WPenner's Blog

Having a shuttle service between the moon and earth would be incredibly useful and this little article proposes using demonstrated technology to create one.¹ The problem is getting out of earth's gravity-well, which takes a rocket's complete energy. Once in orbit, more energy is required to accelerate a vehicle to the moon. To get to the moon in the 3 days of the Apollo missions, instead of the 45 days of the CAPSTONE project requires an enormous amount of energy. Vehicles coming back from the moon need to decelerate to enter earth's orbit and decelerate further to drop back to the earth's surface.

The opportunity is crystal clear: in the next 10 years there will be regular flights between earth and the moon shuttling personnel, equipment and products between the two bodies. Each vehicle leaving earth from the moon requires energy to speed up and returning vehicles need energy to slow down. Several proposed new technologies could provide the needed energy, but three demonstrated technologies could help in shorter timeframes.

The first is a solar sail. JAXA's IKAROS was one of the first demonstrations (2010-2015), sailing to Venus and around the sun before losing contact with earth. A solar sail simply uses the acceleration provided by impact from solar energy to increase velocity. A significant downside of the approach, however, is that solar energy is not strong, limiting the size of vessel which can use this technology.

The second demonstrated technology is ion engines. Companies currently use these engines for maneuvering around orbit but run out of energy for longer trips and are not great for pushing large amounts of mass. Plasma engines might solve the limitations of ion engines by providing greater thrust, but require large amounts of energy. These engines can provide the thrust for acceleration and deceleration, provided they receive the electrical energy.

The final demonstrated technology is solar energy generated from space as a source of power for earth. The US, Japan and India have all shown how large solar collectors (1km\(^2\) or larger) can collect energy that can be beamed to earth where large collectors (several hundred m\(^2\)) receive the energy. The experimenters place collectors into a geosynchronous orbit to provide continuous power unhampered by atmospheric interference or blockage from the earth.

The beams transporting the collected energy are laser or microwave. This is because solar panels, while getting better, are notoriously inefficient at translating solar radiation into energy useful for human consumption. Constructing collectors for laser or microwave are more efficient.

Combining these three technologies in space first is sensible. The solar energy collected should not be directed toward earth, but beamed to vehicles fitted with sails configured to collect laser or microwave energy. Receiving more concentrated energy allows the sails to be more compact and increases the energy available to the engines for acceleration or deceleration, as required. The beam travelling through space will lose very little of its energy compared to travelling through the atmosphere.

The collector station does not have to be in earth's orbit. Nor is the system limited to a single collector. Collectors might be station in earth orbit, lunar orbit and a third at a Lagrange point. Each would provide energy at the best possible time for a vehicle's journey.

One space business to develop from this idea is providing the energy. A second is a shuttle service that provides transportation between the earth and the moon Applying the expertise developed in cislunar space to other planets in the solar system would provide growth opportunities for decades.²