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 Defence 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 tonnes to geostationary orbit, launched by Energia. All of these designs seem to have been essentailly similar; the figures given here are for the last study. The tug would have a propellant supply adequate for 16,000 hours of operation and three years of reactor life.

• Used on stage: ERTA.

• Used on stage: Interorbital Tug.

• Used on: Interorbital Tug.

• Semenov, Yuri P Editor, Raketno-kosmicheskaya korporatsiya 'Energia' imeni S P Koroleva, Moscow, Russia, 1996. Russian in-house history of the Energia Corporation and its predecessors. Unprecedented detail, photographs, designations, and drawings, on the products of Korolev's OKB.

• Semenov, Yu. P., S P Korolev Space Corporation Energia, RKK Energia, 1994. ISBN: 1896522815. Dual English/Russian language picture book of the history of the Energia Corporation. Many unique photos and drawings of Korolev's rockets and spacecraft. Republished by Apogee books in 2000. More at amazon.com...