[extropy-chat] MARS: Because it is hard

Alan Eliasen eliasen at mindspring.com
Thu Apr 15 06:44:28 UTC 2004

Dan Clemmensen wrote:
> If Alan's is correct (I haven't checked) I rounded up to 150Km.

   I'm glad to see that Spike now agrees with me.  Whew!  I guess that's why
I'd hate to compete against anyone who uses Frink.  It makes it hard for even
me to be wrong.  ;)

> OK, how much energy can we dissipate or recapture using a linear
> induction motor system, practically speaking. Assume a 10,000Kg
> capsule and 150Km decel from 1200m/s. We must dissipate the
> energy of 10,000g every 150m, or 1g every 15mm, about like stopping
> a .22cal bullet. This seems to be more like engineering than it is like
> magic. I'm assuming that a 10,000Kg capsule would be a convenient
> size.

   Well, the amount of energy isn't *all* that huge.  Using the (now
agreed-upon) 1680 m/s of low moon orbital velocity, the total kinetic energy
of the ship is given by ke = 1/2 m v^2.

   In Frink notation, (http://futureboy.homeip.net/frinkdocs/  or try it
online at http://futureboy.homeip.net/frink/ ) :

  ke = 1/2 10000 kg (1680 m/s)^2

  Which is a kinetic energy of about 14 gigajoules.

  (Note: kilo is always represented with a lowercase k; Frink will
(pedantically, but correctly) complain if you use uppercase, see
http://physics.nist.gov/cuu/Units/prefixes.html )

  That's a lot of energy, but not a LOT of energy.  For comparison, let's
compare that to the energy in a quantity of gasoline, again using Frink:

  ke -> gallons gasoline

  Gives a result of 100.8 gallons of gasoline, used very efficiently.  (Or 381
liters.)  (Or just under 100 gallons of kerosene.)  Converting to kilowatt
hours, this is:

  ke -> kWh
  ke -> kilowatt hours

  Which gives a value of 3920 kilowatt hours.  This is the energy dissipated
by 1633 100-watt lightbulbs burning for a day.  In Frink,

  ke / (100 W) -> days

  But this has to be dissipated in the previously-calculated 171 seconds:

  ke / (171 s)

   Which gives about 82 megawatts.  That's a lot of power to dissipate, (it
could light 825,000 of those 100-watt bulbs during that time) but potentially

   A shorter accelerator (with higher acceleration) increases the necessary
power dissipation.  A longer accelerator may be more expensive to build,
(anything kilometers long probably gets expensive) but the power requirements
are reduced.  As always, it's a tradeoff.  Fun stuff.

  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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