Phobos and Deimos - The importance of Mars's moons to explor

RobS · 2002-01-19 00:58:44

The Importance of Phobos in Mars Exploration

A crucial and often underappreciated resource for the exploration and eventual settlement of Mars is Phobos and, to a lesser extent, Deimos, its two moons. Phobos is an average of 22 kilometers in diameter, has a mass of 10 quadrillion tons, and orbits about 6,100 kilometers above the Martian surface. Its surface gravity is six ten thousandths that of Earth; thus a five-ton (10,000 pound) boulder on Phobos has a weight of only six pounds.

From the point of view of delta vee (launch velocity), Phobos is about as ?close? to low earth orbit as the Moon; on average, an object in Martian orbit only needs an additional 2.6 kilometers per second (5,800 mph) to enter a Hohmann transfer trajectory to Earth, whereas from the surface of the moon an object needs 2.4 kilometers per second (5,300 mph) to reach low Earth orbit. But this is not the entire story. Some of the most ?interesting? areas of the moon?its north and south poles, where there may be large quantities of volatiles trapped in the regolith?take more delta vee to reach because an orbital plane change is necessary. Furthermore, while the energy needed to reach low earth orbit from either may be approximately the same, the energies needed to go from low earth orbit to Phobos or to the Moon are radically different, because the Martian atmosphere allows aerobraking. Once a vehicle has entered Mars orbit, a relatively small delta vee is sufficient to land on Phobos; but a 2.4 kilometers per second deceleration using a rocket engine is necessary to land on the Moon. Thus from the point of view of round trip delta vee, Phobos and Deimos are the closest objects to the Earth in the solar system. This advantage is somewhat negated by the fact that a flight to them takes six to nine months, the return flight requires the same length of time, and that a round trip requires a wait at either Phobos or Earth of thirteen to seventeen months.

Phobos is also the closest object, in terms of delta vee, to the Martian surface; a rocket needs about 3.8 kilometers per second to reach Phobos. For a methane/oxygen rocket the resulting mass ratio (fuel to payload) is 1.74 to 1.

Phobos is significant because all evidence suggests it is made of carbonaceous chondrite, a stony material rich in water, carbonaceous compounds, and sulfur. The quantity of water and carbon compounds in carbonaceous chondrite meteorites varies; one website gives the average composition of carbonaceous chondrite as 2% carbon, 0.2% nitrogen, 1.8% metals, 83% silicates, and 11% water (http://www.ibiblio.org/lunar/school /solar_system/minecarb.html). The water typically is bound to the silicates, which are clays. The carbon is largely present as ?kerogen? and the kerogen is 77.5% carbon, 7.5% hydrogen, 1.5% nitrogen, 12.0% oxygen, and 1.5% sulfur.

Carbonaceous chondrites can vary from 1% to 5% carbon. We do not know Phobos?s average composition, but clearly it contains a vast amount of carbon, oxygen, and hydrogen, the elements for making methane (CH4) and oxygen fuel. If only 1% of Phobos?s mass could be converted into fuel, the quantity still amounts to 100 trillion tons.

Can the gasses be profitably and easily extracted from the chondrite? The Mars Direct plan already includes many of the elements necessary to set up a fuel manufacturing station on Phobos. A Hab could be landed on Phobos to provide housing for a crew (presumably, because of the moon?s nearly zero gravity, crews could not remain on Phobos more than three to six months, so a permanently inhabited station would require rotating crews down to Mars. Mars would also be the Phobos station?s principal source of supplies). Mars Direct?s Earth Return Vehicle has a first stage that is approximately of the correct power to take crews from the Martian surface to Phobos; if the second stage were replaced by a cargo compartment and modifications that allowed the ERV to be reused, the ERV could serve as the Martian equivalent of the space shuttle, hauling perhaps twenty tonnes of cargo from Mars to Phobos per flight.

More importantly, the Mars Direct plan includes a 4.5 tonne nuclear reactor capable of producing 100 kilowatts of electricity and about 2,000 kilowatts of heat energy. One way to use this energy would be to drill into Phobos. Carbonaceous chondrite is very friable (crumbly); meteorites made from it that land on Earth disintegrate into piles of mud after a few rainstorms. A driller weighing a tonne or two would be capable of drilling hundreds of meters, perhaps kilometers, into the moon. The driller would face two obstacles in doing its work:

1. Drills rely on gravity to press themselves against the surface being cut. Gravity is inadequate for the task on Phobos, so the driller will have to be staked and bolted to the rock.

2. Phobos is cold inside; one website says ?112C (http://www.bbc.co.uk/science/space/ solarsystem/mars/phobos.shtml). Drill bits and other equipment will have to be able to handle exposure to cold materials.

Once a suitable shaft has been drilled, adding heat will drive off water, carbon dioxide, and hydrocarbons (methane and longer chain hydrocarbons of the sort found in petroleum and natural gas). Some of the gasses will enter the drill shaft and rise to the surface, where they can be captured and processed; some will escape into cracks and pores in the rock and freeze solid. Phobos has a mean density of 1,900 kilograms per cubic meter, almost twice the density of water, and research suggests the interior consists of matter that is three times or more the density of water plus 10-35% pore space (http://www.psrd.hawaii.edu/Aug99/asteroidDensity.html). This is not unusual; loose sand can have up to 40% porosity. It will be necessary to test a piece of chondrite (or better, a piece of Phobos) to determine exactly how much heat drives off how much of the carbon, hydrogen, and oxygen. Most of the escaping gas will be water vapor, with carbon dioxide second. Methane, ammonia, alcohols, ethane, butane, benzine, and other simple hydrocarbons can be expected to be produced as well. Water vapor can be electrolyzed into hydrogen and oxygen, with the latter being stored; the hydrogen can be run through a Sabatier reactor to make methane and water vapor from carbon dioxide.

The rate at which the methane, oxygen, and other materials are produced is a function of the energy available to liberate them. A cubic meter of Phobos material weighs almost two tons and requires about 1,000 kilocalories to be heated by 1 degree centigrade (I am here assuming rock takes about a half kilocalorie to heat a kilogram one degree Centigrade. This is half the heat capacity of water and is about right, but will vary depending on the minerals.) A thousand kilocalories is equal to 1.16 kilowatt-hours. Thus 100 kilowatts of heat can raise the temperature of a cubic meter of Phobos material 86 degrees centigrade in an hour.

If the heat is being put into the shaft using a simple electric heater, the heat will travel inward through the rock. If the shaft is 100 meters deep, it has 314 cubic meters of rock within 1 meter of the shaft. One hundred kilowatts will heat that quantity of rock about 6.5 degrees a day; in a month it will be heated from ?112 C to 85C, and in another month to 280C. Such a temperature should be sufficient to drive off a large fraction of the volatiles. In four more months the material within two meters of the shaft can be heated to that temperature. As the rock gradually cools by conducting the heat to material farther from the shaft, volatiles will continue to be released, even without additional heat input.

Within 1 meter of the shaft is 628 tonnes of Phobos material, containing about 60 tonnes of water and 12 tonnes of carbonaceous material (based on previously quoted estimates). Tests would be necessary to determine how much of the released volatiles would go up the shaft. The volatiles escaping laterally, however, will largely freeze to ices and can be captured later by shafts driven parallel to the first and a few meters away.

Yields from a shaft can be increased in various ways. If hydrogen and oxygen (from electrolyzed water) are pumped down the shaft and lit to make a flame, and the amount of hydrogen added is in excess to the amount the oxygen can consume, the hot hydrogen will interact with the carbon compounds to make methane and with the silicates to make water vapor. Conversely, if the oxygen is in excess to the amount the hydrogen can consume, the hot oxygen will interact with the carbonaceous materials to make carbon dioxide. Sulfur and nitrogen compounds will also be produced. The gasses escaping from the shaft will have to be separated cryogenically, stored, and then further combined or split to yield the compounds desired.

Once a quantity of volatiles has been accumulated, it would no longer be necessary to use electricity to heat the rock in the shaft; reactor heat could be sent down the hole in the form of steam. Hot water, interacting with rock, will help remove carbon compounds. If hydrogen is added to the steam, methane will result.

A one hundred kilowatt reactor on the Martian surface, working with atmospheric carbon dioxide and imported hydrogen, can make 108 tonnes of methane and oxygen in six months (Mars Direct, page 5). It appears that a similar quantity should be possible on Phobos in the same timeframe. Some of the energy used on the Martian surface must go into splitting carbon dioxide into oxygen and carbon monoxide to augment the oxygen supply This process is probably unnecessary on Phobos, since the literature suggests more water will be produced than carbon dioxide. Thus it appears a reactor on Phobos could produce more fuel than one on Mars.

An alternative method may need to be considered if the shaft leaks too much volatiles back into Phobos, reducing the yield out the top of the hole. A robotic digging device could be operated from the Martian surface which would transport a tonne or two of Phobos material to an oven attached to the reactor, where it would be baked and chemically treated, its gasses extracted, and then the slag dumped. The advantage of this method is the degree of control gained over the processing; rock temperature and the application of hydrogen and oxygen can be monitored and tailored to the composition of the material, and yield maximized. The disadvantages include the greater involvement of scarce human resources and the problem of controlling vehicles and materials in near zero gravity. Whereas a well shaft would produce relatively little dust but could release a lot of gasses into the space around Phobos, the use of vehicles and ovens could produce dust clouds and create waste disposal issues.

If the assumptions above are approximately correct, they imply that a 100-kilowatt reactor should be capable of producing several hundred tonnes of methane and oxygen propellant per year. Solar arrays erected at the north or south pole of Phobos where there is perpetual sunlight could increase the available electricity, allowing more reactor heat to be pumped down the various shafts, which could be extended deeper and expanded outward in ever larger arrays.

How could the propellant be used? An example may illustrate the implications. The current space shuttle?s external tank weighs a bit less than 30 tonnes and can hold 2,000 cubic meters of propellant. When divided appropriately between hydrogen and oxygen, it can carry 780 tonnes of the two. If the same stage transported liquid hydrogen only, it would hold 143 tonnes. If it carried methane and oxygen it could hold 2,100 tonnes. In all these cases the gasses need to be segregated in tanks of appropriate size, but if the interior space were divided into four or five tanks of different sizes, all the above combinations could be accommodated.

Perhaps half the external tank?s weight is necessary because it must hold together during accelerations of 2 or 3 gees while tearing through the terrestrial atmosphere at thousands of miles an hour. An expert would have to redesign the tank for use exclusively between planets, but I suspect the tank?s weight could be reduced to fifteen tonnes, maybe less.

A tank of size similar to this could be flown to Mars if a nuclear engine were used to push cargo or people to the Red Planet. A 1.5 tonne solid core nuclear engine generating forty-five tonnes of thrust (such as the Timberwind design, specific impulse, 1,000 seconds) could use a tank such as this, with 143 tonnes of liquid hydrogen, to push three hundred tonnes to Mars. Alternately, the tank itself could be pushed to Mars with about twice as much fuel as its final weight (thirty tonnes of liquid oxygen and hydrogen, if the tank?s weight were reduced to fifteen tonnes). The tank could be ?landed? on Phobos ( twenty tonnes of mass weigh 26 pounds there!) and over the next year it could be filled with 2,100 tonnes of liquid oxygen and methane (assuming the facilities on Phobos were designed to produce that much). At the next opposition the tank could take off from Phobos (2,100 tonnes of mass would weigh 2,772 pounds!) and head back to Earth on a Hohmann trajectory. It would arrive nine months later with about 900 tonnes of fuel, and if a series of gentle, incremental aerobraking maneuvers can bring it to low earth orbit with a minimal expenditure of energy, when it arrives it could possibly be the largest object ever placed in low earth orbit in a single launch. Nine hundred tonnes of methane and oxygen could propel four hundred tonnes of cargo back to Mars or soft land 250 tonnes of payload on the moon.

If, instead, the stage flew from Phobos to Venus, it would arrive with 403 tonnes of methane and oxygen, or any other payload desired. If fuel were burned to place a payload into a high Venus orbit (delta vee of perhaps 1 kilometer per second; the payload might be water, carbon dioxide, and processed Phobosian regolith to serve as a basis for agriculture and radiation shielding in a permanent orbiting scientific station) it could deliver about 300 tonnes. If instead the stage flew past Venus and used that planet to bend its trajectory to Mercury, it could arrive in Mercury orbit (delta-vee of 4.3 kilometers per second) with 122 tonnes of payload. This would be enough to send a Hab and crew back to Earth via Venus.

This example shows the potential of Phobos (and Deimos as well) to serve as the ?gas station of the solar system,? as someone once called it. It suggests the following about the exploration of Mars:

1. An expedition to Phobos and Deimos should be mounted as early as possible, possibly the first or second manned mission. It would be easiest to visit the moons upon arrival when the Hab could be landed, then later sent to the Martian surface. If the missions arrived at Mars during its northern hemisphere spring, when dust storms are common, two weeks on either moon could be a valuable use of orbital time.

2. A goal of the first expedition to either moon should be to determine its efficacy for propellant manufacturing. This would be accomplished by extensive sampling, seismic study of the moons? interiors, and possibly drilling.

3. A follow-up expedition should be scheduled for the third or fourth manned mission to Mars with the goal of leaving a reactor, remotely operated drill, gas processing plant, and cryogenic storage tanks, perhaps ten tonnes of equipment altogether.

4. By the fourth or fifth manned mission to Mars, a Hab could be left on Phobos (and later on Deimos) with the astronauts landing on the planet in the ERV instead (to stay in one of the Habs placed on Mars by earlier crews).

5. Possibly as early as the fourth or fifth manned mission, the two-stage ERV could be replaced by a one stage ?Mars shuttle? that could visit Phobos and Deimos at least once during the eighteen-month stay on Mars. Astronauts returning to Earth would fly the shuttle to Phobos, refuel, and then continue to Earth.

6. The capacity to refuel on Phobos opens up the possibility of hauling cargo back to Earth. If a single-stage ERV refueled on Phobos, it probably would be able to transport about twenty tonnes of cargo from the Martian surface to Earth. Twenty tonnes of gold nuggets would be worth about 200 million dollars and could cover a tenth the cost of an expedition. If Mars rocks were sold to eager collectors for ten dollars a gram (that?s about $1000 for four ounces), twenty tonnes of Mars rocks would also be worth $200 million. Current prices for Mars meteorites are in this range, though twenty tonnes might flood the market. If fossiliferous strata are found on Mars, in particular, Mars rocks could be sold for that much or more.

7. If Mars develops the capacity to place 900 tonnes of liquid oxygen and methane into low Earth orbit every 26 months, it revolutionizes transport costs to Mars, reducing the cost of future expeditions significantly, and reduces the cost of other orbital tasks. Currently launch costs are nearly $10,000 per kilogram to low earth orbit. Even if the costs have dropped to $1,000 per kilogram at the time of Mars exploration, 900 tonnes of propellant would be worth almost a billion dollars.

8. Longer term, Phobos and Deimos could be sites for various important experiments. Solid core and gaseous core nuclear engines could be tested on them at sites far from any habitation. Very heavy orbital structures?such as stations with hundreds or thousands of tonnes of rock for radiation shielding and agriculture?could be constructed near them from their materials and transported using their fuel. Phobos and Deimos should play a major role in making transportation from the Martian surface to low earth orbit cheaper and may play an important role in opening Venus, Mercury, the asteroids, and possibly even the near-Jupiter environment to human exploration.

Phobos · 2002-01-19 13:32:17

Carbonaceous chondrites can vary from 1% to 5% carbon. We do not know Phobos?s average composition, but clearly it contains a vast amount of carbon, oxygen, and hydrogen, the elements for making methane (CH4) and oxygen fuel. If only 1% of Phobos?s mass could be converted into fuel, the quantity still amounts to 100 trillion tons.

If your numbers pan out I get the feeling that Phobos will ultimately prove more valuable in outfitting missions to mine
the asteroid belt than Mars itself will be. Phobos's practically non-existant gravity and composition make it that much more economical. I had never thought of extracting water from Phobos, if that turns out feasible, it might be better to just create a small space station around Mars for the purpose of agriculture if missions to the asteroid belt and beyond become manned and routine.

Updated by Moderator 2021/09/22

Alexander Sheppard · 2002-01-19 22:00:51

What I really don't understand, is why go to Phobos when just about any other asteroid orbiting between Earth and Mars will do just fine, and you get the added plus of not having to enter the Martian gravity well at all? Of course, that only applies if your goal is exploration of destinations beyond Mars, because if your goal is Mars, Phobos has some pretty dam obvious advantages!

RobS · 2002-01-20 07:43:32

I was surprised to see that carbonaceous chondrites had so much water in them. The data comes from the web--not always the best source--but I see no reason to assume they're vastly wrong.

As I noted in another posting somewhere, there are stony asteroids, carbonaceous ones, and metallic ones. The metallic ones won't have much carbonaceous content to provide fuel for a return flight, and the carbonaceous ones don't have much metal. Most likely an asteroid can be found that is a fusion of several from collision that will have all the materials one needs for a good mining colony.

But meanwhile, Mars has all three. If one wants to mine asteroids, one can start mining the zillions of tons scattered across the Martian surface; and that effort would have the advantage of a local infrastructure (maybe even a hospital!) to provide support. Yes, Mars has a gravity well, but in terms of fuel it's much less deep than Earth's, and Phobos is smack dab in the middle of it to serve as a permanent "second stage"; Earth's gravity well is 25,000 miles per hour "deep" and that's 2.5 times the exhaust velocity of hydrogen and oxygen, requiring a mass ratio (fuel to payload) of 11.2 to 1. Mar's gravity well is only 12,000 miles per hour "deep," requiring a mass ratio of 2.3 to 1. The Mars Direct's ERV could be modifed into a reuseable "space shuttle" to shuttle back and forth between the surface and Phobos or Phobos and Earth orbit.

This is not to say that the asteroid belt won't be mined. Just that Mars will be the testing ground, because it's cheaper. It could be mined twenty or thirty years before asteroidal mining is tried, giving it a big advantage. And if you want to raise a family, the cosmic radiation and zero gravity may make that impossible in the asteroid belt; those guys (and gals) will have their spouces on Mars or the Earth.

-- RobS

RobS · 2002-01-21 00:13:08

Phobos and Nuclear-Free Mars Exploration

One of the most controversial aspects of the Mars Direct plan is its use of nuclear power. It is difficult to imagine an alternative power source that is both as efficient, per kilogram of weight, as easy to deploy and control remotely, and as reliable. Solar power on the Martian surface requires large arrays and weights, too large to deploy without direct human intervention, and is diminished by dust storms. Wind power requires enormous blades, elaborate deployment, considerable weight (probably close to a ton per kilowatt), and produces variable outputs, maximal during dust storms and much less except in areas with seasonal winds (such as spring near the polar edges). Solar and wind power complement each other and, together, can meet the needs of Martian settlements, but at a high cost.

If a nuclear reactor were not available, the ?Mars Semi-direct Plan? (Case for Mars, pages 67-69) would have to be used. In this plan, in addition to a Hab, it would be necessary to launch to Mars a ?Mars Ascent Vehicle? (MAV) that would land on the Martian surface fully fueled, and an ?Earth Return Vehicle? (ERV) that would go into Martian orbit, fully fueled, for the return trip to Earth. The MAV would carry the crew to the ERV, which would carry them home.

If nuclear reactors are not available, the Mars Semi-Direct Plan probably becomes inevitable for the first few flights, but it need not be followed forever. Possibly the cheapest and most flexible alternative would be to place a solar power array on Phobos and beam it to the Martian surface using microwaves. If the array were placed at the north or south pole of Phobos it would be in constant sunlight, except when Phobos is in Mars?s shadow (which is up to 38% of each orbit). A Phobosian array will generate more power than a similar one on the Martian surface and can be built to track the sun much more easily because of the moon?s near-zero gravity and no need to consider the force of surface winds on the arrays.

An array to collect 250 kilowatts of sunlight on Phobos, assuming the collection of 0.05 kilowatt per square meter (less than half the collection on Earth) and a mass of 4 kilograms per square meter, would require 5,000 square meters and would have a mass of 20 tonnes. When one takes the effect of Mars?s shadow into consideration, the array collects a continual average of 155 kilowatts. In Phobos?s gravity (6/10,000 that of Earth) the array would weigh 26 pounds. Mirrors, which can be constructed more lightly for use on Phobos than on Mars because of the lack of gravity, can be used to concentrate sunlight onto solar cells. Such mirrors conceivably could cut the mass of the array in half. The solar array will also need a fuel cell system with hydrogen and oxygen or (newer) methane and oxygen tanks to store energy for broadcast when the rectenna is above the horizon.

The technology that could beam the power to the surface of Mars has been studied and tested, but not extensively developed (T. A. Heppenheimer, Colonies in Space [N.Y.: Warner Books, 1977], pages 38 and following). It is basically the technology assumed for power stations in Earth orbit, which were extensively studied in the late 1970s. The direct current produced by the solar cells would be converted into a microwave beam and aimed at a rectenna on the Martian surface, where it would be converted back to direct current electricity. The overall system efficiency is about 60%, which means that of the 155 kilowatts produced on Phobos, 93 kilowatts of useable power arrives on the Martian surface. If the energy is beamed at the surface at a density of half a kilowatt per square meter (much more than would be allowable on Earth, but reasonable on Mars, and just equal to the energy density of sunlight there) and the power can be received ten hours a day (because Phobos is above the horizon only half of the time, and is rather close to the horizon some of the rest) the receiving array would require an area of 450 square meters. The rectenna would have a mass of 5 kg/m2 (Richard Johnson and Charles Holbrow, eds., Space Settlements: A Design Study [NASA, 1977], page 158; much of the information in this paragraph comes from this source) or a total mass of 2.25 tonnes. It might be wise to make the rectenna twice as large to simplify the pointing of the beam. The result?4.5 tonnes?is comparable to the mass of the nuclear reactor proposed for the Mars Direct mission.

The power array on Phobos possibly could be deployed remotely, but more likely it would require a human crew to be set up and tested; if no nuclear reactor is available for Mars exploration, presumably it would be set up on the first flight. But once set up, it would be capable of beaming microwave power to much of the surface of Mars. Phobos rises in the west, passes overhead, and set in the east 5 hours and 33 minutes later; thus it appears in the sky twice a day (Deimos, in contrast, takes 5.5 days from moonrise to moonrise, because it orbits Mars once every thirty hours, close to the length of a Martian day). Phobos is not visible north or south of 70 degrees of latitude (Samuel Glasstone, The Book of Mars [NASA, 1968], page 71; much of my information on the orbits of Phobos and Deimos comes from this source), though it will be rather close to the horizon north or south of 55 degrees, which may be the practical limit of receiving beamed power. Once the beamed power system were established, subsequent Mars missions would only need to bring rectennas along. Mobile crews on the Martian surface could take a small rectenna along, deploy it every night (probably a safe kilometer or two away from them), and pick up the power they need for the next day while sleeping.

Once established and tested by the first crew (using the Mars Semi-Direct plan), the power system would permit a switchover to the Mars Direct plan. To be more precise, it would allow a switchover to an even better system involving the manufacture of methane and oxygen propellant from the carbonaceous chondrite material of Phobos itself, allowing vehicles from the Martian surface to refuel before they flew to Earth (see my previous posting, ?The Importance of Phobos in Mars Exploration?). Solar power capture, conversion, and retransmission will be highly reliable if the solar arrays are located on at least three towers a few hundred meters from each other, if at least three fuel cells and associated fuel tanks for power storage are set up, and at least three transmission antennas are available. Such a system would be capable of beaming power to up to three different locations on the Martian surface. As Mars settlement advances, the Phobos Power Station could be expanded in total output and number of transmission antennas to provide power to more and more places.

Whether the system outlined above will work requires the answering of several questions:

1. Whether it is possible to beam energy with sufficient precision to hit a small target on the Martian surface from an object moving around the planet. If it is not, there is another way to transmit power to the Martian surface: one could manufacture methane and oxygen fuel on Phobos (see my ?The Importance of Phobos in Mars Exploration?) use it to fuel a space vehicle, fly the vehicle remotely to the surface to drop off thirty or forty tonnes of fuel, then return it to Phobos to pick up another load. Once on Mars, the methane and oxygen fuel could be run through fuel cells or internal combustion engines to make electricity.

2. Whether the existing technology can function under Martian conditions (especially low temperatures) or whether expensive modifications are needed.

3. Whether dust storms will effect the transmission. I know little about microwave transmission, but I gather a small amount of dust will not diminish the beam significantly.

Another benefit of the system should be noted: The microwave transmission system could also be used to warm small areas of the Martian surface (1,000 square meters) and drive volatiles from the regolith. Astronauts would first cover the area with an airtight plastic tent (by burying its edges), then have the area cooked with microwaves for several days to drive out the water.

A similar solar array and microwave transmitter system could be established on Deimos if high-latitude stations need power. Deimos can be seen as far north or south as 83 degrees, and therefore could power stations located up to 68 degrees, perhaps more if special rectenna towers were built.

Bill White · 2002-02-03 21:06:46

Question for RobS;

Have you looked into solar photocatalytic production of H2 using water as a feed stock?

This month's Scientific American has a brief blurb about splitting water into H2 & O2 using sunshine. Researchers are working on splitting water into its elements using the visible spectrum of light. What caught my attention was the comment that UV light can more easily facilitate the photocatalytic reduction of water but that Earth's atmosphere absorbs most the the solar UV.

See http://www.sciam.com/2002/0202issue/0202inbrief.html

However, Mars has ample UV.

Looking deeper, I found the following site:

www.eren.doe.gov/hydrogen/pdfs/30535v.pdf

which is the abstract of a paper prepared by the Florida Solar Energy Center. The paper claims to have created a "dual bed photocatalytic water splitting system" that can to produce hydrogen using only sunlight and catalysts and a water feedstock.

Obviously, a settlement could simply burn the hydrogen as cooking gas, heating fuel or to power engines and generators. If the system were properly closed, the sole combustion product - water - would be recycled back into the water splitting system.

A more efficient use would be to feed the hydrogen into fuel cells - - which are not quite ready for prime time, but we are very close.

As far as Phobos is concerned, instead of erecting large solar arrays to generate electricity to split out the hydrogen from water bearing rock, perhaps catalysts could be seeded into the Phobian regolith and covered with a transparent tent to capture the hydrogen and oxygen after the sunlight did its work.

Thoughts?

RobS · 2002-02-04 16:16:03

Very interesting ideas. I have the Scientific American here in paper copy and will look for the article, and will look at the website. I wonder whether one could build a solar cell that would make hydrogen from the UV and electricity from the IR part of the spectrum? Then you'd have both! I am not sure a catalyst could be seeded straight into the regolith, because the water is usually not sitting there as ice; it's chemically bound into the minerals, and has to be forced out of them. But maybe there are other catalysts that could do that, especially if the regolith were subjected not to ordinary sunlight, but focused intense sunlight. One could put a one hundred meter mirror in orbit around Phobos maybe two kilometers above the surface and use it to bake the regolith. Of course, the surface itself's probably the driest, because cosmic rays, micrometeoroids, solar x-rays and u.v., and other things will dry out the outer layer.

-- RobS

RobS · 2002-02-19 18:43:19

For those interested in pursuing this subject further, there's an interesting paper I just found on the web at http://www.spacefutures.com/archive/the … any.shtml. The author proposes a series of Russian and cheap commercial rocket launches to send a manned spacecraft to Deimos, mine it for water, ship back 100 tonnes of H2O to low earth orbit, and sell it at $8,000 per kilogram (which is still cheaper than anyone can launch it). He calculates by the second mission one could make a hefty billion dollar profit. I have no way of evaluating the information, but it seems carefully thought through, at least in parts.

-- RobS

John_Frazer · 2008-01-17 21:05:56

Very good stuff, even if the thread is old.
I second the motion, that the moons of Mars deserve a lot more attention.
A lot of my attitude is from ideas plagiarized from Dr.Brian O'Leary's book "Mars 1999". In it, he stresses first going to the moons for a fuel/water plant, and like Dr.Kuck's "Diemos Water Company" it becomes important in leveraging our way into space with fuels in Earth orbit, and for Mars exploration.
Dr O'Leary also suggests possibly not even intending to send people down to Mars on the first manned shots. Instead, they concentrate on building up the capabilities in Mars orbit, around the moons. ("Ph&D" From Dr O'Leary, "Fear & Dread" were the two warhorses which pulled Mars' war chariot)

An interesting addendum to RobS ideas, is to use regolith as a building resource. Very many proposals have been floated over the years on relatively simple early space manufacturing methods to make rolled and stamped metals for trusses and structures, metal cables (Common engineering practices allow much more stress on cables than any other method of building with metals), and rock dust from regolith as some form of artificial rock ("Sinter-crete" or concrete, or possibly as sandbags packed around a hab for shielding.
Most of these are relatively simple with little complex machinery, and allow strong use of local resources.
Trusses could be built up to allow a couple of "tuna can" habs to be shielded and spun up to full Earth G, so crews wouldn't need to be rotated back to Earth, just as they're getting a lot of expertise in exploring Mars.

In "Mars Direct" it's suggested that Mars is made the second most safe place for crews. In this version, Mars orbit is even better.
I submit that it's very premature to suggest that Mars could be a safe place for crews to spend most of their time: we have absolutely no experience in low G living, and no reason to suggest that Mars G will be enough. I'm reminded of the space colony design criteria from the NASA Ames 1970s summer studies, in that building artificial habs with very nearly Earth-normal environment, is the "conservative engineering" path, since readily extrapolated construction techniques allow it to be done with no breakthroughs or new inventions needed, and any human can readily live there completely safely, no "adaptation" needed.

Going to Ph&D and building up infrastructure ASAP, before the first Mars landing, allows a Mars exploration project to be very robust and safe, as crews could be assisted by telerobotics controlled from above, and supported by drops of supplies, and they're never more than some hours away from a hypothetical critical supply drop, or a day or so away from help.

It can't be under-stated, how important a source of volatiles in space could be, in vastly simplifying getting us into space, removing much risk and expense. See the "Deimos Water Company" article, or neofuel.com.
Whenever we launch a payload up to LEO with an upper stage for kicking it beyond LEO to GEO or interplanetary space, 2/3 of the IMLEO is the upper stage, and 2/3 of that is the oxidizer in the upper stage.
"Mars Direct" showed us how to leverage our capabilities in space with in-situ resources, and I leave it to the imagination, what we could do with that much more useful payload, in every cargo we send up.

Terraformer · 2008-01-18 14:57:40

What about the idea now we have 40% efficientcy PV panels?

Why not mine Deimos first and turn it into a space station?

RedStreak · 2008-01-18 21:31:03

Hey I already started a topic in Human Missions section already debating this http://www.newmars.com/forums/viewtopic … tian+moons

Good technically data though, and glad to see someone trying to bring note of Phobos & Deimos.

RedStreak · 2008-01-18 21:38:10

What I really don't understand, is why go to Phobos when just about any other asteroid orbiting between Earth and Mars will do just fine, and you get the added plus of not having to enter the Martian gravity well at all? Of course, that only applies if your goal is exploration of destinations beyond Mars, because if your goal is Mars, Phobos has some pretty dam obvious advantages!

:!: Most of those asteroids are in distant orbits, have never been photographed in detail, and would cost more in fuel and time to reach even with the Martian gravity well factored in. :!:

Phobos and Deimos have been at least mapped - what we know about them compared to these asteroids is like comparing what we know about 'dwarf planet' Eris to our Moon. :?

cIclops · 2008-01-19 18:14:31

The Phobos Grunt mission next year should change all that.

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#1 2002-01-19 00:58:44

Re: Phobos and Deimos - The importance of Mars's moons to explor

#2 2002-01-19 13:32:17

Re: Phobos and Deimos - The importance of Mars's moons to explor

#3 2002-01-19 22:00:51

Re: Phobos and Deimos - The importance of Mars's moons to explor

#4 2002-01-20 07:43:32

Re: Phobos and Deimos - The importance of Mars's moons to explor

#5 2002-01-21 00:13:08

Re: Phobos and Deimos - The importance of Mars's moons to explor

#6 2002-02-03 21:06:46

Re: Phobos and Deimos - The importance of Mars's moons to explor

#7 2002-02-04 16:16:03

Re: Phobos and Deimos - The importance of Mars's moons to explor

#8 2002-02-19 18:43:19

Re: Phobos and Deimos - The importance of Mars's moons to explor

#9 2008-01-17 21:05:56

Re: Phobos and Deimos - The importance of Mars's moons to explor

#10 2008-01-18 14:57:40

Re: Phobos and Deimos - The importance of Mars's moons to explor

#11 2008-01-18 21:31:03

Re: Phobos and Deimos - The importance of Mars's moons to explor

#12 2008-01-18 21:38:10

Re: Phobos and Deimos - The importance of Mars's moons to explor

#13 2008-01-19 18:14:31

Re: Phobos and Deimos - The importance of Mars's moons to explor

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