Boeing has called off its first astronaut launch because of a balky rocket valve. The two NASA test pilots had just strapped into Boeing's Starliner capsule when the countdown was halted Monday night, two hours before the planned liftoff from Cape Canaveral, Florida. A United Launch Alliance spokesman says the problem involves an oxygen relief valve on the Atlas rocket's upper stage. There was no immediate word on when the next launch attempt might be for a flight to the International Space Station. Starliner's first test flight without a crew in 2019 failed to reach the space station and Boeing had to repeat the flight. Read moreBoeing calls off its first astronaut launch because of valve issue on rocket