Project Orion would gather Two thirds of propellant as it went so that All major moons of Saturn or Jupiter could be visited with a mass ratio less...

Centauri Dreams has a look back at the Orion Project plans to fly to Enceladus. Project Orion was the rocket that was use about 800 small nuclear bombs for propulsion. It would drop each one through a hold in a massive metal donut/pusher plate.

Project Orion was intended to loft 1600 tons to low-Earth orbit, or in its advanced version, 1300 tons to a landing on one of Saturn’s moons. The moon that most drew Freeman Dyson’s eye in 1958 was tiny Enceladus.

Each Bomb was only one third of the weight of each propulsion unit

Part of the Orion strategy is to gather propellant for the return trip at the destination, thereby reducing the average takeoff weight of the bombs. “We assume that we can use as propellant either ice, ammonia, or hydrocarbons,” wrote Freeman, explaining why Enceladus was such a good place to stop. “We suppose that each propulsion unit contains one-third of its mass in the form of the bomb and other fabricated parts, and two-thirds of its mass in the form of propellant. This means that, when propellant refueling is possible, only one-third of the mass required for the homeward trip need be carried out from Earth.” When you put these numbers together, the end results were astonishing. “With the use of atmospheric drag a round-trip to satellites of either Jupiter or Saturn could be made with a total velocity increment of the order of 40 km/sec. With refueling and braking, all the satellites become accessible with a round-trip mass-ratio less than 2.”

All major moons of Saturn or Jupiter could be visited with a mass ratio less than 2.

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