[ExI] one way ticket to mars

Eugen Leitl eugen at leitl.org
Tue Apr 23 16:45:24 UTC 2013

On Tue, Apr 23, 2013 at 09:11:27AM -0700, spike wrote:

> I agree the ion engine is feasible, even current technology.  But my

I've seen ITO/InP on Kapton is claimed to have 2 kg/kW.


So if they need 200 MW, that'd take 200 t.

> argument is that it doesn't do as much as they say.  You still need chemical
> propulsion to get to LEO to assemble the ion engines, and I figure you might

But that time is not part of travel, since the crew sits
there terraside, twiddling their thumbs until craft is ready
for departure.

> need chemical propulsion to get out of the earth's gravity well in a
> reasonable amount of time.  Even then, with that marvelous Isp the nuclear

It's not nuclear, it's electric, solar-powered.

There are some data on nuclear VASIMR

There are some fusion-assisted propulsion plans, but I
think it's too speculative at this point


> rockets offer, the optimal mission assuming humans aboard is far waaay
> longer than 30 to 40 days.  Every scenario I ran optimized in an orbit not
> far from a standard Hohmann transfer, perhaps a little over 5 months being
> the shortest practical mission, and even then you hang your lives on the
> system working perfectly at the other end for Mars insertion.  30 to 40

The problem with photovoltaic is that you only have half power at Mars.

> days, no way.  
> My assumptions went up to Isp of about 1200 m/sec, much beyond which your

VASIMR VX-200 claims an Isp of 5000 s.


Zubrin doesn't like Ad Astra, but they've replied to his criticisms
with http://www.adastrarocket.com/VASIMR_development_AdAstra_15July2011.pdf

> energy consumption goes nuts, and the total thrust is way low for the very
> high Isp systems.  The really shorty missions, anything less than about 5
> months, require high total thrust at the far end, otherwise you die of
> boredom and starvation on your way out to Jupiter, waving a sad goodbye to
> Mars, damn.  {8-[
> But you make a good point: I need to get out all those spreadsheets I made
> 15 yrs ago, update them and start calculating again, see if anything will
> change my mind.  Already something has: China and India are going into space
> stuff bigtime, and they have buttloads of money to dump into it.  Those two
> guys may work together, and if they do, you have a couple billion proles
> from which to choose rocket scientists.

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