In space exploration, in situ resource utilization (ISRU) is the practice of collecting, processing, storing and use of resources found or manufactured on other astronomical objects (the Moon, Mars, asteroids, old spacecraft etc.) that replace resources that would otherwise be brought from Earth12.
Today’s race to expand launch capabilities from the Earth and using the Moon as a stepping stone to Mars point towards the recurrent theme of scarcity of material for fuel, food, water and materials for producing whatever is needed to utilize near Earth space for human endeavours. As human space exploration evolves toward longer journeys farther from our home planet, ISRU will become increasingly important. Resupply missions are expensive, and as astronaut crews travel further from Earth they need to be more independent of Earth, hence calling for technology which supports sustained exploration. For travel in space, as on Earth, we need practical and affordable ways to use resources along the way, rather than carrying all resources that may be needed. Future astronauts will require the ability to collect space-based resources and transform them into breathable air; water for drinking, hygiene, and plant growth; rocket propellants; building materials; and more. Also, there cannot be an army of factory workers present to produce everything, so ISRU needs to be highly automated, if not fully autonomous.
If any meaningful human space exploration is to happen, ISRU is a necessity. In other words, if we assume the capability to launch humans to Mars and return them safely, the impact of ISRU technology will allow humans to settle on the Moon and Mars. Together with launch technology, ISRU is the key technology to free humankind from being Earthbound.The Moon as a stepping stone to humans on Mars
In a water molecule, oxygen represents ~89% of the weight, while hydrogen is only ~11%. In the case of space applications, the oxygen required to burn hydrogen as a fuel needs to be brought along for the ride; unless it can be produced on the Moon. Thus, oxygen production alone would reduce required payloads to the moon considerably, even when hydrogen is brought from Earth. To transport 1kg of fuel from low Earth orbit (LEO) to the moon requires ~8kg of fuel and getting 8kg of fuel into LEO requires ~150kg at the launch pad on Earth3. As such, there is much to gain by producing only oxygen on the moon, while still bringing hydrogen from Earth. Oxygen produced locally can be used for propellant to proceed to Mars or for producing water. Hydrogen may also be recycled after usage from water using electrolysis. It seems highly likely that the first ISRU technology to be tested and used on the moon will be oxygen production from the oxides on the moon.
The European Space Agency (ESA) forecasts4that by 2030 the following milestones will be reached:
- Identification of one polar and one non-polar deposit of ice on the moon
- A demonstration of water or oxygen production on the moon
Achieving the above will pave the way for building a pilot plant, in turn setting the foundation for human presence on the Moon sustained by local resources by 2040.
Oxygen is present on both the Moon and Mars in abundance, but it is mainly bound in the Lunar and Martian regolith. Water is also present on Mars and likely the Moon in permanently shadowed areas near the poles. Electrolysis in various forms are key to reducing either water or oxides to extract oxygen and hydrogen. Water electrolysis is a highly developed technology but requires a water source. Although it is now proven that water exists on the moon, detailed information regarding quantities and ease of extraction is not yet available. As such, there is a need to develop technologies for extracting the oxygen also from oxides.
ESA has suggested Molten Salt Electrolysis (MSE)5and points to a British company called Metalysis who focus on metal production on Earth using metal oxide powders in a molten salt solution and reduces the metal directly while in the solid state, transforming oxide powder into metal powder. ESA suggests that this technology can be used for oxygen and metal production on the moon. NASA has suggested Molten Oxide Electrolysis (MOE)6 which is similar but requires the oxides themselves to be molten and thus operates at significantly higher temperatures (>1500C, depending on oxide composition and metal to be reduced), which comes with significant technological challenges related to containment and anode deterioration7
The great advantage of the Metalysis process compared to MOE is that it can be performed at significantly lower temperatures and hence is less complex with regards to containment, anode deterioration and feeding of regolith. The possible downside for utilization on the Moon or on Mars is that the salt used as electrolyte likely needs to be brought from Earth and the process, as it is used on Earth today, requires water for washing the metal powders. Research activities to find alternative methods of removing the salt is likely to start soon5.
The regolith and rocks on both the Moon and Mars contain Fe, Si, Mg, Al and several other metals3, mostly bound in rocks and regolith. Metals production is in principle a by-product of the oxygen production from regolith described above. However, depending on the composition of the oxide, the metal extracted will be an alloy with similar composition. To get the metals in the composition we need, some separation process is required. In general, the technologies for doing this on Earth are resource demanding and there will likely be a need for developing new methods for doing this off Earth. As an example, solar grade Si requires high purity (6N purity, or 99.9999%)8, and Earth-based processes are complex and resource demanding, and will be difficult to do on the moon. Another technology with great potential for extra-terrestrial metals production is Hybrit9, a technology being developed by SSAB, LKAB and Vattenfall in Sweden which uses hydrogen as the reduction agent to reduce iron oxide to iron. The by-product is water which can be recycled into hydrogen and oxygen.
Moon regolith can also be sintered by heating it to create construction materials, and may even be possible to use as a feedstock to 3D printers for construction10. Martian regolith may also be possible to use as bricks, as shown by experiments using simulant regolith and simply pressing them into bricks achieving strength in excess of steel-reinforced concrete11. This has not been studied using real Martian regolith, and much research is needed to gain knowledge on how to utilize Martian as well as lunar regolith for building material.
Carbon is present on Mars in abundance as the atmosphere consist of 96% CO2. This carbon can be used for life support (e.g. plant growth) and for fuel production (e.g. methane, CH4). On the Moon, carbon is scarce and is likely to be found in the permanently shadowed regions near the poles and in the solar wind (~50ppm)3.
Asteroids often contain high concentrations of rare metal elements which are valuable in certain high-tech applications. It has also been estimated that many of the elements we rely on for modern industry could be exhausted in 50-60 years. Elements such as Platinum, Cobalt, Iridium, Palladium and others may be attractive to mine and return to Earth for profit. However, the financial requirements for such an endeavor seems insurmountable at present, and the technologies required are not yet developed to a degree that makes a clear path visible. It is not likely that asteroid mining will be seen or even seriously planned within 2030.
Traditionally steel is produced using carbon (coke) and iron oxide. The coke has two purposes: It provides heat for the reaction and it acts as a reducing agent turning the oxide into metal. For both, CO2 emissions is the result and the steel industry is responsible for up to ~7% of global CO2 emissions12. Steel production using hydrogen or electrolysis for reduction are potential routes to decarbonize steel production on Earth. Should the steel industry become subject to regulation or carbon taxation, this will make ‘green metal’ more attractive on Earth and push technology development, which in turn will benefit space exploration efforts.
NASA is under presidential order to land humans on Mars within 2033, a controversial order that has been criticized as being not very realistic13. Meanwhile, SpaceX claims that it plans to do this during the 2020s14. However, if travels to Mars via the Moon are to become reality, ISRU technology must be ready before launching people towards the Moon. Humans can not live on Mars without the ability to produce oxygen and water via the utilization of local resources and recycling of spent resources.
Currently, ISRU is not in a mature state. While a range of different technologies that are present today on Earth may be used successfully on the Moon and Mars, there is a need to build experience with how both known and new types of equipment reacts to their dusty surfaces. Lunar regolith is highly abrasive and can wear down equipment fast. Uncertainties might be addressed by extensive experimentation using Lunar or Martian regolith simulant, but at a cost. The amount and distribution of resources, e.g. water and carbon on the moon, is highly uncertain so more detailed resource surveys are called for to reduce this uncertainty.
In addition, regulatory and political hurdles will need to be overcome such as ownership of resources discovered in space, ownership of land and international agreements that both government and private agencies will need to abide to. The United Nation Outer Space Treaty and the Moon Treaty15attempt to govern extra-terrestrial bodies to some degree. The latter forbids private ownership of extra-terrestrial real estate but has only been ratified by 18 countries (US, China, Russia and most European countries are not among them). Since humanity is getting closer to a technological level where such governance becomes relevant, the time may be ripe to revise these treaties.
DNV GL is grateful to Dr. Alexandre Meurisse, Research Fellow, European Space Agency, for valuable discussions.
Image 1&2 courtesy NASAContributors
Main author: Knut Erik Knutsen
Editor: Tiffany Hildre
- Sacksteder, Kurt R.; Sanders, Gerald B. (2007). In-situ resource utilization for lunar and mars exploration. AIAA Aerospace Sciences Meeting and Exhibit. AIAA 2007-345.
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- Conversations with Dr. Alexandre Meurisse, Research Fellow – Lunar ISRU preparation, ESA/ESTEC Noordwijk
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