# Re: starship-design: Anti-antimatter

```Steve,

It has been quite awhile since I read about spinning black holes, and I
must point out that his scientific credentials notwithstanding, I think it
was in a FICTION book.  Nevertheless, there are several ways to extract
energy from a spinning black hole.

The first method as you point out is by injecting matter into it in such a
manner that you get some energy back out, and as you point out this is
THEORETICALLY at the expense of angular momentum (the arguments here get a
little abstruse and there are two sides).

The second method invloves directly braking  the rotation using some sort
of magnetic field and thereby transferring momentum as energy into the
braking field, a method which is several orders of magnitude more difficult
than the first, but which offers the advantage of not requiring on board
reaction mass. Of course yo still face the problem of converting the
resultant energy into PROPULSION...and as someone just pointed out it isn't
necessarily a matter of energy conversion efficiency, but momentum
conversion efficiency.

The flaw (or hole if you will excuse the pun) in both of these propositions
is that black holes (or relativistically spinning masses of any sort) have
MASS and lots of it. Will you get sufficient energy usable for a change in
momentum from one of these reactions? I don't think so.

I therefore return to my earlier statement that the source of the energy
that is being used to provide thrust must be external to the vehicle,
requiring an absolute minimum of onboard reaction mass.

> I remember reading that a black hole can have up to 29% of its energy
> tied up in angular momentum.  Unfortunately to get the energy back out
> you have to throw more mass into it in such a way that some of the mass
> is given to the black hole and the rest spews out carrying away some of
> the rotational energy.
>
> Of course, with a quantum black hole you can do partial conversion of
> mass to energy by feeding it at the same rate that it emits mass/energy
> due to quantum evaporation.  If you run out of fuel you have to be able
> to toss the black hole away before it blows up due to runaway
> evaporation; the rate of evaporation is inversely related to the mass of
> the black hole.

(P.S. at least on argument says the black hole will ALWAYS evaporate
QUICKLY and therefore it is useless to attempt this...)

Lee Parker

```