), with its commercial airplane operations rocked by a

series of crises involving its 737 MAX jetliners, needs a win in

space for its Starliner venture, already several years behind

schedule and more than $1.5 billion over budget.

Starliner two years ago completed its first test voyage to

ISS and back without astronauts aboard.

The longtime NASA contractor has built modules for the

decades-old ISS and rockets designed to loft astronauts toward

the moon. But Boeing ( BA ) never before built its own operational

spacecraft, a feat complicated by years of software issues,

technical glitches and management shakeups on the Starliner

program.

Meanwhile, SpaceX's Crew Dragon has become a dependable taxi

to orbit for NASA. That capsule and Starliner are among the

first in a new generation of privately built spacecraft - seeded

with NASA funding - designed to fly astronauts to low-Earth

orbit and the moon under the U.S. space agency's Artemis

program.

Starliner would compete head-to-head with SpaceX's Crew

Dragon capsule, which since 2020 has been NASA's only vehicle

for sending ISS crew members to orbit from U.S. soil.

If all goes as planned, the capsule will arrive at the ISS

on Thursday and dock with the orbiting research outpost some 250

miles (400 km) above Earth.

Although Starliner is designed to fly autonomously, the crew

can assume control of the spacecraft if necessary. The test

flight calls for Wilmore and Williams to practice maneuvering

the vehicle manually en route to the space station, where it

will remain docked for at least eight days before returning to

Earth.

Wilmore and Williams are due to join ISS's current seven

resident crew members before riding the capsule back to Earth

for a parachute and airbag-assisted landing in the U.S. Desert

Southwest - a first for a crewed NASA mission.

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 having two different U.S.

rides to the ISS, an outpost expected to retire around 2030.

Meanwhile, SpaceX's fourth test launch of its Starship

rocket system, another chapter in its quest to build a reusable

satellite launcher and moon lander, is due for liftoff on

Thursday from Texas.