Launching Mass From the Moon Helped by Lunar Gravity Anomalies

Placing a mass driver on the Moon has long been a dream of space exploration enthusiasts. It would open up so many possibilities for the exploration of our solar system and the possibility of actually living in space. Gerard O’Neill, in his work on the gigantic cylinders that now bear his name, mentioned using a lunar mass driver as the source of the material to build them. So far, we have yet to see such an engineering wonder in the real world, but as more research is done on the topic, more and more feasible paths seem to be opening up to its potential implementation. 

One recent contribution to that effort is a study by Pekka Janhunen of the Finnish Meteorological Institute and Aurora Propulsion Technologies, a maker of space-based propulsion systems. He details how we can use quirks of lunar gravity to use a mass driver to send passive loads to lunar orbit, where they can then be picked up with active, high-efficiency systems and sent elsewhere in the solar system for processing.

Anomalies in the Moon’s gravitational field have been known for some time. Typically, mission planners view them as a nuisance to be avoided, as they can cause satellite orbits to degrade more quickly than expected by nice, simple models. However, according to Dr. Janhunen, they could also be a help rather than a hindrance.

Typical models of using lunar mass drivers focus on active or passive payloads sent into lunar orbit. Active payloads require some onboard propulsion system to get them to where they are going. Therefore, these payloads require more active technology and some form of propellant, which diminishes the total amount available for use elsewhere in the solar system.

On the other hand, passive payloads will typically end up in one of two scenarios. Either they make one lunar orbit in about one day and then deorbit back to the lunar surface, or they end up in a highly randomized orbit and essentially end up as lunar space junk. Neither of those solutions would be sustainable for significant mass movement off the lunar surface.

Dr. Janhunen may have found a solution, though. He studied the known lunar gravitational anomalies found by GRAIL. This satellite mapped the Moon’s gravity in great detail and found several places on the lunar surface where a mass driver could potentially launch a passive payload into an orbit that would last up to nine days. These places are along the sides of mountains, and three of them are on the side of the lunar surface facing Earth. Importantly, all of them have their gravitational quirks.

More time in orbit would mean more time for an active tug to grab hold of the passive lunar payload and take it to a processing station, such as a space station at the L5 point between Earth and the Moon. This active tug could be reusable, have a highly efficient electrical propulsion system developed and built on Earth, and only need to be launched once.

All that would be required for the system to work would be a mass driver that could accelerate a payload up to a lunar orbital velocity of about 1.7 km/s. That is well within our capabilities to build with existing technologies, but it would require a massive engineering effort far beyond anything we have built-in space so far. However, every study that shows a potential increased benefit or lowered cost to eventually exploiting the resources of our nearest neighbor to expand our reach into the solar system takes us one step closer to making that a reality.

Learn More:
P Janhunen – Launching mass from the Moon helped by lunar gravity anomalies
UT – Moonbase by 2022 For $10 Billion, Says NASA
UT – NASA Wants to Move Heavy Cargo on the Moon
NSS – L5 News: Mass Driver Update

Lead Image:
DALL-E illustration of a lunar electromagnetic launcher