Over the next decade, several space agencies and commercial space partners will send crewed missions to the Moon. Unlike the “footprints and flags” missions of the Apollo era, these missions are aimed at establishing a “sustainable lunar exploration program.” In other words, we are going back to the moon with the intention of staying, which means that infrastructure must be created. This includes spacecraft, landers, habitats, landing and launch sites, transportation, food, water, and energy systems. As always, space agencies are looking for ways to use local resources to meet these needs.
This process is known as in-situ resource utilization (ISRU), which reduces costs by limiting the number of payloads that must be launched from Earth. Thanks to new research by a team at Tallinn University of Technology (TalTech) in Estonia, it may be possible for astronauts to manufacture solar cells using locally sourced regolith (moon dust) to create a promising material known as pyrite. These findings could be a game-changer for missions in the near future, which include ESA’s Lunar Village, NASA’s Artemis program and the Sino-Russian International Lunar Research Station (ILRS).
The research team was led by Kätriin Kristmann, Ph.D. researcher at TalTech and Head of Communications of the Estonian Student Satellite Foundation (ESTCube). She was joined by a host of researchers from TalTech’s Materials and Environmental Technologies and Physics division and Advenit Makaya, an advanced manufacturing engineer at ESA’s European Space Research and Technology Center (ESTEC). As they pointed out in their study, the Moon has the right elements to create monogranular layer (MGL) solar cells using pyrite.
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As Christman told Universe Today via email, their research addresses a fundamental need for future lunar missions: the ability to generate power in a way that is independent of Earth. That means focusing on renewables and relying on fuel cell batteries only as a backup. As Christman explained:
“Energy generation on the Moon is essential if we aim to establish a permanent settlement there. The use of solar energy is one of the most promising candidates, since most of the conventional energy sources available on Earth today are not available on the Moon. The main challenge is to use the resources that are available in situ from the lunar regolith to build the power station and take as little material as possible from Earth.
Christman and her colleagues at TalTech have been working with pyrite for many years because of its potential as a solar cell substrate (a layer placed over a photovoltaic cell to make it more absorbent). The term “monolayer” refers to the structure of the material, which is made of microcrystalline powders, resulting in a light and flexible cell. Pyrite has an atomic structure of one iron atom bonded to two sulfur atoms (FeS2), both of which are abundant on the lunar surface.
Marit Kauk-Kuusik, head of the Photovoltaic Materials Laboratory at TalTech and co-author of the study, explained the benefits of the material in an article published by TalTech in January 2022:
“Scientists at TalTech have been working on monograin solar cell technology for terrestrial applications for several decades. The main innovation is the unique light-absorbing layer made of single-crystal powder, which contains abundant and cheap elements. Solar cells based on this technology will bring innovation to the field of solar energy integrated into buildings.”
Taltech researcher Kätriin Kristmann. Credit: Tallinn University of Technology (TalTech)
For the purpose of this study, Christman and her colleagues designed a solar cell structure that consists of a pyrite absorber layer combined with a graphite nickel oxide (NiO) layer and a transparent conductive oxide (TCO). These would be combined with Schottky diodes made of pyrite and platinum. As Kritman explained, incorporating this material provides many benefits:
“Pyrite is an advantageous material because the energy input used to produce a pyrite-based solar panel is remarkably lower than for conventional silicon solar cells. This is because we can proceed at much lower temperatures in the preparation of this solar cell material. Lower temperature means lower energy consumption and lower costs. Consisting of iron and sulfur, pyrite also does not contain any elements dangerous to humans.
To create pyrite, the team relied on the liquid salt synthesis method, which combines iron and sulfur in a solution of potassium iodide, which is then heated to 740 °C (1,364 °F) for a week. The solution was then slowly reduced to a temperature of 575 °C (1067 °F), then rapidly cooled to room temperature, yielding a single-phase pyrite monograin powder suitable for the preparation of pyrite MGLs. These tiny crystals can easily be shaped into MGL using 3-D printers and technology that space agencies already plan to send to the moon.
“The potassium salt acts as a medium to create single crystal grains of FeS2, and at the end of the reaction the salt is removed by washing,” Christman said. “This process can be easily adapted to the lunar environment because it does not use any complex equipment with hard-to-obtain prerequisites such as high-purity vacuum chambers or strong lasers or magnetic fields.”
This work builds on previous work by Christman and many other researchers at TalTech’s Photovoltaic Materials Laboratory. For over ten years, Taltech has been researching MGL solar cells with renewable energy applications here on Earth. In addition to being simple, the manufacturing process creates highly efficient monocrystalline solar cells that are flexible and thin, making them very valuable to the growing renewable energy market. But it’s the potential to provide renewable energy for astronauts on the moon and beyond that drives Christman’s team to find better energy solutions.
Habitats clustered together on the rim of a lunar crater known as the Lunar Village. Credit: ESA
As a member of the European Space Agency, Estonia is contributing to the organization’s plans to create a lunar habitat known as the Lunar Village. This proposed base would serve as a spiritual successor to the International Space Station, where rotating crews of astronauts from around the world would live for months at a time and conduct vital research. According to Dr. Taavi Radik (Christman’s PhD supervisor), ESA became interested in TalTech’s photovoltaic research about six years ago when they looked at the MGL solar cell technology and found it promising.
Dr. Advenith Makaya worked with Christman and her colleagues as part of the collaborative relationship between ESA and TalTech. For many years he has worked through ESTEC to support the development of promising advanced materials and processes for space applications. As he explained to Universe Today via email:
“The requirements of power systems to support lunar exploration depend on the volume of activities carried out on the surface and the duration of the missions. Several international space agencies and private companies have indicated plans for long-term missions to the lunar surface. This will require power systems that provide sufficient power for the range of activities that must be performed, as well as adequate reliability and resilience of the space environment to provide power for long-duration missions.
“Therefore, sustainability becomes essential. Until now, solar energy has been the traditional power source for space missions and is expected to still provide a large share of the power required for lunar missions. The ability to manufacture solar cells from indigenous materials could increase the sustainability of missions and help reduce dependence on supplies from Earth and associated costs.
The ISS’s many solar panels give it the shape of the letter “H” when viewed through a telescope. Credit: NASA
Initially, their collaborative efforts focused on testing the technology to see if it was suitable for applications in space. After proving that the technology could work in the extreme cold and vacuum of the Moon, their efforts have since turned to deploying MGL solar cells to power a future lunar outpost and how they can be manufactured using lunar regolith. The success of this latest study shows it can be done, which will have drastic implications for future lunar missions. Christman said:
“The implications that the ability to produce sustainable energy could have for lunar exploration are significant. With reliable energy production [method], we can focus on other important topics such as science and infrastructure when talking about the lunar settlement. Reliable solar energy production would allow us to explore a new world (lunar or beyond) without pollution, ensuring that we as humans have been able to learn from our past and the challenges we have faced on our own planet.
As Dr. Makaya added, there is also a benefit to long-term self-sufficiency when it comes to long-duration missions. In addition to food, water and other basic needs, the International Space Station (ISS) also relies on regular supplies of spare parts and components. This includes backup solar cells and the electronics and tools needed to keep them in working order. But on the Moon, deliveries will be fewer and farther between, making the ISRU aspect of MGL solar cells very attractive:
“With the prospect of long-term missions to explore the lunar surface, including potential large-scale settlements, replacing solar power hardware will become particularly…
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