[extropy-chat] MARS: Because it is hard

Adrian Tymes wingcat at pacbell.net
Mon Apr 26 20:14:25 UTC 2004

--- Spike <spike66 at comcast.net> wrote:
> Emlyn, Gene, Adrian, Robert, the rest of you space
> guys,
> what we need to do is put together or look for an
> existing 
> spreadsheet to aid Mars mission design, one that
> includes 
> necessary delta-vees and required fuel load and tank
> size requirements.  Zubrin has already made some
> pretty
> competent looking weight estimates in The Case For
> Mars.
> Perhaps I need to take that on for my next project,
> or
> look around at what has already been done.

I know this is a bit late, but...

lists 4815 m/s total delta-v from LEO to (highly
eccentric) Mars orbit, taking about 10 months (not an
optimal trip for people by any means; this was for a
robotic probe).  A more extensive set of delta-V vs.
time, including the much more dominant delta-V to
orbit, can be found at
http://www.projectrho.com/rocket/rocket3o.html .

Quoting from other sources:
> mass fraction = e^(dV / Ve)
> where
> mass fraction = Mi / Mf
> Mi = mass of rocket including fuel
> Mf = Mass of rocket after burning the fuel
> dV = deltaV
> Ve = exhaust gas velocity 

At a good (for chemical rockets) exhaust velocity of
4000 m/s, I get a mass fraction of about 3.33, or
Mf/Mi of just under 30%.  Adjust for other propulsion
methods as desired (like the much higher exhaust
velocity of nuclear propulsion), then calculate for
desired Mf (rocket structure, including empty tanks,
plus payload, including life support).

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