The Air Force is not encouraging or discouraging a possible proposal where Boeing and Northrop Grumman team up to build the Ground-Based Strategic Deterrent, Air Force Assistant Secretary for Acquisition Will Roper told reporters Wednesday on the sidelines of the Defense News conference.

“We are looking for the proposal that is best value to the Air Force,” he said, noting that the government should “always be open” to considering the best solution for a program.

“We think that we have an RFP that allows us to have a very wide spectrum of proposals and we’ll evaluate them based on the criteria laid out to those vendors,” he added. “We don’t know enough now to know what the right acquisition approach is. … So we’ll see what happens when the window closes.”

In July, Boeing said it would not bid on the contract to provide the next-generation intercontinental ballistic missile because Northrop Grumman had an “unfair” advantage through ownership of solid-rocket motor manufacturer Orbital ATK.