The spacecraft and the United Launch Alliance Atlas V that carried it into space were operating normally during what has been described as a perfect launch. But upon separating from the booster rocket and continuing on its own independent flight, the CST-100 failed to achieve the necessary altitude to rendezvous with the ISS. While the craft is still fully functional, it simply doesn’t have enough propellant onboard to correct the situation.
Boeing currently believes the failure lies with the spacecraft’s Mission Event Timer (MET), an internal clock that starts running as soon as the spacecraft leaves the launch pad and is used to orchestrate automated systems during the mission. For reasons that are not yet known, the MET either failed or was not properly synchronized, which led to the engines not firing according on schedule. To make matters worse, the CST-100’s Reaction Control System (RCS) depleted the vehicle’s propellant reserves by attempting to make maneuvers that were unnecessary at the time.
Because of this, there’s some debate as to how this situation will play out in terms of the CST-100’s certification for human flight. While issues with the autonomous systems obviously need to be addressed, astronauts are trained to handle precisely these sort of computer glitches. For better or for worse, there’s a long history of human crews having to take over when their vehicle’s systems have gone haywire.