Only a test dummy is aboard. If the capsule reaches the International Space Station on Friday and everything else goes well, two or three NASA test pilots could strap in by the end of this year or early next for the company's first crew flight.

Thursday's launch is Boeing's third shot at the high-stakes flight demo.

At least this time, Starliner made it to the proper orbit, quickly giving chase to the space station. But the all-important rendezvous and docking looms.

Starliner's first test flight in 2019 was stricken by software errors so severe that the capsule ended up in the wrong orbit and had to skip the space station.

The spacecraft came close to being destroyed as ground controllers hastily cut short the mission.

Boeing returned a different capsule to the launch pad in the middle of last year, but corroded valves halted the countdown, resulting in another round of repairs.

The drawn-out test flight program has cost Boeing about $US600 million.

Boeing is seeking redemption as it attempts to catch up with SpaceX, NASA's other contracted taxi service. Elon Musk's company has been flying astronauts to and from the space station for two years and delivering cargo for a full decade.

Eager to reduce its high-priced dependency on Russia for crew transport, NASA hired Boeing and SpaceX to launch astronauts to the space station after the shuttle program ended in 2011.

Different in looks but similar in function to SpaceX's Dragon capsule, Boeing's fully automated capsule will attempt to dock at the space station on its own.

Station astronauts will steer the capsule by remote control, if necessary.

Starliner will spend close to a week at the space station before aiming for a touchdown in the New Mexico desert.

Australian Associated Press