Two key lawmakers are calling for the Air Force to stop divestment of the Delta IV Heavy rocket until a “certified, reliable” replacement launch system is available.

“We do not believe the interests of the national security space community, or the warfighter, are well-served by allowing the phase out of the Delta IV Heavy capability before there is a certified, reliable replacement launch system available,” House Armed Services Committee (HASC) Chairman Mac Thornberry and HASC strategic forces subcommittee Chairman Michael Rogers (R-Ala.) write in a Feb. 28 letter to Air Force acting Secretary Lisa Disbrow and Pentagon acting Under Secretary of Defense for Acquisition, Technology and Logistics (AT&L) James MacStravic.

“That is precisely what is occurring at the present and the Air Force must stop it,” the two lawmakers write. CAPITOL

Thornberry and Rogers require the Air Force not obligate or expend any additional funding to United Launch Alliance (ULA), other than that required for the launch of the current Atlas and Delta launch vehicles. This is until ULA agrees to provide the federal government full access to, oversight of and approval rights over decision making about any engine downselect on its next-generation Vulcan rocket, assuming ULA will request government funding. The lawmakers said if ULA plans on requesting hundreds of millions of dollars from the federal government for development of Vulcan and associated infrastructure, then it is not only appropriate, but required, for the federal government to have a role.

ULA is developing its Vulcan launch vehicle as its next-generation rocket to replace the Atlas V and Delta IV. ULA is a joint venture of Lockheed Martin [LMT] and Boeing [BA].