Liftoff, targeted for 10:34 pm ET (0234 UTC May 7), was halted due to a valve problem on the upper stage of the United Launch Alliance Atlas rocket.



"The next launch opportunity will be no earlier than Friday, May 10," the company said in a statement.



"The scrub was recommended after launch control teams detected unusual behavior by the pressure regulation valve in the liquid oxygen tank of the Centaur upper stage of the ULA Atlas V launch vehicle," the company said.



The aerospace company said its engineers were analyzing the data to understand the problem and "determine any corrective actions."



"Boeing, NASA, and United Launch Alliance have decided to assign engineering teams to evaluate the data on Tuesday, May 7," the statement said.



The first manned mission of the CST-100 Starliner spacecraft aims to carry NAS astronauts Butch Wilmore and Indian-origin Sunita Williams to the space station.