Dec 22 (Reuters) - The Boeing Co Starliner spacecraft that failed in its mission to reach the International Space Station was due to barrel down to the Earth's surface early on Sunday with the daunting task of landing safely.
Boeing and NASA officials said they still do not understand why software caused the unmanned craft to miss the orbit required to rendezvous with the space station following its successful launch on Friday.
All efforts were now focused on ensuring the Starliner touched down in White Sands, New Mexico, without any problems.
"Entry, descent and landing is not for the faint of heart," Jim Chilton, senior vice president of Boeing's space division, said in a Saturday conference call with reporters. "Make no mistake, we still have something to prove here on entry."
In one of Boeing's most complex and crucial safety demonstrations required by NASA to eventually fly humans, the capsule will fire a suite of thrusters and later deploy three parachutes to slow down its violent descent from 25 times the speed of sound entering the atmosphere to land harmlessly on the white sands of New Mexico.
Boeing said the Starliner's first window to land would be at 5:57 a.m. Mountain time (7:57 a.m. ET; 1257 GMT).
The CST-100 Starliner astronaut capsule was successfully launched from Florida on Friday, but an automated timer error prevented the spacecraft from attaining the correct orbit for it to meet and dock with the space station.
NASA and Boeing officials said during the Saturday conference call that they were surprised extensive testing before the flight did not turn up any issues.
The Starliner's debut launch to orbit was a milestone test for Boeing. The company is vying with SpaceX, the privately held rocket company of billionaire high-tech entrepreneur Elon Musk, to revive NASA's human spaceflight capabilities. SpaceX carried out a successful unmanned flight of its Crew Dragon capsule to the space station in March.
The Starliner setback came as Boeing sought an engineering and public relations victory in a year punctuated by a corporate crisis over the grounding of its 737 MAX jetliner following two fatal crashes of the aircraft. The company's shares dropped 1.6% on Friday.
The implications for any further design and testing requirements before Starliner is approved for its first crewed mission also remained unclear. The prospect that Boeing might need to repeat an unmanned orbital test flight could substantially delay NASA's timeline and drive up costs.
If successful, Sunday's landing will mark the first time a U.S. orbital space capsule designed for humans landed on land. All past U.S. capsules, including SpaceX's Crew Dragon, splashed down in the ocean. Russia's Soyuz capsules and China's past crew capsules made land landings.
The now-retired Space Shuttle glided in like a plane.
Reporting by Joey Roulette in Orlando, Florida, writing by Brad Brooks; Editing by Scott Malone and Sonya Hepinstall