require fuel to execute the braking and re-cycling maneuvers. The castles could be inserted into cycler orbits with considerable savings in fuel by performing a series of low thrust maneuvers: The castle would be placed into an interim orbit upon launch, and then use an Earth-swing-by maneuver to boost it into the final cycler orbit. Assuming the use of conventional fuels, 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. Other cyclers showed less impressive improvement, due to the shape of their orbits, and when they encounter the Earth. In the case of the VISIT-1 cycler, the benefit would be around , less than one percent, which would hardly justify the additional three years required to establish the orbit. See also Interstellar cycler Lunar cycler Notes References Additional references } Spaceflight concepts Missions to Mars Buzz Aldrin