[extropy-chat] now that's fuel efficiency

Alan Eliasen eliasen at mindspring.com
Wed Nov 17 03:03:17 UTC 2004


Al Brooks wrote:
> So far having used 130 pounds of xenon 'fuel' the
> European Union's Smart-1 has arrived in lunar orbit.
> The craft has gotten the equivalent of 5 million miles
> to the gallon, better than expected.

   I'm curious about this odd "miles per gallon" figure.  How was it derived?
 What densities are assumed for the xenon?  Anyway, anyone getting less than
infinite miles per gallon in space is squandering fuel.  :)  But still,
specific impulse of 1500 s is great.

>  Detroit, are you paying attention?

   Considering that the thruster has a thrust of a whopping 70 millinewtons,
(that's the force exerted by about 7 U.S. dollar bills, or about 7 raisins,
sitting in earth's gravity) a 2000-lb car could go from 0 to 60 mph in ... 4
days?  If you eliminate all sources of friction, that is.  That's probably the
guy who was in front of me in traffic tonight.

-----

   Appendix:  Calculations in Frink ( http://futureboy.homeip.net/frinkdocs/ )

   70 mN / (2000 lb) / (60 mph) -> days

   70 mN -> gravity grams

-- 
  Alan Eliasen                 | "You cannot reason a person out of a
  eliasen at mindspring.com       |  position he did not reason himself
  http://futureboy.homeip.net/ |  into in the first place."
                               |     --Jonathan Swift



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