Dulles, Virginia-based Orbital had withheld public announcement of the engine until Dec. 16 despite widespread reports in Russia of the selection, saying it did not want to show its hand in advance of one or more U.S. rocket-selection competitions.

Orbital announced its choice via Twitter and through an article in Aviation Week and Space Technology.

Khimki, Russia-based Energomash also supplies the RD-180 engine to United Launch Alliance of Denver for U.S. government launches of ULA's Atlas V rocket. The ULA contract with Energomash is handled through RD Amross of Cocoa Beach, Florida, whose contract terms are now under review in the U.S. Congress.

Orbital apparently will contract directly with Energomash. Russia's Izvestia press agency on Dec. 17 quoted an official from the Russian space agency, Roscosmos, as saying the Energomash-Orbital deal is valued at about $1 billion and includes a firm order for 20 engines, plus two options for 20 engines each. [Antares Rocket Explosion in Pictures]

Orbital spokesman Barron Beneski said in a Dec. 17 statement:

"Our order with Energomash can take us through 2020, with firm orders that will allow us to fulfill our CRS commitments for NASA and several more options that can be exercised along the way as needed. Naturally, we are not discussing price."