Since the end of the Winter Olympics in Sochi, Russia, U.S. and Russian relations have deteriorated significantly due to the Russia-Ukraine crisis. One of the important questions on many minds is: "What will be the impact of this crisis on the U.S. space program?"

So far, joint U.S.-Russian activities related to the International Space Station (ISS) appear to be normal, i.e., NASA pays Russia exorbitant amounts of money to fly astronauts to and from ISS, and Russia enjoys ripping off the U.S. There's nothing new here.

On the other hand, there are national security issues that may be affected by the crisis. One important area of concern addresses the continued availability of Russian-manufactured rocket engines for U.S. launch vehicles.

In the near-term, there are sufficient engines on hand to continue space launches for about another two years. However, if the crisis continues, it may jeopardize the supply of future engines. The U.S. Air Force is studying potential impacts on national security risks if the engines are not available for use after 2016.

There are two liquid-rocket engines that the U.S. relies on for space launch vehicles: the RD-180 and the NK-33. The RD-180 is manufactured by NPO Energomash and marketed in the U.S. by RD AMROSS, a joint venture between Pratt and Whitney and NPO Energomash. This engine is used by United Launch Alliance (ULA ) to propel the Atlas V first stage.

The RD-180 design is based on the Russian RD-170/RD-171 engines. The RD-170 was used on the Energia launch vehicle, which had only two launches. The RD-171 is in service on various versions of Ukrainian/Russian Zenit rockets. Since Sea Launch uses the Zenit launch vehicle, RD-171 engines have been imported to the U.S.

However, Sea Launch is not a U.S. launch vehicle, and therefore, does not launch U.S. government payloads. It is worth noting that Pratt and Whitney had intended to produce the RD-180 engine in the U.S., but all of the engines used for Atlas V have been produced in Russia.

NK-33 rocket engines were designed and built in the late 1960s and early 1970s by the Kuznetsov Design Bureau. Aerojet purchased 36 of these engines from the Russians about 20 years ago. An early version of this engine was originally intended for use on the USSR's N-1 launch vehicle for its first stage.

Although the N-1 project was cancelled, the early engine design was improved and has led to the NK-33. A total of roughly 150 NK-33 engines survived over the decades, since the 1960/70s. Presumably, there are still over 100 engines stored someplace in Russia. Aerojet modified and renamed the engine as the AJ26.

In the 1990s, Kistler Aerospace planned to use the modified NK-33 engines for its K-1 two-stage reusable launch vehicle, but failed to complete the development program and later closed its doors. Currently, two AJ26 engines are used on each first stage of Orbital Sciences' Antares launch vehicle.

Since there appears to have been no recent orders for additional Russian rocket engines, the level of concern is still low. However, if the crisis continues for many more months we can expect ULA and Orbital to become anxious about the future. In addition, NASA and the Air Force may have to look beyond current options for launch capabilities.