WASHINGTON — The U.S. Department of Defense and National Reconnaissance Office (NRO) signed a memorandum of understanding in March formalizing a previously announced plan to commit to buying eight Evolved Expendable Launch Vehicle (EELV) cores per year, while NASA, the third signatory to the newly released memo, did not commit to a minimum EELV buy.

The memo also stated that the Pentagon and NRO by July 31 will publish a framework for allowing new entrants to compete to launch EELV-class national security payloads. A copy of the memo, which was signed by Air Force Secretary Michael Donley, NRO Director Bruce Carlson and NASA Administrator Charles Bolden, was provided to Space News by the Air Force.

The U.S. government for the past decade has relied on the Atlas 5 and Delta 4 rockets developed under the EELV program by United Launch Alliance of Denver to launch its largest and most important spacecraft. The Air Force’s budget request for the EELV program in 2012 shot up nearly 50 percent to $1.76 billion, due to a combination of factors. Some Atlas 5 and Delta 4 component suppliers are forecasting — and passing to United Launch Alliance — sharply higher costs they have attributed to the ending of the U.S. space shuttle program and cancellation of NASA’s follow-on Constellation program. Additionally, the government until recently had benefited from relatively low EELV prices that the government had last negotiated in 1998.

To provide some semblance of stability for the rocket industrial base, the Air Force and NRO announced in February they would commit to purchasing five booster cores and three booster cores, respectively, for each of the next five years. Though the industrial base may have been further stabilized by a commitment from NASA, the civil space agency balked at the prospect.

“Based on mission requirements, NASA has not budgeted to purchase additional cores in [2013 through 2017],” the memo said. “Should an acquisition need arise, NASA will continue to use the NASA Launch Services 2 contracts as the primary contractual mechanism to acquire launch services across all performance classes, including EELV, to meet civil launch requirements for robotic missions.”

NASA’s Launch Services 2 contract was established last year and, like the previous contract vehicle, includes options to purchase Atlas 5 rockets for its larger payloads. But in December the agency added to the contract the medium-class Falcon 9 rocket built by Space Exploration Technologies Corp. (SpaceX) of Hawthorne, Calif., which may be suitable for some NASA payloads that would have previously been the exclusive domain of an EELV.

The decision not to commit to a specific number of EELV cores was made because each NASA mission is responsible for paying for its own launch, rather than having a single, dedicated funding line for all launch costs, said Jim Norman, NASA’s assistant associate administrator for launch services.

“Within the [Defense Department] they actually have an Evolved Expendable Launch Vehicle program, and they budget as a separate program to buy rockets,” Norman said in a June 2 interview. “We don’t do that. We have missions, so the launch cost is contained within the mission. That’s what that language is frankly telling the [Defense Department]: ‘We don’t budget the way you budget.’”

NASA has purchased on average two EELV launches per year, and United Launch Alliance expects that rate to continue through the 2013-2017 timeframe, company spokeswoman Jessica Rye said in a June 1 email. The trend could be put to the test in 2013. The budget submission NASA will send to Congress next February will likely include funding to buy launches for two EELV-class missions: the ExoMars orbiter that is being developed with the European Space Agency, and the asteroid-bound Osiris-Rex mission, Norman said. Both missions are targeting 2016 launches, which is congruent with NASA’s standard practice of initiating launch procurements three years ahead of launch.

Norman said he has not received the technical requirements for the ExoMars orbiter or Osiris-Rex and thus could not say which rockets would be in contention. Depending on the trajectory needed for the Osiris-Rex mission, the Falcon 9 could be an appropriate launch vehicle, SpaceX spokesman Robert Block said in a June 2 email.

Meanwhile, SpaceX applauded the government’s decision to move forward with a plan to on-ramp new rockets for launching national security payloads. The Air Force in February 2009 released a draft EELV new entrant evaluation plan that included specific payload-to-orbit requirements, but the service had made no visible progress to put that plan into action.

“I think overall the frustration we have had in the past is definitely changing because we’re seeing movement by the Air Force and others on new entrants for EELV,” Adam Harris, SpaceX’s vice president for government affairs, said in a June 2 interview. “So that’s really a positive step from that standpoint.”