Powering the Space Elevator

This report presents the results of research into several different methods to power the climbers on the space elevator. The climber in the report is the reference conceptual design from [Wright et al. 2023]. The first part of the report states the requirements common to any climber power system and establishes the power requirements for multiple climbers on the tether simultaneously. Chapter 2 also identifies all of the components on a climber that use electrical power.

The power delivery methods shown are laser power beaming, microwave power beaming, solar-powered climbers, and climbers powered by an electrically conducting tether that is energized.

The short wavelength of the laser-powered climbers allows for the smallest, lightest receivers on the climbers. Laser systems do not have the efficiency of microwave-powered systems, but the longer microwave wavelength leads to a rapidly diverging beam that forces the receivers on the climber to be very large for microwave systems. Microwave power beaming may also be limited to a maximum power density in the ionosphere of 230 W/m2 to avoid communications disruptions. Further work is needed to determine the appropriate power density limit.

Both laser and microwave power beaming systems require large and expensive infrastructure on the ground to power the transmission systems. Laser transmitters on the ground are small enough that they can be made mobile on ships at sea. Microwave transmitters on the ground are too large to mount on ships and must be in fixed positions.

The solar-powered climber does not need extensive ground power infrastructure, but its challenges come from the fact that sunlight is much lower in power (by up to a factor of 1,000) than the light intensities of power beaming, it is not available at night (for climbers at low altitudes), and the source moves around throughout the day. The low intensity of sunlight forces the receiver to be larger than any of the power beaming receivers, and as such it is a large target to orbital debris in LEO.

The tether-powered climber requires an additional level of manufacturing complexity on the tether above the already daunting process of making a tether strong enough out of singlecrystal graphene or hexagonal boron nitride. The conductive tether requires interleaved layers of conducting graphene and insulating boron nitride to create a tether with sufficiently conductive ”wires” to deliver power to the climber at any altitude. This tether manufacturing process is currently completely unknown.

The difference between ascending and descending climbers is described, highlighting the radically different power infrastructures required by each. No current technology exists to fully recover the energy of a descending climber.