The Chicago-based company confirmed yesterday that its participation in the contest had come to an end. "We received some information as part of the letter we received from NASA this morning but until we get the debrief we can't say much," Boeing spokeswoman Kelly Kaplan told AFP.
By leaving the race, Boeing has left three companies behind to battle it out: SpaceX, Orbital ATK and Sierra Nevada Corp.
Once awarded, the Commercial Resupply Contracts (CRS2) will require the winner to haul supplies and experiments to the International Space Station for seven years from 2018 to 2024.
The first round of Nasa's commercial cargo contracts to supply the ISS was split between SpaceX and Orbital ATK, which are currently carrying out deliveries.
One of SpaceX's strong points in the new competition is that it's the only company offering US-made rockets, while Orbital ATK and Sierra Nevada both rely to some extent on rockets with Russian engines.
That said, both SpaceX and Orbital ATK have weaknesses in their track records – in June this year, SpacceX's Falcon 9 rocket exploded at take-off in Florida, while in October last year an Orbital Antares rocket was destroyed just after lift-off.
Boeing’s blow is the second piece of bad news it has received in under two weeks – its joint bid with Lockheed Martin for the US Air Force's $80bn programme to build the long-range strike bomber was rejected.
It was expected that Nasa would announced the winner of its CRS2 this year, but the space agency said on its site that it has delayed confirmation to 30 January.