Recent tensions over Russia's move to annex Crimea have prompted some to question the reliability of U.S. access to the Russian-made RD-180 engine, which is used to power one of two rockets that loft national security payloads into orbit.

Russia is a source for these engines as well as other aerospace materials, such as titanium. The U.S. government has placed targeted sanctions on 11 Russian and Ukranian officials—the most comprehensive of such measures since the end of the Cold War—as a response to Russia's bold move into Crimea. But the dispute has thus far not affected the supply chain for the United Launch Alliance (ULA) Atlas V rocket.

“We hold a license to manufacture and deliver RD-180 engines,” says Matthew Bates, a spokesman for Pratt & Whitney, which formed a joint venture with Russian engine manufacturer NPO Energomash in 1997 called RD Amross. The sole purpose of RD Amross is to provide the engines to the U.S. “A deviation from the contracted, agreed-upon delivery amount would represent a contractual breech,” says Maureen Schumann, a Pentagon spokeswoman.

If Russia were to hold the RD-180 hostage, the Defense Department estimates it would need $1 billion over five years to establish production on U.S. soil.

The RD-180 sourcing plan was established over years of regulatory review once Lockheed Martin, which developed the Atlas V in the late 1990s, selected the engine as its propulsion system. To mitigate concerns about supply, the U.S. Air Force maintains a stockpile of roughly two years' worth of engines, ULA CEO Mike Gass told lawmakers this month. The stockpile was approved as a change to the U.S. policy with regard to foreign sourcing in 2000.

The policy today is three-pronged. In addition to the stockpile, the Pentagon also has a plan to “gracefully” transition to U.S. production if needed. And, finally, should the supply be interrupted, Pentagon officials can prioritize what missions would use Atlas V while a production facility is being established stateside.

The coproduction requirement for the RD-180 that was set early in the program was eventually lifted by the Pentagon in part because missions could be offloaded to the Delta IV family, Schumann says. The Pentagon has long held to a strategy of “assured access” to space by operating two distinct rocket systems.

The Delta IV was originally developed by Boeing as a competitor to the Atlas V, but both rockets were subsumed into ULA in 2006 when the government approved a monopoly for such missions in the U.S. However, the Delta IV is a less attractive option for some payloads because its RS-68 propulsion system is less effective. “For some missions [such as lofting Lockheed Martin Advanced Extremely High Frequency and Mobile User Objective System satellites on the A2100 bus] this would be more expensive than using an Atlas V because it would require a multi-core heavy launch vehicle instead of a single-core vehicle,” Schumann says.

Defense Secretary Chuck Hagel said he would review the Pentagon's policy on the Russian sourcing in response to queries from Rep. Robert Aderholt (R-Ala.) during a House Appropriations Defense subcommittee hearing March 17. The Air Force regularly reviews supply for both the Atlas V and Delta IV Evolved Expendable Launch Vehicles (EELV), Schumann says.

The diplomatic volley with Russia has piqued scrutiny of the supply strategy.

Not one to miss such an opportunity, Space Exploration Technologies (SpaceX) CEO Elon Musk has suggested that the Pentagon eliminate its dependence on the Russian engine by using the SpaceX Falcon 9v1.1 in place of the Atlas V. The SpaceX rocket is still in the process of being certified by the Air Force to compete to launch national security payloads.

Although raising the issue amid political tensions over Crimea may grab headlines, it remains to be seen whether this new backdrop will fracture the Pentagon's stalwart support for maintaining the Atlas V and Delta IV.

It has become an almost annual drill for budgeteers to suggest cancelling the Atlas V and relying on a single supplier for financial reasons, but the Atlas V remains intact.

Musk's argument for replacing the Atlas V is hardly new; Boeing used it when competing against Lockheed Martin for work during the first round of EELV competitions.

But this dynamic could be changed if SpaceX can make good on its proposition of supplying launches to the Pentagon at a lower cost despite the rigorous oversight required for mission assurance.