WASHINGTON – The U.S. Air Force said it plans to award United Launch Alliance a sole-source contract to build and launch two Delta 4 Heavy rockets for National Reconnaissance Office between 2020 and 2023, according to an Aug. 4 announcement,

The launches appear to be the first sole-source awards outside of ULA’s $11 billion block buy deal with the Air Force, sources said. That contract, which was awarded in 2013, includes production of 36 new Atlas 5 and Delta 4 rocket cores and launch services for vehicles ordered as long ago as 1998.

The Air Force did not announce a contract value, but ULA previously has said a Delta 4 Heavy rocket costs about $350 million, suggesting the contract could be worth roughly $700 million.

The announcement comes as the Air Force is working to re-introduce competition into the national security launch industry. In April, SpaceX won the first of nine launch contracts the Defense Department intends to put out for bid in the next three years.

But in this case, in a pre-solicitation notice posted to the Federal Business Opportunities website Aug. 4, the Air Force said it opted for a sole-source contract for classified National Reconnaissance Office missions slated to launch in 2020 and 2023. The NRO builds and operates the country’s spy satellites.

The Air Force said it chose ULA due to the timing and complexity of the integration of the satellites to the rockets, unique requirements, and the need to have a certified launch vehicle by the award date.

ULA is “currently the only responsible source,” the notice said.

The conventional wisdom within industry and within the Defense Department has been that ULA’s Delta 4 Heavy rocket would compete against SpaceX’s Falcon Heavy rocket for such launches. The Falcon Heavy is expected to make its long-awaited maiden launch later this year and could earn certification from the Air Force to launch national security payloads as early as 2017.

But SpaceX, which sued the Air Force in federal court in 2014 for the right to compete for national security missions, said it understood the Air Force’s decision.

“These particular missions had very specific technical requirements,” John Taylor, a SpaceX spokesman said in an email to SpaceNews. “We worked closely with the DoD and the USAF on this action and decided jointly it was the right approach.”

Jessica Rye, a ULA spokeswoman, referred questions to the NRO.

In its announcement, the Defense Department said it plans to award a formal contract for the first mission, known as NROL-82, later this year for a 2020 launch. It also plans to award a contract for the second mission, known as NROL-91, in late 2017 with a tentative launch date of 2023. Because NRO payloads are classified, very few details about the launch is publicly released.