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Acemcbean

What is up with Mars?

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It is, as far as I can tell, a conservative estimate, using the figures for perihelion and the equilibrium blackbody temperature there (people forget how cold most of the earth's atmosphere actually is, it's far colder than the average surface temperature).

Current models actually suggest that the solar wind is not the dominant factor in atmosphere loss, thermal diffusion is thought to be the main driver. Obviously, models aren't perfect, however.

We don't know if Mars has significant amounts of nitrogen, there are theories that it is fixed in large deposits of ammonia. If that is not true, the best source would probably be to redirect an asteroid with a significant ammonia content onto a collision course with Mars, but that's something for the far future. Just now, all I'm talking about is Mars' ability to hold an atmosphere, wherever it may have come from.

So we think that large portions of any nitrogen Mars once had might be fixed with ammonia, possibly in underground liquid ammonia/water solutions/aquifers?

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So we think that large portions of any nitrogen Mars once had might be fixed with ammonia, possibly in underground liquid ammonia/water solutions/aquifers?

It's a theory I've heard, but I don't have the qualifications to judge whether it's accurate or not. It has enough support to make it into peer-reviewed papers, however: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=191609

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The stress will "build up"? That doesn't make any sense. Where?
I'm sorry I didn't explain well.

Gravitational forces of the two moons will pull the elevator. It may not fall immediatly to the ground (I guess it can withstand some pull) but every pass of the moons will pull it more out of its ideal place. It may even swing back and forth a few times but it will eventually crumble.

And there is the atmosphere, too. Winds will pull the lift.

Centrifugal force, balanced by tension in the tether, keeps it in place.
Ah that's what you mean. Unfortunately it won't work exactly as you imagine as I explained above. The lift will move and you have to give it the space to move. Fixing it on the planet surface will only result extreme forces building up which will rip everything apart.

The current idea of a space elevator is to fix one end on a movable platform (i. e. a [giant] ship in the ocean). The CoM of the tether will have to be at the geostational orbit and rest of the tether extends further out. At the end there is a movable counter weight for the elevator cabin. As the elevator moves up, the weight comes down and vice versa cancelling out the forces.

So in the first step the freight gets to geostationary orbit height. In the second step the freight will be moved to the counter weight. As it's goes to further out the elevator cabin gets down to the planetary surface.

The counter weights movement capability can also be used to balance the lift in case it starts to swing.

This design is more fexibile and than the pure "centrifugal design".

@Error404brain

It's easier to live in space.

1) Mars has a thin atmosphere. It can't protect us like our atmosphere does. In fact Mars is clustered by craters! And we have to care about gravity as Mars has only 1/3 g which isn't quite enough for humans.

It's easier to build a rotating space station and evade meteorites.

2) "Near" is relative. The Moon is near, Mars isn't.

3) We don't need to transform asteroids into space stations. We just build one in Earth's orbit, fly it to the asteroid and process it. Processing will be easy as we almost don't need to care about weights. On an asteroid an astronaut can lift tons of material with one hand.

4) There is (almost) no gravity on an asteroid and we don't have to think about to survive an atmospheric entry and how to get out of it again.

Btw, who want's to terraform an asteroid?

Edited by *Aqua*

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Centrifugal force, balanced by tension in the tether, keeps it in place. Go attach a ball to a string. Twirl the ball around your head in a circular motion. What keeps the ball in place? Hint: It's not orbiting in your gravitational field. (Umm... well, hopefully not :D)

Ouch! The wrongness, it must hurt!

That is not how a hypothetical space elevator works, not on Mars, not on Earth, not anywhere. The whole point of a space elevator is to reach orbit. The end station therefore must be at a geostationary (or areostationary in this case) orbit. If it's any lower, then you don't reach orbit and you fall down when you step off the elevator.

A space elevator is built by launching the end station into an equatorial geostationary (areostationary) orbit, and unreeling two tethers: one down to the ground and one away from the ground to act as a counter-weight. The satellite has to, at a minimum, carry both reels of unobtanium tether material that is strong enough to support a climber vehicle, rigid enough to withstand traction over 36000km (or 17000km for Mars), and light enough to be launched. So far we don't have such a material. Without the counter-weight, the CoM moves away from the satellite and your end station is no longer where it should be.

How would you build a centrifugal space elevator exactly? How could you assume that it's easier to build one on Mars than on Earth if you don't understand how it's built? The answer is, you can't, because that's not how a space elevator works. If the centrifugal force was that strong, Mars would be ejecting it's own mass rocks and would gradually destroy itself.

GEO satellites in Earth orbit require station-keeping because of orbital resonance from the Moon and even from planets and tiny irregularities in Earth's orbit. Phobos and Deimos are smaller satellites, but they will be passing much closer, above and below the elevator CoM station, causing a much stronger disturbance. They *will* influence the orbit of the elevator, at best causing its orbit to "wobble", at worse causing it to fly off course, which will create tension on the tether. Just like any GEO satellite, the station needs station keeping to remain at the exact point over the equator. At one point, because all orbits end up crossing the equator, the orbit of Phobos *will* intersect the elevator.

I am talking about a hypothetical future where we already have a large presence- probably one or several permanent colonies and thousands (or millions) of people on Mars. Then building it on Mars isn't bad.

Which makes your argument a non-sequitur. You suggest that the main reason to build a Mars colony is because it's a good place to build a space elevator, but you need a large Mars colony to build a space elevator. If we have a large presence on Mars, then the problem of mass transport to build and support that large presence will already have been solved.

The truth is, there is no compelling reason to build a Mars colony in the first place.

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Because it's easy to live on a planet. I mean, we, as humans, obviously need to expand to the solar system.

Why is that obvious?

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1) And we have to care about gravity as Mars has only 1/3 g which isn't quite enough for humans.

We actually have pretty much no idea of the effects of low gravity on humans. Microgravity, sure, we know pretty well what's going to happen in zero-g, but 1/3g? There have been no experiments done. One of the first experiments needed if we're going to go to Mars is probably a long-term 1/3g centrifuge habitation experiment in earth orbit.

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Nibb, I'd say he does understand, he just didn't explain it perfectly well.

Also there is confusion between the "end station" and the "end mass"... ie the end of the cable.

The end of the cable(which may have an additional mass, not just the cable) is higher than geostationary orbit. This means that if it were cut from the rest of the cable, it would be flung off into a higher orbit or possibly even escape velocity.

The whole point is that "centrifugal force" is keeping the cable taught... or if you prefer, the end of the cable is moving at faster than orbital velocity.

When you send something up the cable, you of course want to release it directly into orbit... so most often this will be at the geostationary point... releasing it higher up sends it into a higher eliptical orbit/ to escape velocity.

If it's any lower, then you don't reach orbit and you fall down when you step off the elevator.

Indeed, so the end of the space elevator is *higher* than geostationary.

How would you build a centrifugal space elevator exactly?

By having the end mass higher than geostationary. Below Geostationary orbital velocity is higher than needed to maintain position over a spot on the ground.

Above it orbital velocity is lower than needed to maintain position over a spot on the ground - but you're tethered to the ground, and your velocity is higher than orbital velocity, the force of gravity is not sufficient, and the tether is pulled taught and exerts a force on the end mass.

As to how its constructed, most plans involved sending stuff of to geostationary, and lowering the cable and raising the "counterweight" simultaneously.

but you know this:

The satellite has to, at a minimum, carry both reels of unobtanium tether material that is strong enough to support a climber vehicle, rigid enough to withstand traction over 36000km (or 17000km for Mars), and light enough to be launched. So far we don't have such a material

Supposedly, carbon nanotubes are at that strength... we just can't make them very long, and we need strands of many many kilometers.... but on mars, the tensile strength required is much lower. Similar rotational period, much less gravity, to a first approximation, the tensile strength would only need to be 1/3 of that of carbon nanotubes, which is well within our capabilities.

If the centrifugal force was that strong, Mars would be ejecting it's own mass rocks and would gradually destroy itself.

No, because the surface velocity would be lower than the geostationary velocity (proportional from distance to the center of Mars), while the orbital velocity is higher at the surface, and lower at areostationary orbit.

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Btw, who want's to terraform an asteroid?

People who wanna live in space. An asteroid is perfect. Many matérials for the humanity to expand and almost no energy for to go to another asteroid.

Why is that obvious?

Because we are human ?

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We actually have pretty much no idea of the effects of low gravity on humans. Microgravity, sure, we know pretty well what's going to happen in zero-g, but 1/3g? There have been no experiments done. One of the first experiments needed if we're going to go to Mars is probably a long-term 1/3g centrifuge habitation experiment in earth orbit.

Actually, we've got a decent handle on what happens to humans subjected to low gravity long term: nothing good. Muscle wastage, calcium loss, and severe disturbance of the vestibulo-ocular system. Microgravity to Mars gravity is a matter of scale, not kind; there's no such thing as zero-g.

http://www.psych.usyd.edu.au/vestibular/

This is the group that used to have the lab next to mine; they specialise in the effects of microgravity on vestibular systems, and research ways of minimising the effects on astronauts.

So far, the results ain't real promising. Artificial gravity is harder to achieve than you'd think; rotating habitats do very bad things to people (coriolis forces in the inner ear, "explosively nauseogenic") unless you make them the size of a town. That sort of thing is beyond our current practical launch capability.

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Btw, who want's to terraform an asteroid?

People who wanna live in space. An asteroid is perfect. Many matérials for the humanity to expand and almost no energy for to go to another asteroid.

Rubbish. Very few asteroids share the same orbits. Going from one orbital inclination to another is extremely expensive in terms of delta-v and can potentially take years. Flybys can be coordinated if you're lucky, but actually matching orbits is hard and expensive, even more so if you are moving hundreds of tons of construction material from one orbit to another.

Why is that obvious?

Because we are human ?

Humans have only ever migrated to pursue a better life. That is human nature. We seek to increase the wealth, the comfort, or the safety of ourselves and our children. Migrating to space increases none of those things. In fact, living in space typically costs more, is less comfortable, and much more dangerous than living in even the most inhospitable places on our planet. It might be fun to travel to space for the thrill of a short vacation or an adventurous job opportunity, but moving their permanently with your children and expecting them to have a better life than they would have anywhere on Earth is simply wreckless.

Edited by Nibb31

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Humans have only ever migrated to pursue a better life. That is human nature. We seek to increase the wealth, the comfort, or the safety of ourselves and our children. Migrating to space increases none of those things. In fact, living in space typically costs more, is less comfortable, and much more dangerous than living in even the most inhospitable places on our planet. It might be fun to travel to space for the thrill of a short vacation or an adventurous job opportunity, but moving their permanently with your children and expecting them to have a better life than they would have anywhere on Earth is simply wreckless.

Yup. As described in the link I posted upthread, if you want a plausible idea of humans on Mars, don't think "Plymouth Colony", think "oil rig in the middle of the North Sea". We might send a very small number of people there for highly-paid short-term work, but there ain't gonna be anyone living there permanently.

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Ouch! The wrongness, it must hurt!...

Nibbs... you simply haven't a clue how space elevators work. You don't have any answer for how tension is built on the cable- and you need tension in order to raise loads up the cable. Have you NEVER twirled a ball on a string before? Or even just a string? What the heck do you think keeps tension on the string?!?! It's centrifugal force.

I am also well aware of how space elevators are built; not only have I read many articles on them over hte years, but I also read the Fountains of Paradise by Arthur C. Clarke, one of the modern inspirations for space elevators (though we've known about them from before then).

Yes, the satellite that drops the cable must START at geostationary orbit, but it has to raise its altitude as the cable is dropped, because the center of mass moves downward towards the planet. ONCE the cable is secured on the planet's surface, then the cable is lengthened so that enough tension is built (through centrifugal force acting on the end station and cable being greater than the gravitation force pulling down) to allow loads to climb up the cable.

Oh and you don't have to take my word for it. Here's Wikipedia:

A space elevator is conceived as a cable fixed to the equator and reaching into space. A counterweight at the upper end keeps the center of mass well above geostationary orbit level. This produces enough upward centrifugal force from Earth's rotation to fully counter the downward gravity, keeping the cable upright and taut. Climbers carry cargo up and down the cable.

http://en.wikipedia.org/wiki/Space_elevator

And if you don't trust wikipedia, here are some scholarly sources:

In the exploration and use of space there is currently only one system that can deliver payloads to their destinations, rockets. However, during the first decades of the space age, 1960s and 1970s, an alternative means of getting to space was proposed, a space elevator [1], [2], [3], [4] and [5]. The basic concept is to string a cable from the Earth's surface to an altitude beyond geosynchronous orbit ( altitude). The competing forces of gravity at the lower end and outward centrifugal acceleration at the farther end keep the cable under tension and stationary over a single position on Earth (Fig. 1). Theoretically, the cable could be constructed long and would be balanced in equilibrium [5]. However, placing a counterweight at the far end of a shorter cable, once the Earth end is anchored, would simplify construction and give the same stability. The cable would be tapered such that it is thickest at the point of highest tension (geosynchronous orbit) and thinnest where the tension is the lowest (at the ends) [5]. This cable, once deployed, can be ascended by mechanical means to Earth orbit. If a climber proceeds to the far end of the cable it would have sufficient energy to escape from Earth's gravity well simply by separating from the cable. The space elevator thus has the capability in theory to provide easy access to Earth orbit and most of the planets in our solar system [5].

B.C. Edwards, DESIGN AND DEPLOYMENT OF A SPACE ELEVATOR, Acta Astronautica, Volume 47, Issue 10, November 2000, Pages 735-744, ISSN 0094-5765, http://dx.doi.org/10.1016/S0094-5765(00)00111-9.

(http://www.sciencedirect.com/science/article/pii/S0094576500001119)

Artsutanov's idea is based on the fact that a massive string moving on a circular trajectory around the Earth, under the action of gravitational and centrifugal accelerations, finally will reach a relative equilibrium position, which is its stretched radial position. In this equilibrium position the string is under tension [4]. To explain this we note that the motion center, which is defined by the equality of centrifugal and gravitational accelerations, is located at the geostationary orbit (one revolution/sideric day). The motion center is different from the center of mass and the center of gravity of the string. For a mass element of the string located below the geostationary radius the value of the gravitational acceleration acting on it is larger than the value of the corresponding centrifugal acceleration and for a mass element above the geostationary radius the value of the centrifugal acceleration is larger than that of the gravitational acceleration. Thus below the geostationary height the net force acting at a string element is pointing towards the Earth and above the geostationary height the net force is pointing away from the Earth. Decomposing these forces into a component in the direction of the straight line connecting these two elements and perpendicular to this line, results that the string is under tension and further a moment is created turning the string into the radial direction, as it is depicted for a dumb-bell satellite, which is a system of two point masses connected by a massless rigid rod, in Fig. 2. This intuitive reasoning convinces some scientists that the radial configuration is stable.

Nicola Pugno, Michael Schwarzbart, Alois Steindl, Hans Troger, On the stability of the track of the space elevator, Acta Astronautica, Volume 64, Issues 5–6, March–April 2009, Pages 524-537, ISSN 0094-5765, http://dx.doi.org/10.1016/j.actaastro.2008.10.005.

(http://www.sciencedirect.com/science/article/pii/S0094576508003391)

A space elevator is extremely simple. It's simply a tether that is so long that the center of mass is above the geostationary orbit of the planet its attached to. The planet simply twirls the tether around in space, causing the tether to be tight under the tension created by centrifugal force. If you put a large massive end station on the tether, then your tether only needs to be slightly longer than geostationary orbit, because the center of mass will be effectively at the end station.

Space elevators may potentially have issues with damping out oscillations on the tether- which is something I believe this last source I linked talks about. However, if the station on the planet's surface can move, I think you can cancel out those oscillations. I haven't studied it too closely though.

So please, before you start attacking people for being ignorant of something, it's best to make sure that you are not ignorant yourself.

Edited by |Velocity|

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Anyway, the point I'm making about Mars and space elevators is that if we ever gain a large presence on Mars, it could serve as an excellent space port due to the ease of building space elevators there- especially if space elevators remain difficult to build on Earth. Assuming that manufacturing and mining became easy there, then it could be a FAR better place to build and launch spacecraft than Earth. Mars could potentially become "Spaceport Sol".

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Rubbish. Very few asteroids share the same orbits. Going from one orbital inclination to another is extremely expensive in terms of delta-v and can potentially take years. Flybys can be coordinated if you're lucky, but actually matching orbits is hard and expensive, even more so if you are moving hundreds of tons of construction material from one orbit to another.

There are tons of them between mars and jupiter that share a similar orbit.

Humans have only ever migrated to pursue a better life. That is human nature. We seek to increase the wealth, the comfort, or the safety of ourselves and our children. Migrating to space increases none of those things. In fact, living in space typically costs more, is less comfortable, and much more dangerous than living in even the most inhospitable places on our planet. It might be fun to travel to space for the thrill of a short vacation or an adventurous job opportunity, but moving their permanently with your children and expecting them to have a better life than they would have anywhere on Earth is simply wreckless.

We want to protect our genes. Going to another planet reduce the probability of the human going exctinct. Thus protecting part of the genes. Even if we die, our family will survive. Our genes will survive.

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I think being able to return some valuable rocks and minerals back to earth would be exciting, it would be an expensive undertaking but it would most likely pay for itself.

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Rubbish. Very few asteroids share the same orbits. Going from one orbital inclination to another is extremely expensive in terms of delta-v and can potentially take years. Flybys can be coordinated if you're lucky, but actually matching orbits is hard and expensive, even more so if you are moving hundreds of tons of construction material from one orbit to another.

Are you talking to me? Why are you bringing up asteroids? I'm not talking about mining asteroids, I'm talking about mining Mars, and using materials on Mars to build spacecraft, sometime in a hypothetical future where manufacturing on Mars is just as easy as manufacturing on Earth, Mars has a large population, and building space elevators on Earth remains difficult. It's a hypothetical future that may very well never come to pass, but if those conditions are in fact met, would not Mars be an excellent spaceport? Mars has volatiles in abundance, something that asteroids have little to none of (mostly none).

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That's part of a post from Nibb31. He seems to be trying to respond to his post without having any idea how to use the quote function.

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I think being able to return some valuable rocks and minerals back to earth would be exciting, it would be an expensive undertaking but it would most likely pay for itself.

'Fraid not.

1) Space is insanely expensive, and the expense is measured in $/kg terms. Mining gear ain't lightweight.

2) The highly valuable minerals to be found off-Earth are only valuable on-Earth because they are rare. The immediate effect of dumping a thousand tons of platinum or whatever onto the market would be to annihilate the value of platinum (or whatever).

Space exploration is awesome and important, but space as a thing to be commercially exploited just doesn't exist beyond the orbit of Earth. The economics just don't add up.

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The economics just don't add up.

Yet.

A 16' aluminum boat costing $12,000 with no engine. And $30,000 motorcyles. But I can buy a brand new car for under $15,000 with all the bells and whistles.

I realize that space is expensive, but I find that its specifically the very small amount of stuff done for it (especially production of parts) that make it so expensive.

There is currently no economy of scale in anything space related (just like when compared to cars that sell thousands, there are comparatively fewer motorcycles, or boats).

As we start doing more with space, and private industry starts driving costs down. And heavens forbid, reusability, becomes a thing. You might be surprised to see how much cheaper it becomes. Especially if there were some form of driving force behind it.

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Yet.

A 16' aluminum boat costing $12,000 with no engine. And $30,000 motorcyles. But I can buy a brand new car for under $15,000 with all the bells and whistles.

I realize that space is expensive, but I find that its specifically the very small amount of stuff done for it (especially production of parts) that make it so expensive.

There is currently no economy of scale in anything space related (just like when compared to cars that sell thousands, there are comparatively fewer motorcycles, or boats).

As we start doing more with space, and private industry starts driving costs down. And heavens forbid, reusability, becomes a thing. You might be surprised to see how much cheaper it becomes. Especially if there were some form of driving force behind it.

Space can become several orders of magnitude less expensive (and hopefully will), but even if that happens it will still be insanely expensive. The economic equation isn't just tipped a bit towards unprofitable; it's so far off that end of the scale that the idea of the balance shifting is totally implausible without magic.

Again, I'd highly recommend having a read through http://www.antipope.org/charlie/blog-static/2007/06/the_high_frontier_redux.html

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As we start doing more with space, and private industry starts driving costs down. And heavens forbid, reusability, becomes a thing. You might be surprised to see how much cheaper it becomes. Especially if there were some form of driving force behind it.

Reusability actually goes against economies of scale. If you were suddenly able to reuse your rocket stages 10 times without multiplying the number of launches by 10, the actual cost of each rocket stage goes up, not only because a reusable stage is more complex than an expendable one, but also because you still have the same fixed costs to build those stages and you are producing less of them. And there is no market for 10 times more launches than what we have now, even if you divided the launch cost by 10 (which simply reusing hardware can't).

But even if you do manage to reduce hardware costs through mass production, the cost of going to orbit will always be super-expensive, simply because the amount of energy needed to accelerate stuff to 27000 km/h is huge. Large amounts of energy are expensive to produce, to store, to handle, and to convert into velocity.

Edited by Nibb31

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Hmm, I do believe that either a large mars-base or terraforming mars is technically feasible.

It would be the greatest undertakings we have ever done, but... feasible...

...

During world war 2, we could afford to have around 100 million people out of 2 billion, fighting. In todays numbers that's about 350.000.000 people we could, theoretically, dedicate to a project.

I think we underestimate, what we could potentially do, if everyone worked together, that dedicatedly.

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I do think that a self sufficient Mars colony is very important. Humanity needs a backup in case something hits earth.

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I think that level of commitment requires some sort of world goverment (union, federation, etc.).

If there's no world goverment then everything will get complicated quickly. For example there is no nation's law which applies to Mars. If somebody commited murder on Mars which nation's law will be applied? The one the murderer comes from? The one depending on the country which build the module the crime scene is in? The country which shoot the astronaut into space? (What about an US astronaut who fly from French Guyana to Mars and murdered an Indian in a Chinese habitation module?)

Or a less extreme example: Colonists will probably have babys. What do you say about the nationality of the newborn? (Italian/European Mother & Russian father living in an Australian module)

A Mars colony will depend on Earth a long time, I guess a Marsian state with its own law won't form during that time. I don't know what they will do.

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I do think that a self sufficient Mars colony is very important. Humanity needs a backup in case something hits earth.

If Humanity is destroyed, then there isn't much point in having a backup. It's not like you could rebuild everything or bring people back. If everything is gone, you won't be there to lament about it being gone and there won't be anyone left to care.

But seriously, what sort of event could really wipe out Humanity totally? If we can survive in closed-loop habitats on Mars, we could survive any of the extinction-event impactors that have hit Earth in the past. We could dig ourselves underground and live off the same hydroponic tomatoes and recycled urine that would keep us alive in space. Even if 99% of humanity was wiped out, there would still be millions of survivors that would still find life much easier on a scorched Earth than on Mars.

Edited by Nibb31

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