ON MAKING USE OF LUNAR AND SOLAR GRAVITY ASSISTS IN LUNAR-A, PLANET-B MISSIONS

ISAS (the Institute of Space and Astronautical Science, Japan) is currently planning to launch the LUNAR-A spacecraft to the Moon in 1997 and the PLANET-B spacecraft toward Mars in 1998. Since these two spacecraft have been facing mass budget hurdles, ISAS have been studying how to make good use of lunar and solar gravity effects in order to increase the scientific payload as much as possible. In the LUNAR-A mission, the current orbital sequence uses one lunar swingby via which the spacecraft can be thrown toward the SOI (sphere of influence) boundary for the purpose of acquiring solar gravity assist. This sequence enables the approach velocity to the Moon to be diminished drastically. In the PLANET-B mission, use of lunar and solar gravity assist can help in boosting the increase in velocity and saving the amount of fuel. The sequence discussed here involves two lunar swingbys to accelerate spacecraft enough to exceed the escape velocity. This paper focuses its attention on how such gravity assist trajectories are designed and stresses the significance of such utilization in both missions.