Re: potential energy

Adrian Hurt [email removed] writes:

> Of course, things don't balance out quite so neatly when the destination
> star has more or less mass than the departure star.  Maybe part of the jump
> calculation involves arranging that you exit jump space at a distance such
> that the escape velocity from the destination star at that distance, is equal
> to the escape velocity from the departure star at the distance at which you
> entered jump space.  Using distance from the star to balance out the different
> mass of the star ensures that the escape energy at each end is about the same,
> and the jump drive doesn't get overloaded trying to compensate for the
> different energies.
>
> The jump drive would then convert the ship's kinetic energy into jump energy,
> and back again when the ship exits jump space.  Kinetic energy would probably
> be meaningless or totally different in jump space.

That was kind of what I was thinking.  If you think of stars and planets
as "gravity wells", then you would jump to a point with the same "depth"
as the other "well".  The 100-diameter rule would be to keep you clear of
planets and stars, no matter what their relative densities are.  I'm sure
you can still imagine jumping from an near a small star into the inside
of a red giant since the gravity is the same (has anyone read A Mote in
God's Eye?  Hope that black globe is working 8-).  The biggest worry I'd
have is being too close to the planet, and jumping out closer to the star
than I expected since the "gravity well" is the same depth there.

I like the idea of requiring that you be at escape velocity first, since
that means your ship is at "zero energy" overall.

Note, if you don't allow direct and immediate conversion of kinetic to
potential energy upon leaving jump space, then it would be impossible to
jump to a point of higher potential energy (further from the star), since
that would require you to add potential energy to the ship.  Also, if you
tried to jump to a point nearer to the star, there would be a great deal
of excess energy, which nature often expresses as heat.  Can you say BOOM?
And a vacuum is a great insulator!

(If you don't want Niven-style jump drives, then you still must account
for the extra energy.  In this case, simply start with enough kinetic
energy to reach escape velocity and end at near rest when well away from
any start, allowing kinetic energy to be converted to potential energy
by the jump.  Similarly, add kinetic energy when you jump towards a
star.  If you jump from deep space towards a large star, you'd end up
hurdling towards the star when you arrived -- don't arrive too close!
Of course if you use this, there is the problem of momentum -- are you
allowing ships to store up momentum in different directions?).

> > Of course, there will have to be extra energy expended for the jump
> > itself.  Probably that energy would be expended as lost heat energy
> > or something.
>
> That's accounted for by the huge amount of fuel which has to be burned by the
> jump drive.

Now, where does this energy go?  If it goes into the mysterious "jump
space", then jump drives are slowly leaking energy out of our universe.
I think more likely it would be radiated into space as heat.  Of course,
that heat had better be left behind, not brought with you (Have you ever
watched a ship enter jump space?  Well, the ship looks like it's
stretching for a split second as the jump drive activates, followed by
a great white flash when the ship disappears.  No doubt boldly going
"where no one has gone before". 8-)

Jerry Williams
[email removed]