From: kare@sirius.com (Jordin Kare)
Newsgroups: sci.space.tech
Subject: Re: Pellet Stream Propulsion
Date: 6 Sep 1997 06:29:48 GMT

In article <3410A550.1734@eau.net>, random@eau.net wrote:

> Jordin Kare wrote:
> > Jordin (ask me about the Bussard Buzz-Bomb) Kare
>
> LOL- that gave me one heck of a visual!
> Consider yourself asked.

Very briefly, the Bussard Buzz-Bomb is the catchy name for
a concept I came up with a few years ago (in the middle of a
conference on robotic interstellar probes, in fact); the
formal paper is titled Impact Fusion Runway for Interstellar Propulsion.

The problem is that the only more-or-less existing propulsion
technology that will get you above a couple per cent of c is
fusion (that being the limit for Orion-type fission systems).
But neither magnetic nor inertial confinement fusion will work for
a small probe (due to the large "reactor" needed),
nor give a very high thrust/weight (except for Orion),
nor work at all with current technology (again, except for Orion).
(Bussard's current project, electrostatic confinement fusion, would solve
the first problem if it works, but I will be surprised if it does).

However, there is another type of fusion:  impact fusion.  If you
slam a couple of macroscopic pellets of fusion fuel together at high
enough velocity, you can ignite a fusion burn.  The threshold velocity,
though, is around 200 km/s -- too high to make building an impact-fusion
power plant reasonable.  But if you're trying to fly at, say, 0.1c =
30,000 km/s, a measly 200 km/s is no big deal.

So imagine a long "runway" of fusion-fuel pellets sitting in space.  Along
comes a spaceship at >>200 km/s.  Said ship has a hole down the middle, and
carries its own batch of pellets.  It drops one on-board pellet into the middle
of the hole.  The "on board" pellet and the "runway" pellet collide - BANG!
The explosive products are directed aft by a magnetic nozzle, and the ship
accelerates forward.

There's a bunch of technical details to worry about, like:
How do you put the runway pellets in place?  (Laser propulsion, of course!)
How do you get up to "ignition velocity"?  (There's an elegant bootstrapping
  scheme that involves getting a few pellets up to 200 km/s...)
How do you hit, literally, one BB with another BB at 30,000 km/s
  (REEEALLY good aiming :-) and various other tricks)
How do you build the magnetic nozzle, and shield the rest of the ship?
  (TBD, but not exorbitantly difficult)

Do all these tricks, and it's possible to launch, say, a 1 ton probe at
0.1c with technology that's readily foreseeable within a few decades --
comparable to that required for solar power satellites, for instance.

Why Bussard Buzz-Bomb?  Because it's a distant descendant of Bussard's
original ramjet interstellar vehicle, and it's a pulse jet, just like the V-1.
And because it really will buzz -- that 1-ton probe, at the end of its
acceleration run, is riding a string of 1/10 kiloton explosions going off
at 30 per second.

Jordin (give me a buzz) Kare

Jordin Kare