Russian-made RD-180 engines propel an Atlas V rocket heavenward.

When the National Defense Authorization Bill comes to the Senate floor, lawmakers will face an important choice regarding the future of national security space launch. The Defense Department has relied upon United Launch Alliance’s (ULA) Delta IV and Atlas V rockets — the latter powered by the Russian-built RD-180 engine. Maintaining redundant launch system capabilities — known as Assured Access to Space — is mandated by law, Title 10, Section 2273.

Given Russia’s recent hostile behavior, it’s only prudent to develop a domestic alternative. The question facing Congress is how to best attain this goal. Given budget pressures and the necessity of keeping military space launches on track, we may have to extend the use of the RD-180 as a bridge until a new American design is fielded.

This issue dates back to the Fiscal Year 2015 National Defense Authorization Act, when Congress mandated the military not procure launches that utilized Russian engines. This legislation stipulated that Atlas V launches would terminate after RD-180 stocks were consumed — requiring the construction of a new engine to power either the Atlas V or a substitute.

The US space enterprise is dedicated to meeting this goal. SpaceX has gained Air Force certification to launch national security payloads with its recently developed Falcon 9. Aerojet-Rocketdyne is developing the AR-1 engine as a potential replacement for the RD-180. Blue Origin is also designing a new engine, the BE-4, with this same objective. ULA is constructing a new rocket named Vulcan, which will be powered by either the BE-4 or the AR-1. The US has not seen this amount of energy and industrial effort in space launch development since the 1970s. Technical experts have had to relearn important skills involved with rocket engine design and production, given that the last generation of experts have either retired or are deceased.

Despite the herculean efforts of these engineering teams, a rocket with a new US-built engine is not expected to be certified for national security missions until 2022. “All of the technical experts with whom I’ve consulted tell me this is not a one or two or three-year deal,” Air Force Chief of Staff Gen. Mark Welsh testified recently. “You’re looking at maybe six to seven years to develop an engine, another year or two beyond that to be able to integrate it [with a rocket].” This means a bridge solution must be found until a new system becomes available in the early 2020s.

Given the need to maintain redundant launch options, two paths exist: the first, continue missions with Space X’s Falcon 9 rocket and ULA’s Delta IV, or allow limited use of RD-180 engines to sustain Atlas V national security launches until at least one domestic alternative is available. Given that both the Falcon 9 and Delta IV are powered by US-built engines, the choice appears clear.

The Pentagon should buy the additional 18 RD-180s and use the Falcon 9 when necessary. Why? Because the alternative of buying Delta IV launches is so expensive that it would break the Air Force’s budget. Pursuing this path would add an additional $1.5 billion to $5 billion to the launch budget, equating to upwards of 50 F-35s or two Arleigh Burke Class Destroyers.

“The impact on the existing Air Force space mission would be significant because you have to take billions of dollars out and try to do something else with it,” Air Force Space Command’s Gen. John Hyten explained. “What are you going to take out? Are we going to stop doing GPS? Are we going to stop doing missile warning?”

The House Armed Services Committee agrees with the department’s approach to the challenge and authorized the use of an additional 18 RD-180 engines. The Senate Armed Services Committee disagreed and only authorized the use of nine Russian rocket motors—half the stated requirement. With the NDAA coming to the Senate floor this week, this issue will undoubtedly drive much debate.

The imperative for developing a US-made replacement for the RD-180 is undeniable. Given the difficult choices driven by Congress imposing sequestration, the US must chart a prudent path to meet future launch requirements while fiercely championing the development of a new domestically-developed launch design as the enduring solution to guarantee America’s access to space.

Doug Birkey, is executive director of the Mitchell institute for Aerospace Studies, an affiliate of the Air Force Association.