Goals
The Surface Power focus area will develop and mature technologies and systems to supply continuous power throughout the day and night for lunar surface missions. In the short-term, our interdisciplinary community that includes members from industry, government, academia, and non-profits is pursuing solutions to provide power for near-term lunar missions and the development of a lunar grid. It is crucial that this initial grid is also scalable in order to support the much larger power demands of initial production-scale ISRU operations in the 2030s. The primary multi-kW power generation technologies being investigated within the LSIC Surface Power community are Fission Surface Power (FSP) and Vertical Solar Array Technologies (VSAT). It is highly likely that a combination of both of these types of units will ultimately form the foundation of the initial Lunar grid. At the sub-kW power scale, the LSIC community concentrates on radioisotope power sources (RPS) and low-temperature batteries. Additionally, power distribution (cables and beamed power), large-scale energy storage (e.g. Regenerative Fuel Cells), and radiation-tolerant electronics represent key technology gaps that the Surface Power team and our collaborators focus on.
The group will conduct a phased, system level assessment of possible power architecture solutions for the planned Artemis missions to the lunar surface missions and beyond. To work towards this, we connect power experts to their potential user base, framed by the economic and institutional drivers that set the scale of power demand. This approach enables us to identify near-term needs for immediate prioritization, and long-term goals that impact early architectural decisions.
Recent Accomplishments
- Led a Low-Temperature Power and Energy-Storage Workshop in July of 2022 to discuss novel solutions for surviving the extreme conditions of the 14-day lunar night, and better connect industry and academic community members working on cutting-edge battery and thermal management technologies with NASA engineers, technologists, and policy makers.
- Hosted all three NASA FSP Phase I awardees (Lockheed Martin, Westinghouse, and X-Energy) for an extended January 2023 telecon that included presentations and a panel discussion. The event illuminated the current state of the blossoming space nuclear industry, and also highlighted a number of potential challenges requiring imminent attention.
- Continued to broaden the LSIC Surface Power Community by hosting new industry members working on power beaming and radiation testing of space electronics as speakers for the February and March 2023 telecons, respectively.
Current Efforts
- Hosting all three NASA VSAT Phase II awardees (Astrobotic, Honeybee, and Lockheed Martin) for an extended telecon and panel discussion on May 25, 2023.
- Planning a 2-day Power System Reliability Workshop (July 26-27, 2023) to better characterize what “reliability” means for lunar systems and better bridge the gap between early technology development at the component level to the systems-level approach to reliability, redundancy and interoperability.
- Investigating various potential lunar surface power grid architectures using a variety of approaches.
Surface Power meetings occur on the fourth Thursday of the month at 11:00 AM ET. For meeting information and agendas, please use the LSIC Wiki on Confluence and/or sign-up for the "Surface Power" Listserv.
The Surface Power focus group has defined 8 subgroups associated with each of the technology gaps identified in NASA STMD's Envisioned Futures. The group breaks into dedicated subgroup sessions twice yearly: once at the summer workshop, to discuss how the subgroup topics relate to the overall workshop topic, and once at the December telecon, to review what work has been done (or is ongoing) for each subgroup area over the year. Regular monthly telecons will frequently address one or more subgroup topics in a general sense, but dedicated subgroup conversations can always be held on Confluence as needed. Descriptions for each of the subgroups below are pulled from the technology gap descriptions in STMD's Envisioned Future Priorities document for the LIVE thrust (published December 2022).
Fission Surface Power
No multi-kWe-scale power sources have been developed to be capable of providing sun-independent, mobile power on the Lunar or Martian surface. Such power is needed not only to supplement solar power for sustainable operations on the Lunar pole but also to bootstrap the printing of power system components from Lunar regolith as infrastructure expands toward lower latitudes.
Though fission reactors have been operated on Earth land and sea for many decades, no reactors have been operated in space since the Soviet Topaz I (~5 kWe) flight in 1988. The Soviet TOPAZ II development unit (~6 kWe) was briefly ground tested in the US in 1994. A space fission reactor development unit (~1 kWe) was tested in the US in 2018.
Reliable and Efficient Long Distance Power Transmission Systems
Earth-sourced power converters, transformers, cables, and load connection and deployment systems do not provide capability at specific power, voltage, and radiation-, thermal-, and dust-tolerance levels sufficient to support reliable power distribution among Lunar pole surface elements. Flight-qualified technologies for all these components are not adapted for the Lunar polar environment.
The technology required to print long distance conductors (100’s of km) on the Lunar surface from locally sourced aluminum has seen little conceptual development.
Power converters of sufficient reliability for current missions are at TRL 9 for near-Earth, geosynchronous, and deep space missions at <200 V. Cables, dust-tolerant load connection systems, and cable deployment systems for the Lunar surface have been developed only to the \bench-top" level. Terrestrial microgrid topologies of similar capacity are well understood.
Solar Power
Earth-sourced solar array blankets do not provide sufficient durability or scale to support full scale ISRU production in the Lunar Pole thermal, dust, and radiation environment. Technology for reflectors/mirrors is likewise not optimized for the Lunar surface environment nor for gathering sunlight low on the horizon as at the Lunar poles.
The technology required to print photovoltaic arrays on the Lunar surface from Lunar silicon has seen little conceptual development.
Photovoltaic arrays (<200 V) and deployment mechanisms suitable for LEO operations are at TRL 9. Vertical array deployment mechanisms for Lunar gravity are at a benchtop level of development. Large 10's kWt-scale reflectors/mirrors are at a concept-level of development. Large scale, surface-level photovoltaic arrays, at a Gwe scale and printed from Lunar-sourced silicon, are at a very early stage of conceptual development.
Long-Life Grid-Scale Secondary Energy Storage
Eclipse-period support of industrial scale ISRU production facilities and a crewed outpost at the Lunar pole will require Earth-sourced, large-scale, long life, maintenance-free electrical energy storage at a MWhe scale.
Expansion of Lunar infrastructure toward the Equator will require large scale electrical and thermal energy storage sourced from Lunar regolith.
SOA: For Earth-sourced, electrical energy storage, H2/O2 Primary fuel cells are nearing TRL 6/7 at a 1 kWe scale with ~5000-hour operating life. High pressure electrolyzers of similar life and scale will be at TRL 5 at completion of NASA STMD’s RFC project. Prototype flywheel energy storage systems of ~5 MWhe capacity have been built for terrestrial grid storage applications. Electrical and thermal energy storage sourced from Lunar regolith, such as metal-oxygen flow batteries and thermal “wadis”, remains at only a conceptual level of development.
Wireless Power Transmission
ISRU ice mining operations in PSR (from prospecting to full-scale industry) will require power transmitted from isolated regions to mobile assets in the PSR interior.
Subscale wireless power transmission systems have been developed to the bench-top level. Relevant pointing mechanisms have been developed for terrestrial applications.
Radioisotope Heat/Power Source in 500 We Increment
A key strategic mission for NASA's Science Mission Directorate (SMD) and for STMD is an understanding of the distribution of resources in the permanently shadowed regions of the Lunar South Pole. A multi-100We, sun-independent power source is required for mobility assets to conduct through prospecting in the 2026 timeframe. Smaller power sources (~100 We) required for CLPS-class science exploration missions in PSR.
The current MMRTG can deliver ~125We BOL from 238Pu General Purpose Heat Sources (GPHS). Its availability for the Lunar PSR prospecting mission is constrained.
Low Temperature Secondary Battery Modules up to 50 kWhe Increment
The principal challenge from Artemis for battery technology is mobility energy storage for ISRU operations in PSRs. SOA (Li-ion) batteries lose 75% of their room temperature (295 K) capacity when operating at 235 K. Battery modules that can deliver SOA 295 K performance in a 70 K environment can thus increase specific energy for batteries in PSRs by well over a factor of three. Such performance might be achieved with a combination of cells developed to perform better at lower temperatures, improved insulation/thermal management hardware, and supplemental radioisotope heat sources.
Li-ion battery modules at 50 kWh-scale can deliver ~500 cycles at 150 Whe/kg at 290 K. Insulation and active thermal management hardware are required to maintain the cells in this temperature range when operating in colder environments.
CH4/O2 Primary Fuel Cell Power up to 10 kWe Increment
Primary power from LO2/LCH4 reactant storage may be the mass-optimal solution for certain Lunar/Mars mobility assets and Landers.
Air/Natural Gas Solid Oxide Fuel Cells are in common terrestrial use up to ~50 kWe scale. Multi-kWe-scale Jet Fuel/O2 power plants tested by USN NUWC in operational configurations. NASA and vendors have tested LO2/LCH4 SOFC 1 kWe-scale in breadboard configurations.
