What is In-situ Resource Utilization (ISRU) ?
In-situ resource utilization (ISRU) describes the proposed use of resources found or manufactured on other astronomical objects (the Moon, Mars, Asteroids, etc.) to further the goals of a space mission.
According to NASA, “In-situ resource utilization will enable the affordable establishment of extraterrestrial exploration and operations by minimizing the materials carried from Earth.”
ISRU can provide materials for life support, propellants, construction materials, and energy to a science payload or a crew deployed on a planet, moon, or asteroid.
It is now very common for spacecraft to harness the solar radiation found in-situ, and it is likely missions to planetary surfaces will also use solar power. Beyond that, ISRU has not yet received any practical application, but it is seen by exploration proponents as a way to drastically reduce the amount of payload that must be launched from Earth in order to explore a given planetary body.
Proposals have been made for “mining” atmospheric gases for rocket propulsion, using what is called a Propulsive Fluid Accumulator.
Solar cell production
It has long been suggested that solar cells could be produced from the materials present on the lunar surface. In its original form, known as the solar power satellite, the proposal was intended as an alternate power source for Earth. Solar cells would be shipped to Earth orbit and assembled, the power being transmitted to Earth via microwave beams. Despite much work on the cost of such a venture, the uncertainty lay in the cost and complexity of fabrication procedures on the lunar surface. A more modest reincarnation of this dream is for it to create solar cells to power future lunar bases. One particular proposal is to simplify the process by using fluorine brought from Earth as potassium fluoride to separate the raw materials from the lunar rocks.
Rocket propellant from water ice has also been proposed for the Moon, mainly from ice that has been found at the poles. The likely difficulties include working at extremely low temperatures and extraction from the regolith. Most schemes electrolyse the water and form hydrogen and oxygen and liquify and cryogenically store them. This requires large amounts of equipment and power to achieve. Alternatively it is possible to simply heat the water in a nuclear or solar thermal rocket, which seems to give very much more mass delivered to low Earth orbit (LEO) in spite of the much lower specific impulse, for a given amount of equipment.
The monopropellant hydrogen peroxide (H2O2) can be made from water on Mars and the Moon.
Aluminium as well as other metals have been proposed for use as rocket propellant made using lunar resources, and proposals include reacting the aluminium with water.
The spacecraft could use the propellant itself or supply a propellant depot.
Oxygen to breathe and water to drink
Water ice could replenish a space ship’s water tanks. Water is needed for hygiene and obviously to drink, but may also be used for radiation protection in deep space (living quarters inside a double-walled cylindrical water tank). Splitting water allows the creation of rocket propellant, but can also liberate oxygen that could be used to replenish the atmosphere in a closed-loop recycling system.
Metals for construction or return to Earth
Asteroid mining could also involve extraction of metals for construction material in space, which may be more cost-effective than bringing such material up out of Earth’s deep gravity well, or that of any other large body like the Moon or Mars. Metallic asteroids contain huge amounts of siderophilic metals, including precious metals.