51
$\begingroup$

My question is very close to the question answered in the link below and is raised by the answers that question received:

Is a Moon-base inherently more dangerous than a Space Station?

Why are we struggling to get to Mars prior to building something substantial on our own moon?

$\endgroup$
  • 2
    $\begingroup$ Related: What are the synergies between human landing on the Moon and on Mars? $\endgroup$ – kim holder Jul 5 '15 at 21:53
  • 14
    $\begingroup$ Who exactly is the 'we' in your question? AFAIK, no one is seriously trying, or even in a position to try, to do either yet. $\endgroup$ – jamesqf Jul 6 '15 at 5:06
  • 1
    $\begingroup$ In the US, politics: "Back to the Moon" was a Bush thing, so Obama wanted a "Journey to Mars" so it would be his thing. $\endgroup$ – MissMonicaE Dec 20 '16 at 15:57
81
$\begingroup$

At the moment, there are a few groups trying to reach Mars, and a few groups who are trying to reach the Moon. Mars One has grabbed headlines lately, SpaceX states Mars colonization as its long term goal, and there are numerous smaller groups. For the Moon, there is the Google Lunar X prize, Shackleton Energy Corp, and OpenLuna, and again numerous other groups. Different space agencies have gone back and forth favoring one destination or the other at different times over history, and that is a matter of politics as much as science and technology. The arguments for each destination are many and varied, but can be grouped and outlined.

Material Resources

  • Mars has a carbon dioxide atmosphere. The technology and resources needed to process that into oxygen and methane for fuel are not that demanding (page 11 here). At first hydrogen for the process would need to be brought from Earth, later the frozen water that exists in large quantities beneath its surface could be used.
  • The frozen water on Mars would need to be dug up, melted, and separated from the soil it is mixed with. That takes heavy infrastructure, but nothing complicated. The frozen water is distributed over a large area too.
  • The Moon has frozen deposits of volatiles1 in craters in permanent shade at its poles, and beneath the surface near the poles. How big these reserves are is still a matter of investigation, but there is a fair bit of evidence that they are quite substantial. They seem to be a mixture of chemicals, mostly water, some carbon dioxide, and others, and may be mixed with a lot of soil. How difficult it would be to extract them and process them is not yet clear. Because they are only in a few places, that are deep, and extremely cold, it could be complicated.

Access

  • Mars is really far away. With current technology it takes 6 to 10 months (depending on alignment of the planets and how much money is poured into the rocket) to get there, or get back, and launch windows occur every 2 years.
  • The Moon is 3 days away at any time, there or back.
  • The atmosphere of Mars makes it necessary to have heat shields on any lander, and to come in at the right angle and with the right orientation. But the atmosphere is not thick enough to slow a vehicle much as it comes in, just enough to heat it up. If rockets are used to slow the ship down, then they must handle firing into a wind whose dynamics constantly change as speed lowers from hypersonic to subsonic. If parachutes are used, they must handle supersonic velocities unless deployed only near the end. These are huge technical challenges.
  • On the Moon shields aren't necessary, and there is never any complication with using rockets. A ship landing on the Moon can come in at any angle with any orientation. No aerobraking can be done to save fuel by using friction with an atmosphere to slow a ship down enough to enter orbit. Thus the delta V to get to either destination is similar. However, the technology needed to land is known, and can be scaled.
  • Because of the time it takes to reach Mars, a ship needs to shield its occupants from radiation on the way. It may be possible to use the supplies of food and water already needed for the trip and the time on the surface for that, or that may not be enough. This is still not known. At any rate the required supplies make the ship much heavier, which adds considerable expense.
  • Radio waves take between 3 and 20 minutes to make the trip between Earth and Mars, depending on how far apart they are. They take 1.3 seconds to go between Earth and the Moon. One interesting aspect of this is that it makes it possible to operate equipment on the Moon remotely from Earth, but that wouldn't work for Mars.

Impact

  • Mars can be terraformed. At least, that seems to be the case, although it would take a vast, vast effort over centuries. There is much we don't know about this, but it seems like a reasonable, if ambitious, conjecture. There is enough water for shallow seas, and may be enough frozen carbon dioxide2 for an atmosphere about 30% the density of ours, very roughly, and plants could process that into oxygen.
  • The Moon would open up the solar system if colonized. Because it has so little gravity and no atmosphere, and it is right next door, all the heavy stuff could be made there and launched from there, saving tremendously on the resources needed to send missions far and near. Some say space stations could be used instead, and resources from asteroids, and the Moon could be skipped. That puts a 3rd horse in this race. The factors in that one are distance weighing against, and low gravity weighing in favor.
  • Mars may harbor life. 'Nuff said. Then again, that also complicates things, see the next list.

Problems

  • The Moon is covered in very fine sharp dust that sticks to everything because it has a static charge. Breathing it in would be a health hazard because the fine particles would lodge in the lungs and could cause silicosis. Moving mechanical parts outdoors will need protection or things will seize. Seals will fail if not protected.
  • Mars is also covered in fine dust that is not so sharp because it is weathered. But the fine particles remain suspended in the atmosphere and that makes it harder to keep them out of the indoors. Silicosis again is a hazard, and there are other toxic constituents as well. And the dust also has a static charge that makes it stick to everything.
  • Mars has toxic chemicals in its soil. Perchlorates have been identified and may be widespread. They are toxic to people.
  • Mars may harbor life. That life must be protected. Colonizing a planet while protecting its native life may be very difficult and would certainly require special precautions that add complexity and cost to such an endeavor.
  • The Moon has 1/6 the gravity of Earth. Living long-term in such an environment may cause health problems, and muscles and bones could change so much that returning to Earth would be difficult or impossible. Mars has 2/5 the gravity of Earth. There is a better chance this can be adapted to. However, much is not known about this. The right exercise program may eliminate this problem. In other respects, different gravity levels each have a suite of advantages and disadvantages.

So. Depending on how people weigh the advantages and disadvantages of each place, some feel we should go to Mars first, some feel we should go to the Moon first. One extra spin on the argument is that if the Moon is colonized first, then sending a lot of stuff to Mars is much easier. But you have to build all the infrastructure on the Moon to do that, so maybe that should be a long term consideration, but first a base should be established on Mars. Once you get into all the possible combinations of missions, the question becomes even more complex than has been briefly conveyed here. There is more discussion of the possibilities here.

And we haven't even gotten into the more subjective qualities of each place. Does it matter more that Mars has a day the same length as Earth's and has an atmosphere that creates a sky a lot like we are used to here, or does it matter more that the Earth hangs in the sky on the Moon, big and beautiful?


1 - 'Volatiles' refers to any chemical that is lost to space when subjected to the barrage of radiation and particles from the Sun, on bodies that are too small to hold them by gravity or with the help of a magnetic field.

2 - The real carbon dioxide reserves on Mars are unknown. Models predict frozen CO2 mixed into the frozen water of the poles and in the ground. In the early history of Mars when the atmosphere was much thicker, carbon dioxide may have been sequestered in carbonate minerals such as calcium carbonate. See here, here, and here.

$\endgroup$
  • 2
    $\begingroup$ There's also the aspect of human competition & the perceived kudos in getting there first. In some ways the various proposed Mars landings of humans are a bit like a second space race. $\endgroup$ – Fred Jul 6 '15 at 3:55
  • 2
    $\begingroup$ One thing that may be a major factor is that gravity on mars is stronger than the moon. It may not be possible to be stationed at a moon base for a long period without adverse health effects. Mars gravity may also not be sufficient, but at least has a better probability. $\endgroup$ – neelsg Jul 6 '15 at 11:08
  • 2
    $\begingroup$ A good deal of research went into this answer. Lots of info, +1. But I disagree that vaporizing the frozen CO2 would give an atmosphere 30% the density of ours. I believe this is a very optimistic projection by Zubrin and others based more on wishful thinking than hard evidence. The frozen CO2 deposits at the Mars poles are inadequate to do this. $\endgroup$ – HopDavid Jul 6 '15 at 15:42
  • 3
    $\begingroup$ Yes but don't forget the giant terraforming machines that were never activated that the ancient martians completed mere seconds before getting extincted. Took a long time for them to suffocate apparently but not quite long enough. $\endgroup$ – Erik Reppen Jul 6 '15 at 16:26
  • 2
    $\begingroup$ On the CO2 on Mars, the ice caps are thought to be mostly water, but the amount of CO2 that could be trapped in and under it's surface that might be released if the planet was terraformed and warmed up is a much larger unknown. Not sure of the quality of this link, but it's related: spacedaily.com/news/mars-water-science-00g1.html $\endgroup$ – userLTK Jul 7 '15 at 9:37
2
$\begingroup$

The one big advantage Mars has over the moon is that it has a very wide range of chemicals available there. Probably everything we would eventually need is available on Mars. This is not the case with the Moon.

However a Settlement on Mars and a settlement on the Moon would be essentially the same thing: large structures underground. Mars has almost no more radiation protection than the moon. The Martian atmosphere is so close to a vacuum, it is of no help in terms of the pressure differential around the spacesuit. The fact that a Martian day approximates an Earth day would not matter much since everybody would be living underground.

In the very long run a martian colony could live without imports from elsewhere. A lunar colony would probably always need imports. However a lunar colony is also much more capable of doing trade. With lower gravity, and no atmosphere to create aerodynamic demands on spacecraft, a lunar settlement is more accessible. The moon could participate in commerce involving exploitation of asteroids much more easily than a martian settlement could. If large orbiting structures are to be built, it’s not hard to imagine lunar aluminum and glass being more economical than lifting the same stuff from the earth. That gives the lunar colony a product to sell in exchange for it’s imports like carbonaceous chondrite asteroid material for agriculture. It’s hard to picture anything that martians could economically export.

While a martian settlement could become self sufficient, a lunar settlement would probably be much more a part of a moon / earth / asteroid economic system.

Recent studies have speculated that a lunar cave, either man made or natural, could be quite large. http://www.airspacemag.com/daily-planet/cave-living-moon-180961494/

$\endgroup$
  • $\begingroup$ The one big advantage Mars has over the moon is that it has a very wide range of chemicals available there. Could you explain what you mean by this? Both the moon and Mars have a wide variety of chemical elements. For example, oxygen is present on both bodies, although in different forms. $\endgroup$ – Ben Crowell Dec 21 '16 at 1:23
  • $\begingroup$ @BenCrowell, Mars is known to have abundant hydrogen, while the Moon is known to be quite deficient in it. $\endgroup$ – Mark Dec 21 '16 at 3:09
  • $\begingroup$ The water and other volatiles at the poles of the Moon is approximated as being 600 million metric tons or more. A population could become independent over time as long as it isn't too big and it creates a closed ecosystem. $\endgroup$ – kim holder Dec 21 '16 at 14:40
  • $\begingroup$ Just from years of reading I remember that the moon is rich in oxygen silicone, several metals including iron, aluminum, magnesium, titanium, as well as calcium. However carbon and nitrogen, not so much. There is some that is deposited by the solar wind, but just in trace amounts. That's why I mentioned carbonaceous chondrite asteroids as a source. Of course there is also all this interest in volatiles at the poles. But we have just scratched the surface (literally). Who knows what concentrated deposits might be found deep underground. This rather prompts me to ask the question myself. $\endgroup$ – Johnny Robinson Dec 22 '16 at 2:58
  • $\begingroup$ Natural lunar cave? OK, so there are some interesting pictures which have been interpreted as showing possible cave entrances, but how could caves have formed on the Moon? For Mars, it's easy to understand - the same way caves formed on Earth, but there has never been any flowing water on the Moon. $\endgroup$ – Anthony X Jan 1 '17 at 16:46

protected by Community Jan 2 '16 at 12:18

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.