Musk just addressed this. Mars has an atmosphere of CO2 and Nitrogen, so we can grow plants, a day length similar to Earth's (24.5 hours), and is larger.
You can pressurize a chamber using the thin atmosphere, rather than being restricted to the gasses you bring with you.
You can use ISRU and atmosphere resource extraction to generate rocket fuel on the surface of mars, rather than being restricted to the rocket fuel you bring with you.
Ultimately, the answer is Mars has the necessary resources and when you look into the details just makes more sense and is easier.
But it's still much easier to grab even a thin gas than it is to mine anything. An extremely convenient source of both carbon and nitrogen is going to be a huge benefit in terms of trying for long term sustainability. The Moon does have plenty of oxygen in various minerals and hydrogen in the polar ice but you need more than that.
When the pilgrims originally sailed to North America from England, it took on the order of two or three months. A six month trip to Mars seems reasonable in that context.
The pilgrims didn't have to worry about being subjected to deadly cosmic radiation. They could also bring various tools with them and build habitats in their new home using readily-available materials, and grow food there from seeds (though they should have picked a more southerly landing spot...). They also didn't have to worry about having pressurized environmental suits just to walk around outside once they made landfall.
No, they just had to worry about weird diseases, storms destroying their boat en-route, not having any clue where they'd land or what the territory would be like, and being attacked and killed by angry natives. Oh and they were doing it all with pretty basic "science".
None of those problems exist on Mars. Others exist, but you can't just directly say it was easier.
There are other important reasons for this that don't make such a great subject for a public presentation, such as getting away from Earth's political and military sphere of influence and achieving greater redundancy in case a large asteroid impact event happens on the Earth/Moon system.
I see this as a disadvantage; the major difficulty of space exploration is getting out of the Earth's gravity well. I don't think it's wise to fall back into another one.
Elon actually addressed this, you only need the booster from Earth. For all interesting targets the spacecraft can launch by itself and get back to Earth.
The point of the booster for Earth is both to get out of Earth's gravity well and through its atmosphere (both of which are far less of a problem on Mars).
What if that gravity well has the resources you need to get out of it?
The moon also has a small gravity well, but no real resources to help you escape it. Mars has a bit of a gravity well, but has many more resources to help you escape that gravity well.
Mars has no magnetic field so you get cooked with radiation.
Mars' soil contains tons of perchlorate at levels which are very toxic to humans.
TBH Venus seems like a better candidate for long term terraforming.
You can build floating complexes in it's upper atmosphere, and it has enough oxygen and water locked in it's atmosphere and we might be able to fix the rotation and the density of the atmosphere in one go by using the atmosphere to speed up the rotation of Venus.
While both of these are quite "far fetched" technically, as far as terraforming goes we aren't any closer to terraforming mars than Venus, and at least for Venus we don't need to figure out how to give it a magnetic field.
Venus also has no magnetic field. It has much stronger gravity as well, requiring larger rockets to take off from it, and it is quite difficult to mine resources from due to the high temperatures and pressures at the surface, meaning all materials for a colony would need to be sent from Earth.
Additionally the current theory is that if Venus will be sped up to below 56h per rotation it would regenerate it's intrinsic magnetic field which should be near earth levels.
And while Venus does have higher gravity than Mars, it's still lower than Earth's, and overall the delta V for venus insertion orbit is slightly lower than what you need for Mars.
"Additionally the current theory is that if Venus will be sped up to below 56h per rotation it would regenerate it's intrinsic magnetic field which should be near earth levels."
That's great and all, but how exactly do we realistically speed up the rotation of a _planet_?
One of the more "probable" and more or less energy sane suggestions would be using mass drivers to eject the atmosphere at high speeds to induce spin.
The mass of the venusian atmosphere is high enough for this to actually work and still leave you a lot of atmosphere to work with, it will take 20-30 years but it still doable.
And pointing those canisters at Mars or the moon. Once you've hit Venusian escape velocity you might as well move that atmosphere somewhere else that needs it.
But compressing acidic gasses makes the corrosion problem worse, doesn't it? How do you deal with that?
Mars is much smaller than Earth. From Wikipedia: "Mars is less dense than Earth, having about 15% of Earth's volume and 11% of Earth's mass, resulting in about 38% of Earth's surface gravity."
I wonder if the 1-way ticket to mars would appeal to older folks who can survive the trip, but don't have the physical strength for much adventure on earth.
Nice idea, but I assume anyone recruiting for space travel is going to insist on people who are very fit and in 100% good health, which usually means fairly young people. Certainly there could be some older people, but probably not a majority.
Which is why the ISS is populated by PhDs in their 40s?
Of course you want the first colonists to not be sickly, but they won't need to be Olympic decathletes in their 20s. Equipment for lifting heavy objects can be sent more cheaply than people (it can go slowly and doesn't need life support).
I think for a venture like this maturity and patience is going to be more important than physical strength. There will be a lot of tedious tasks with long checklists that need to be followed near exactly to succeed. There will be a lot of disappointment and frustration when things fail or timelines slip. There will be the irritations of being stuck in a small social circle with a few people you intensely dislike but have to depend on for survival.
Add in the fact that your sperm or eggs will probably get exposed to large doses of radiation until they figure out how to get to Mars faster, and it will be far less attractive to anyone who is planning to have kids someday.
With substantially less gravity, you can lift 2.6x the weight as you can on earth. People in their 40-50s in good health with moderate strength, good maturity, advanced skills, and already-grown children are good candidates. And yes, with the radiation they'll get hit with, it's better than kids burning away their lives.
> There will be the irritations of being stuck in a small social circle
in my own personal experience, this thing works worse for older folks, who get territorial, grumpy and so on. But we aren't discussing folks in their 40s, rather 50s and 60s
Some possible reasons; Mars has a c02 atmosphere, water ice, it has a ~24 hour day as opposed to the moons 28 day-day, Earth and Mars have similar sizes.
Besides, it wouldn't exclude the possibility of an extinction level event that disables the earth-moon system. Moon seems more suited for the role of an outpost, re-fuelling station and the final flight to Mars/elsewhere.
It is a coincidence. The rotational speeds of planets formed through a lot of chaotic events in the early solar system. E.g. Venus spins in the "wrong" (retrograde) direction, completely violating conservation of angular momentum, probably because of a planetary scale collision.
We can try to explain solar system formation through mathematical models and simulation (Phobos and Deimos would be clues) but we can't go back in time and find the real explanation. No law of physics mandates that Mars' rotational period should be similar in magnitude to Earth's.
I don't know why you got downvoted but I couldn't find anything helpful regarding your question. I found some references to the fact that mars and earth have ~24hr days but no explanation as to why they are so similar. Mars also rotates (on its axis) the opposite direction of Earth which I found interesting. So many questions about our little local solar neighborhood, so few answers!
I'm pretty sure everything about the particular properties of our solar system is, strictly speaking, a coincidental result of the initial conditions of the big bang. But to speculatively address the intent of your question, I'd guess it has to do their relatively similar size, solidity and distance from the sun.
I suppose it could, but of all possible values, it seems exceedingly strange that they'd fall on essentially the same number. It seems much more likely that it has basic physics behind it, but I'm not sure what it is.
random chance is as good as physics. the earth was hit by a mars-sized impactor allegedly, so if not for the moon, we would have a completely different day length. (assuming there would be some 'us'.)
Why does the Mars 24.5 hr day versus the Moons 28 day-day matter? What are the consequences of this big difference between Earth day and the moon/Mars day?
I think you underestimate the importance and cost of the artificial lighting :P
On the moon it means you need enough solar power in batteries to power your gear, and to power appropriate spectrum lighting for plant growth.
If you can rely on solar power more reliably, then you can construct (significantly more complex than those required on earth) green houses which still benefit from natural light.
In all fairness, my parent poster was talking about human circadian rhythms, not greenhouses.
I actually agree that there are numerous challenges associated with very long days and nights. Artificial lighting per se is not among them. Solar power is a reasonable one.
Well for one thing living in a gravity well is healthier for humans. We don't do very well long term in 0 gravity. Our systems work best when gravity is helping things along.
You spin up your station. You're not limited to whatever accidental value holds on the planetary surface. This was all studied back in the 1970s and 80s, and free-space development makes way more sense: http://www.nss.org/settlement/ColoniesInSpace/
Of course space settlement is many steps away; so is a permanent settlement on Mars. You need to analyze the payoffs and costs and intermediates and uncertainties for each.
To me the moon would be the obvious place to start, especially as the NASA plans I've seen for Mars have been based on using a space station at a Earth-Lunar Lagrange point, and associated moonbase, as ideal staging post. That and I might one day afford a ticket.
I agree --- Mars is a pit. It's a barren desert at the bottom of a great big hole.
Its biggest, and perhaps only, advantage is that it has an atmosphere, and gas is so much easier to deal with for ISRU than anything else, as you don't need to mine it: just open a valve and suck it in. I notice Musk's ISRU plan is to mine ice; I do wonder how he's going to do that, as it won't be easy.
But... you know what... if you can get to Mars, you can get anywhere.
If you can get to Mars, getting to the Moon is so trivial you might as well build and maintain a base there just to test the equipment.
If you can get to Mars, you can get to near-Earth asteroids with enough spare capacity to take a whole a mining plant in tow.
If you can get to Mars, Ceres is only 400 m/s further away. (And Ceres is interesting.)
If you can get to Mars, then the outer solar system is reachable (with preparation and some disposable boosters).
If you can get to Mars, anyone who can afford a IST ship can have a space station.
So, hell yes, let's go to Mars. (And I'll cheerfully wave goodbye to you from my ice-mining cometary habitat.)
I've nothing against Mars, more surprise that it's not via lunar orbit staging as the last several explanations of how we'd get there that I've seen. Like it was a big obvious advantage.
Mars first has the enormous advantage that it's tangibly in progress, however early, rather than being a great NASA idea that isn't getting funded. So I don't actually care which if only one is having rockets built. I saw enough artist impressions in the 80s. ;)
My recollection of the NASA idea was a Mars voyage would reconfigure/refuel at the space station but never land on the moon. The moonbase is the warehouse, fuel and whatever else would be needed to keep space station fed, and gets developed into manufacturing.
Lower G meaning larger vehicles, lower launch cost and so forth. The station at L2 was supposed to be a good jumping off point for anywhere - Mars, asteroids, rest of solar system - supposedly the most fuel efficient way to all(?) of them from here.
It's a while since I last read about that, so I may be mistaken on details.
Mars is sexy and looks like a place --- people can see the pictures from the Mars rovers and imagine themselves being there. It's got weather and wind and interesting landscapes. It's featured in myths and legends for so long that it has a special place in people's heart. I can totally see it being used as the end goal of a fairly long plan.
The Moon's not very sexy. It's all dusty blacks and greys. Everyone knows it's a dead rock, we've already been there, and public consciousness is dominated by the Apollo program pictures of astronauts in gigantic, bulky spacesuits.
(This is mostly perpetrated by NASA unaccountably not sending any decent rovers to the Moon. Even the most recent lander, China's Chang'e, deliberately landed in the most boring place they could find. There aren't any interesting pictures of the moon because we haven't been anywhere interesting.)
ISRU's hard there, too. There's water ice you can mine, but carbon? I don't know where you'd get that.
But... if I were building a water ice mining plant destined for Mars, I'd want to test it somewhere. The Moon's a good place. So now I've landed an ITP ship with a mining rig. I'm going to load it with scientific instruments, too. And scientists. In fact, I might as well land two; it's good practice for Mars. And we're mining water, so we might as well use it, and help test the recycling systems. After all, the Moon's close enough that you can dash back to Earth in an emergency; it's the ideal place. We've got two ships; let's use one to recycle the crew on the other, and leave it there long term; there's plenty of interesting science to do, and it's all excellent practice.
So I'd be really surprised if a long-term presence on the Moon didn't sneak into this plan by the back door. And then if a carbon source were to be discovered in large enough quantities for meaningful ISRU, then sourcing methane from the moon would slot neatly in.
Landing on the moon is just as difficult as la to mars. Operating on the moon is much much harder. Getting back is hard because there is no easy ISRU way to do it. Nobody will go to the moon to test stuff.
Getting water on the moon is a completely different problem then getting water on mars. Testing these things on the moon is totally insane anyway.The moon has some water, we don't know how much, and not exactly were it is. Mining it would be extremely difficult, specially without a nuclear reactor.
As for recycling systems, we are already good at them. We can and do test them on earth. We do test them on ISS. There is no need to go to mars, to these systems.
On Mars the most important resources for ISRU is easily and everywhere available, on the moon that is not the case.
The Science on Mars could answer fundamental questions about live, that is almost impossible on mars. Mars is clearly far more interesting from a scientific perspective. That is not even a point worth debating.
I am all for going back to the moon eventually, but mars is far more important. If you want to go to mars, go to mars.
Going to a body with atmosphere is easier than going to one without. You get free braking (~8500m/s of delta-v according to Elon, for Mars) thanks to the atmosphere.
Anything without an atmosphere you have to carry the fuel to stop after chasing it down, then land on it slow enough not to die. For robotic missions we can approach these objects in very favorable orbits with transit times measured in years, so the delta-v needed to slow down is manageable.
For human-based missions we have to get there fast. Going there fast means you have to dump alot of speed to stop once you get there. Without an atmosphere, that takes fuel. Not as much as it took you to reach that velocity, since you're lighter now, but still just about as much in terms of delta-v.
I learned this playing KSP. It will open your eyes to the real challenges of orbital mechanics. The hardest planet to land on in the entire game is the one with a mass/gravity approaching the game version of earth, except with no atmosphere. The in-game numbers aren't realistic, but the concepts are.
And hell yes, lets go to Mars. Where do I sign up?
> I notice Musk's ISRU plan is to mine ice; I do wonder how he's going to do that, as it won't be easy.
Load up the icy dirt into a chamber using a digger, heat it up and precipitate out the water vapor. The only potential problem is separating out other volatiles, but fractionation is pretty basic tech.
Provided you have a decent power source that's easy: the hardest part is getting your raw material into the chamber and disposing of the debris afterwards. Humans driving flat-pack bulldozers, most likely.
You could probably heat up the regolith while it's on a conveyor belt and use a negative pressure system to draw off the vapour through cooling tubes, so it could operate continuously.
Go to the moon for its own rewards--a lunar base or whatever--but don't go there as a stepping stone. The challenges of landing on the two bodies are vastly different and you'd throw away half your effort reworking for Mars after you got some moon landings.
Not sure why you'd go out to the lagrange point? Or the moon? It's much farther away (a few days travel instead of a few minutes), it's way outside the limited shielding the earths magnetic field gives, and there's nothing there. Why's it better than LEO?
The moon is high ground from anywhere on Earth, which makes state action involving colonization efforts very likely. It's easy to point out that there will be no bombardment or invasion from Mars in the next half century, regardless of how things go for settlements there.
