Trans-Formers for Lunar Extreme Environments: Ensuring Long-Term Operation in Regions of Darkness and Low Temperatures

The Moon is a highly valuable asset in humanity's move beyond Earth. Its polar regions harbor some of the most valuable real estate in the solar system. The regions are rich in solar energy, as their elevated altitude and polar location (the rotation axis of the Moon is almost perpendicular to the incoming sunrays) enables them to see the Sun for extended periods of time. Their permanently shaded regions (PSRs), such as the polar craters, are also rich in water resources. Yet, the Moon's natural environment is rather inhospitable for humans, as well as for equipment designed to operate on Earth, especially due to its freezing temperatures in areas that are not exposed to the Sun. The cold darkness restricts operations to 14 Earth days of exposure to sunlight (a lunar daytime), followed by 14 days of hibernation in the night, or to a few short hours, if robots venture into shaded areas like the polar craters powered only by batteries. Radioisotope thermal generators (RTGs) can ensure operation of certain classes of landers and rovers. However, each rover or asset deployed would need to carry one. They cannot satisfy the needs of power hungry equipment needed for mining and processing in-situ resources (MW). There is, however, an intriguing alternative to warm up and power the robots, and illuminate the darkness: one can project solar energy into the area of exploration, transforming the extreme environment (EE) of operation into a more hospitable one. The transformation of the local environment around the robotic or human explorers could be done by TransFormers (TFs). This constitutes a novel approach to addressing NASA's Space Technology Grand Challenge of Surviving Extreme Environments. The simplest TFs would be reflective surfaces placed in Sunilluminated places (e.g., on high ground, such as mountain peaks or rims of craters), which redirect sunlight onto the assets in the shaded areas, to power their solar panels, heat them, illuminate them and their surroundings, and relay communications. The more sunlight is visible to TFs, the more it is potentially available to the assets they irradiate in the darkness. As a wider area gets illuminated, the sunlight can heat and power more than one asset operating in the light 'spot' at no additional cost. TFs also make possible the operation of multiple smaller rovers/probes, which are challenged to accommodate their own power due to their compact size. As such, TFs could enable lower-cost missions, with increasing cost benefits for repeated missions in the same area, and for powering/warming multiple rovers/vehicles/habitats. TFs could redirect sunlight to locations kilometers away, e.g., from the rim of the lunar south pole's Shackleton Crater to its bottom, where it could ensure operations of both prospecting rovers and in situ resource utilization (ISRU) equipment. A 40-m diameter TF on the rim fully reflecting all incident solar radiation would provide an irradiation of ~300 W/m2 at 10 km into the crater. A solar-powered MSL-class rover with 6 m2 solar panels, operating inside the crater, would thus obtain the needed ~300 W electrical to move around and perform measurements, in what would otherwise be low 40-90 K temperatures. Ice water near the surface would take tens of minutes to sublimate under direct illumination of the soil, and longer for deeper ice deposits. Thus, short exposures, as may take place as 'side spill' during illumination of a rover as it traverses a region, should not impact the environment. On the other hand, in the absence of such concerns, concentrated heating from TFs could be used to sublimate water from the soil. In other words, rovers should not stop long over water deposits unless they are trying to extract the water; they should stop in rest areas or be prepared to protect the terrain otherwise, e.g., by using intermittent illumination, etc. An important challenge in our study of the TF concept was to determine survivability in the PSR, by providing uninterrupted power (day and night, every day of the year). This was shown to be possible to a large extent: the projection of solar power from a set of TFs properly positioned on the rim of Shackleton Crater in an arrangement in which at least one is illuminated at any moment in time could ensure needed quasi-continuous illumination in specific areas where its rays can reach. Hours of darkness due to lunar eclipses are inevitable, and there is additional obstruction from some mountain peaks. Our study has examined trade-offs in the size, height, and number of TF reflectors. For example, either a single 1000 m2 reflector at a height of 800 m, or an arrangement of two reflectors at 450 m, or of three reflectors at 300 m, could provide close to 99% continuous solar illumination within a few km from the reflectors; the coverage area depends on the topography (constrained by having a line of sight from the illuminated point on the ground to the reflectors). In principle, a single reflector, high enough to see the Sun continuously, and large enough so it is able to have the entire disc of the Sun seen at the locale of projection, would satisfy the requirements. However, by using multiple reflectors, the size of each reflector can be reduced, and the height at which they need to be positioned can be reduced because local obstructions of the Sun are mitigated. Energy storage is needed to deal with interruptions in sunlight, and it influences trade-offs. Ensuring higher energy storage capacity reduces the requirements on the height of the tower. Another key challenge in our study was to consider the mass and volume constraints for packaging TFs for delivery to the surface of the Moon. The TFs need to be relatively low mass and low volume during transportation from Earth. Both Mylar and the more space-robust aluminized Kapton designs were analyzed. A TF reflector design with a Kapton layer, stowed using a spiral crease origami folding pattern weights 235 kg and fits in 1.34 m3 volume. A tower over 100-m tall made of 2-m diameter inflatable beams to structurally support the reflectors was designed and analyzed. A 50 g/m2 inflatable surface requires ~8 m3 and ~900 kg, which means that a TF composed of the tower plus two 40 m-diameter reflectors could be built within the same mass and volume constraints of an MER-class rover A TF and a prospecting rover could be designed and deployed in a Discovery-class mission. In addition to establishing the feasibility of TFs, examining trade-offs in their design, and analyzing their mass and volume packaging, the study focused on application of the TF concept to the development and maintenance of a Lunar Utilities Infrastructure at the lunar south pole. For this application, the amount of power to be projected relates to the amount of water needed in different scenarios. An affordable/sustainable humans-to-Mars architecture supported by lunar propellant was formulated during the study and indicates a need for 7.5 tons of propellant. To obtain it, it would require10 tons of water per day, for which an estimated ~0.6 MW thermal power (assuming 10% water in regolith), and, in a lossless transmission, ~0.6 MW solar power needs to be reflected. About 2 MW electric power, which may add to 6 MW of solar power reflected, would be needed for obtaining LH2 and LO2. From 10 km away, a 40-m diameter reflector would provide ~1.2 MW; a 100-m diameter would reflect ~8MW. A more ambitious vision emerges. The TFs located on high ground could send energy to each other, not only to the energy 'oases' they are designed to illuminate. Energy could also reach the final destination through multi-hop relays. The network could extend tens of kilometers radially from the south pole (and similarly at the north pole). Such an energy infrastructure would be an enabler for establishing a Moon village and a true lunar economy. The energy infrastructure would to a large extent eliminate the extreme environment barrier. We would be able to send cheaper solar-powered robotic systems built for Earth-like conditions. Using this energy infrastructure as the basis for establishing additional infrastructure for water and propellant processing would enable the lunar economy to truly flourish.