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Comment by humanfromearth | Hacker News Reader

I don't get the fascination with this barren gravity well called Mars. Other than scientific curiosity there is nothing there of value that is not 1 billion times more abundant in the belt. I genuinely don't understand why there is this need to be multi-planetery species and not just space-fairing civ? the tech we need for either seems kind of the same to me, but the belt has a much higher return so what am I missing?

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> why [...] not just space-fairing civ? the tech we need for either seems kind of the same to me

cstross has a web of old blog posts about the difficulties of spaceships, generation ships

http://www.antipope.org/charlie/blog-static/2009/11/the_myth...

> how simple can you make a minimal self-maintaining interstellar transport system"?

> To a first approximation, the best answer I can come up with is "not very".

Separately from "the tech"

http://www.antipope.org/charlie/blog-static/2009/11/designin...

> If you can crank yourself up to 1% of light-speed, alpha centauri is more than four and a half centuries away at cruising speed.

> We humans are really bad at designing institutions that outlast the life expectancy of a single human being.

I must admit, I don't understand this often repeated notion of "cruising speed" in interstellar space.

To me, it feels like some people think of crossing the void between stars as crossing the the Atlantic in a bottle, trying to blow my mind with how long the crossing will take, even if that bottle is given an absolutely amazing initial throw.

For interstellar travel to make sense, there _must_ be a 'cruising acceleration', not speed. The notion isn't that strange - after all, cruising speed in a ship on earth requires a constant engine power, which in space would mean constant acceleration.

IIRC, a comfortable cruising acceleration of 1G would make it a 4 year trip (6 as experienced by Earth). We just need a whole lot of efficient fuel and an interstellar propeller :P

How do you think a ship is going to power a continuous acceleration? 1G for 4 years is... I don't really know, but it's a heck of a lot of energy even if you've somehow beaten Tsiolkovsy's rocket equation. You don't get to hand-wave this away in a remotely serious conversation. There's also the small problem of the interstellar medium wrecking your hull at high velocity, if you ever get there.

You can cheat a bit by making use of laser propulsion[0] to propel a rocket that contains the necessary fuel for deceleration.

To almost completely eliminate fuel requirements in subsequent trips you would bring the self-replicating equipment necessary to scale up the industrial capacity to build an complimentary laser system in the destination star system. This would allow you to propel ships on return voyages and slow down ships coming to the planet.

The downside of course is that you've now built a death laser in each star system that could be used to wreak havoc. But then again in this scenario you've also built self-replicating space bots that can turn asteroids into stuff or planets into asteroids into stuff.

[0] https://en.wikipedia.org/wiki/Laser_propulsion

>... that contains the necessary fuel for deceleration.

Is it not possible to plot an interstellar course that utilizes gravity for deceleration?

Well, the hull problem is there at 1% or 15% of c or whatever is reached. You don't get to wave how you get to the 1% of c speed away either, so let's not set double standards; interstellar transport for humans _is_ all scifi-land.

IMO, we simply can't get there with chemical rockets as we know them. Continuous acceleration in space is just any kind of engine that keeps running and provides thrust. We're not talking cars here.

The estimation of the energy needed is easy to make sense of - what does it take to have a rocket (or more likely, some other engine) hover over the ground for 4 years using some kind of thrust?

When we have that capability, we can pretty much do non-suicidal interstellar transport. But it requires new technology and for me, that constitutes sci-fi. Doesn't mean a conversation can't be remotely serious though, IMHO.

But the point I actually wanted to make was, that whenever people talk of cruise-speed in interstellar transport, it seems to me like they haven't grasped the scope of interstellar travel with an intent of conquering it. Rather, they are implying it just can't be done - without arguing for it.

The term 'cruise-speed' itself becomes an annoying passive-aggressive attack on the notion of interstellar transport. That was my original reason for posting.

Maybe replace it with "coasting speed" and see if that feels better? It's a valid strategy. We have proposals for drive systems that get to .01c where the physics sort of works. I'm not aware of any realistic proposals that can supply 1g for any length of time. Maybe a ramjet, but last I heard those work better as brakes because, again, interstellar medium. Drag is another reason "cruising speed" might be a coherent concept even under thrust.

Wait - didn't Newton say that a body will not accelerate nor change direction unless a force enacts upon it? Once you set an initial velocity in void space with no air, you should never decelerate unless you accelerate in the direction inverse from your motion.

Yes, that was indeed implied for the line "For interstellar travel to make sense..." to make sense :P

I don't mean to be annoying, but I don't think I understand why you ask?

Humans are very fragile to sudden acceleration. Unless we assume really out there, indistinguishable-from-magic tech, manned spaceflight cannot "set an initial velocity" suddenly, nor a sudden breaking at the end. To get to any other star in years, not centuries, the only way to go is to accelerate on the whole first half of the way, and then decelerate on the remaining half.

I think you're mistaking Mars to be an end goal. Much like the Moon exploration missions, it's only an extension of the frontier and another rotation in the humanity progress wheel.

You're absolutely right in terms of absolute financial value the belt is a better bet, but the goal is more of if we can, and starting the effort of spreading humanity beyond Earth permanently.

Mars isn't the end goal. It's just the closest starting point.

I interpreted @humanfromearth as not talking about end goals either: presumably setting up shop on some near earth asteroids is easier than Mars. It is arguably more useful too.

So yeah: I suspect that in 1000 years time when we look back at the history of space colonisation (however the heck it happens) my guess is that Mars will not figure strongly in the story until we are much more advanced than we are now.

> It's just the closest starting point.

The closest starting point is right here on earth. Are we yet able to make it work here? I don't think so.

We will while preparing for making Moon or Mars work. Actually we already are, though there isn't much effort going into it as it is still driven by non-economic reasons.

Mars isn't the closest starting point. Asteroids are. Some are far closer, and even those in the belt are easier to reach than Mars because you don't need atmospheric braking and a ton of fuel on your return flight just to get back out of the gravity well. And the asteroids provide us with more livable habitats and access to far more resources.

Having two planets with launch capability makes resupplying, servicing, and responding to emergencies for eventual facilities in the belt would make logistics across the solar system an order of magnitude easier. Suddenly, you have twice as many launch windows over the course of a year to any given point as well as two 'ports' to return to if something goes seriously wrong.

Launching from the surface of Mars takes a lot less fuel, too. Martian gravity also happens to be high enough for earth manufacturing machinery to mostly work as it does here on earth, meaning that we can mostly reuse the systems we're using today. These two factors combine to make Mars quite ideal for building and launching staggeringly huge space vehicles, habitats, and mining machinery which in turn makes bootstrapping a human presence in the asteroid belt and other locations in the solar system a lot easier than if we were to just start at those destinations.

You have it backwards. Mars is a deep gravity well that adds huge energy costs to both landing and return trips. You don't want to build anything on Mars. Asteroids are much less costly to reach, offer better living environments and far more resources. You want to build out a few asteroids with fuel depots, ship construction/maintenance equipment, and mine cheap extra delta V to spend on mars.

> I don't get the fascination with this barren gravity well called Mars. Other than scientific curiosity there is nothing there of value that is not 1 billion times more abundant in the belt.

Well, it's the very gravity well that's useful. The fact that you'd have lots of solid ground under your feet.

Also, lots of space to use (including underground), stable orbit, lots of potential for expansion.

Sure, resources will be easier to get from the belt (and even easier from near-Earth asteroids). I expect resource-driven space exploration to focus there. But Mars is primarily about alternative habitat.

> Other than scientific curiosity there is nothing there of value that is not 1 billion times more abundant in the belt.

Gravity? Sunlight? Atmosphere acting as radiation shield?

> Atmosphere acting as radiation shield?

Does Mars have much atmosphere to speak of? The figure on Wikipedia is that surface pressure is a measly 0.6% of mean sea level pressure on Earth. And there's no magnetosphere at all.

It's not great. But it's better than spending your time in the interplanetary vacuum.

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

Another thing-- radiation shielding, once installed, has little to no continuing maintenance cost on Mars. Space borne shielding constantly requires additional fuel just to move around.

Asteroids are free space borne shielding.

It's an interesting point. The potential advantage would be if Mars has resources like water and hydrogen that we can use to colonize it which would not be possible in the barren expanse of space. Also radiation and gravity have a rather large effect on human physiology...

It's sexy! It's cool! Space ships! SOLAR FREAKING ROADWAYS!

Oh, wrong thread...

Dreams are nice. Dreams don't feed people.

But they do give people reason for hope. Which is why it's easier to concentrate on "OMFG we colonize Mars!", than the engineering realities of:

* climate change could very well destroy modern human civilization. Fixing that will involve convincing rich, powerful, people that they're wrong. And, spending lots of money which they'd rather spend on pretty toys or lining their pockets

* feeding the planet is easy (from an engineering point of view). Getting the food to people involves dealing with psycho warlords, or corrupt politicians

Etc. etc...

It's easier to dream about "OMFG MARS!" than to go through the decade-long daily grind of fixing problems at home.

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