(Updates throughout with comments from news conference)
CAPE CANAVERAL, Fla., Dec 20 (Reuters) - A timer error prevented Boeing Co's new astronaut capsule from reaching the desired orbit as it embarked on an unmanned debut journey to the International Space Station on Friday, U.S. space agency NASA said.
The CST-100 Starliner astronaut capsule successfully launched earlier from Cape Canaveral in Florida, but then failed to reach the orbit that would have put it on track to meet up with the space station.
The mission was a milestone test for the U.S. aerospace firm, which is vying with SpaceX to revive NASA's human spaceflight capabilities.
The plan was now for the capsule to head back to Earth, landing at White Sands, New Mexico on Sunday, Boeing's space chief executive Jim Chilton told a news conference.
This is the landing site that would have been used if the capsule had completed its planned week-long stay at the space station.
That was the absolutely the right decision for this mission, NASA Administrator Jim Bridenstine told the news conference.
He said the timer error meant that the capsule burned fuel too soon, preventing it from reaching the desired orbit.
We did obviously have some challenges today. When the spacecraft separated from the launch vehicle we did not get the orbital insertion burn that we were hoping for, Bridenstine said.
He said that had astronauts been on board, they would have been safe.
"The challenge here has to do with automation, he said of the unmanned spacecraft, adding that if astronauts had been on board they would have been able to override the automated system that caused the error.
The spacecraft, a cone-shaped pod with seven astronaut seats, blasted off from Cape Canaveral at 6:36 a.m. (1136 GMT) atop an Atlas V rocket from Boeing-Lockheed Martin Corp's United Launch Alliance.
Minutes after liftoff, Starliner detached from the main rocket booster, aiming for a rendezvous some 254 miles (409 km) into space on Saturday morning with the space station.
Both Boeing and NASA said that while the capsule had not reached the intended orbit it was in a stable position.
Nicole Mann, one of three astronauts slated to fly on Boeings first crewed flight test, said We are looking forward to flying on Starliner. We don't have any safety concerns.
NASA astronaut Mike Fincke added, Had we been on board, we could have given the flight control team more options on what to do in this situation.
The test is one of the most daunting milestones required by NASA's Commercial Crew Program to certify the capsule for eventual human spaceflight - a long-delayed goal set back years by development hurdles from both Boeing and SpaceX.
Despite the delays, and a blistering November government watchdog report that found Boeing received an "unnecessary" contract boost from NASA, a successful mission would hand Boeing an engineering and public relations win in a year punctuated by a corporate crisis over a ban on its 737 MAX jetliner following fatal crashes.
Boeing was awarded $4.2 billion and Elon Musk's SpaceX $2.5 billion by the U.S. space agency in 2014 to develop separate capsule systems capable of ferrying astronauts to the space station from American soil for the first time since the U.S. Space Shuttle was retired from service in 2011.
The program, primarily meant to end America's reliance on Russia's space program for rides to the space station, had initially expected its first crewed flights on Starliner and SpaceX's Crew Dragon capsule in late 2017. A slew of design and safety concerns for both vehicles have led to schedule delays.
The current target date for the first crewed flight is planned for mid-2020 for Boeing and SpaceX.
Occupying one of Starliner's astronaut seats on Friday was a mannequin named Rosie, outfitted with sensors to measure the pressure a real astronaut would endure on ascent to the space station and during hypersonic re-entry back through Earth's atmosphere.
If the mission went to plan, the intention was for Starliner to stay at the space station for a week before undocking and beginning its return to Earth early on Dec. 28, deploying three parachutes to slow its descent to the desert surface of White Sands, New Mexico.
SpaceX's Crew Dragon capsule carried out its unmanned test flight to the space station in March. (Reporting by Joey Roulette and Gabriella Borter Editing by Frances Kerry)