The Russian government has issued a contract to RSC Energia to develop a new class of rockets for lunar exploration and the contract documents indicate that a nuclear-powered space tug will be develop as well.
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The mission of the space tug is to transport cargo from Earth orbit to the lunar orbit.
NASA looked into the idea of a nuclear powered tug for Earth orbit to lunar orbit back int he 60’s. Basically its nuclear reactor with a tank of liquid hydrogen on top. Sending the the LH through the reactor turns it instantly to gas and you MOVE.
Its a great idea but the problem NASA found was the first time you use it, the thing becomes VERY radioactive. Its a nuclear reactor without any shielding except on top to shield the crew/cargo area. They couldn’t figure out how to refuel the hydrogen tank because you could’t get near it from most angles. The safety distance was thought to be about 100 miles. Anyone riding the thing would get a hefty dose even with the shielding.
https://www.wired.com/2012/09/nuclear-flight-system-definition-studies-1971/