Launch of the classified payload for National Reconnaissance Office was delayed due the technical reasons connected with launch vehicle.
Launch of the NROL-42 was planned for today at 05:38 UTC from LC-3E at Vandenberg Air Force Base in California. Rocket was ready at the launch site with payload encapsulated and attached with fairing on September 16, 2017. Weather forecast were describing launch chance as 60% for Friday's night, launch preparations planned for Thursday were already started. Unfortunately at around 23:00 UTC on Thursday, launch preparations were stopped - launch was officially halted by United Launch Alliance and announcement about delay was given to public. Ground service teams were tasked with battery swap operation on the Atlas V booster, what also was unveiled as main reason for delay of the NROL-42 mission.
Rocket and satellite remain safe surrounded by service tower. United Launch Alliance claims that launch is possible even on Saturday or Sunday, but no specific date and time were given.