for a telescope housed in the upper portion a small heat insulated ion engine in its lower portion with one lateral surface having a specified slope a solar cell and a heat reflector and a heat radiator on the opposite surface the spacecraft may be operated to make a turn once a half year about the sun earth axis and a station keeping strategy involving the attitude control may be devised to maintain the position and attitude requirement mentioned above the spacecraft may also serve as an intermediate relay station to and from which another spacecraft can leave for and return from deep solar system and beyond then it may be necessary to apply a thrust along the station axis to maintain the station location around the intended site near a lagrange point the direction of propulsive force coincides with the radial direction of a circular orbit whose projected locus draws a circuit onto a reference plane thus the intermediate relay station will be able to admit those spacecraft using the station without amending the attitude while it continues the station keeping description will be given below on the premise that the first celestial body is represented by the sun and the second celestial body by the earth for the sun earth system the equation of motion of a spacecraft around the lagrange point l 2 can be expressed as follows the same equation will also be true for the point l 1 the symbols used in the equations have following meanings the center of combined masses of the sun and the earth is taken as the original point a bury center the original balanced point a lagrange.