For every Hohmann transfer to or from another celestial body's orbit, there is an optimal altitude to start from. For instance if you start a Hohmann burn from Kerbin to Eve at 12,908km, you'll save about 500m/s relative to starting from a 100km orbit. I thought this information might be useful for planning refueling station altitudes. Simplifications: - no inclination changes - eccentric orbits are assumed circular with radius equal to the semi-major axis Notes: - All values in