Why colonize Mars and not the Moon?

[lifeonmercury]

I watched the 6-episode series called Mars this week. Elon Musk kept emphasizing that humans must spread out to at least one other planet to ensure human survival in the event of some extinction event on Earth.
Wouldn't colonization of the Moon achieve the same purpose? Seems like that would be a more viable option.

 

[phyzguy]

It's certainly a good question, but I think there are two main reasons that people have fixated on Mars rather than the moon:
(1) Mars has a day/night cycle very close to Earth. The moon has a 4 week day/night cycle. During the two week night, it gets extremely cold, and solar power is not available for generating energy.
(2) Mars has a ready supply of water, which is essential for any human colonization. The moon may have water in permanently shadowed craters at the poles, but this has not been proven. Elsewhere on the moon is extremely dry, so water does not appear to be available.

 

[mfb]

Mars has carbon, hydrogen, oxygen, and probably nitrogen available, several metals are available, and various other elements can be found in smaller amounts. The moon has oxygen and a few metals, but everything else is challenging. Mars has a 24 hour day and a higher gravity THAN MOON[/color]*. Building a small station on Moon is easier, but for a colony Mars is better.

In terms of extinction: If an asteroid hits Earth, secondary impacts could also hit the Moon. Diseases can spread better between Earth and Moon due to the shorter travel time.* that should have been obvious from the context, but as I got misunderstood twice, better make it absolutely clear

 

[PeroK]

I watched the 6-episode series called Mars this week. Elon Musk kept emphasizing that humans must spread out to at least one other planet to ensure human survival in the event of some extinction event on Earth.
Wouldn't colonization of the Moon achieve the same purpose? Seems like that would be a more viable option.

Colonising Mars or the Moon sounds like pure fantasy to me. What extinction event on Earth could possibly make life on Earth less tenable than life on Mars or the Moon? If the worst comes to the worst we're better having a few people living in a bunker on Earth than a bunker on Mars.

 

[mfb]

What extinction event on Earth could possibly make life on Earth less tenable than life on Mars or the Moon?

A really big asteroid impact. Bunkers don't work forever, and their tolerance for seismic waves is limited as well.

A virus maybe, natural or artificial, if it spreads fast enough without obvious warning signs.

 

[PeroK]

A really big asteroid impact. Bunkers don't work forever, and their tolerance for seismic waves is limited as well.

A virus maybe, natural or artificial, if it spreads fast enough without obvious warning signs.

If bunkers don't work forever on Earth, they won't work forever on Mars. The Earth, even after an asteroid impact, would be a paradise compared to Mars, where there is absolutely nothing to sustain human life.

Instead of going to Mars, you could put many secure colonies here on Earth.

And, if the Vogons came to destroy the Earth, they would no doubt turn their death ray on our Martian colony as well!

 

[mfb]

If bunkers don't work forever on Earth, they won't work forever on Mars.

They don't have to, because Mars didn't have a massive impact in this scenario: you can use solar energy, for example. Not just for electricity - most of our indirect power consumption is used to produce food.

where there is absolutely nothing to sustain human life.

Not at the moment. That is exactly what colonization would change.

And, if the Vogons came to destroy the Earth, they would no doubt turn their death ray on our Martian colony as well!

No one claimed it would help against an alien invasion.

 

[PeroK]

They don't have to, because Mars didn't have a massive impact in this scenario: you can use solar energy, for example. Not just for electricity - most of our indirect power consumption is used to produce food.Not at the moment. That is exactly what colonization would change.No one claimed it would help against an alien invasion.

I can't see that building a series of secure habitations across the planet: power sources, food and water supplies etc. is more infeasible/impractical than building a similar colony on Mars.

As I see it, IF we had the technological capability of building and maintaining a Martian colony, we would certainly have the technological capability to build a secure colony on Earth that overall had a much greater chance of long-term survival.

Getting, say, 100,000 people safe on Earth must be more practical than getting a sustainable existence for 100,000 on Mars.

Eventually, if we had the technology to transform Mars into a habitable planet, it might be different. But, any Martian settlement in the foreseeable future would be on the edge of existence and almost certainly dependent on Earth.

 

[mfb]

I can't see that building a series of secure habitations across the planet: power sources, food and water supplies etc. is more infeasible/impractical than building a similar colony on Mars.

Getting completely independent of solar energy? We don't know how to do that yet.
Anyway, a lot of R&D for those two options would be shared.

Who would build a massive completely independent and isolated underground colony on Earth? With no contact without months of quarantine to avoid any infection spreading? On Mars you can explore a new world, maybe even terraform it over very long timescales.

Making extinction less likely is a nice feature of a Mars colony, but it is not the only argument. I would say it is not even the most important element.

 

[PeroK]

Getting completely independent of solar energy? We don't know how to do that yet.
Anyway, a lot of R&D for those two options would be shared.

Who would build a massive completely independent and isolated underground colony on Earth? With no contact without months of quarantine to avoid any infection spreading?

Given the choice between such a colony on Earth and a life on Mars, I know which one I would choose. Also, what could be achieved on Earth in, say, 10 years with $10 billion dollars would take centuries and an unimaginable budget for Mars. The secure Earth settlements could be built before we even had a viable shuttle to Mars.

Very long term is different, But, as I see it, for the next century or so, we are earthbound.

 

[russ_watters]

I agree that there are no good reasons to put a colony on either Mars or the Moon, however if we accept the starting premise that we should explore Mars, then an exploration mission practically has to be a colonization mission due to its distance from Earth.

 

[mfb]

I agree that there are no good reasons to put a colony on either Mars or the Moon, however if we accept the starting premise that we should explore Mars, then an exploration mission practically has to be a colonization mission due to its distance from Earth.

There are perfectly viable mission sketches for two-way trips with a few months on Mars.
A colony would allow much better exploration of course.

Given the choice between such a colony on Earth and a life on Mars, I know which one I would choose.

One has the sole purpose of making extinction less likely (but still possible), the other one is actually doing something new. The scientific progress from a Mars colonization would be massive. Without trying something new, we would still be in the stone age.

A completely independent underground Earth-based colony in 10 years? Construction time alone would exceed that. We had attempts to make that work on a small scale using sunlight - so far, no system was completely independent, the food/oxygen/CO2 balance didn't work. Now add the need for an independent power source - which means the technology to run a sizable nuclear reactor for decades.

The secure Earth settlements could be built before we even had a viable shuttle to Mars.

We might have that shuttle in 10 years. SpaceX is building components of such a shuttle already.

Very long term is different, But, as I see it, for the next century or so, we are earthbound.

The very long term would be for terraforming attempts. I don't see a reason why we should be earthbound for the whole 21st century. 100 years is a really long timespan.

 

[PeroK]

It is extraordinary to me that if we initiated two projects:

Project A: to have somewhere secure on Earth

Project B: to establish a colony of Mars

Then, somehow, project A runs into all sorts of problems of feasibility and cost (we can't even do "X" yet). But, project B, by contrast, has few additional problems!

Let's just take one small example:

A) Cost of building and maintaining a major hospital on Earth?

B) Cost of building and maintaining a major hospital on Mars?

There is no comparison. Building modern medical facilities on Mars is pure fantasy. Building them on Earth in some sort of "secure" area that might survive an asteroid strike is at least possible. And, critically, if that is not possible, then the impossibility of doing it on Mars is all the more apparent!

I know a lot of people think that if the Earth gets trashed, we just upsticks to Mars, but I don't see it that way!

 

[mfb]

Then, somehow, project A runs into all sorts of problems of feasibility and cost (we can't even do "X" yet). But, project B, by contrast, has few additional problems!

I don't say that.
Both projects have a lot of common things to figure out. Both have their own unique challenges.
A Mars colony will cost much more, but it will also have different funding sources.

But those projects don't have the same goal! They are completely different.

 

[Potopea Daniel]

Well,I think that this is linked with the Sun itself.
Without atmosphere,both Moon and Mars are vulnerable,but Mars is (at least) farther from the Sun,so it is more protected than the Moon.

 

[PeroK]

I don't say that.
Both projects have a lot of common things to figure out. Both have their own unique challenges.
A Mars colony will cost much more, but it will also have different funding sources.

But those projects don't have the same goal! They are completely different.

I found this, which is quite interesting:

http://www.universetoday.com/14883/mars-colonizing/

This guy (Elon Musk) seems to be quite serious about it. My favourite bit is this:

"But according to http://aeon.co/magazine/technology/the-elon-musk-interview-on-mars/, the most likely scenario (at least for the foreseeable future) would involve an economy based on real estate. With human populations exploding all over Earth, a new destination that offers plenty of room to expand is going to look like a good investment."

Okay, so let's say I decide to move to Australia. Cost of a one-way flight, let's say, is $1000. What would a flight to Mars cost? It would have to be in the millions (even if possible).

How Musk believes I could retire to Mars is just unimaginable. Even if you exclude the annual costs of food, power, water, oxygen, how many of the 7 billion of us here on Earth can afford a few million dollars (or tens of millions of dollars) for a flight to Mars? The cost of building a house? And what am I going to do there? I'm just going to be stuck inside on a planet with no oxygen, no food, no nothing.

For example, the current costs of space tourism are about $20 million dollars, according to:

https://en.wikipedia.org/wiki/Space_tourism#List_of_flown_space_tourists

I don't get this at all. I can't believe what I'm reading and that people are serious about this stuff.

 

[mfb]

This guy (Elon Musk) seems to be quite serious about it.

"I want to start Mars colonization. I don't have any money. I'll start multiple companies, become a billionaire, get into the spaceflight industry and spend billions to make it possible" is a bit more than "quite serious".

What would a flight to Mars cost? It would have to be in the millions (even if possible).

Musk estimates $500,000, potentially as low as $150,000 (in 2016 dollars) - with the first generation of transport ships.

For example, the current costs of space tourism are about $20 million dollars, according to:

Yes, because we throw away rockets after each use. How much would the trip to Australia cost if everyone would parachute down and the aircraft crashes into the ocean? A million, probably even more. Re-use makes airplanes 1000 times cheaper, and it can make rockets cheaper by a similar factor.

All those plans are public. You can read them. People are serious about stuff because it is in development right now. It is not a sketch on a drawing pad. They build components already.

 

[russ_watters]

There are perfectly viable mission sketches for two-way trips with a few months on Mars.

I suppose there is an additional assumption or principle behind my view that a trip should should at least spend as much time at the destination as on the ride there. It isn't necessarily logical/is more of a feeling, but then a lot of this topic is.

One assumption people operate on here is that the "colony" should be self-sufficient. I don't see why that is a necessary feature unless it is to be a "perpetuating the species" colony, which I don't see as necessary either.

 

[PeroK]

It's interesting that Musk can convince people, if that's what he has done, that there is viable real estate on Mars to expand into, with the tacit assumption that there is none on Earth. Yet Australia and Canada - for example - are vast, largely uninhabited regions.

It's also interesting that there can be any discussion about the tenuousness of life on Earth - climate change, energy costs, feeding the population, when we live on a planet with essentially everything we need; yet, we can might consider life on Mars where there is essentially nothing to support human life

 

[mfb]

I suppose there is an additional assumption or principle behind my view that a trip should should at least spend as much time at the destination as on the ride there. It isn't necessarily logical/is more of a feeling, but then a lot of this topic is.

The usual two-way trip plans have 4-6 months in transit, about 1.5 years on the surface and 4-6 months back. Total mission duration ~2.5 years, more than half of the mission at the surface of Mars.
Changing those times significantly would need much more powerful rockets.

One assumption people operate on here is that the "colony" should be self-sufficient. I don't see why that is a necessary feature unless it is to be a "perpetuating the species" colony, which I don't see as necessary either.

As self-sufficient as possible, especially for bulk material, is certainly interesting to limit transportation needs. You don't want to produce computer chips on a Mars colony (unless the colony is huge already), but you certainly want to produce most of the goods you use there.A colony on Mars would tell us a lot about the ecosystem on Earth as one of many byproducts.

 

[rootone]

Mars does offer a possibility that it could in the long term be terraformed, the Moon doesn't.
While that is way beyond what can be done with our present technology, the basic raw resources exist on Mars,
Certainly it would be an extreme engineering challenge, but it isn't impossible in principle.

 

[Vanadium 50]

A colony on Mars would tell us a lot about the ecosystem on Earth as one of many byproducts.

I would say it's the reverse - we need to understand a lot more about ecosystems before sending people somewhere where their lives depend on it and it takes a couple years to send help. Biosphere 2 was not an overwhelming success.

 

[russ_watters]

I would say it's the reverse - we need to understand a lot more about ecosystems before sending people somewhere where their lives depend on it and it takes a couple years to send help. Biosphere 2 was not an overwhelming success.

Well, unlike Roanoke we would be able to learn a lot from a colony as it struggles (and perhaps fails) to survive while learning about the ecosystem the things it needed to know to survive.

Hopefully, @mfb was saying that through the program we would learn a lot...not necessarily just through the mission itself. And I would agree with that. Apollo helped a lot with technology advancement just to make it possible to go.

 

[Potopea Daniel]

Plus,it seems that Mars has more water than Moon.

 

[mfb]

I would say it's the reverse - we need to understand a lot more about ecosystems before sending people somewhere where their lives depend on it and it takes a couple years to send help.

It works in both directions.
You can also add the ISS to the list. Research on Earth is necessary for the ISS, and research on the ISS is relevant for Earth.

Biosphere 2 was not an overwhelming success.

And we'll certainly need a successful example before we start colonization of anything. But it does not have to use trees and so on. Algae plants and similar approaches would be fine as well.

 

[jkn]

Large enough (about 500 km) meteorite could sterilize Earth. It would boil away all oceans. After this 'safe Earth base' proposed here must stand pressures many times that on surface of Venus and about a year heavy rain of liquid, almost boiling, rock. Vaporized rock in atmosphere would still have enough energy to heat up top of Earth crust and kill all bacteria living there.

1. We need cheaper access to space. SpaceX is trying.

2. We need to develop and test lot of tech for independent space colony. This testing is much safer, cheaper and faster to do on the Moon. Note that most work for Moon base can be done by remote control from Earth. So initial Moon base would be much smaller than initial Mars base.

3. Eventually we need to expand to space or we all die. In worst case all life on Earth dies with us. I don't know if we have 100 years or 1 000 000 000 years to do that. But eventually we must expand or die.

First to the Moon. Then to other moons and asteroids. Best places to study Mars is from base on martian moon. Distance is so short that telerobotics is possible. Single Mars base or robots can only study small area. Moon base can control robots everywhere. Moon is needed for radiation protection of the crew. We need significantly less fuel to go from Earth to martian moon than to the Moon (both with soft landing). But because of longer travel time we need to practice with Moon base first.After life on Mars is checked, we can decide to go to Mars.

Moon base could earn some money by producing materials for other space projects.
Base needs to produce solar cells and rocket fuel. Perhaps solar cells produced on the Moon could be used to provide continuous solar power for whole Earth. (From GEO of course.)

Moon base could also build (heavy parts) and maintain telescopes on Moon. Yes I know, space is better for telescope than Moon, but Moon base can provide service when needed. Only export for Mars base would be software. I doubt it will be enough. Even base with million inhabitants would need some import from Earth, so export is necessary. Moon base costs less to maintain, because some work can be done remotely from Earth. So Moon base has better change of success.

 

[Vanadium 50]

Large enough (about 500 km) meteorite could sterilize Earth.

Number of such objects inside the orbit of Neptune = 3.
Number of such objects that get within 100 million miles of Earth = 0

 

[lifeonmercury]

That we know of at least.

 

[Vanadium 50]

That we know of at least.

Hogwash.

Sorry, but there is as much chance we are missing a Ceres-sized object in the inner solar system is there is that we are missing a continent on Earth.

 

[Carrock]

Number of such objects inside the orbit of Neptune = 3.
Number of such objects that get within 100 million miles of Earth = 0

Number of such objects in interstellar space = unknown
Number of such objects that will get within 0 miles of Earth = unknown
Should we worry about a perhaps once in five billion year event that could kill seven billion people?

 

[mfb]

We know all 500 km objects up to the orbit of Neptune. Everything undiscovered larger than that would need a very eccentric orbit.
We know most 1 km objects in the inner solar system.

In terms of mass-extinction impacts within 1000 years, long-periodic comets are the main threat. Every other object in the inner solar system is known well enough.

For longer timescales, Chiron is the most interesting object larger than 100 km. It is currently in an orbit between Saturn and Uranus, but that orbit is not stable over astronomical timescales. It might fly through the inner solar system within a million years. Smaller objects like 1996 AR20 could fly through the inner solar system much earlier. Not within 1000 years, but within 100,000 there is a reasonable probability.

1. We need cheaper access to space. SpaceX is trying.

They are not just trying. They have the cheapest rocket on the market already.

First to the Moon. Then to other moons and asteroids. Best places to study Mars is from base on martian moon. Distance is so short that telerobotics is possible. Single Mars base or robots can only study small area. Moon base can control robots everywhere. Moon is needed for radiation protection of the crew. We need significantly less fuel to go from Earth to martian moon than to the Moon (both with soft landing). But because of longer travel time we need to practice with Moon base first.

A base on the surface can control rovers all over the Martian surface as well. The surface provides better radiation protection than the moons. In terms of fuel to get there, the surface is similar to the moons, as you can use the atmosphere to slow down in both cases. Getting back is much easier from the moons of course. The moons don't provide relevant gravity, however - long-term stays there are problematic. If you don't want to land on the surface, better stay in a spacecraft in orbit and make artificial gravity there.

 

[lifeonmercury]

I get it that Mars has an atmosphere and the Moon doesn't. I don't understand why this matters though. The low air pressure and high carbon dioxide levels would make the Martian air unbreathable. Do scientists really think they can eventually transform the Martian atmosphere so that people can be outside without a spacesuit?

 

[ikihi]

Some people on this forum have no imagination. Almost anything is possible to achieve with the right amount of will power and funding.

 

[jkn]

Number of such objects inside the orbit of Neptune = 3.
Number of such objects that get within 100 million miles of Earth = 0

Correction: Number of known such objects that get within 100 million miles of Earth = 0. We might even have unknown planet!

I admit it is very unlikely event. There are unknown number of events which could destroy life from Earth. All hopefully very unlikely (evidence: Life exists). An event destroying our civilization is much more likely (evidence: SETI has not found anything). Anyway life has been here about 3000 million years. It has only 1000 million years left.

 

[anorlunda]

Anything is possible to achieve with the right amount of will power and funding.

PF is dominated by scientists and engineers who are more reality based than that. We can all imagine FTL travel. Would you disparage those who believe that we will never achieve that?

 

[Vanadium 50]

Some people on this forum have no imagination.

And some people on this forum have no knowledge. Are you willing to argue that we could be missing a continent on Earth because of lack of imagination?

 

[Vanadium 50]

Number of such objects in interstellar space

If it's in interstellar space, it's not a threat until it gets closer. That has a time scale of centuries.

 

[Sankar Raman]

It is more sensible to build habitable space ships near earth. As the numbers expand we can consider colonizing Mars or ths satellites of Jupiter and Saturn. To start with we should promote a massive population explosion. 7 billion is too small, at least 30 billion is needed. Near outer space can easily sustain 15 billion to start with.

 

[jkn]

We know all 500 km objects up to the orbit of Neptune. Everything undiscovered larger than that would need a very eccentric orbit.
We know most 1 km objects in the inner solar system.

In terms of mass-extinction impacts within 1000 years, long-periodic comets are the main threat. Every other object in the inner solar system is known well enough.

For longer timescales, Chiron is the most interesting object larger than 100 km. It is currently in an orbit between Saturn and Uranus, but that orbit is not stable over astronomical timescales. It might fly through the inner solar system within a million years. Smaller objects like 1996 AR20 could fly through the inner solar system much earlier. Not within 1000 years, but within 100,000 there is a reasonable probability.

They are not just trying. They have the cheapest rocket on the market already.A base on the surface can control rovers all over the Martian surface as well. The surface provides better radiation protection than the moons. In terms of fuel to get there, the surface is similar to the moons, as you can use the atmosphere to slow down in both cases. Getting back is much easier from the moons of course. The moons don't provide relevant gravity, however - long-term stays there are problematic. If you don't want to land on the surface, better stay in a spacecraft in orbit and make artificial gravity there.

If SpaceX rockets keep on exploding once a year, they are not cheapest. So no success yet.

A base on surface needs satellites to control rovers all over Mars. Moon base needs satellites only if they want continuouss acces for all rovers. There is no point to land if work can be done without.

Martian moons provide same radiation and meteorite protection as Mars. Perhaps they need to dig slightly deeper. But that's easy because nothing weights much.

Using rotating structure to replace gravity is easier on moon than on orbit. Build circular tunnel deep enough. Then build maglev track inside it. Then a train going around. On orbit very strong structure is needed to provide centripetal force. Moon rock does it for free. Moons also give

Yes aerobraking to Mars saves fuel. It has also destroyed many probes. How many failures while landing to the Moon?

 

[jkn]

I get it that Mars has an atmosphere and the Moon doesn't. I don't understand why this matters though. The low air pressure and high carbon dioxide levels would make the Martian air unbreathable. Do scientists really think they can eventually transform the Martian atmosphere so that people can be outside without a spacesuit?

In very long time scale yes. How fast would it leak to space? Could we prevent leak by creating artificial magnetic field? In short time scale atmosphere gives easily O2 and C. It can also create dust storms preventing solar energy production for weeks. So Mars base needs nuclear reactor.

Base on pole of Mercury would be interesting. Unfortunately not practical target with chemical rockets.

 

[mfb]

I get it that Mars has an atmosphere and the Moon doesn't. I don't understand why this matters though. The low air pressure and high carbon dioxide levels would make the Martian air unbreathable. Do scientists really think they can eventually transform the Martian atmosphere so that people can be outside without a spacesuit?

The atmosphere is a convenient source of carbon and oxygen. Melting the ice caps could lead to a larger pressure, rising temperatures and making spacesuits unnecessary (you would just need an oxygen mask). And in the very long run, it is possible to make a breathable atmosphere.

If it's in interstellar space, it's not a threat until it gets closer. That has a time scale of centuries.

The free-fall time from 50 AU is about 80 years, with some initial velocity an object can come to the inner solar system in less than 50 years. Not so much warning time for a comet that could potentially kill all life on the surface of Earth.

It is more sensible to build habitable space ships near earth. As the numbers expand we can consider colonizing Mars or ths satellites of Jupiter and Saturn. To start with we should promote a massive population explosion. 7 billion is too small, at least 30 billion is needed. Near outer space can easily sustain 15 billion to start with.

A massive population explosion is the worst thing that can happen. We don't have the technology or the resources to have billions living in space. A larger population means we'll fight even more over resources on Earth. There is not even an advantage of such a huge population, apart from slightly more R&D capabilities.

If SpaceX rockets keep on exploding once a year, they are not cheapest. So no success yet.

2 failures in 29 attempts is roughly the industry average of 5%. Commercial satellites are insured, and insurance rates for Falcon 9 are similar to other rockets. It is the cheapest rocket (in its payload range of course).

A base on surface needs satellites to control rovers all over Mars. Moon base needs satellites only if they want continuouss acces for all rovers. There is no point to land if work can be done without.

We have those satellites already, and even if we wouldn't, they are cheap compared to a manned base. Controlling rovers only a few minutes per day is stupid if you can control them all day.

Martian moons provide same radiation and meteorite protection as Mars. Perhaps they need to dig slightly deeper. But that's easy because nothing weights much.

Microgravity makes construction harder, not easier. And it makes it much slower.

Build circular tunnel deep enough. Then build maglev track inside it. Then a train going around.

Okay, now we are certainly in the science fiction range.
The moons are not solid rocks, you have to stabilize every tunnel you want to dig. And maglev trains ... yeah, okay. No.

On orbit very strong structure is needed to provide centripetal force.

A long string and a counterweight. Which is something like a 100 times cheaper than a maglev tunnel on a moon.

Yes aerobraking to Mars saves fuel. It has also destroyed many probes. How many failures while landing to the Moon?

Aerobraking didn't destroy any probe so far. One probe got lost when it entered the atmosphere while not being designed for it. A few probes crashed while trying to land. So what? We had many successful missions to the surface already. We didn't have any missions landing on a Martian moon so far (3 were launched to land on Phobos, but none of them reached it).

How fast would it leak to space? Could we prevent leak by creating artificial magnetic field?

Leaking would be a process that takes millions of years, and we can create an artificial magnetic field. It would be possible (but extremely expensive) even with current technology.

Dust storms reduce the solar power output by ~50%, maybe a bit more. Inconvenient, but not fatal for a colony. You can store a lot of energy via methane and oxygen with reasonable conversion efficiencies.

 

[jkn]

If it's in interstellar space, it's not a threat until it gets closer. That has a time scale of centuries.

Interesting question is: When would we notice it? Dino killer was 10 km (20 km?). It would destroy our civilization, if not all of us. Would you survive, if you had to collect, hunt and grow you own food? How long before impact would we see it? New Horizons went to Pluto in 10 years. Interstellar object could come in much faster. If it comes from Kuiper belt or from Oort cloud, it would be slower. Even then I doubt we could find it more than few years before impact. Not enough time to do anything.

 

[jkn]

...
2 failures in 29 attempts is roughly the industry average of 5%. Commercial satellites are insured, and insurance rates for Falcon 9 are similar to other rockets. It is the cheapest rocket (in its payload range of course).We have those satellites already, and even if we wouldn't, they are cheap compared to a manned base. Controlling rovers only a few minutes per day is stupid if you can control them all day.Microgravity makes construction harder, not easier. And it makes it much slower.Okay, now we are certainly in the science fiction range.
The moons are not solid rocks, you have to stabilize every tunnel you want to dig. And maglev trains ... yeah, okay. No.A long string and a counterweight. Which is something like a 100 times cheaper than a maglev tunnel on a moon.Aerobraking didn't destroy any probe so far. One probe got lost when it entered the atmosphere while not being designed for it. A few probes crashed while trying to land. So what? We had many successful missions to the surface already. We didn't have any missions landing on a Martian moon so far (3 were launched to land on Phobos, but none of them reached it).Leaking would be a process that takes millions of years, and we can create an artificial magnetic field. It would be possible (but extremely expensive) even with current technology.

Dust storms reduce the solar power output by ~50%, maybe a bit more. Inconvenient, but not fatal for a colony. You can store a lot of energy via methane and oxygen with reasonable conversion efficiencies.

5% failure rate is not good enough for manned missions. Even Space Shuttle was better. I guess insurance companies assume new launcher is not better than industry average, so their insurance has not risen. If this explosion / year continues, they are in trouble.

Controlling rovers only a few minutes per day! How do you get that? Even Phobos is 6000 km above Mars. Rovers near poles need satellite link.

I doubt that microgravity makes construction very hard. We have not done anything in such gravity. I don't know if micro gravity is correct term. It's used in Space Station. Perhaps milli gravity would be better. It is not possible to jump to escape velocity from Deimos. Running at escape v with space suit is also impossible. So gravity is not useless. Cubic meter of solid rock would weight about one kg. Tunneling machinery on Deimos would look very different than on Earth. Perhaps martian moons are too unstable to build on. Even then we need lot of mass radiation protection. Best source for that is moons.

Maglev trains are in use already. What is problem here? Structure of moons might be a problem. Stabilizing it is not an enormous problem. Gravity is low -> pressure against tunnel wall is low. Rather thin wall is enough. I repeat: we need Moon base to provide materials for expansion. Lifting everything from Earth is not possible.

A long string and a counterweight. Now you forget cosmic radiation. Lot of mass is needed to block it. Perhaps humans can tolerate it few months during trip to Mars. But for longer time protection is needed. String cannot support rotating radiation shield. Rotating part must be light. Heavy shield must not rotate.

Not aerobraking directly. How about heat shield and parachute separation failures? Moon lander can have antennas, solar panels and landing legs in position before landing. Mars lander must open up after heat shield and parachute separation. Lot of moving parts that could fail.

Do we know that dust storm reduce the solar power output by ~50%? Has any probe been active during planet wide dust storm?

 

[Sankar Raman]

"
"We don't have the technology or the resources to have billions living in space."
Yes we do. To start with we can mine the asteroids and comets.
Further a distributed space colony is the safest against any disasters. Of course a global cooperation is needed to implement space colonization.
We have to develop Robotics to mine asteroids as well as even Venus for energy resources. Space travel will become as common as Air Travel today!

 

[mfb]

5% failure rate is not good enough for manned missions.

It is the failure rate for unmanned missions. If the missions would have been manned, the crew would have been fine in both cases. In the second explosion it wouldn't even have been in the rocket.
The failure rate (=crew died) for manned spaceflight so far is about 1%: 315 launches, 4 crews died.

Controlling rovers only a few minutes per day! How do you get that? Even Phobos is 6000 km above Mars. Rovers near poles need satellite link.

Fine, a few minutes were too pessimistic. You are still limited by the condition that the moon has to see the rover, and that the rover needs sunlight at the same time. Anyway, the point is irrelevant, as satellites are easy: you would want them even if you stay on a moon to cover the time where the moon is over the night side. The crew will have access to rovers basically 24/7 (as we have now already).

Experience with very low gravity: We built MIR and the ISS. Gravity on the tiny moons is irrelevant compared to inertial forces for most steps.

Jumping to escape velocity on Deimos is impossible thanks to the space suit, but jumping for 1 minute with every step is bad enough. Free-fall time for 1 m height is ~25 seconds, for a final velocity of just ~7 cm/s.

Even then we need lot of mass radiation protection. Best source for that is moons.

Or Martian regolith. It is literally just lying around in unlimited amounts. Ice would also be possible, potentially doubling as water reservoir for a station.

Maglev trains are in use already.

Yes, on Earth, constructed by an army of highly skilled workers, with tons of specialized materials constructed by even larger armies. Add even more people and a heavy tunnel boring machine for the tunnel. How many kilotons of material did you plan to ship to Mars for the first few astronauts? No, you cannot quickly build a superconductor factory on a moon - all that stuff has to be shipped.

Pressure against the wall would be coming from the train, no gravity involved.

A long string and a counterweight. Now you forget cosmic radiation.

No. Take material from the moons ;). You don't need any fancy assembling. Have some (inflatable?) empty containers, fill them with stuff from a moon, go back to a Mars orbit (negligible delta_v), attach them to the station.

Where do you see the problem with the string? With two equal masses rotating, something like 200 m of string should be fine. At that length, existing fibers just need 0.1% of the station mass as cable mass (safety factor of 2 included already). You can support 1000 tons of station plus shielding with a single ton of cable.

Opening antennas and so on wouldn't be a large problem for a manned missions, humans can fix things if they get stuck.

Do we know that dust storm reduce the solar power output by ~50%? Has any probe been active during planet wide dust storm?

Spirit and Opportunity, 2007. 750 Wh/sol -> 490 Wh/sol for Spirit. Dropped later to 260-300, probably due to dust accumulation. You can clean the solar cells of a Mars outpost.
There is an additional nice effect: those dust storms occur close to perihelion (with a causal relation), where Mars receives 40% more sunlight than during aphelion. The first 30% decrease in sunlight are "for free" - you need that contingency for aphelion anyway.
Older publication: http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources30.pdf - Figure 6. You need a really serious storm to get below 50% irradiance. The direct component can become negligible, but scattered light is sufficient.

"We don't have the technology or the resources to have billions living in space."
Yes we do. To start with we can mine the asteroids and comets.

Total amount of matter mined from asteroids and comets so far: Less than 1 gram. I wouldn't call that "asteroid mining".
Not even the most overoptimistic proposals for space exploration would lead to billions of people in space within our lifetime.

 

[PAllen]

Is it possible to estimate the order of magnitude probability of a 500 km interstellar object getting anywhere near Earth in the next e.g. 100 million years? I have no idea how to quantify this; my intuition suggests many orders of magnitude less than other possible extinction scenarios.

 

[rootone]

That's about the size of Vesta, the second biggest asteroid known in the solar system, and a lot bigger than many planetary moons.
Since these are clearly visible we can safely assume there are no undiscovered bodies of that size any closer than Neptune.
Beyond Neptune there are a number of minor planets, (Pluto having been now reclassified as such.)
That region is not yet well explored, but indications are that it probably is mostly empty.
The Oort cloud is hypothesised to exist way out beyond Neptune and may be the origin of occasional large comets that arrive in the inner solar system.
However Jupiter steers most of these away from Earth and even if it didn't, the Earth really is a very small target, much more easy to miss than to hit.

 

[lifeonmercury]

How would the Mars settlers communicate with Earth during periods when the two planets are on opposite sides of the sun?

 

[rootone]

One or more satellites could be parked in an orbit around the Sun from where both Earth and Mars are contactable at these times.
It would act as a relay for signals, (so slightly greater transmission times, but that's better than no signals)

 

[1oldman2]

Interesting question is: When would we notice it? Dino killer was 10 km (20 km?). It would destroy our civilization, if not all of us. Would you survive, if you had to collect, hunt and grow you own food? How long before impact would we see it? New Horizons went to Pluto in 10 years. Interstellar object could come in much faster. If it comes from Kuiper belt or from Oort cloud, it would be slower. Even then I doubt we could find it more than few years before impact. Not enough time to do anything.

As an example, today on January 9th 1247 GMT we had a two day "heads up" as an asteroid estimated at 11 to 34 meters passed at a distance of half way between the Earth and the Moon, certainly no "dino killer" but this highlights the advanced warning problem we face. Of course the size and Albedo make a huge difference in detection time but there's a lot of surprises in store for us out there in space.
http://www.space.com/35257-asteroid...-2-days-after-discovery-commentary-video.html