Comment by kakarot | Hacker News Reader

Comment by kakarot | Hacker News Reader

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I do understand the orbital mechanics of getting to Mars. It's the same as the orbital mechanics of getting to anywhere.

I assume you're talking about the Hohmann transfer [0], which is the most efficient path a ship could take. We're not optimizing for efficiency here, we're optimizing for delivery. You should also realize that while there is a specific moment of peak efficiency in launch times, you have a window on the order of months before a Hohmann transfer becomes less efficient than other methods. Once every 2 years sounds less drastic when it's 6 months out of those 2 years.

All that being said, the Hohmann transfer is a lot sketchier in practice than one would think. Neither Mars nor Earth has a perfectly circular orbit. It's often easier just to take the old-fashioned route.

Take a look at this chart [1] for an idea of the spread of trip length vs launch time.

[0] http://www.planetary.org/multimedia/space-images/charts/hohm...

[1] https://mars.jpl.nasa.gov/spotlight/images/porkchop_lg.gif

> I do understand the orbital mechanics of getting to Mars. It's the same as the orbital mechanics of getting to anywhere.

Then you don't understand the economics. Or maybe it's something else you don't understand, but you are clearly missing something. The orbital mechanics of getting to any target in the solar system are unique to that target. Designing orbital trajectories is a profession unto itself.

Yes, it is theoretically possible to have staggered deliveries so that spacecraft arrive at Mars on a schedule other than every two years. But think about it: how would this help? The schedule on which the supply craft arrive doesn't matter. What matters is the latency between when a need manifests itself and when it can be fulfilled. Fundamental physics lets you get to Mars in a matter of days if you could accelerate and decelerate the entire time at 1-G. But you can't, not because orbital mechanics forbids it, but because technology and economics and the rocket equation forbids it.

The one thing you're going to need to optimize for more than anything else is kilogram delivered per dollar spent. That means being as efficient as you possibly can because launch costs are ridiculously high even with reusable boosters. That means using Hohmann orbits, and that means eight month transfer times with launch windows every two years. Yes, those windows are fairly broad, but that doesn't matter. You're still going to have to wait for periods of time measured in months and years for your Amazon order to be fulfilled on Mars.

Orbital mechanics is orbital mechanics. The math doesn't change just because it's Mars and not some random object in the Kuiper belt.

> But think about it: how would this help? The schedule on which the supply craft arrive doesn't matter. What matters is the latency between when a need manifests itself and when it can be fulfilled.

Think about this: You're no longer disagreeing with my premise, and are now moving goalposts. My premise remains true, so your accusation that I don't understand the orbital mechanics involved here is unfounded and unwarranted. A little deconstructive to meaningful conversation, which you seem keen on having with people.

> Fundamental physics lets you get to Mars in a matter of days if you could accelerate and decelerate the entire time at 1-G

It's also a bit deconstructive to talk about extremities. Keeping the discussion within rational limits helps us tackle this realistically and collaboratively.

Now this discussion has shifted to latency vs regularity and yeah, it will take some planning ahead to smooth things out, and everything must come in triplicate in case the replacement breaks while you'r installing it. But that's entirely feasible and the only barrier is money. So what we need to focus on with regards to the great Nevada desert is things like terraforming. Sustainability is no problem if you have a water source and a climate something can grow in.

> The math doesn't change just because it's Mars and not some random object in the Kuiper belt.

That depends on what you consider "the math." In principle, it's all F=ma. In practice it's a good deal more complicated than that. There's a reason people make careers out of designing orbital trajectories.

> the only barrier is money

Well, yeah, the only barrier was only ever money. But that's a pretty big barrier right now.

> what we need to focus on with regards to the great Nevada desert is things like terraforming

Yes, terraforming is one way to solve the problem of sustainability. But I don't think we're any closer to being able to have a serious discussion of terraforming than we are about having a self-sustaining settlement without terraforming first.

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