What are the issues related to mining the water? How difficult is it to exploit these resources? The issues include those related to the high and low gravity environments, the purity of the product water, the economics, and the environment humans can expect to find when there. The two classes of space water mining environments, at high gravity objects and at low gravity objects, have completely different problems:
HIGH GRAVITY OBJECTS
Mining on an object with some gravity is similar to such mining on Earth, where up is up, down is down and all things fall. The key difference is the lack of an atmosphere. Any wells will probably leak. That is, pressurizing the hole will not work, as drillers do on Earth. The ice on the poles of moons and planets is almost certainly not directly at the surface. But it is probably not farther down than the tens of meters a radar can penetrate, because radar did see it. The ice is expected to be at least colder than about -50 Celsius. It will be permeated with sand, very much like permafrost. One can almost certainly expect cracks and slippage planes. The Alaskan drilling experience indicates new methods will be needed to dig space permafrost. One may need to develop tools that drill by heat.
One can not easily have "drilling mud" because it will freeze solid in the extreme cold, or boil or sublime away into the vacuum of space. None of the water objects has enough gravity to keep an atmosphere. The operations will almost certainly be completely in the dark. And dust will be a major problem if it comes in contact with any joints, gears or rubbing surfaces.
The composition of the water bearer is not known.
Lowering mining hardware down to the surface of the Moon, or to a planet like Mercury or Mars, requires powerful reverse thrusting maneuvers. This limits the mass of hardware payloads to be less than what a powerful rocket can deliver, which happens to be about what a single train car can hold, and will certainly be less than 100 tonnes at a time. Lifting payloads off these high-gravity objects is only slightly easier because the rocket fuel is abundant on the object surface.
LOW GRAVITY OBJECTS
Mining a low gravity object requires that the rig grab the NEO and pull itself into the region to be drilled. Drilling mud will not stay put, nor will it fall into the hole. The drilled hole will almost certainly leak if an attempt is made to pressurize it. Even an overburden hundreds of meters deep may be lifted with very little pressure. If you pressurize a hole drilled into the comet, you risk blowing the comet to pieces.
The billion year irradiation by Galactic Cosmic Radiation (GCR) dissociates the water ice in its path, causing about 1% of the energy to go into radiolytic dissociation. The products, a solid solution of stoichiometric hydrogen and oxygen gas, are locked in a matrix of the permafrost. The ice would burn if put in an airtight bell jar and lit with a match. A 1 billion year residence time in the 50 rad per year bath of GCR would cause the first meter of ice to store an energy of about 2 Megajoules per pound, or the same energy as the high explosive Baritol. The entire comet could detonate and vaporize in a brief flash if mistreated.
No one knows how competent the material will be, that is, whether it is as delicate as fluffy snow, or as sturdy as permafrost. The mining system may find the "soil" to be a fine powder, incapable of supporting hardware.
The composition of the comet interior is expected to be more like a frozen solid, -50 Celsius cesspool, saturated with organic poisons, tar and sand. The drilling device may become stuck or corroded in the tar and what may likely be highly corrosive free radical materials. The material may foam upon heating under sufficient pressure to form liquid water.
The water must be pure enough to be put into red hot stainless steel reaction vessels without causing reactions or precipitation. The dissolved salts and hydrocarbon concentrations must be low enough to be measured in units of tens of parts per million. The separation of hydrocarbons may not be trivial because the only simple separation method, distillation, does not readily remove all the hydrocarbon.
Mining claims must be honored before the resource discovery rights can be sold as assets. The rights must be sellable to raise capital to mine them. The current laws are unclear and may inhibit sales of claims. All operations must be either performed by autonomous robotics or with people. The support systems for people are very expensive. The use of robotics is uncertain.
The robots must be autonomous [or very slow] because the radio wave transmission delay is so large, typically several tens of minutes for a control signal to reach the robot and for any feedback signal to return.
Virtually all the environments will subject humans to a constant flux of Galactic Cosmic Radiation. If shielded only by the hull of the Shuttle, a human would receive 50 R per year. This is about 150 times the yearly radiation received at sea level. To shield GCR requires that the humans place at least a meter of a dense material (such as water, ice or dirt) between them and space. The result will be to keep people in small spaces and in the dark.
SUMMARY & CONCLUSIONS
Accessible water in the form of ice or permafrost has recently been found at nearly every location in the inner Solar System. Radar signatures indicate water ice at the forever-dark North Pole of the planet Mercury and possibly in a dark crater at the South Pole of the Moon. Visible and other data indicate water ice on the poles of Mars. Dissociated water has been observed in the transient atmospheric region above the north pole of Ceres, strongly suggesting the asteroid may contain massive quantities of water ice. Ceres is the largest asteroid and is located in the inner region of the asteroid belt. During 1992 a somewhat common type of Near Earth Object (NEO) was found to be a comet, now referred to as the comet Wilson-Harrington. Its orbit comes within 20 Earth-moon distances to the orbit of Earth about every 4.3 years. Observations and comet tail fly-through experiments of a similar comet revealed that comets contain about 1/3 water ice, 1/3 hydrocarbons very similar to high grade oil shale, some ten percent CO2, and about 1% nitrogen compounds. About a dozen comets in the Jupiter family formation have accessible orbits, based on travel time and propulsion considerations.
Water is key to the exploitation of space because as a rocket propellant it requires only heat energy to provide thrust. The simplicity is the value. Further, mixed with the equally abundant hydrocarbons recently discovered on comets, and heat, it produces hydrogen, also a premier rocket propellant.
The principle barriers to mining the water include the darkness, the vacuum of space, low gravity, and most important: our near total ignorance of the composition or environment in which the water resides. Space laws inhibit mining because they do not provide a way to own and sell the mineral rights necessary to provide the capital for prospecting, assay and development.
The orbits of the objects with water pass close to the orbit of every location humans may want to travel in the Solar System, and in this sense the discovery provides a bridge to space. The accessibility, location and amount of the water and hydrocarbons recently discovered provide the raw materials needed to transport the nearly unlimited resources of space back to Earth itself.
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Powell, James R., Hans Ludewig, and George Maise, Nuclear Thermal Propulsion Engine Based On Particle Bed Reactor," in Proceedings of Tenth Symnposium on Space Nuclear Power and Propulsion, M. S. El-Genk, and M. D. Hoover, eds., American Institute of Physics, new York, 1993, Part One, pages 579 through 583
Worden, Col. S. Pete, USAF, "Satellite on a Chip," Eighth Annual Idaho National Engineering laboratory Computing Symposium, October 4-7, 1994, Idaho Falls, Idaho
Zuppero, Anthony C, "Simple Propulsion to Mine Rocket Fuel from Near Earth Comets", Tues 2 July 1991, Missions to NEA's and Utilization, at "First International Conference on NEAR-EARTH ASTEROIDS," 30 June - 3 July 1991, San Juan Capistrano Research Institute, San Juan Capistrano, California, USA
Anthony C. Zuppero, Idaho National Engineering Laboratory, Idaho Falls, ID 83415 208 526 5382, FAX 208 526 7146, firstname.lastname@example.org