Hacker News Reader

On the contrary, Mars has all the resources of asteroids but the advantage of a water cycle that has concentrated and reformed minerals like on Earth. The ability to process the atmosphere directly is a massive and under-rated advantage. MOXIE proves it’s not just possible but feasible to generate fuel (carbon monoxide) and oxidizer (oxygen) from the Martian atmosphere, and nitrogen and even a bit of water (hydrogen and oxygen) as well as argon are available anywhere on the planet.

The “let’s just build cylinders” (which I think we should eventually do!!) often strikes me as a knee jerk contrarian position, an attempt to avoid hard questions about environment, and a “grass is always greener in fields further in the future and with less solid understanding.”

Planetary bodies with water cycles (or a history of them) are rich. Airless bodies have massive difficulties that are often handwaved away.

And now we have powered flight (without needing propellant) demonstrated. Mars really is a much better place to establish a permanent human presence.

I think a lot of it will ultimately depend on whether Mars has enough gravity to avoid the health issues that we see in orbital microgravity environments.

Do we have any idea, based on our experiences with space stations & lunar landings? Genuine question, I'd really like to know.

Mars has about a third of the Earth's, so it's not microgravity and is about twice as powerful as the Moon's. There are not many reasons to expect it will create huge health issues for earthlings but if you spend too much time on Mars without exercising on a centrifuge, adapting back to Earth could be a problem. There will be some loss of muscular mass, at least.

I suppose the core of my question is just wondering what the shape of the g-dose response curve is. 1g is nominal. 0g has significant long-term problems, even with countermeasures like daily exercise.

Is the physiologic response between the two extremes linear? My intuition says no, but I don't have real data to check.

> what the shape of the g-dose response curve is

And to make matters more complex, that dose could be spectrum, rather than a constant value. Eg, spend X hours doing Y in the compact ~2 meter centrifuge at Z g, plus ... and ... .

Just one data point. The astronauts on the ISS spend 2 hours a day exercising. That apparently works in that once they get back on Earth after 6 months, they don’t have issues with weakened musculature. ISS is a microgravity environment.

> Do we have any idea

IIRC, largely no - it's a very open research question.

> I'd really like to know

I fuzzily recall seeing an applicable NASA space medicine slide deck last year, but I'm not quickly finding it - sorry.

> depend on whether Mars has enough gravity

While it's common to oversimplify and exaggerate minimum-size constraints on rotational gravity, even if greater than Mars gravity is needed almost continuously, it might perhaps turn out easier engineering to maintain that on Mars (with mounted spinning things, or maybe pods in curving tunnels) than in space (spinning habitats). You still have vacuum at hand, but also support and workspace - things are more easily stopped, stood next to, and kicked.

> Do we have any idea

https://rendia.com/resources/insights/vision-problems-in-spa....

and

https://en.wikipedia.org/wiki/Effect_of_spaceflight_on_the_h...

Building 'cylinders' gives us an environment that's a lot easier to control, manage and safeguard compared to a whole planet. Most planets will be entirely hostile to complex earth based life to begin with. They'll require either complex terraforming or some sort of isolated environment, and that's not even bringing up issues concerning gravity.

Furthermore, in future wars planets would also be far easier, bigger and immovable targets compared to asteroids and space-stations. Just look up what happens when you drop a 10ton tungsten rod from outer-space. Thanks to gravity, when it hits the ground it has the same impact of a small nuclear device.

When humanity starts to create colonies outside of earth, I expect most planets will only become fully automated mining colonies. Colonizing planets is a Star Trek fantasy that, most likely, will not be worth it.

> Just look up what happens when you drop a 10ton tungsten rod from outer-space. Thanks to gravity, when it hits the ground it has the same impact of a small nuclear device.

That’s... not as good as a nuclear device? Susceptibility to 10 ton tungsten rods is pretty lame to worry about when a 10 ton actual nuclear bomb would be so much worse.

You're missing the point. The point is how easy it becomes to destroy planetary targets once you start having an extra-earth presence as a society. You literally drop heavy stuff from orbit and you have a nuke. You need an actual, guidable, nuke (or self propelled object) to have the same effect on a space station or asteroid.

Does that make Tesla a nuclear power though? Or do they need to conduct a test first?

You may not realize it yet, but they've already become our new overlords. Do you think they bothered with getting a certified driving license for that puppet they put in the car they launched a few years back? They don't care about our earther laws. Yet there he is, drifting in space.

If you live at the bottom of a well, don't make fun of the guy peering down at you from the top.

See also The Moon is a Harsh Mistress

> You literally drop heavy stuff from orbit

If you literally drop something in orbit then it stays in orbit. In order to make it fall to the ground you first need to de-orbit it.

I don't think Earth is substantially more vulnerable than anywhere else in the solar system.

A heavy object picks up some kinetic energy as it falls into a gravity well, but realistically a tungsten rod moving at orbital velocities could destroy a space station or asteroid habitat just as effectively as it could destroy an Earth target. And there'd be somewhat of a difference: with Earth, we have an atmosphere to slow fast-moving objects down and provide an early warning that something is coming at us. (Probably not enough early warning to do usefully react, but still. A couple seconds is more than 0 seconds, and maybe there's some way to use that to a tactical advantage.) In space you'd have no warning at all, unless you can track it on radar or telescope, in which case Earth could do the same.

Earth's big advantage is that everything we do is so geographically distributed that any damage done is a temporary setback. It would be a sad day, but the human race will go on. Unless it was a really big rock, in which case it would be hard to redirect one into Earth's orbit without anyone noticing.

I suppose if you really want to be protected from flying rocks, the best bet may be to find some moon or minor planet with weak gravity, and tunnel deep into the surface and set up shop there. You could do something similar on Earth, though there's a limit to how deep you can go before it gets too hot. (In Consider Phlebas by Iain M Banks, there is planet whose original inhabitants had built a deep underground subway system where train cars house the military command structure, and in time of war the trains would always be moving around so that a nuclear-armed adversary wouldn't know where to strike. That approach could work too.)

Realistically, though, I think if humanity develops the technology to start moving large heavy objects around the solar system, then almost everyone is going to be very vulnerable. The best defense is to be on friendly terms with all your neighbors, and have very good visibility into where everyone is and what they're doing.

Living in a asteroid belt, makes the poorest person capable of getting a ion-engine on a rock the ruler over all the well-dwellers by default - after all you have the high ground.

Thus speaks the lord thy over-lord:

I. You shall not erect asteroid defences.

II. You shall not send others to space to rule beside me.

III. Once every aeon i shall send a rock to test your faith. You shall fight one another, to proof your worthiness.

IV. Be nice to one another.

V. Game-theory applies, but in a similar way for everyone living in system, to everyone else out-system.

Things are going to get weird once private orgs start doing asteroid redirect activities (as in: massive build up of orbital railguns, hypervelocity nukes etc. once someone points out that in 10 years or 50, it's trivial to setup a rock that'll end a moderate sized nation state).

> Just look up what happens when you drop a 10ton tungsten rod from outer-space. Thanks to gravity, when it hits the ground it has the same impact of a small nuclear device.

Is that actually true? I mean, you could hoist two and a half of those tungsten rods into LEO with a single Falcon 9 expendable launch, and if we're just looking at kinetic energy, you can't get more out than you put in. So, the tungsten rod's re-entry wouldn't create any more energy than it took to lift it into orbit in the first place (assuming tungsten doesn't do anything weird like combust), and there'd be a lot of energy lost in the process. I wouldn't consider a Falcon 9 launch to be "equivalent to a small nuclear device" in terms of energy.

Another way to look at is is that a 10,000 kg mass at a height of 1,000 km above a planet with gravity of 9.8 m/s^2, is 10,000 * 9.8 * 1,000,000 = 9.8 * 10^10 joules. 1 kilowatt hour is 3.6 megajoules, so that comes out to 27,222 kilowatt hours of energy. A kiloton is (according to a google search) equal to 1,162,200 kilowatt hours, so that comes out to about 0.023 kiloton TNT equivalent. With some of that energy lost as atmospheric heating.

That isn't to say that dropping tungsten rods from orbit isn't a serious threat, or that you couldn't impart a lot more energy by flinging them at the Earth with much greater velocity. I just don't think the comparison to nukes is quite right.

The original idea was dubbed "rods from God" and it was proposed by the U.S. Air Force to target bunkers, silos, and other hardened targets without using nuclear detonations. The rods would have orbital velocity—7 km/s at LEO—giving them, at 10,000kg, about the momentum of a jumbo jet at cruise (an unfortunate comparison, to be sure). Except the kinetic force would be targeted at an area the diameter of a telephone pole, so they would penetrate deeply (100m or more) and cause enough of a shockwave in the earth to collapse almost any buried structure. Their thin profile and solid tungsten construction ensured most of their mass would survive re-entry at close to their original speed.

They also evaded the 1967 Outer Space Treaty, which forbade "objects carrying nuclear weapons or any other kinds of weapons of mass destruction"[0].

I'm not sure they actually reach the yield of a nuclear device, but "bunker-buster" nukes are relying on overkill in yield since they can't achieve that kind of ground penetration in delivery.

[0] https://history.nasa.gov/1967treaty.html

You're calculating the resting potential energy, aren't you?

"Dropping a tungsten rod on earth" is not picking it up and dropping it. It's firing it at the earth. Depending on what body you're firing it from, that's a lot of additional delta v.

Something coming at the earth from the Moon, for instance, is moving at least 2.3 kps, plus another kps if you fire it forward. This calculator is telling me that's 55.2 gigajoules, about 15 thousand times higher.

Assuming your math is right, and then my math is right, .35 megatons is still an exceedingly bad day.

> Something coming at the earth from the Moon, for instance, is moving at least 2.3 kps, plus another kps if you fire it forward.

What do you mean "fire it forward"? If you fire it forward, it will never fall on Earth. To get from Moon to Earth, you need to fire it backward in Moon orbit, to slow it down. Essentially, you need to slow it down a lot if you want it to get to Earth surface, as opposed to orbiting it alongside Moon.

Not if it’s in an elliptical orbit with a low enough apogee.

Yeah, I was ignoring sideways velocity. I was taking "just look up what happens when you drop a 10ton tungsten rod from outer-space" perhaps a bit too literally.

If we add in 1/2 * 10,000 kg * (7500 m/s)^2, to account for sideways LEO-equivalent momentum, I have it coming out as about 0.0906 kilotons: about 4 times more energy. Which isn't too surprising, since the hardest part about getting into orbit isn't the going up part, it's the going sideways fast enough enough part.

My whole formula is this: (((10000 * 9.8 * 1000000) + (0.5 * 10000 * (7500 * 7500))) / 3600000) / 1162200

Basically, (mgh + 1/2 mv^2) converted from joules to kilowatt hours to get it into a larger unit I can sort of relate to, and then converting that in turn to kilotons equivalent TNT in order to compare with nuclear yields.

That's assuming I didn't leave off some zeroes somewhere or apply a formula incorrectly.

10^10 Joules converted to TNT directly is 2 ton TNT. All the energy should be released at the time of impact in a short period of time. Even assuming >50% energy loss due to atmospheric interference, 1ton TNT should be left.

I used to be a big fan of space mega constructions until I got further into my engineering career. Now whenever I think of a O'Neill cylinder or other mega constructs I can't help but imagine stress fractures, metal fatigue, vibrations and resonant frequencies, cascading failures, and high-risk repairs.

It surely could be done, but the amount of trial and error required and the potential for high stakes failures is a daunting challenge.

Dzhanibekov effect makes me pretty sure you should spin the cylinder the other direction, in which case it doesn't have to be as long.

What do you think about Kim Stanley Robinson's hollowed out asteroids? Less efficient use of materials and angular momentum, but possibly a more stable arrangement.

"Colonizing planets is a Star Trek fantasy that, most likely, will not be worth it. "

Worth what? Some people may be willing to pay a high price in order not to be submitted to Earthly governments anymore. We do not know yet how our home planet and its politics will look like in 2050 or 2100. There is a chance that it may be a cruel dystopia.

I agree with that. The way I look at is is that Mars has the resources needed to support a population and interplanetary travel, whereas the asteroids are (probably) where the lucrative mining opportunities are. Eventually we may colonize the belt, but if so we'll probably do it by using Mars as the local gas station and supermarket.

There is a HUGE difference in metals concentration in planetary crust and an asteroid that's mostly that element. Also a huge difference in gravity if you want the materials offworld.

You don't have to colonize them, but mining asteroids makes tons of sense.

> On the contrary, Mars has all the resources of asteroids but the advantage of a water cycle that has concentrated and reformed minerals like on Earth.

The water cycle concentrates diffuse elements into usable mineral deposits, yes. But those elements are only diffuse in the first place because of the planetary environment. The base abundance of industrially useful elements in asteroids can be tens, hundreds, or thousands of times higher than Earth (or Mars) precisely because these materials sank to the core or mantle of planets, or get chemically locked up in expensive to refine oxides. Indeed many of the rare metals we prize are actually of asteroidal origin, because they have been completely depleted in the Earth's crust in geologic antiquity.

What's more, chondritic or M-class asteroids typically have extremely accessible minerals, such as pure metals already in reduced form, or mixtures of loosely compacted minerals that can be sorted with a crusher and a centrifuge.

One thing you can’t ever change about Mars is its gravity though. All of our biological construction over billions of years was in 1g. Maybe we could thrive from birth, for 100 years or so, in one third G, but I’m skeptical. Even more so on an asteroid. Even on Earth, reduced muscle mass is associated with poorer health outcomes. To maintain that in reduced gravity would mean a lot of hours per day in resistance exercise.

Going from 1g to micro/no-gravity seems like a much more dramatic change than going from 1 to 0.3, so I think that's an argument for going to Mars ahead of asteroids.

That’s what I thought I said. Mars bad, asteroids worse.

It is possible that we will hack our own biology to grow stronger muscles without exercise or at least not as much exercise. Famously, Neanderthals, a very close species, were more muscular than us. It probably translated to higher consumption of food, though; a muscular body needs to eat a lot to maintain itself. That might be a problem on Mars.

> To maintain that in reduced gravity would mean a lot of hours per day in resistance exercise.

There's zero evidence for this at all. We have no experimental data on living in partial gravity, only microgravity(zero-G). It may be perfectly fine, it may be just as bad as no gravity, we truly don't know.

There was a module for the ISS that was designed to test this but it got scrapped, a massive waste IMO, as it seems to be one of the most outstanding questions we have right now for space biology. Other big issues like radiation exposure is well understood.

I wanted to like Red Mars, and the science stuff was well made, but a lot of the book is about politics, and to me, those parts were painful to read.

I found it incredibly naive and unrealistic. Clearly many others disagree :)

I couldn't really like, or care for, the characters.

The funny thing is that just when the politics were getting interesting, the author takes a detour into the effects of memory and hand-waves away all the tensions between Earth and Mars.

Kim Stanley Robinson is insufferable. He has so many deep misunderstanding about politics, economics, and even things like climate science and limits to growth that are his core schtick. And the flaws are so embedded into the central plots of his books that it is really hard to suspend disbelief and ignore.

I originally encountered the Mars Trilogy as a teen and it is fair to say that it changed my life. I feel in love with the romantic portrayal of Mars colonization, and eventually ended up working at NASA. Recently I decided to go back and re-read the trilogy and found myself unwilling to finish even the first book. I just couldn't stand it. So you're not alone.

You might like Icehenge though. It works more as a stand-alone novel (or 3 novellas, really) set in the same universe, but with a focused plot and the politics mostly relegated to the background. It's a very under-rated book, being overshadowed by the more well-known RGB Mars trilogy that followed.

> We already don't care about externalities here on Earth, there's no way we can police them on Mars.

That depends very much on how the putative Martian society is set up.

There used to be an idea in cultural anthropology that a society becoming heavily dependent on technology and coordinated labour (specifically, sophisticated irrigation systems) went hand in hand with the evolution of a centralized authoritarian state to manage that.

The idea has fallen out of favour, but you can see how something similar might apply in spades on Mars. Life there is going to be marginal at the best of times; living off-grid would be a truly daunting prospect.

[1] https://en.wikipedia.org/wiki/Hydraulic_empire

You want Mars because you want the asteroids. You want the moon because you want asteroids. Moon because you need to get the material to Earth and it is better to mine in space. Mars because you need access to the asteroid belt. They are just different steps towards the same goal.

One thing I liked about Red Mars is how it brought up independence. Astronauts are well known to rebel against their respective commands (US, Russian, etc). It'll be interesting when command cannot do anything about it on a longer timeframe than your stay on the ISS (or skylab).

Also going to voice my love for Red Mars, I found Green Mars to be much more of a slog to get through, but I really like anything KSR writes. Blue Mars was a nice finale though.

I love Red Mars. The whole series is good but Red Mars itself is fantastic, one of my favorite books.

You practically get an undergrad in areology reading it. Super curious to see how our reality lines up with the timelines in the book.

Speaking of areology, there is a small subreddit for precisely that field which is quite good: reddit.com/r/Areology

Interesting anecdote, KSR as of 2015 didn't believe in mars colonization any more. The perchlorate issue really got to him and he basically said we'd never live there. Maybe he's changed his mind again but I got a chance to ask him some questions at a reading from Aurora and the scales really fell from my eyes at his answers.

> I've swung around to the idea that colonizing asteroids

Metal asteroids can, with some luck, provide us with boundless supplies of pretty much all metals, as I understand it. This will be one of the great milestones in human civilization.

But I think it's a place you go to work. Mars is far more interesting as a place to live and build a society.

You can fit a lot more people in the asteroids, and it'll be easier to transport stuff between them.

Mars has a lot of the same disadvantages that earth does. Its got a lot of gravity, and you can't communicate through the planet from one side to the other

Gravity does seem like a disadvantage, but satellites have worked pretty well for the other problem... we've even got some in place around Mars already.

Well, the underclass always gets the shit jobs, and habitat.

Owkwa beltalowda.

What you lack in the asteroid belt is the feeling of a planet with a reasonably short day/night cycle, some kind of skies and a diverse landscape. Maybe we can live without them, but for people who grew up on Earth, living on Mars might be psychologically easier.