- 東海大学紀要. 工学部 (ISSN:05636787)
- vol.32, no.2, pp.187-197, 1992
This paper describes the guidance strategies of solar sails which leave the circular orbit with 50,000km radius around the earth towards the moon. The solar sail is a spacecraft which is thrust by the light pressure (radiation pressure) of the sun. The design of the orbit targeting the moon using the solar sail is complicated due to reasons as follows : 1) The thrust obtained by the solar light pressure is so small that the long flight time is needed in the lunar mission. 2) As the thrust vector is determined by the relative angle between the sun and the sail, magnitude and direction cannot be controlled independently with a sail. One of the typical control method of the solar sail is "Maximum velocity increment control", where the sail direction is always kept along the instantaneous velocity of the spacecraft to get the maximum acceleration. It is efficient to increase the radius of orbit in the initial phase, but insufficient in the last phase to hit the moon. Therefore, other control procedure should be adopted to approach to the lunar orbit. In this approaching phase maneuver, the principle of "Maximum velocity increment control" is still used in conjunction with the control of the magnitude of acceleration between zero and 100% of the maximum level, which can be achieved by means of the specially designed sail. With this method, the apogee distance as well as the arrival time to the apogee can be adjusted to hit the moon. The most efficient time to switch from the initial to the approaching phase is also discussed with R-T (the apogee distance the apogee passage time) diagram proposed in this paper.