Launching mass from the Moon helped by lunar gravity anomalies

Abstract

Normally a passive object launched from the Moon at less than the escape velocity orbits the Moon once and then crashes back to the launch site. We show that thanks to lunar gravity anomalies, for specific launch sites and directions, a passive projectile can remain in lunar orbit for up to 9 Earth days. We find that such sites exist at least on the lunar equator for prograde equatorial orbit launches. Three of the sites are located on the lunar nearside. We envision that this can be used to lift material from the Moon at low cost because it gives prolonged opportunities for an active spacecraft to catch the projectile. Passive projectiles can be made entirely from lunar material so that a stream of Earth-imported parts is not needed. To reduce the mass and cost of the launcher, the projectile mass can be scaled down with a corresponding increase in the launch frequency. The projectile launcher itself can be a coilgun, railgun, superconducting quenchgun, sling or any other device that can give a projectile an orbital speed of about 1.7 km/s.