From: kare@sirius.com (Jordin Kare)
Newsgroups: sci.space.tech
Subject: Re: explosive rocket
Date: Tue, 03 Feb 1998 18:52:26 -0700

In article <higgins-2001980037440001@132.206.200.31>,
higgins@me.mecheng.mcgill.ca (Andrew Higgins) wrote:

> In article <19980110024201.VAA18323@ladder01.news.aol.com>,
> guff12345@aol.com (Guff12345) wrote:
> >
> > If you built a column of explosive, placing the cargo at the top, and then
> > ignited the bottom what would happen?

> A *real* rough estimate:
>
> If you put light plate on one end of a block of explosive and initiate the
> other end, the highest speed the plate can reach is the same as the speed
> which the detonation products expand into the surroundings.  This is about
> 4 or 5 km/s.  So, that is the highest velocity your plate can achieve, but
> it will be obtained impulsively, at the instant the detonation reaches the
> plate.  Probably not what you had in mind, since any cargo will be
> destroyed (even solid metals).

This arrangement is routinely used in some types of materials research;
it's called a "flyer plate", and your figures for velocity are typical.
The usual application is to accelerate a flat slab of material to high
velocity, then let it slam into another flat slab of the same or different
material, generating extremely high pressures and temperatures at the
collision plane.  Measurements of the temperature and compression
(density) give "equation of state" data for high temperatures and
pressures.

There are ways to get higher velocities with conventional explosives.  One
is a multistage flyer plate, in which a heavy flyer plate accelerates a
lighter one through an intermediate compressible medium (think of a
bowling ball with velocity v hitting a stationary pingpong ball, which
accelerates to 2*v).  Another is a shaped charge, which can generate a jet
of metal with a velocity well over 10 km/s.

There have been concepts for rockets which use a series of small
detonations rather than one large detonation or a continuous burn.  They
are easier to cool (think piston engine vs. turbine), potentially more
efficient, and much more efficient when operating into a high back
pressure (say, in a Jovian atmosphere probe).  Look for references to
"detonation wave propulsion".  It is possible to get efficient thrust from
such detonations without any nozzle, by making the detonation scale length
small compared to the engine diameter.  This was the principle behind the
pulsed laser-supported-detonation wave (pulsed LSD wave) engine for laser
launch.

Jordin Kare

Jordin T. Kare Technical Consulting
(510) 735-8012    jtkare@ibm.net