Future human exploration of the Moon and deep space beyond will require novel power generation and storage technologies.
Almost 50 years since the last human mission to the Moon, the race is on for a return with the United States planning its Artemis programme to land the next man and the first woman there in 2024.
Unlike the Apollo missions when the Moon was the final destination, this time with Artemis it is considered also as a stepping stone to human exploration of Mars. This in turn presents an array of new human support challenges to overcome to make possible a long duration presence in space.
In preparation, a sustained human presence is proposed at a base camp on the Moon. There, from its intended location at the south pole, a whole range of science and exploration activities are proposed, including one to two month expeditions away from the village, both to advance the requisite technologies as well as learn more about the Moon and the universe at large.
Alongside in situ resources, power is an essential requirement for human life on the Moon and for a possible future base on Mars. A number of potential options are now under development to support a lunar habitat and to power travel rovers and other operations.
Vertical solar arrays
Among the most advanced is the vertically deployable solar array concept.
Existing space-rated solar array structures and deployment systems are designed for use in microgravity or horizontal surface deployment. The vertical position and height of this new concept are intended to maximise the capacity and prevent losses at the lunar pole where the Sun does not rise very far above the horizon.
With rocky formations like hills and slopes, low angled light can cast a shadow over the surface, which can block horizontally structured solar arrays from obtaining light. A tall vertical solar power structure would increase the likelihood of getting uninterrupted light.
NASA is working with five companies to mature the technology. In the first phase, the companies – Astrobotic Technology, ATK Space Systems (Northrop Grumman), Honeybee Robotics, Lockheed Martin and Space Systems Loral (Maxar Technologies) – will complete designs of arrays that can autonomously deploy up to 9.5m high and retract for relocation if necessary.
In addition, the designs must remain stable on steep terrain, be resistant to abrasive lunar dust and minimise both mass and packaged volume to aid in delivery to the lunar surface.
At the end of the design phase, NASA plans to select up to two of the designs to build prototypes and perform environmental testing, from which one will be selected for eventual deployment near the end of this decade.
Chuck Taylor, who is leading vertical solar array development at NASA’s Langley Research Center in Hampton, Virginia, anticipates that developments to make solar arrays more efficient when they encounter lunar shading should be implemented here on Earth. For example, home and business owners could benefit from adapted designs that increase the efficiency of rooftop solar arrays that are occasionally shaded due to trees or tall buildings.
Another novel concept under development for a lunar south pole base deployment is the Light Bender, which utilises a combination of mirrors and lenses to capture, concentrate and focus the sun’s light.
This light is then collimated by a Fresnel lens for distribution to multiple end-users at distances of a kilometre or more away, where it is converted to electricity using small (2-4m diameter) PV arrays that can be mounted on habitats or assets such as mobile rovers.
The Light Bender concept is considered superior to alternatives such as laser power beaming, as it only converts light to electricity once, and with its approximately 5x mass reduction, to traditional power distribution architectures that rely on mass intensive cables.
It also enables the powering of scientific and other assets in permanently shaded areas.
The initial design has the primary mirror capturing the equivalent of almost 48 kWe of sunlight. End-user electrical power is dependent on the distance from the primary collection point but preliminary analysis has suggested that at least 9kWe of continuous power would be available within 1km.
The phase 1 studies underway will address system design issues that impact the performance and operational suitability of the system. Of importance is the optical mirror/lens design and how this design manifests in a mechanical structure meant to deploy autonomously from a small packaged volume. The primary figure of merit will ultimately be the minimisation of the landed mass.
Next-gen power distribution
Alongside these initiatives, NASA’s Lunar Science Innovation Initiative first funding opportunity has selected three power distribution technologies for investigation that could be deployed to support activities on the Moon.
Project Moonbeam led by Philip Lubin, professor in Physics at the University of California in Santa Barbara, is developing a compact and modular ‘directed energy’ system for wireless power transfer utilising near-infrared laser light. Potential applications include exploration and resource utilisation in the permanently shaded regions of the Moon with multiple rovers at ranges beyond 1km.
A project by Arthur Witulski at Vanderbilt University in Nashville and GE Research aims to deliver silicon-carbide (SiC) power components that are radiation-tolerant and can operate near the rated voltages without the radiation-induced burnout or degradation to which they are susceptible in the space environment. With their low losses and high voltage and current ratings, SiC power diodes and transistors are otherwise ideal for space applications.
Control methodologies for flexible energy distribution between multiple different power grids is the focus of an investigation led by Jin Wang at the Ohio State University in Columbus. The goal is to develop a modular DC energy router that can function not only as a power flow controller but also as an intelligent circuit breaker.
Some of the applications envisaged with these technologies include drilling for water, oxygen extraction and analysis of the strength and composition of the lunar surface strata, all of which will support a growing presence on the Moon increasingly reliant on the local resources.