Why colonize Mars and not the Moon?

[mfb]

You can put enough regolith overhead to make the asteroid risk on the Moon the same as the risk on Earth.

I don't think that is practical. The atmosphere protects nicely against objects up to ~10 meters, and reduces the effects of a direct impact even above that size. On the moon, we would probably need more than 100 meters of rock to get a similar protection.
I don't think it is necessary either. Impacts of meter-sized objects are extremely rare. Earth is hit by about one object with 4 meters diameter per year. Moon would get hit by at most 10% that rate (conservative upper limit), the probability that such an object hits a large 1 square kilometer installation directly is 3*10^-8, for an expected impact once every 300 million years. Objects with 1 meter diameter are probably more frequent by a factor 20-30, for an expected impact once every 10 million years - still completely negligible. Due to the lack of relevant atmosphere, an impact elsewhere would just generate some seismic waves and a few rocks and dust particles thrown around - for a meter-sized object this is completely irrelevant.

 

[1oldman2]

On the subject of Meteorite impacts I came across this recently, illustrates rather nicely the effects on a body with atmosphere, an advantage the moon lacks. (This is a very recent impact)
From, https://www.nasa.gov/image-feature/jpl/pia21451/unlocking-an-impact-craters-clues
"Mars is a dynamic planet. HiRISE has witnessed many surface changes over the past ten years, including hundreds of new craters formed by ongoing impacts. Most of these impacts are likely caused by asteroids that have strayed into collision courses with Mars. The planet's much thinner atmosphere compared to Earth makes small asteroids less likely to burn up prior to hitting the Martian surface.

This new impact was discovered using the lower-resolution Context Camera (CTX), also on board Mars Reconnaissance Orbiter. An older CTX image of this region from May 2012 shows a uniformly dust-covered surface, while a newer CTX image from September 2016 reveals the crater's dark blast zone. New craters on Mars are easiest to locate in such dust-coated terrains, where they provide opportunistic "road cuts" that allow scientists to see beneath the dust blanket and determine the underlying rock compositions and textures."

 

[Al_]

I don't think that is practical.

100 metres is a lot of dirt to dig. But a robot could do it I'm sure!
Or you could be in a cave or a mine.

 

[Al_]

2. LLO (or space elevator counterweight) to highly eccentric Earth orbit. On Earth approach, release the payload, then raise the perigee enough to avoid the atmosphere.

Great!
But are you sure that an unguided payload can hit the rght part of a desert if it's released into a fast, eccentric, grazing trajectory?
If it can, you nailed it!

 

[rootone]

I guess it could be arranged that the delivery capsule does have limited guidance which would home into a beacon on the ground.
It wouldn't matter if accuracy was only within 1 or 2 km.

 

[mfb]

Great!
But are you sure that an unguided payload can hit the rght part of a desert if it's released into a fast, eccentric, grazing trajectory?
If it can, you nailed it!

A release from an eccentric orbit makes a steeper re-entry trajectory easier compared to re-entry from LEO, which reduces the size of the landing ellipse. Aim for some desert.

 

[chasrob]

Yep
Ok
I just said
It isn't impossible to overcome this problem
But colonizing moon ain't such a good idea
Building a space station on moon=great

Colonizing on moon = not so great

Colonizing on Mars= great

How about the dust on Mars?

 

[sophiecentaur]

Even on Earth the large ones are a risk.

And the risk is so much higher for 'someone' getting hit on Earth because the density of population is so much higher. I would imagine that the structure of any living space on the moon (or Mars) would have very few large pressurised cavities and there would be safety shutters between all of them.

 

[Aditya Shende]

How about the dust on Mars?

Dust on Mars isn't regolith

 

[Al_]

I guess it could be arranged that the delivery capsule does have limited guidance

Well, I'm trying to envisage a method for regular delivery of precious metal payloads from the Moon that does not require much, or any, regular launches from Earth. (Because those are expensive)
If we can manufacture the guidance devices on the Moon, fine, but this was intended to be done in the early stages of Lunar colonisation.
No matter, we seem to have agreed that it's not needed.

A spin-off thought here: What would be economically viable for a space colony to purchase from Earth?
Cheapest is brainpower! That can be transmitted upward at nearly zero cost. This includes engineering designs and architecture as well as remote control of robots.(Remote control of robots works a lot better if they are on the Moon with a second or so time lag, rather than the long half hour-ish for Mars.)
Next is anything small and light, that takes a lot of infrastructure to make. e.g. raw unmounted silicon chips as well as precision components like valves and scientific instruments and sensors.

 

[nikkkom]

Well, I'm trying to envisage a method for regular delivery of precious metal payloads from the Moon that does not require much, or any, regular launches from Earth. (Because those are expensive)
If we can manufacture the guidance devices on the Moon, fine, but this was intended to be done in the early stages of Lunar colonisation

Depends on how you define "early". As I see it, for the first 100 years or so of the colony, any material goods from the Moon will be uneconomical to export to Earth.
One thing which _can_ be exported at a profit are souvenirs. "Buy our Moon rocks!", "This sapphire was grown from Moon's aluminium oxide!", "This titanium coin was made from the material of the fuel tank of the actual Moon descent stage". But the market for these is not that big.

 

[Al_]

Dust on Mars isn't regolith

Dust on Mars is potentially problematic in it's own way.
It is partly perchlorates, which have a corrosive effect like an alkali.

As I see it, for the first 100 years or so of the colony, any material goods from the Moon will be uneconomical to export to Earth.

Even Platinum?

 

[mfb]

Dust on Mars isn't regolith

It is. Or, to be more precise, the surface is covered in regolith, the smaller grains in it can become dust. Here is a discussion of how to reproduce it on Earth.
Regolith exists on Earth as well.

 

[Aditya Shende]

Dust on Mars is potentially problematic in it's own way.
It is partly perchlorates, which have a corrosive effect like an alkali.Even Platinum?

Didn't know that[emoji106]

 

[lifeonmercury]

The dust on Mars seems like a real nuisance. What if a patch of Martian ground was watered and covered with fertilizer. Would any plants be able to grow there?

 

[nikkkom]

>> As I see it, for the first 100 years or so of the colony, any material goods from the Moon will be uneconomical to export to Earth.

Even Platinum?

Yes, even Platinum. I don't understand your fixation on expensive metals. They cost a lot because they are rare. *And they are rare on the Moon too*. There are no places with platinum bars just lying on the surface, waiting to be picked up for free.

Even if (not proven) there can be locations on the Moon with somewhat more Platinum than in Earth platinum deposits, it will still need to be mined - and that costs money. In "early" colony, mining on the Moon is more expensive than mining on Earth, because infrastructure is not there, or insufficiently developed.

 

[rootone]

The dust on Mars seems like a real nuisance. What if a patch of Martian ground was watered and covered with fertilizer. Would any plants be able to grow there?

Plants definitely don't like perchlorates, it;s a bit like bleach, your topsoil layer would need to be separated from the martian soil,
so in effect your aren't using Mars soil, just replacing it with more plant friendly earth-like soil.
Where is the fertilizer to come from anyway?, other than recycled organic waste made from supplies originally shipped from Earth.

 

[nikkkom]

Nitrogen fertilizers can be made from atmosphere.

 

[Al_]

What if a patch of Martian ground was watered and covered with fertilizer. Would any plants be able to grow there?

On Earth, there are common organisms in soil that convert perchorates into harmless chemicals.
Presumably on Mars you would mix old soil that had plenty of these bugs with new regolith and dust, and organic matter, as a kind of composting process before it was used for plants.

There are no places with platinum bars just lying on the surface, waiting to be picked up for free.

Nuggets.

 

[lifeonmercury]

Plants definitely don't like perchlorates, it;s a bit like bleach, your topsoil layer would need to be separated from the martian soil.

The concept of growing plants on other planets is an interesting one. Let's say that some good potting soil is brought from Earth to Mars. Assuming this soil (and not any Martian soil) is used and the required water and fertilizer are provided... Are there any plants, shrubs, weeds, or algae that could survive outside somewhere on Mars?

 

[Al_]

Are there any plants, shrubs, weeds, or algae that could survive outside somewhere on Mars?

In a frozen state some things might. Some lichens seem to have survived a Mars-climate test, but i don't think they grew during the test. You mention green plants, and for them you need liquid water, without too much salt or perchlorate, above freezing point. At the lowest point on Mars (Hellas Basin) in the deepest crater, you just get enough pressure to stop pure water boiling away. Where would the water your plants need come from? But it might be very dry so even if it didn't boil, water would evaporate very quickly. I suppose if, at that spot, you had an unpressurised greenhouse, to keep the salt and perchlorate out and the water vapour in, and you got water from somewhere...

I don't understand your fixation on expensive metals.

- trying to argue that a Moon colony could sell stuff to Earth much earlier in it's growth than a Mars colony, and so be less draining on Earth budgets, and grow faster. And be less likely to fail!

 

[ian127]

Elon is the boy! Parachute rockets ,electric cars, asteroid colonies on Mars - who knows what he would come up with if terrorists kidnapped him to build them a missile?

 

[lifeonmercury]

Elon is the boy! Parachute rockets ,electric cars, asteroid colonies on Mars - who knows what he would come up with if terrorists kidnapped him to build them a missile?

Then we'd have ISIS to deal with on Mars. Not good.

 

[Karlms]

Seems to me like we should first build a base on the moon with robots, and then do the same on Mars. I don't see any point in planning to put humans on Mars as long as doing so would essentially be a suicide mission.

 

[mheslep]

Im having difficulty justifying the extinction event rationale used to start this thread. Most disaster scenarios I consider don't have a Mars Colony as the best survival strategy. Better survival scenarios can be found on Earth it seems to me, or a Mars Colony likely offers no better outcome.

1. 100% lethal plague? How does a Mars Colony help, unless all Earth-Mars travel is banned, permanently, shortly after a colony is established? Same problem applies for killer AI, worse in fact, as all data transfers also wound need to be banned. A killer plague (or AI) would need a very long incubation period to infect the total population before notice and contagion defeating quarantines are set. That same long incubation allows the plague to travel to Mars aboard a host.
2. K-T event like Earth impact. Surely constructing long term subterranean shelters on Earth are more feasible, and predictable, than the effort required for a sustainable Martian colony, which BTW is also likely going to be partially subterranean (radiation).
3. Killer solar event. Surely these are still more survivable, if at all, under Earth's atmosphere and magnetic field than at 1.5 AU and half the flux, though with a thousand times less atmosphere and nill magnetic field. Same goes for any extra solar system radiation event.

 

[rootone]

4. Greenhouse catastrophe, but then even fixing that is probably easier than trying to modify a habitat which didn't support life in the place.

 

[mfb]

@mheslep: We discussed this before. Making us more resilient to extinction is a nice feature, but I don't think it is the reason to go.

Concerning plagues: Diseases can spread in weeks. SARS had an incubation period of just a few days, but managed to spread to ~30 countries. The same disease with an incubation period of a month could have been a massive global catastrophe. Not enough to eradicate all humans, but enough to lead to serious trouble everywhere.

I'm not sure how well shelters survive a massive asteroid impact.

Solar events are directed - they can hit Earth or Mars, but not both at the same time. But they won't lead to extinction anyway.

 

[mheslep]

@mheslep Making us more resilient to extinction is a nice feature, but I don't think it is the reason to go..

Agreed

 

[Al_]

There is also the threat of nuclear war. It's debatable whether this could cause extinction, but I wouldn't like to bet on it.
A space colony could, if it is developed enough, be more robust in the face of such attack, harder to reach, and less of a priority target. A Mars colony is less vulnerable than a Moon colony.

As for disease, the sealed habitats in space are already perfect for quarantine, even if the bugs made it there with human travellers. I take the point about 100% lethal needing long gestation, but if plague combines with collapse of law and order, or war, it could lead to extinction even without 100% fatality from disease. Again, the longer trip to Mars means that a disease is more likely to be evident during the voyage, so Mars wins here too.

Having said that, a Moon colony offers substantial defences, and it would be a good stepping stone to even more protected places further away.

I think that extinction events are a good reason to go.
I know that such natural events are very rare, but given that we would want to go eventually to avoid an event, why not go sooner rather than later?
And man-made extinction events, how rare are they? Who knows? We could just sit on Earth and wait to see...

 

[mheslep]

...be more robust in the face of such attack, harder to reach

In the age of a Martian Colony and frequent heavy manned missions to/from Mars, sending a couple unmanned tons that don't land to Mars becomes trivial for some malevolent actor in power. Even today's Falcon 9 FT can deliver four tons to Mars, or multiple thermo nuclear weapons. Any hardened shelter on Mars can be done better and more efficiently on Earth.