Engineers Design an Electrical Microgrid for a Lunar Base

For seventy years, Albuquerque-based Sandia National Laboratories has been developing electrical microgrids that increase community resilience and ensure energy security. Applications include the Smart Power Infrastructure Demonstration for Energy Reliability and Security (SPIDERS), designed to support military bases abroad, and independent power systems for hospitals and regions where electrical grids are at risk of being compromised by natural disasters (like hurricanes, flooding, and earthquakes).

In the coming years, Artemis Program, NASA will be sending astronauts back to the Moon for the first time since the Apollo Era and establish a “sustained program of lunar exploration.” To ensure that astronauts have the necessary power to maintain their habitats and support operations on the surface, NASA has partnered with Sandia to develop microgrids for the Moon! This technology could also support future endeavors, like mining, fuel processing, and other activities on the Moon.

One of the main objectives of the Artemis Program is the creation of lunar infrastructure that will allow for long-duration surface operations and eventual missions to Mars. To ensure that rotating crews can explore and conduct science experiments on the surface, NASA will establish the Lunar Gateway (by 2024) and the Artemis Base Camp before this decade is over. This concept will serve as a technology demonstration that will validate design elements and systems for an eventual Martian habitat, allowing for short stays with the eventual goal of staying up to two months.

The Base Camp concept consists of a habitation unit capable of accomodating up to four astronauts as well as a mining and processing facility that will use local resources (lunar regolith and water ice) to fashion rocket fuel, water, oxygen gas, and building materials – a process known as in-situ resource utilization (ISRU). This will extend the duration and range of surface exploration while reducing dependence on resupply missions from Earth. This facility and its microgrid will be located far from the base camp to avoid disrupting other science and technology activities.

But to ensure resiliency and robustness, the electrical grids for both units will be connected during emergencies. While NASA is designing the electrical system controller for the habitation unit, which will be very similar to the International Space Station’s (ISS) direct-current (DC) system, Sandia’s engineers are developing the system that will connect the two microgrids and studying the power flow and operation between them. Said Jack Flicker, a Sandia electrical engineer, in a Sandia LabNews statement:

“There are some very important differences between something like an ISS-type microgrid to something that has the extent of a moon base. One of those differences is the geographic size, which can be problematic, especially when running at low DC voltages.

“Another is that when you start to extend these systems, there will be a lot more power electronics as well as a lot more distributed energy resources that will exist throughout the base. Sandia has been looking at microgrids with a lot of distributed energy resources for quite a long time.”

Microgrids are part of a larger field of technology that includes distributed energy resources (smaller sources of electricity like solar panels and wind turbines) and power electronics – devices that keep electrical systems operating within specifications (like converters). Since 2021, electrical engineer Lee Rashkin and control engineer Dave Wilson have been designing the software to regulate the electrical system controller for the mining and processing center’s microgrid.

This controller needs to maintain an even voltage over different timescales ranging from milliseconds and minutes to entire lunar nights (28 days). In many respects, said Dave, this controller is similar to a vehicle’s cruise control system in that it maintains an even level of voltage on the grid amid changing external situations:

“Our goal is to come up with a lunar energy power management system that can efficiently maintain a level system on all those timescales. We’ve got a specialized Secure Scalable Microgrid [SSM] facility and control-system-design methodology that analyzes this. The facility also has specialized energy storage emulators that can help us determine the specifications for how much energy storage the base needs and their requirements.”

The SSM testbed is a unique Sandia research facility with a scaled and simplified version of the DC lunar microgrid. The testbed consists of three interconnected DC microgrids with custom-built electronics that can mimic different power-production systems and devices (like diesel generators, photovoltaic arrays, energy storage emulators, and power converters). A computer can control each emulator, and the microgrids can be configured to test various scenarios.

This platform provides an excellent means for conducting experiments with slightly-adjusted control software to compare how the system responds. The team will use the SSM to fine-tune their control system and study questions about power system controllers, including the interactions between distributed energy resources, energy storage, and power electronics. Said Wilson:

“The goal here is top-down engineering: We’re trying to determine the control design first, come up with the specifications for the energy storage, and then NASA could use those specifications to get the flight-ready components that meet those specs,” Dave said. “A lot of the time people will do the reverse; they’ll bring you a battery and say, ‘make it work,’ which may degrade the microgrid performance.”

The Sandia researchers’ second focus is to develop the system that will connect the mining facility and habitation module microgrids to ensure resiliency in emergencies. One way to do this is to develop a system that can reroute power to where it’s needed with flexibility. Another is to scale up the system, so there’s enough power if multiple parts fail. Said Jack:

“Usually, we have some combination of those two, where it’s oversized to some extent, but you are also able to flexibly route power how you need to within a microgrid or between independent, yet cooperative microgrids like we’re exploring for the moon. In a contingency event such as an energy storage system failing during an eclipse, we want to be able to port the power at the mining facility over to the base camp to keep astronauts safe.”

Additional considerations include the impact the distance between the microgrids will have on the efficiency and stability of both. The team is also investigating the optimal voltage the connection should operate at and whether NASA should stick with a DC system or develop something that uses alternating current (AC) for the mining unit, then switches DC once it reaches the habitation unit. To explore these questions and investigate contingency scenarios, the Sandia team is using two research facilities.

The first is Sandia’s Distributed Energy Technologies Laboratory (DETL), a multipurpose research facility designed to integrate new energy technologies with new and existing electrical infrastructure. This lab is equipped with the tools to conduct hardware-in-the-loop experiments, where hardware is subjected to various simulated scenarios, including catastrophic blackouts and weather conditions. These experiments, said Sandia engineer Rachid Darbali-Zamora, are a crucial step between lab simulation and actual field tests:

“With this DC power-hardware-in-the-loop setup that we’re building in the lab, we can test power converters, the impedance of electrical lines between lunar facilities, we could also test actual energy generation and storage devices. Basically, we can use it to study a variety of situations so we can design a system that is self-sustaining and can continue operating even if a solar panel array goes down.”

The team will also use the Emera DC microgrid on Kirtland Air Force Base to see how their power system operates and distributes power in low-energy contingency scenarios. In addition, the teams will be working closely together and using toolboxes from NASA and the SSM Testbed in their connection simulations – and eventually plan to test Dave’s controller in these simulations as well. As Rachid indicated, this research will also have applications here on Earth.

“Even though this work is for a microgrid on the Moon, the research is also relevant to creating resiliency for communities on Earth,” he said. “I’m originally from a small town in Puerto Rico. I hope that some of the lessons that come out of this project in terms of resilience, are lessons I can implement back home.”

This project is being funded by the DOE’s Office of Electricity as part of a DOE-NASA partnership to develop the necessary systems for future lunar missions.

Further Reading: Sandia LabNews