In-Situ Resource Utilization

From Wikipedia, the free encyclopedia

ISRU Reverse Water Gas Shift Testbed (NASA KSC).

In space exploration, In-Situ Resource Utilization (ISRU) describes the proposed use of resources found or manufactured on other planetary bodies (the Moon, Mars, 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."^[1]

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.

1 Mars
2 The Moon
- 2.1 Solar cell production
- 2.2 Criticism
3 ISRU classification
4 Other proposals
5 See also
6 References
7 External links

[edit] Mars

ISRU research for Mars is focussed primarily on providing rocket propellant for a return trip to Earth - either for a manned or a sample return mission - or for use as fuel on Mars. Since the proposed techniques are with the well characterised Martian atmosphere which can be easily simulated on Earth these proposals are relatively simple to implement, though it is by no means certain that NASA or the ESA will favour this high technology approach over a safer direct mission[1].

A typical proposal for ISRU is the use of a Sabatier reaction, CO₂ + 4H₂ → CH₄ + 2H₂O, in order to produce methane on the Martian surface, to be used as a propellant. The usefulness of this reaction is that only the hydrogen (which is light) need be brought from Earth[2].

Another reaction proposed for Mars is the reverse water gas shift reaction, CO₂ + H₂ → CO + H₂O. This reaction takes place rapidly in the presence of an iron-chrome catalyst at 400 Centigrade^[2], and has been implemented in an earth based testbed by NASA^[3]. Oxygen is liberated from the water by electrolysis, and the hydrogen can be recycled back into the gas shift reaction, meaning that only a small amount of hydrogen is needed and can be brought from Earth.

[edit] The Moon

Footprint in lunar regolith.

On the moon, the lunar highland material anorthite is similar to the earth mineral bauxite, which is an aluminium ore. Smelters can produce pure aluminum, calcium metal, oxygen and silica glass from anorthite. Raw anorthsite is also good for making fiberglass and other glass and ceramic products.^[4] Over twenty different methods have been proposed for oxygen extraction on the Moon. Oxygen is often found in iron rich lunar minerals and glasses as iron oxide. The oxygen can be extracted by heating the material to temperatures above 900°C and exposing it to hydrogen gas. The basic equation is: FeO + H₂ → Fe + H₂O. This process has recently been made much more practical by the discovery of significant amounts of hydrogen containing regolith near the moon's poles by the Clementine spacecraft^[5].

It has also been proposed to use lunar regolith as a general construction material^[6], through processing techniques such as sintering, hot-pressing, liquification, and the cast basalt method. The cast basalt method is used on Earth for construction of, for example, pipes where a high resistance to abrasion is required. Cast basalt has a very high hardness of 8 Mohs (diamond is 10 Mohs) but is also susceptible to mechanical impact and thermal shock^[7] which could be a problem on the moon.

Glass and glass fibre are straight forward to process on the moon and mars, and it has been argued^[4] that the glass is optically superior to that made on the Earth because it can be made anhydrous. Successful tests have been performed on earth using two lunar regolith simulants MLS-1 and MLS-2[3].

In August 2005, NASA contracted for the production of 16 metric tons of simulated lunar soil, or "Lunar Regolith Simulant Material."^[8] This material, called JSC-1a, is now commercially available for research on how lunar soil could be utilized in-situ.^[9]

[edit] 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 the proposal was intended as an alternate power source for Earth, the power being transmitted to Earth via microwave beams^[10] . However despite much work on the costings 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 Flourine brought from Earth as potassium flouride to separate the raw materials from the lunar rocks^[11] .

[edit] Criticism

While it is without doubt that ISRU will provide a spur to technological innovation that will one day prove useful, a question mark hangs over whether it is a cost effective techniqe for accelerating present exploration of space. One critique [4]^{[not in citation given]} points out that the rather long lead in time for lunar ISRU means that for the first decade of lunar base build up ISRU will actually hinder the program by taking up valuable cargo space for little return. However, lunar resources are only one of those available for use.

[edit] ISRU classification

In October 2004, NASA’s Advanced Planning and Integration Office commissioned an ISRU capability roadmap team. The team's report, along with those of 14 other capability roadmap teams, were published May 22, 2005.^[12] The report identifies seven ISRU capabilities: (i) resource extraction, (ii) material handling and transport, (iii) resource processing, (iv) surface manufacturing with in-situ resources, (v) surface construction, (vi) surface ISRU product and consumable storage and distribution, and (vii) ISRU unique development and certification capabilities.

[edit] Other proposals

Other proposals are based on Phobos and Deimos. These moons are in reasonably high orbits above Mars, have very low escape velocities, and unlike Mars have return delta-v's from their surfaces to LEO which are less than the return from the Moon.

Phobos in particular has shown signs of possessing water, and water (steam) is a very adequate rocket propellant in its own right^[13], and at least one study has shown orders of magnitude lower costs and higher production rate from simply using steam rather than electrolysing the water and then liquifying the resultant gases.^[14] In addition, water is stable and space storable.