Artist depiction of the landing of the ESA spacecraft Huygens on Titan.
Earth has sustained multi-form life by providing accessible resources to humans and a multitude of living organisms. This rich environment shared by all specie is unique in our Solar System and has evolved over time in a symbiotic relationship with living creatures that learn to utilize it. Examples abound that demonstrate how resource utilization is a fundamental precept of life as we know it from diatoms building shells of silica to plankton fixing dissolved carbon dioxide in oceans to plants releasing oxygen using sunlight and decaying into soil when devoured by land insects. Humans developed a global view of the planet and built civilizations by extracting and transforming every imaginable resource; from metals and oxides in minerals to precious gases from its atmosphere and water and salts from its oceans.
Crater on Mars with deposit of carbon dioxide ice (Image credit: ESA)
Our 55-plus years of experience of leaving Earth has taught us that we can only survive in space by carefully adapting and utilizing the environment. In free space, spacecraft make use of vacuum, solar radiation and the background temperature of space to generate power and regulate their internal temperature. Solar sails now use the pressure created by solar winds as a source of propulsion. So far, our technology has allowed us to voyage through space and to other planets by carrying what we need and adapting to the space environment in a relatively passive way and in limited fashion. Our quest to push our spacecraft further for longer periods of exploration and to send humans on Mars and beyond still forces us to actively seek and use the accessible resources on other worlds to ensure the survival and performance of both crew and machines. Ultimately, the reach of machines and humans in space will depend on how we learn to utilize space resources as we did on Earth.
Lunar regolith dug by astronauts during Apollo 16 mission.(Credit: NASA)
Current work in NASA's ISRU Technology Development Project is focused on three major types of space resources: regolith, atmosphere, and solar energy.
Regolith is a term that defines unconsolidated material that overlies solid rock on planetary bodies. It is generally used instead of soil because the use of the latter often evokes material that contains organic matter, which is not typically the case outside Earth. All planetary bodies are rocky in nature in the inner Solar System that stretches to the asteroid belt between Mars and Jupiter.In the outer part of the system, the surface of many moons of the gas giants Jupiter, Saturn, Neptune and Uranus offer the same silicate regolith. Throughout the inner solar system, regoliths are typically mixtures of mineral oxides dominated by silicates similar to those found on Earth but in different ratios. Beyond that common trait, the characteristics of regolith differ significantly from one planetary body to another due to their environment. Lunar regolith is weathered by thermal cycles, meteorite impacts and solar radiation and does not interact with an atmosphere. All physical resources on the Moon are embedded in the regolith from recently discovered water ice to metals, glass, and implanted volatile ions. Martian regolith has been much more altered by winds, thermal cycles, ancient water, and the atmosphere. Asteroids are the studied extensively for the resources they may hold. Indeed, some of them may be composed of large quantities of concentrated metal oxides while others are reservoirs of water ice. Simulant materials of regolith are critical for technology development in ISRU and the Regolith Simulant Development project led by NASA MSFC establihes requirements and standards for their characterization and their use.
The atmosphere of Mars is mostly made of carbon dioxide (95%) with nitrogen and argon. (Image credit: NASA)
Atmospheres hold vast resources of critical importance. Oxygen and carbon in the form of carbon dioxide (CO2) constitute 95% of the Martian atmosphere and buffer gases such as nitrogen (N2; 2.7%) and Argon (Ar; 1.6%). Although present at low pressure (~ 7 mbar or 1/100 of Earth pressure), it offers a major source of important gases accessible through simple chemical processes. The reaction of CO2 with hydrogen in a Sabatier reactor yields methane (CH4) and water (H2O). Methane is sought as a propulsion fuel and water can be electrolyzed to yield oxygen (O2) to burn the methane in a rocket engine. Nitrogen extracted from the Martian atmosphere is also very valuable as a buffer gas for breathing air in habitats and spacecraft. Atmospheric ISRU can potentially revolutionize our abilities to reach the outer Solar System by accessing the vast reservoirs of high value gases around the giant planets; Titan, a massive moon of Saturn offers nitrogen and methane and Europa, the Jovian moon has an oxygen-rich atmosphere.
Solar energy is a critical complementary resource for ISRU processes. The Sun provides critical photonic radiation for photovoltaic power generation but its radiant heat can also be harnessed to bring reactors to operating temperatures or provide heat to robotic systems in very cold environments.