An ice-mining lunar rover powered by Americium-241

Conceptual illustration of the ice-mining lunar rover showing its main components including a Radioisotope Power System (RPS) employing Americium-241. Credits: Mazzotti et al. (2024)

Lunar space settlements will need supplies of water for life support and rocket fuel in the coming water economy in cislunar space. Given how expensive it is to launch water out of Earth’s gravity well, mining the liquid gold in situ on the Moon makes the most economic sense. Until recently, it was thought that most of the water on the Moon was trapped in the permanently shadowed regions (PSRs) in craters near the poles. Although recent data from the Indian Space Research Organization’s Chandrayaan-1 mission has found evidence that water and hydroxyl is more wide spread across all latitudes, the icy deposits in the PSRs may be more concentrated and readily accessible then that bound up in regolith away from the poles.

A team of researchers* in the UK and Italy have developed a lunar rover capable of mining for ice in PSRs. In a paper in Acta Astronautica they describe their approach using an innovative power source, a Radioisotope Power System (RPS) using Americium-241 (241Am). One of the problems for ice mining in a PSR is that by definition, the crater floors never see sunlight and they are as cold as 40o K. Solar powered mining equipment would be severely challenged in this environment as its batteries would have to be frequently recharged at the crater rim and the extreme cryogenic temperatures would affect performance. Rovers utilizing an onboard RPS could operate autonomously and continually in a PSR. 241Am has a half life of 432 years enabling decades of power output without the need to refuel. It is the preferred isotope in Europe because it can be economically separated from spent nuclear fuel produced in civil reactors.

The current state of the art for ice mining methods are either mechanical or thermal. Mechanical processes require beneficiation of excavated regolith by either pneumatic, magnetic or electrostatic separation. SSP has covered one such mechanical extraction technique called Aqua Factorem proposed by Philip Metzger at the University of Central Florida. These techniques require prior assessment of the regolith so that the appropriate type of separation method can be tailored to the specific ice content.

Thermal mining employs various ways of heating the regolith to induce sublimation of the icy deposits directly to water vapor which is then refrozen in cold traps for collection. One method is direct solar heating perfected by George Sowers at the Colorado School of Mines. Heating can also be induced by electricity, microwaves or, as proposed by the authors, radioisotope decay heating. Such methods can skip the step of characterizing the regolith for ice content prior to mining operations.

The rover described in the paper is innovative in that the RPS, which would generate a total of 400W, not only provides electrical power, its waste heat could be utilized for ice mining. The electrical power would be generated by thermal input to a Stirling convertor with an efficiency of ∼20% to produce ∼80W of electric power leaving ∼320W for the mining operations. A related program in Europe is developing such a Stirling convertor using 241Am for deep space applications.

Here’s how it works: waste heat from the RPS is directed to a plate in a sealed enclosure lowered beneath the rover to sublimate icy deposits in the lunar regolith. The extracted water is directed to the cold trap via a pressure differential in the sealed environment. A PSR ice mining campaign would be divided into four Phases. Phase I (Roving to Ice Deposit) starts with the rover operating on battery power to traverse the PSR surface to the target area. Once an ice deposit has been located Phase II (Isolating ICE Deposit) would situate the rover over the deposit and lower a sealing enclosure over the deposit beneath the rover. Phase III (Volitile Extraction) directs waste heat from the RPS to the plate initiating sublimation of the ice in the regolith for collection in the cold trap. This phase lasts about 2 days. Finally, Phase IV (Separation from Deposit) raises the sealing walls after full extraction of the ice deposit. The rover is then ready to move on to the next target area and repeat the process.

Validation of the heat transfer and thermal management was caried out using 3D Finite Element Methods on the rover design and anticipated environment conditions, i.e. the temperatures of the primary rover elements including the sublimation plate, cold trap, and volatiles tube. Four simulations of ice mining were conducted under varying conditions of icy regolith volumetric content ( 1.0, 5.0, and 10.0%, respectively). The experiment showed that most element temperatures were stable for each ice content scenario.

From the results of the study, the researchers conclude that “…it is feasible to extract ice in a PSR crater of the lunar poles using the waste heat from a RPS radiated downwards to the icy Lunar regolith by a sublimation plate. Ice deposits within the regolith can be successfully sublimated, volatiles can be collected in a pressure-controlled environment, directed to a cold trap, and captured.”

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* Authors of the paper Ice-Mining Lunar Rover using Americium-241 Radioisotope Power Systems : Marzio Mazzotti 1 2, Hannah M. Sargeant 1, Alessandra Barco 1, Ramy Mesalam 1, Emily Jane Watkinson 1, Richard Ambrosi 1, Michèle Lavagna 2

1 University of Leicester, Space Park Leicester, 92 Corporation Road, LE4 5SP Leicester, UK
2 Politecnico di Milano, Piazza Leonardo da Vinci, 32, 20133 Milano MI, Italy

Masten’s Rocket Mining System

Artist depiction of a lander descending to the lunar surface carrying a rover housing Masten’s Rocket Mining System. Credits: Masten Space Systems

Called RocketM for Resource Ore Concentrator using Kinetic Energy Targeted Mining, Masten Space Systems has partnered with Honeybee Robotics and Lunar Outpost to design a novel system for blasting ice out of lunar regolith for ISRU under NASA’s Break the Ice Lunar Challenge program.

Lunar Outpost rover decending to the lunar surface down a ramp deployed off a Masten lander. Credits: Masten Space Systems

RocketM equipment would be housed aboard a Lunar Outpost rover delivered to lunar surface via Masten’s lunar lander. After unloading, the rover would be robotically navigated by a geologic team to an excavation site in the Aitken Basin near the Moon’s south pole. Upon arrival over the target area, the RocketM dome is extended down to the surface to create a seal over the regolith. A rocket is then ignited in a series of 1/2 second pulses fluidizing the regolith into icy grains which are conveyed out of the dome via a Honeybee Robotics PlanetVac pneumatic sampling system for processing. Beneficiation of the particles is accomplished using an Aqua Factorem process for separation into purified ice and other useful components. Aqua Factorem has been covered by SSP in a previous post. The whole process would only take 5-10 minutes.

A view of the inner workings of RocketM showing a centrally located pressure dome extending down to form a seal on the lunar surface. Credits: Masten Space Systems
Cutaway view showing a 100lb thrust rocket engine firing half-second bursts to heat the regolith to a depth of 2 meters releasing icy grains for processing to extract water. Credits: Masten Space Systems.

The stored water can subsequently be electrolyzed using solar energy into hydrogen and oxygen for lunar operations. What is so exciting about this ISRU system is that the rocket engine can be refueled by the mined products enabling an estimated useful life of 5 years.

Masten has tested the system using simulated lunar regolith providing groundwork toward optimizing conditions within the pressure dome. Further testing is needed at the system level to validate flight readiness.

As stated on Masten’s blog: “Usable as drinking water, rocket fuel, and other vital resources, lunar ice extraction is critical to maintain a sustained presence on the Moon and allow future missions to Mars and beyond. It can also be used in conjunction with other volatiles found in lunar regolith, such as oxygen and methane, to support energy, construction, and manufacturing needs. There’s a lot of promise – water excavation is just step one!”

Watch Masten’s video describing the system.