Upper stage / space tug - nuclear electric space tug, to be launched by Energia-2. Developed 1978-1991, ultimately cancelled.

Beginning in 1978 the 11B97 nuclear electric engine was studied for use in a reusable interorbital space tug for launch by Energia-Buran. In 1982, according to the decree of 5 February 1981, NPO Energia developed for the Ministry of Defense the interorbital tug Gerkules with 550 kWt maximum output and continuous operation in the 50-150 kWt range for 3 to 5 years. In 1986 a civilian interorbital tug was studied to solve the specific application of transporting heavy satellites of 100 metric tons to geostationary orbit, launched by Energia. All of these designs seem to have been essentially similar; the figures given here were for the last study. The tug would have a propellant supply adequate for 16,000 hours of operation and three years of reactor life.