In 1994-1995 KB Arsenal collaborated with NII PME MAI, NPO Lavochkin, and others in international group to study interplanetary flight using nuclear-electric and solar-electric engines. The final selected design was a nuclear-electric interplanetary tug. While OKB Fakel conducted experiments with nuclear-electric and ion engines, KB Arsenal remained the only bureau with actual flight test experience with such engines. Such a tug would have been a practical approach to solar system exploration. Japan joined the collaborative group when nuclear power became an important part of their lunar exploration plans. But in the end the group had to convert the tug design to use non-traditional, environmentally-friendly power sources.