A version of this article appears in the August 11/18 double issue of Aviation Week & Space Technology.

Almost five years after beginning its search for a U.S.-developed spacecraft to carry humans into orbit, NASA is poised to award at least one contract to its industry partners in the Commercial Crew Program.

The three contenders—Boeing, Space Exploration Technologies (SpaceX) and Sierra Nevada Corp.—could hear as soon as the end of August which of their proposed vehicles has been selected for a Commercial Crew Transportation Capability contract to fly to the International Space Station. 

With NASA widely expected to support multiple solutions, the biggest question is how the awards might be spread over differing vehicle concepts, launch vehicles or both. Assuming two contracts are awarded, NASA must decide whether to support the two capsule designs on offer from Boeing and SpaceX or one of them in combination with the lifting-body concept proposed by Sierra Nevada. 

Another factor that may influence the decision is Boeing’s and Sierra Nevada’s selection of the United Launch Alliance (ULA) Atlas V as primary launch vehicle. Although both assert that their designs are “launch-vehicle-agnostic,” concern over the guaranteed supply of the Atlas V’s Russian-made RD-180 main engines could prove a factor. Worries about threats to the engine supply, originally posed by Dmitry Rogozin, Russia’s deputy prime minister, in response to U.S. economic sanctions imposed on Russia after the annexation of Crimea in March, have reemerged following the shootdown of Malaysia Airlines Flight 370 last month.

However, Mark Peller, ULA director of hardware value stream, said at the American Institute of Aeronautics and Astronautics Space 2014 conference here Aug. 4-7 that the company is working to “reduce the perception of the risk,” adding, “at a working level we have seen no changes in the relationship; at our level, it’s been business as usual.” ULA agreed a 29-engine deal with RD Amross, the NPO Energomash and United Technologies Corp. joint venture earlier this year and expects to receive the first two RD-180s from this batch on Aug. 20. Three more engines are scheduled for delivery in October and eight per year in 2015-17.

The three contenders are signaling varied responses should they not be selected. Boeing Commercial Space Vice President John Mulholland says, “it will be difficult to support the business case” without a NASA contract for CST-100. Dragon 2 program manager Garrett Reisman says if Space X’s capsule is not selected, “there would be a lot less resources, and we’d have to bear all the development costs, so things would change. But we are not going to stop.”

Sierra Nevada Space Systems President Mark Sirangelo says the company is committed to the Dream Chaser orbital test flight in November 2016, regardless of a negative decision. “We are now in a place where it is possible to continue,” he says. “We are laying the potential for other things as it goes on, so that the companies that are not chosen have the potential to carry on.”