The Pentagon cannot find a replacement for the Russian rocket engines it buys anytime soon, a senior official has revealed. The import of the engines has for now been banned via a court order lobbied by SpaceX and based on sanctions against Russia.

United Launch Alliance LLC, a partnership of Lockheed Martin Corp. (LMT) and Boeing Co. (BA), has been purchasing RD-180 rocket engines from joint Russian-American enterprise RD-Amross LLC since 1997. The engines in question have been produced at a plant of NPO Energomash near Moscow, and over 40 of them were delivered between 1997-2007 alone.

The US has used RD-180 engines to power its Atlas III and Atlas V rockets, which mostly deliver commercial or military communications satellites, as well as reconnaissance and navigation satellites.

So far, the replacement options outlined by the Air Force for Hagel have reportedly included building RD-180s in the US under an existing license from the Russian maker, or using different Delta-class rockets altogether. Each of the options has its drawbacks, such as the need to harness the time and know-how for setting up engine production in the US, or the limited production capability for another class of rockets, according to Kendall.