[ExI] one way ticket to mars

spike spike at rainier66.com
Tue Apr 23 16:11:27 UTC 2013

-----Original Message-----
From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Eugen Leitl
Sent: Tuesday, April 23, 2013 7:45 AM
To: extropy-chat at lists.extropy.org
Subject: Re: [ExI] one way ticket to mars

On Tue, Apr 23, 2013 at 07:16:45AM -0700, spike wrote:

> >>...Novel propulsion seems to make travel in 30-40 days feasible...
>>... Disagree.  The only thing we have even vaguely plausible for a 
> non-Hohmann transfer orbit is fission nuclear, assuming any reasonable 
> extrapolation of

>...Do you disagree that
is a near-future technology?

I agree the ion engine is feasible, even current technology.  But my
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
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
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
days, no way.  

My assumptions went up to Isp of about 1200 m/sec, much beyond which your
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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