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I am curious about your communication faster than the speed of light. It doesn't sound like a technology we'll have working in a decade or two, but who knows.
Robert, I'm concerned or curious about another aspect of your plan. The Mars Ascent Vehicle you postulate would be the smallest and lightest thing possible; just a skin around the spacesuited astronauts, who would have to wear their spacesuits on the trip for life support. I know this has been suggested for the moon. But it seems to me the Apollo spacecraft orbited very low; 60 miles (100 km) or less. From launch to rendezvous was a matter of six or eight hours (which translates into two or three loops around the moon). But the space shuttle has to fly to a 400 km orbit and rendezvous takes twenty-four hours. No doubt, it could be done faster. Yet the Mars Ascent Vehicle has to catch up to a vehicle in an elliptical orbit which has about 400 or 500 km as its periapsis and something like 25,000 km as its apoapsis. If the mother vehicle is in a low orbit the rendezvous could be faster, but then the mother vehicle is rather deep in Mars's gravity well and would take much more energy to achieve trans-Earth injection. Furthermore, the mother vehicle will probably have to execute a plane change to be oriented right for TEI, and that's much easier to achieve at a high apoapsis.
I don't know how long rendezvous with the mother vehicle in a sun-synchronous elliptical orbit (which is what is usually used) would take, but I bet it would be 24 hours minimum, and you have to accommodate the possibility of delays and setbacks. Under those circumstances, a rendezvous could take two or three days. So my guess is that the Mars Ascent Vehicle needs to be more robust than you are suggesting, and therefor more massive. It'll at least need to have waste facilities and food, and it'll have to be pressurized.
Also, a small MAV probably would not transport consumables from the surface to the mother vehicle. The return flight involves about three tonnes of consumables per person. Zubrin's Mars Direct plan aerobrakes the stuff onto Mars in the ERV, then launches it to Earth with the astronauts. Yes, this seems inefficient; but it is also safe, because if the MAVs you are envisioning both fail for some reason, the astronauts will be stranded on Mars while the twelve tonnes of supplies they need to survive will be orbiting above their heads, out of reach. This probably could be solved by leaving the twelve tonnes on the mother vehicle and dropping onto Mars the supplies for the NEXT mission; but then when the next mission arrives, their TV dinners and tang is two years old, and might not taste great.
Any ideas about this problem?
-- RobS
Thank you, Robert, for the correction about wing size.
Regarding the Helios, it uses solar cells that are 22% efficient on top and 11% efficient on the bottom. The wing is transparent and thus can pick up reflected light from underneath; very clever. Anything sent to Mars in 20 years time would certainly be at least 33% efficient, partially making up for the lower level of insolation there. If the new breakthroughs have matured by then, 50% efficiency may be possible. If the Helios were meant to be used by astronauts, you'd probably fly up five or six-meter wing sections and bolt them together on the surface.
-- RobS
The thinner air makes airplanes less useful, but not impossible. Lift is a function of the density of the air, not its pressure. The pressure at "Martian sea level" is 0.7% of Earth's atmosphere, but the density is 0.7/0.38 = 1.8% that of Earth. Thus to lift the same weight, Martian wings have to have 55 times as much area. However, with lower gravity, an object weighs 0.38 as much, so the wing surface ends up being 55.5 x 0.38 = 21 times bigger.
This apparent disadvantage, however, presents one advantage: the large surface area can be used as a solar collector, and the airplane can run off of solar electricity instead of an engine burning something. A solar powered aircraft named "Helios" has actually been flown at 100,000 feet on the Earth, an altitude where the air is of similar thinness. You can find information about it on Google. The wings were the length of a 747's, but their mass was less than 4 kg per square meter, which was basically the mass of the solar panels. Helios eventually will be able to store power for nighttime flying using fuel cells and fly independently for weeks at a time. Its total mass is 600 kg and its cargo is 300 kg, if I remember right. Helios has 14 propellors along its wing, too; it can probably fly on half of them, so the plane is able to fly for months at a time without maintenance. They are being developed to test technology for Mars, but they have a practical application; they can serve as a cell phone tower in the sky, floating for half a year at a time above the weather, able to be moved quickly to a disaster site to bolster communications there.
I suspect Helios-like aircraft will be the ideal early transport for crew and cargo. They can't go very fast; it would take 3 or 4 days to travel half way around Mars. But two crew in a very light-weight capsule could handle that. The cargo transportation would be limited to a half tonne at a time, but the vehicles could make repeat trips easily and inexpensively. They would need very wide, smooth landing strips, but takeoff and landing speeds apparently are very low (which would allow the use of airbags in case of a crash). They would also be ideal for closeup photographic reconnaisance of the surface, able to take photographs with resolutions of a few centimeters, the sort of resolution you need to plan a manned expedition crossing the terrain.
-- RobS
I doubt the governments of the world will let anyone move a comet or asteroid into Earth orbit--even high Earth orbit--any time soon. Even a 100 meter asteroid, if it crashed to Earth, could kill a million people. Even if the chance is small, it would not allowed because of the danger of it getting weaponized.
Maybe in a century after the earth is more politically stable, though.
-- RobS
If nothing else, you can insert weights into special pockets in your clothes. It would be a pain walking around with them, but it would provide the stress the bones need.
-- RobS
So far, no one has developed the technology to keep liquid hydrogen liquid. The energy to electrolyze water into hydrogen and oxygen can be obtained, but developing the equipment is the trick.
Part of the problem is that we still know very little about the environment of space. I was reading about the International Space Station the other day. Someone calculated that static electric charges could build up on the station as a result of the huge solar panels that could be so strong that astronauts could get shocked and the space shuttle could get shocked when docking. So they spent $27 million to build equipment to neutralize any possible electrical fields. It turns out, the ISS did not have electric field problems and the money was a waste; but they had no way of knowing ahead of time and couldn't take the chance. These are the kinds of problems that make creation of new equipment so slow and expensive.
-- RobS
Regarding tethers, they have the potential to make a big impact on the total mass needed for a flight between planets. But who knows when one will be built. We don't even know yet whether the technology will actually work when placed in orbit.
-- RobS
One thing that occurs to me: astronauts going outside on a regular basis will be wearing space suits weighing almost as much as themselves. This means their bodies will be experiencing a vertical stress closer to 0.75 gravities. Sometimes it will be more, because their bodies will still be dealing with the momentum of all that mass when walking. Furthermore, the air pressure in suits will make bending and moving arms more difficult.
Physicians tell us on Earth that we need to get about a half hour of exercise two or three times a week to keep our cardiovascular system functioning well. If a geologist is going outside for two or three hours at a time three or four days a week, you'd think that amount of exercise would have a big impact on the skeletal system and cardiovascular system. But only medical research in a 0.38 gravity environment will verify that guess.
Of course, exploring the moon and putting astronauts there for several months at a time would provide a very valuable datapoint.
-- RobS
Thank you, Robert, for a very interesting posting. I have a question about the use of ion engines, though. How long will it take a manned mission to get to Mars with such an engine? To fly to Mars from a GTO, if you do it quickly and close to the Earth, takes 1.3 km/sec; but if you use an ion engine you need 3.8 km/sec instead. My source is Arthur C. Clarke's book *The Promise of Space,* which shows that a flight to Mars requires (from the surface of the Earth) 26,000 mph if you apply the energy close to Earth, but 25,000 mph (to escape from Earth) and 7,000 mph (in interplanetary space) to adjust the spacecraft into an orbit that reaches Mars.
The mass ratio for 1.3 km/sec using hydrogen-oxygen engines is 1.34 (0.34:1 fuel to payload). The mass ratio for 3.8 km/sec using a 5,000 second ion engine is 1.08 (0.08:1 fuel to payload). So you save a lot of fuel, sure. But it'll take two or three months longer to get up to that speed, won't it? And if you accelerate to a higher speed, that burns more fuel and decreases the advantage.
-- RobS
Why do you think NASA should be privatized? They've privatized the shuttle launching already and all that means is that Boeing makes a lot of money launching the shuttles. And as Zubrin has shown, the cost of private launching has not dropped in the last twenty years. The French are trying to gain as much of the launch market as possible and have actually managed to grab a lot of it; but not by launching at a tenth of the cost! Their costs are about the same.
And there's no point to mass producing space shuttles when the machines are too expensive to fly. There's inadequate demand for it.
-- RobS
This is a rather old article. Its advantage, for us, is that it reminds us of the arguments made against Mars exploration. Some are outdated; we know it needn't cost trillions, and we know the surface does provide radiation shielding. Others are right on: it may very well be that 0.38 gravity isn't enough for healthy humans, long term.
Another thing about the article to remember is that it cites all the psychological and mythic reasons for going to Mars, and calling them "mythic" does not diminish them. Mars has far more potential to excite than visiting an asteroid named, say, 2002AG11.
Finally, remember that the L5 arguments have now collapsed in the face of their own economics. We can't go to L5 to make a profit OR to Mars. If we want the Earth to have cheap electricity, it will remain cheaper to cover every roof on Earth with solar panels than to build the equivalent area in space. We get about six times as much power per square meter in space, but the construction and launch costs are a lot more than six times as much.
So the article has many lessons for us.
-- RobS
The tether information I gave was for Mars, and the idea was to have the tether swinging in such a way that it would come straight down, at least in the lower Martian atmosphere. I suppose it ends up swinging sideways in the upper atmosphere. But Mars's atmosphere is pretty thin.
The Earth's atmosphere would generate a lot of drag and the tether would have to be much thicker, because of the greater gravity. Tether proposals usually involve a tether coming only to the upper atmosphere, where a high-speed jet or rocket aircraft would intercept the hook and transfer cargo to it, already moving at several thousand miles per hour. That sounds pretty complicated to me.
At least the Earth has a magnetic field. A tether with solar panels at the counterweight could generate a magnetic field in the tether to push against the Earth's magnetic field and boost the tether's orbit. A few years ago NASA experimented with this idea, but the short experimental tether broke. They were interested in the technology to maintain the ISS's orbit.
-- RobS
I think the reference to books in the Hab in the Case for Mars may partly reflect the time: the book was written in the early 1990s before ebooks. Or it may reflect the fact that people will always want to read books, and astronauts will have a personal mass allowance for their own possessions, which no doubt will include some books.
-- RobS
Launching an aerospace plane on an EELV might not be so bad as a transition to the next stage of technology. If it brings launch costs down by a factor of three, maybe it would open the tourist market. Let's say seven people can be put in orbit for $170 million; that's $24 million each. Maybe demand at that price will grow somewhat and help wedge open the tourist market, which has the potential to improve safety and cut costs. If the shuttle is retired and replaced by something that is a third as expensive, that will help make the ISS viable and speed the day when the moon or Mars can be considered.
-- RobS
No, I haven't presented them elsewhere, because it is always dangerous for amateurs to tread in areas where there are experts. But possibly I can refine the plans a bit more, at which point they could be good enough to bounce off some experts. Maybe the Mars Society annual meeting would be the next stop.
The big problems with all Mars plans are not engineering; they are political. The politics occur within the agency launching the plan, which has to accommodate the plan among existing constituencies struggling for money; and then there are the inter-space agency politics, Congress, and foreign relations to take into consideration.
As is clear from the New Mars Forums, there are no shortages of ideas. But even simple matters like how to get the Mars vehicle to low earth orbit is complicated. A heavy lift vehicle is cheaper, but politically difficult because of the up-front costs and because it might look like an admission the space shuttle was a bad idea. From low earth orbit to trans Mars injection: a big rocket would allow chemical boosters like the Saturn V and Apollo; the Star Wars types in the Pentagon would love to see a nuclear booster and reactor developed because they could then use it; the anti-nuke people will oppose even peaceful uses of nuclear power in space because of their possible military applications; solar-electric engines are expensive to develop and would allow smaller boosters to put high-orbiting satellites into low earth orbit, thereby undercutting the existing rocket market. Then there are these issues: a Mars program undercuts the moon lobby; a moon project undercuts the Mars lobby; many prominent scientists repeatedly emphasize that it is unsafe to send people and machines will do the work just fine, though slowly; anyone wanting to send anything up has to be careful not to "dejustify" the space station or compete with it for funds; etc., etc. These are the REAL problems!
-- RobS
I am not sure I agree that a terraform-oriented society will make Mars beautiful while a Red-Mars oriented society will ruin the place. We know this is our only Earth and we ruin it all the time. Humanity has a way of making short term self interest supreme over ideology and theology of all sorts, and I don't see that changing any time soon.
But I am interested in another problem with terraforming: it takes too long and it also makes Mars more inhospitable before it makes it more pleasant. Let us say we can thicken the atmosphere relatively quickly--100 years--but can't oxygenate it in less than a thousand. Maybe the numbers really are 1,000 years to thicken the atmosphere and 10,000 to oxygenate it; I don't know. Either way, there is guaranteed to be a thick and unbreathable atmosphere for a while. That means we have to have domes to hold in the oxygen, but they won't have to hold in pressure. Such domes would blow away when hit by a martian hurricane or tornado; and there will be such things. A martian city could have most of its domes punctured by a really bad storm, and thousands could be killed or inconvenienced (just like a storm surge in a coastal city prone to hurricanes). This is a serious problem that will have to be addressed. The thick atmosphere will also suspend lots more dust; Mars could be a constant gray overcast if the atmosphere were thickened (even if the amount of liquid water greatly increased). Such global dust storms would cause surface temperatures to drop; they may be part of the feedback mechanism that keeps Mars cold and thin-aired right now.
-- RobS
Someone must have this information somewhere. The Mars Direct plan proposes about 1/3 or 1/2 of an atmosphere, with oxygen pressure the same as earth and less inert gas (say, 40% O2 and 60% N2 at half an Earth atmosphere of pressure). For the pressurized rover (which is often depressurized) and space suits, Mars Direct proposed pure oxygen at a low pressure.
I can think of three problems with low air pressure: (1) sound does not transmit as well, so you can't hear as easily; (2) cooking is more complicated because of the lower boiling point of water; and (3) your farts would last longer (because the same mass of gas takes up a larger volume). My, my, think of the jokes. . .
-- RobS
Mars Direct envisions only two vehicles being sent to Mars: the hab and the ERV. The latter is designed to carry about ten tonnes of cargo right now, but it's a reactor on a truck and six tonnes of liquid hydrogen. If those are no longer needed, it could carry other items. Other plans for Mars exploration postulates cargo landings. The big problem with automated cargo landings, though, is making sure everything comes down in the same place. You wouldn't want the crew and two cargo landers in one place and the inflatable hab in another; or the three landers in one place and the crew in another. In Mars-24 I sort of solved the problem by sending two sets of everything; three cargo landings and one set of crew each opposition, with three cargo landers and the extra crew return vehicle going first. That way if one of the cargo landers crashed during the first (unmanned) expedition, you could send an extra the next time (in addition to the three automated landers already scheduled) and if the crew landed in the wrong place there would be three automated cargo landers following with everything they needed. Still, you wouldn't want the lander with their inflatable hab to crash; they'd have to live in the shuttle's cramped quarters, plus the pressurized rover, plus the greenhouse for eighteen months!
-- RobS
Regarding tethers, I think they need a counterweight that stays in space, and presumably has engines to stabilize the orbit. I have no idea how one avoids the Laurel and Hardy scenario; it's a good image of what could happen! The tether enthusiasts probably have an answer, but then they haven't built one of these things yet, so one can wonder whether the answer will work.
Regarding Martian scram jets on the mass driver: of course, that's a great idea! Silane burns in carbon dioxide with a specific impulse of about 280 seconds or so. The details are in *The Case for Mars.* Your mass driver could be used to accelerate the payload to about half of orbital speed--say, two kilometers per second--and accelerate at three gees or less. That'd keep the track short. Then the scram jet could do the rest, or most of it. Rather than shooting the payload vertically, you'd want to send it closer to horizontal so as to use the atmospheric CO2 for your scram jet.
-- RobS
Subsistence is always a possible problem when one pumps water out of the ground. That's one reason Venice is getting flooded right now. But usually the ground sinks uniformly. If your well was not next to your base, you could let a sinkhole develop and ignore it.
A bigger problem is abration from flying dust scratching the envelope and diffusing the sunlight, which would not allow it to focus on the panels. Rolling the cylinder to keep the focus pointed toward the sun would abrade the plastic membrane as well. So it would have to be replaced every few years. And, of course, solar energy simply is not as reliable as nuclear because the former are affected by dust storms. Nukes are better, but their political incorrectness may prevent their use.
The best nuclear scenario, actually, is to build a breeder reactor using natural plutonium on the Martian surface, mine the uranium on Mars, and export the U-235 and plutonium to space operations elsewhere. That way the space program could be nuclear and the greens wouldn't have to worry about nuclear materials being launched into space on top of tonnes of explosive propellants.
-- RobS
I don't have a book. I have started a novel using Mars-24 technology; it's one of the best ways to "test" it. Taking inspiration from Mr. Commarmond, I'm starting with two shuttles and Ihabs flying six astronauts to Mars (two Americans, two Europeans, a Russian, and a Japanese). But I don't have anything to "report" yet.
I have become intrigued by the question of extracting water from the ground. It occurs to me that if one can "easily" drill a "well" that is, say, 200 meters deep, one will probably encounter a reasonable amount of water almost anywhere on the planet. A solar heater that heats Martian air to 100 C, and a pump to compress it and pump it down the well shaft, will be enough to heat the rock walls of the well shaft significantly, to 100C or so. This would cause any ice in the rock to evaporate into the heated air, which, upon exiting the shaft, is run through a heat exchanger to cool it, thereby condensing the water. As the ice in the premafrost melts, the porosity of the bedrock opens up to the penetration of the heated martian air. If the top 20 meters of the wellhead were sealed with concrete around the shaft, then one could pump the heated air down the shaft and build up considerable pressure underneath; say, 1 or 2 terrestrial atmospheres. This would push the heated Martian air into the porosity of the rocks where it would encounter colder, icier rock; then you'd let the air pressure drop, the Martian air would rush out of the shaft, it would flow back through the pores to the shaft and up carrying water with it.
If you heated up the rock with solar-heated air for eight hours every day for a year or two, you could produce quite a reservoir of heated rock underground, and as that heat diffused outward it would melt, the vapor moving inward toward the heat source where it could be extracted. If eventually you heated up all the rock in a sphere underground with a radius of 50 meters, that rock would have a volume of half a million cubic meters and a mass (at two tonnes per cubic meter) of a million tonnes. If the rock contained 5% water, that's 50,000 tonnes of water! And since it comes out of the well as water vapor, it does not require desalination or other purification measures.
So this system over a long period of time could yield a lot of water, I think. But that's not all; it could also yield heat at night and during dust storms, because the heated rock will cool very slowly, deep under ground. You could pump cool air down the well shaft and it would come out heated up. I don't know how long it'd yield heat, but I suspect after a year of pumping 100 kilowatt-hours of heat into the ground every day, you could extract half that much (5 kilowatt-hours) for a month or so. So such a "regolith well" could be very valuable.
-- RobS
Some geologists are comparing Mars to Africa, where mineralization is concerned; and Africa is very rich in gold and other minerals. Mars has had extensive igneous activity throughout its history, and probably had an ocean's worth of water moving around its surface and subsurface for a billion or two years. There have been plenty of geological forces at work to concentrate minerals. This is in contrast to the moon, which is much, much drier. Venus may have minerals, but we may never be able to find out. Mercury may be in an intermediate situation, with extensive igneous activity but no water activity.
-- RobS
Here's a bit more data. The book *On to Mars* (available through Amazon, contains highlights of papers from the 1998-2001 Mars Society annual meetings) has a CD rom in its back with additional papers, and one is about mass drivers. It says the top of Olympus Mons has only 0.67 millibars of air, and that air has a mass of 18 kg per square meter of surface area. My calculation, assuming 1 millibar, was 500 kg per 20 square meters or 25 kg per square meter, so I was about right. This means there's even less air to deal with.
The mass driver that was proposed was 400 kilometers long, so that it could accelerate passengers as well (which require less than 3 gees of acceleration). They were figuring on losing about 100 meters per second of velocity to the air. I suppose this was not a serious proposal; such a device would be massively expensive.
More practical for transportation to and from low Mars orbit, according to another article on the same CD, is a rotating tether 300 km long. It would rotate counterclockwise as it went around Mars so that its tip, when it "touched down" on the surface, was moving westward at the same speed as the counterweight in orbit goes eastward, so that it would be stationary relative to the touchdown point. This also greatly reduces atmospheric drag. While the tip is stationary one can drop off one payload and attach another. Tethers less than 300 km long generate over 3 gees of acceleration as they lift things to Martian orbit (not at take off, obviously, but later in the tether's rotation). Longer tethers generate less gee force (a 700 km tether generates 1 gee of maximum acceleration). The 300 km tether would touch down something like 22 times along the orbit, about every 900 km along the Martian equator. Thus settlements spaced that far apart would all have access to each other and to orbit. Longer tethers could be built that would touch down as far north or south as 55 degrees latitude, though those tethers have to be 10,000 kilometers long.
Tethers work best if the total mass in them stays constant. Thus if you have a "car" of 10 tonnes, plus passengers, to take up to orbit, you have to drop off a car of the same mass on the way down. So you have to plan your transfer of masses carefully.
-- RobS
One way to get a maximum figure for the amount of atmospheric drag is to calculate the energy it takes to accelerate the 0.5 tonnes (or whatever it is) of air to the terminal velocity desired (5.5 km/sec to escape, 6.4 km/sec to Earth). If you are launching a 1 tonne object to those speeds, 0.5 tonnes of air requires an additional 50% more energy. Of course, the amount would really be less because you are shoving the air out of the way instead of accelerating it to the same velocity. But this assumption at least allows one to calculate a maximum figure. If you assume the air is accelerated to 10% of the final velocity of the payload--which may be more correct--that reduces the energy you are wasting quite a bit.
If the payload is more like 10 tonnes, rather than 1 tonne, the amount of energy wasted on air friction would be pretty small.
-- RobS
Regarding the problem of air friction on Mars, somewhere I read that the tops of the big volcanoes are so high, you can't use parachutes for Viking-style landers there. The Earth's atmosphere has a mass of ten tonnes per square meter, so if you launch something at sea level that is five meters in diameter (with a circular area of 20 square meters) it has to punch through 200 tonnes of air to get to space. naturally, that creates a lot of drag. But Olympus Mons has a pressure of something like 1 millibar, a thousandth that at the Earth's surface, and that is produced by a mass that has 38% as much weight on Earth; therefore the mass you are dealing with is a thousandth divided by 0.38 = 0.0026 X 200 tonnes = 0.5 tonnes of air between the space vehicle (5 meters in diameter) and space. It seems to me the vehicle could deal with 500 kilograms of air, and at 5 km/sec it would pass through that air in about 30 seconds (to get to 150 km, which is about the top of the atmosphere). Most of that air will be in the way in the first few seconds.
I have not verified the air pressure on top of the volcanoes is 1 mb; I just used it from the previous posting. But I think it's about right. If it is 2 mb, we are dealing with 1 tonne of air instead.
As for velocities, according to http://222.pma.caltech.edu/~chirata/deltav.html, low orbit around Mars (from the surface in all these cases) takes 4.1 km/ sec; Phobos transfer orbit, 5 km/sec; Deimos transfer orbit, 5.3 km/sec; Mars escape, 5.5 km/sec; flight to Earth (Hohmann trajectory), 6.4 km/sec.
-- RobS