Re: potential energy

"C. Roald" [email removed] writes:
> >>		On the other hand, GmM/r is the escape energy of Sol,
> >> which is the kinetic energy required to produce a velocity of ~30 km/s.
> >> For a ship weighing say, 1 T, that's 4.5e11 J, or 450 000 MJ. Not to
> >> be sneezed at.
> >
> >A ship accelerating at 1-G will achieve that velocity in less than an hour,
> >using just its manoeuvre drive.  (To get to 30000 m/s using an acceleration
> >of 9.8 m/s^2 will take 3061 seconds, i.e. 51 minutes.)  Maybe not to be
>
> You realise what you just said?  A spacecraft with a 1-G maneuver drive
> can produce 4.5e11 J in 3000 s, for an average power output of 150 MW.
> Constant-acceleration drives are scary.

That's nothing.  See what happens if the same ship leaves its drives on for
a week.  (Actually, I'll tell you what happens.  TML gets bogged down with
another discussion of how to destroy a planet.  :-)  But approximately
constant acceleration for about an hour should be possible; and even if it
isn't, a ship with 2-G acceleration should still be able to get to 30000 m/s
without too much trouble.  The ship in question is likely to be the good old
Type S scout/courier, mass at least 840 tons, kinetic energy 3.78e14 J.  Like
I said, these might be big numbers, but they're what you have to deal with if
you want to move starships around.  I'll let you figure out the kinetic energy
available to some of the big warships, mass in the hundreds of thousands of
tons, acceleration 6-G!

> >So the ship expends its 4.5e11 J, and get into jump space.  One week later,
> >it emerges from jump space near Alpha Centauri, and gets 4.5e11J back -
> >what happens to this energy?
>
> Depending on how jumpspace is supposed to work, I shouldn't think the
> hundred billion joules of GPE would have to be 'spent'.

Not so much "spent" as "lent" for about a week.  The ship gets the energy
back (or at least, some of it) when it comes back out of jump space.

>							   The only
> relevent number ought to be the difference in initial and final
> energies.  If the energy did have to come from somewhere, it would be
> a very blatant violation of the 2nd law of Thermodynamics to get it back
> in the capacitors.

Why?  The jump drive converts energy, presumably electrical energy and lots
of it, into some sort of "jump energy", in order to get the ship into jump
space in the first place.  It may be able to convert it back into electrical
energy, although some energy will be lost in the process, either as heat or
left behind somehow in jump space.  Otherwise, what happens to all the energy
produced when the jump drive burns up all that fuel?

>		     More plausible would be to get it as kinetic energy,
> but physical reality would almost certainly produce it as heat. Which
> would vapourise the ship, very quickly.

Great.  Every ship that executes a jump gets fried when it re-enters our
universe.  This ought to ruin the day of a good few traders!  :-)

- --
 "Keyboard?  How quaint!" - M. Scott

 Adrian Hurt			     |	JANET:  [email removed]
 UUCP: ..!ukc!cs.hw.ac.uk!adrian     |  ARPA:   [email removed]