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

ISAS (the Institute of Space and Astronautical Science, Japan) is curr ently planning to launch the LUNAR-A spacecraft to the Moon in 1997 an d the PLANET-B spacecraft toward Mars in 1998. Since these two spacecr aft have been facing mass budget hurdles, ISAS have been studying how to make good use of lunar and solar gravity effects in order to increa se the scientific payload as much as possible. In the LUNAR-A mission, the current orbital sequence uses one lunar swingby via which the spa cecraft can be thrown toward the SOI (sphere of influence) boundary fo r the purpose of acquiring solar gravity assist. This sequence enables the approach velocity to the Moon to be diminished drastically. In th e 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 s equence discussed here involves two lunar swingbys to accelerate space craft enough to exceed the escape velocity. This paper focuses its att ention on how such gravity assist trajectories are designed and stress es the significance of such utilization in both missions.