Re: Real Life Thrust (was: hyperspace)

In message <199608272223.SAA11968@cliff.cris.com> Mike wrote:

> Daryl wrote:
> >Also, something to think about, the net kinetic energy stays the same
> >in a system ... so if you could throw a miniscule amount of mass out
> >at close to the velocity of light you could probably keep a sizable
> >amount of thrust up for a pretty good period of time before you ran
> >out of fuel (sorta a particle accelerator/rail gun down the center
> >of your ship).

It's a trade off between energy efficiency and mass efficiency. To
get twice the exhaust velocity (and hence twice the thrust) you need
four times the energy. So high-mass efficiency drives either need
very large energy sources (matter/anti-matter?) or keep to low
thrust (but high efficiency).

> I remember some scientists discussing a laser powered craft some time
ago,
> not to mention in sci-fi novels.  I always wondered what might happen
if
> something strayed in its path.  Many authors only described it for use
in

If it's powerful enough to accelerate a massive craft at decent
velocities, I think we can assume that you don't want to get in
its way. Much like other high-energy drives.

> initial acceleration, due to beam convergence problems and enormous
energy
> requirements for the laser.

Depends on the size of the lasers. The Moties in _Mote in Gods Eye_
had one going for a long time if I remember to power their scout
across several light years.

-- 
Be seeing you,
Sam.