It's just the third launch from the Defense Department to be competitively bid between ULA and SpaceX.
The Air Force declined to discuss how SpaceX got the contract and if it was sole-sourced.
The Air Force expects a replacement for the Delta 4 Heavy rocket will be ready by 2023, with one of several vehicles under development able to take its place.
A bipartisan group of 20 House members has asked the Defense Department not to alter the U.S. Air Force’s plans to fund development of new launch systems.
Boeing and United Launch Alliance showed off an astronaut safety system during a media event the day before the 33rd Space Symposium.
“Everybody agrees on the long term,” said William LaPlante, former Air Force assistant secretary for acquisition. But getting to those goals is the hard part.
The Delta 4 carrying the Wideband Global Satcom 9 satellite lifted off at 8:18 EDT.
In a letter, the representatives said the service should not provide funding for ULA's development of Vulcan unless it has "full access, oversight of, and approval rights over decision-making."
The launch was scheduled for March 8, carrying WGS-9, the Air Force’s next Wideband Global Satcom satellite.
NASA awarded a contract to United Launch Alliance March 3 for the launch of the second in a series of next-generation polar-orbiting weather satellites.
NROL-79 took off at 12:50 pm Eastern from Vandenberg Air Force Base, California, on ULA’s 21st mission for the intelligence agency.
SBIRS GEO-3 launched successfully aboard a ULA Atlas 5 from Cape Canaveral, Florida, on Jan. 20.
The launch of an Air Force missile warning satellite didn't go as planned Thursday as technical and range issues scrubbed the launch for a day.