sentences:  Upon launch, the castle would be placed into an interim orbit, and then use the Earth's mass to assist it into the cycler orbit.Assuming the use of liquid hydrogen and liquid oxygen fuel, which has a specific impulse of about , in the vicinity of Earth, and monomethylhydrazine and nitrogen tetroxide fuel, which has a specific impulse of , as was employed by the "Galileo" spacecraft for deep space maneuvers (since Cryogenic fuels cannot be used in deep space, as they would boil off in the time), it is possible to estimate the fuel required to establish a cycler orbit.In the case of the Aldrin cycler, use of a gravity assist reduces the fuel requirement by about , or 15 percent.