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Old 21st June 2018, 05:53 AM   #41
Dave Rogers
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Originally Posted by Craig B View Post
But we can step over them, and we know it.
Do we? We know we can land humans on a world a quarter of a million miles away where heavy and complicated space suits can sustain them for a few days. We don't know that we can set up anything more self-sustaining over a longer term anywhere but Earth or Earth orbit, or that we can keep people alive for months outside the protection of a planetary magnetic field. Mars would be a tough enough challenge to learn quite a lot from.

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Old 21st June 2018, 08:14 AM   #42
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Originally Posted by Orionsword View Post
I appreciate the joke. But what I am failing to argue well is that we have no choice but to try. I don't mean going wherever we fancy for a free pint. I mean the ability to avoid annihilation. You certainly must agree that we - as earthlings - ought to avoid that. No?
There are many reasons for wanting to visit other planets, and my imagination is stirred by contemplating that.

But avoiding annihilation in the event of the failure of the Sun is not a rational motive for such undertakings. Other planets are as dependent on the Sun as Earth is, and I imagine it's easier to rescue a population from one planet than from several, if need should arise.

To scatter the population so that samples of our species might survive, for example, an asteroid impact on Earth is rational, however, and I can see the sense of that. For that purpose lunar colonies would perhaps not suffice, as a large impact on Earth might make conditions on the Moon temporarily inhospitable, and of course vice versa, through impact debris ejected from one body falling on the other, which it is known does occur.
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Old 21st June 2018, 08:58 AM   #43
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Originally Posted by Craig B View Post
That's five billion years away.
The sun will get a lot hotter, though, in the meantime. In a few hundred million years the oceans will boil. Still a long way away though.

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If we require to do something about that, in what way does going to Mars help us? Mars will die too if the Sun conks out. And travelling to the planets of another star is a proposition so much more formidable than a trip to Mars, that one is not relevant preparation for the other. Like stepping over a puddle teaches us how to swim across the Atlantic Ocean?
To follow your analogy, how many people learned to swim before learning to crawl? But it's just an analogy. I'm having a hard time how we're going to develop interstellar travel without developing more efficient interplanetary travel than we have now first. The scales certainly are on a different level, but they are nevertheless the same technologies. Interstellar travel may require some technologies that are not required for cheap and efficient interplanetary travel, but it also requires the technologies of the former.

One of the first steps on the way to landing people on the moon (and returning them safely to the earth) was to put a person into orbit (and return him safely to the earth). The latter really is a much easier problem, but that doesn't mean it didn't solve important technical problems that were necessary for the former.

Further interstellar travel will probably require space-based industry as it's just much more efficient to get your fuel from a source that's not deep in a planet's gravity well. But that industry won't develop until we actually develop it, and going to mars could potentially be one of the things that spurs that development.

None of this is to say that interstellar travel is even something we will ever be likely to engage in (we've had other threads about that if you are interested in my thoughts), but if we don't become interplanetary* we're not going to become interstellar.

*Well, maybe we'll skip planets and stick to asteroids, comets, and moons, but I'm having a hard time thinking of a term that's neutral to that choice.
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Old 21st June 2018, 09:13 AM   #44
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Originally Posted by Craig B View Post
But we can step over them, and we know it. Settling humans on Mars will in no way preserve humanity from the effects of a catastrophe befalling the Sun. On the contrary.
Earth will be uninhabitable long before the sun dies out, there will be a runaway greenhouse effect in under a billion years when the oceans boil off and the surface temps will be like Venus.

Mars, on the other hand, will warm up also, and move into a *more* habitable phase.

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Neither is Mars a stepping stone to other stars, in the sense that paths with puddles on them are the road to the Atlantic shore, if that's what you mean.
It is a stepping stone in the sense that we'll have to develop technologies to get there and survive there that will also be useful in generation ships going to other stars.
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Old 21st June 2018, 11:25 AM   #45
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Originally Posted by NoahFence View Post
Doesn't look too bad, unless I'm misinterpreting the image that accompanies that article.

The before shot shows a hole drilled into the rock, with a pile of material surrounding it. The after shows the same thing. So how strong are these winds if it can't pick up the dust created by drilling those holes?
The pressure exerted by wind is dynamic pressure, or velocity pressure and it is given by the formula,

q = ½ρv2

where

q is the pressure
ρ is the density of the atmosphere
v is the velocity of the wind.

Martian air density is about 0.020 kg/m3
Earth's air density (at sea level) is 1.225 kg/m3

The maximum wind speed ever detected on Mars is about 100 km/h (27.8 m/s). This wind speed on the Earth would exert a pressure of:

qE = (0.5 x 1.225) x 27.82 = 473.4 Pa

The pressure from a 100 km/h wind on Mars would be:

qM= (0.5 x 0.02) x 27.82 = 7.7 Pa

Working the equation backwards...

v= √(2q/ρ)

v = √(2 x 7.192 / 1.225) = 3.5 m/s = 12.6 km/h

So the highest known Martian wind speed (~100 km/h) is only capable of blowing stuff around as much as a 12.6 km/h wind on the earth.
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Old 21st June 2018, 11:32 AM   #46
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Originally Posted by smartcooky View Post
So the highest known Martian wind speed (~100 km/h) is only capable of blowing stuff around as much as a 12.6 km/h wind on the earth.
And I imagine a 12.6 km/h breeze would sit one on one's backside on Venus!
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Old 21st June 2018, 12:14 PM   #47
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Originally Posted by jonesdave116 View Post
And I imagine a 12.6 km/h breeze would sit one on one's backside on Venus!
If I've done my sums right, then a 12.6 km/h breeze on Venus would exert the same pressure as a wind of ~ 94 km/h on Earth.
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Old 21st June 2018, 12:16 PM   #48
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Originally Posted by jonesdave116 View Post
And I imagine a 12.6 km/h breeze would sit one on one's backside on Venus!
Well, no, because first you will be crushed to a pulp by the 1.3 tonnes per square inch of atmospheric pressure and simultaneously cremated by the 450°C temperature.

But the 12.6 km/h wind will blow your cremains away.... very, very quickly!
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Old 21st June 2018, 12:59 PM   #49
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Originally Posted by smartcooky View Post
But the 12.6 km/h wind will blow your cremains away.... very, very quickly!

And yet, also relatively slowly, presumably at no faster than 12.6 km/h.
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Old 21st June 2018, 02:38 PM   #50
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I'm all for a mission to put people on mars but the rhetoric of a "life boat" doesn't make much sense. A life boat gives one very temporary refuge until you can get more permanent refuge on another ship or land. It wouldn't accomplish much to hop into a life raft with no chance of being rescued by another ship or hitting land.
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Old 21st June 2018, 02:43 PM   #51
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Originally Posted by Myriad View Post
And yet, also relatively slowly, presumably at no faster than 12.6 km/h.
Yep
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Old 22nd June 2018, 06:14 AM   #52
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I suggest the planet is a disgraceful stepping stone from degenerating Earth to the stars.
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Old 22nd June 2018, 01:01 PM   #53
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Originally Posted by portlandatheist View Post
It wouldn't accomplish much to hop into a life raft with no chance of being rescued by another ship or hitting land.

It will accomplish more than just sitting on a sinking ship clutching our pearls and bemoaning the lack of another identical ship will. At the very least, we'll survive longer than the ship.

And we don't know that there is "no chance" of hitting land. There's a whole lot of technological development that has to occur before we can reasonably interpret our chances of getting off this rock and going interstellar. Planet-hopping is a necessary next-step to getting there, just as LEO was an important step to getting to the moon, and the moon was an important step to getting to the other planet.

Technology cannot be developed in a vacuum (metaphorically speaking), for each technological advance, there were precursor technologies that had to be developed first. Practical steam engines wouldn't have been possible without the development of, for example, significant advancements in metallurgy. And steam-powered ships plying the oceans needed both the technology of ship-building and the technology of engine-building, and all the corresponding technologies that got them to that point.

We know that it's theoretically possible to get off this rock and reach the distant stars. After that, all the rest is just a matter of engineering.

Of course, no appeals to curiosity or long-term survival are going to convince the non-curious who are perfectly happy to see the human race die out so long as it doesn't happen within their lifetimes.
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Old 22nd June 2018, 11:53 PM   #54
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Originally Posted by Samson View Post
I suggest the planet is a disgraceful stepping stone from degenerating Earth to the stars.
Then what would be a respectable stepping stone? I don't understand how you can believe that.

Hypothetically I give you 50 years to move a species survivable population off earth. What planet do you choose?

My argument is that if humanity is to make its way into the universe, Mars seems like the best first step. And we eventually as earthlings will inevitably have to try to make that step.
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Old 22nd June 2018, 11:55 PM   #55
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Originally Posted by luchog View Post
It will accomplish more than just sitting on a sinking ship clutching our pearls and bemoaning the lack of another identical ship will. At the very least, we'll survive longer than the ship.

And we don't know that there is "no chance" of hitting land. There's a whole lot of technological development that has to occur before we can reasonably interpret our chances of getting off this rock and going interstellar. Planet-hopping is a necessary next-step to getting there, just as LEO was an important step to getting to the moon, and the moon was an important step to getting to the other planet.

Technology cannot be developed in a vacuum (metaphorically speaking), for each technological advance, there were precursor technologies that had to be developed first. Practical steam engines wouldn't have been possible without the development of, for example, significant advancements in metallurgy. And steam-powered ships plying the oceans needed both the technology of ship-building and the technology of engine-building, and all the corresponding technologies that got them to that point.

We know that it's theoretically possible to get off this rock and reach the distant stars. After that, all the rest is just a matter of engineering.

Of course, no appeals to curiosity or long-term survival are going to convince the non-curious who are perfectly happy to see the human race die out so long as it doesn't happen within their lifetimes.
so much better put
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Old 23rd June 2018, 12:18 AM   #56
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Originally Posted by luchog View Post
Of course, no appeals to curiosity or long-term survival are going to convince the non-curious who are perfectly happy to see the human race die out so long as it doesn't happen within their lifetimes.
Who's perfectly happy to see the human race die out? Who is not curious? Suggesting that putting a human population on Mars is not the best way of addressing the increased luminosity of the Sun hundreds of millions of years from now is neither of these things.
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Old 23rd June 2018, 12:33 AM   #57
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Originally Posted by Craig B View Post
Who's perfectly happy to see the human race die out? Who is not curious? Suggesting that putting a human population on Mars is not the best way of addressing the increased luminosity of the Sun hundreds of millions of years from now is neither of these things.

OK, so what would be the best way to avoid that? I didn't mean to imply it was the only solution. Just a step in the right direction. A better one would be...?
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Old 23rd June 2018, 12:36 AM   #58
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Originally Posted by Craig B View Post
Who's perfectly happy to see the human race die out? Who is not curious? Suggesting that putting a human population on Mars is not the best way of addressing the increased luminosity of the Sun hundreds of millions of years from now is neither of these things.
I agree. I actually think trying to put humans on Mars at this point is a pretty big waste of resources. All else being equal there are much better ways to explore and develop our solar system.

It may be the case that all else is not equal, that people in general will be more excited about colonizing Mars than doing other things and that for those interested in developing space will then see their goals more likely to reach fruition if they support that goal, but I don't think that's a given.
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Old 23rd June 2018, 01:12 AM   #59
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Originally Posted by Craig B View Post
Who's perfectly happy to see the human race die out? Who is not curious? Suggesting that putting a human population on Mars is not the best way of addressing the increased luminosity of the Sun hundreds of millions of years from now is neither of these things.
Maybe I seemed that person, but my contention is that Mars is so bleak, and interstellar travel so impossible, that all efforts are better expended here.
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Old 23rd June 2018, 01:20 AM   #60
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Originally Posted by Samson View Post
Maybe I seemed that person, but my contention is that Mars is so bleak, and interstellar travel so impossible, that all efforts are better expended here.
Expended here until the end? Mars may not be optimal. Interstellar travel very hard. But staying here will one day be a losing option. What is your alternative if you imagine humanity surviving what will be the inevitable end in our solar system?
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Old 23rd June 2018, 01:26 AM   #61
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Even if interstellar travel ends up being impossible and we are destined to an end in our own back yard how will we know until we make an effort?

Wouldnt we be better off and more engaged in the situation if we tried and failed rather than assume all is lost and wait for the end?
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Old 23rd June 2018, 01:34 AM   #62
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I suppose if you could prove that interstellar travel, escaping the death of our solar system is impossible then yes, let us make our bed as cozy as we can. I just don't believe you have proven that. Or can prove it without trying.
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Old 23rd June 2018, 02:21 AM   #63
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Originally Posted by Samson View Post
Maybe I seemed that person, but my contention is that Mars is so bleak, and interstellar travel so impossible, that all efforts are better expended here.
Translation: Curl up into the foetal position and await oblivion.
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Old 23rd June 2018, 02:27 AM   #64
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Oh, and interstellar travel is not impossible. We already have four spacecraft on solar system escape trajectories and heading out into interstellar space.

Its not much, but its a start.
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Old 23rd June 2018, 11:58 AM   #65
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The death of Earth due to the brightening sun is far enough in the future that we won't be talking about humanity, we'll be talking about humanity's descendants. However, there won't be any of those if we don't expand out of our niche, as there are much more immediate threats.

And no, extending our reach to Mars and the rest of the solar system isn't sufficient for travel between stars, but it certainly puts us in a much better position to make the attempt someday, and does a lot to improve the odds of some kind of civilization surviving long enough for it to become an issue. And while we are capable of starting the process now, there's no guarantee that conditions will remain suitable indefinitely or that some future civilization will regain them once we've lost them. The next century or so may well be the one and only chance to get any kind of civilization not bound to Earth's surface.
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Old 23rd June 2018, 03:42 PM   #66
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Originally Posted by smartcooky View Post
Oh, and interstellar travel is not impossible. We already have four spacecraft on solar system escape trajectories and heading out into interstellar space.

Its not much, but its a start.
Five, Pioneers 10,11 Voyagers 1,2 New Horizons.
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Old 23rd June 2018, 03:53 PM   #67
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Originally Posted by cjameshuff View Post
The death of Earth due to the brightening sun is far enough in the future that we won't be talking about humanity, we'll be talking about humanity's descendants. However, there won't be any of those if we don't expand out of our niche, as there are much more immediate threats.

And no, extending our reach to Mars and the rest of the solar system isn't sufficient for travel between stars, but it certainly puts us in a much better position to make the attempt someday, and does a lot to improve the odds of some kind of civilization surviving long enough for it to become an issue. And while we are capable of starting the process now, there's no guarantee that conditions will remain suitable indefinitely or that some future civilization will regain them once we've lost them. The next century or so may well be the one and only chance to get any kind of civilization not bound to Earth's surface.
Sagan once remarked that "The gates of Heaven and Hell are adjacent, and unmarked" He was talking about the Earth, and Venus.

Venus gives us a very good idea of what the result of planet-wide runaway greenhouse effect looks like. If we don't stop what we are doing to this planet NOW, then the surface will likely become unliveable within 500 years. In another 80 years, temperatures in the Middle East will go over 45°C (113°F) several times each year, with spikes closer to 60° C (140°F). That is simply not survivable.

The Earth could become Venus-like within a few thousand years.
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Old 23rd June 2018, 05:22 PM   #68
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Originally Posted by Roboramma View Post
I agree. I actually think trying to put humans on Mars at this point is a pretty big waste of resources. All else being equal there are much better ways to explore and develop our solar system.

It may be the case that all else is not equal, that people in general will be more excited about colonizing Mars than doing other things and that for those interested in developing space will then see their goals more likely to reach fruition if they support that goal, but I don't think that's a given.
People are going to want to do it anyway, despite the cost.
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Old 23rd June 2018, 05:35 PM   #69
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I would like to point out, that staying here, until we've exhausted all the available resources, and then trying to get to space...

...that's a losing proposition.

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Old 23rd June 2018, 05:42 PM   #70
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For all these reasons, now is a great time to be planning for it.
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Old 25th June 2018, 07:33 PM   #71
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Originally Posted by Samson View Post
I suggest the planet is a disgraceful stepping stone from degenerating Earth to the stars.
Why? Mars has a atmosphere, if limited, The temperature range is one that humans can easily survive in. It has vast minerals that can be mined and used to build ships. It has gravity that while not as great as Earth, still allows humans to work in with ease, and because it has less gravity it requires less energy to get those ships out of its orbit. It is also travelling faster than Earth is around the Sun, so it would require less energy to reach escape velocity from the Sun's gravitation field. All in all, Mars is a pretty good place to use as a ship yard and stepping stone to the Galaxy beyond out solar system.
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Old 25th June 2018, 07:43 PM   #72
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Originally Posted by PhantomWolf View Post
Why? Mars has a atmosphere, if limited, The temperature range is one that humans can easily survive in. It has vast minerals that can be mined and used to build ships. It has gravity that while not as great as Earth, still allows humans to work in with ease, and because it has less gravity it requires less energy to get those ships out of its orbit. It is also travelling faster than Earth is around the Sun, so it would require less energy to reach escape velocity from the Sun's gravitation field. All in all, Mars is a pretty good place to use as a ship yard and stepping stone to the Galaxy beyond out solar system.
Nope, other way around; Mars' average VO = 24km/s, Earth's average VO = 30 km/s. However, it being a lot further out of the Sun's gravity well would likely compensate for that (just guessing on that.. I haven't done the math).

Other than that, I agree. In fact, we are probably lucky that Mars is so "earthlike" (although I use that term with some caution)

Its also worth nothing that the rocket equation works much better on Mars for getting stuff into orbit; SSTO is very, very difficult to do on the Earth, but will be pretty much standard operating procedure on Mars. Also, chemical engines are more efficient in low pressure, so they would likely be able to use vacuum engines for lift off...
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Old 25th June 2018, 08:58 PM   #73
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Enough of an atmosphere to handle ~6-7 km/s of the delta-v required for landing, leaving <1 km/s that your engines need to handle.

Enough of an atmosphere to provide 2-3 times as much radiation shielding as Earth's magnetic field provides for the ISS. Meanwhile, without a substantial global magnetic field and with the increased distance from the sun, solar storms shouldn't be nearly as disruptive.

Enough of an atmosphere for near ambient pressure greenhouses, lots of water ice, and enough sunlight and with an Earthlike enough rotation rate for those greenhouses to use natural light.

Enough atmosphere and water to provide feedstock for propellant production. Both LOX/CH4 for chemical propulsion and argon for ion propulsion. Enough nitrogen for all the chemical industry that depends on that, not to mention fill gas for breathing. Thin enough atmosphere that vacuum nozzles can be used from the surface.

Shallow enough gravity well that SSTO is not only useful for barely reaching low orbit, but can get you into interplanetary transfer trajectories with only moderate performance chemical engines, while having enough surface gravity to provide an environment substantially different from microgravity.

Roughly the same land area as Earth, with a history of liquid water that has left a variety of concentrated minerals (such as the iron sulfate patch that trapped one rover).

A location midway between Earth and the belt, with the atmosphere and volatile chemical resources making it feasible to stop there and resupply/refuel for trips further out into the solar system.

Oh, but it's all covered in icky dust. If we went to Mars, we might get dust on us, and then we'd get depressed. Clearly, humans can't survive anywhere that has dust. Oh well.
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Old 25th June 2018, 09:15 PM   #74
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Yeah, though I disagree with it I can understand the argument that we should be allocating limited resources to robotic missions at this time, but I just don't get why it should be "disgraceful" to be considering crewed missions.
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Old 26th June 2018, 01:54 AM   #75
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Originally Posted by PhantomWolf View Post
Why? Mars has a atmosphere, if limited, The temperature range is one that humans can easily survive in. It has vast minerals that can be mined and used to build ships. It has gravity that while not as great as Earth, still allows humans to work in with ease, and because it has less gravity it requires less energy to get those ships out of its orbit. It is also travelling faster than Earth is around the Sun, so it would require less energy to reach escape velocity from the Sun's gravitation field. All in all, Mars is a pretty good place to use as a ship yard and stepping stone to the Galaxy beyond out solar system.
But not even remotely as good as Earth.
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Old 26th June 2018, 02:27 AM   #76
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Originally Posted by GlennB View Post
But not even remotely as good as Earth.
California is a pretty nice place to be; sunshine, warmth, (mostly) friendly people , beautiful coastline, lot of trees, picturesque interior.

Antarctica is bitterly cold, spends a good part of the year totally in the dark, icy coastline, barren interior.... not even remotely as good as California.

But in the summer, over 4000 people live and work in Antarctica (about 1,000 winter over) doing science, despite all the harsh and hostile conditions.

Reason? Because they choose to do so.

This is me, 42 years ago at McMurdo Sound having just hopped of the white Herky Bird you see in the background. I was only there overnight on that occasion, but the following year, I wintered over at Scott Base.



Now the guy in that photo, if he was around now at the age you see him there, if offered the chance to go on a scientific mission to Mars, couldn't sign up quick enough.
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Old 26th June 2018, 03:47 AM   #77
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Missing the point entirely. Interstellar ships would be much easier to construct on Earth. Doing it on Mars would be perverse in the extreme, a little like growing grapes and citrus in Antarctica, or building underwater colonies underwater.
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Old 26th June 2018, 03:57 AM   #78
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Originally Posted by GlennB View Post
Missing the point entirely. Interstellar ships would be much easier to construct on Earth. Doing it on Mars would be perverse in the extreme, a little like growing grapes and citrus in Antarctica, or building underwater colonies underwater.
Well, in fact doing it on Mars would result in lower escape velocity requirements, both planet to orbit and from Solar orbit. But then again, constructing interstellar ships on the surface of a planet doesn't seem like a very sensible idea either, because it imposes a massive energy requirement on them to get off the surface of said planet. High Earth orbit is much more sensible. But that's not the sense, IMHO, in which going to Mars would be a stepping stone to interstellar exploration; going to Mars would be a valuable technological stepping stone, because as I said earlier, at present we have no experience of constructing a long-term survivable habitat anywhere other than Earth or Earth orbit. If we can learn how to survive long term on Mars, our understanding takes a quantum leap, because we have then tried for the first time surviving on a planet we didn't evolve on.

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Old 26th June 2018, 04:14 AM   #79
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Originally Posted by Dave Rogers View Post
Well, in fact doing it on Mars would result in lower escape velocity requirements, both planet to orbit and from Solar orbit. But then again, constructing interstellar ships on the surface of a planet doesn't seem like a very sensible idea either, because it imposes a massive energy requirement on them to get off the surface of said planet. High Earth orbit is much more sensible. But that's not the sense, IMHO, in which going to Mars would be a stepping stone to interstellar exploration; going to Mars would be a valuable technological stepping stone, because as I said earlier, at present we have no experience of constructing a long-term survivable habitat anywhere other than Earth or Earth orbit. If we can learn how to survive long term on Mars, our understanding takes a quantum leap, because we have then tried for the first time surviving on a planet we didn't evolve on.

Dave
I'd suggest if there are to be in-space construction activities, they should happen out at EML-2 rather. Gateway to the solar system.
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Old 26th June 2018, 01:28 PM   #80
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At this point, we can't say much in specifics about what an interstellar spacecraft would look like, but you almost certainly wouldn't build it on a planetary surface. The requirements of launch are nothing at all like the requirements of interstellar flight, and hauling the mass overhead required for the former through the delta-v required for the latter would be ridiculously inefficient. Plus any reasonable interstellar craft would likely simply be far too large.

As far as orbital mechanics go, the requirements of interstellar travel mean any location within the solar system is as good as any other as a starting point, a 10 km/s difference would be utterly irrelevant. What would matter would be the cost of access to the construction site, probably including transportation of huge quantities of dumb structure, shielding, and supplies. Mars or some nameless asteroid wouldn't be unreasonable locations. If we can't establish a reasonably capable space-based civilization in our solar system while having access to planetary and asteroid natural resources, we're certainly not going to manage in the closed system of an interstellar spacecraft. Earth orbit might be a better location due to accessibility to Earth's industrial base, but it's hard to say if that would be a significant advantage by the time we're building interstellar craft.

Probably not EML1 or 2, though. They're only "gateways" for low thrust, low energy, and very, very slow transfer trajectories, they're inefficient to ship to if time is any sort of priority, and you can't take advantage of aerobraking to reach them.
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