From: "Andrew Higgins" <higgins@mecheng.mcgill.ca>
Newsgroups: sci.physics,sci.physics.electromag,sci.space.tech,
	rec.arts.sf.science
Subject: Re: Orbital cannons (was: Re: Gerald Bull)
Date: Sun, 13 Feb 2000 03:36:08 GMT

Bill Bonde <stderr@mail.com> wrote in message
news:38A5F7CA.F460DC48@mail.com...
>
>
> Allen Thomson wrote:
> >
> > In article <Fpts39.BoC@spsystems.net>,
> > Henry Spencer <henry@spsystems.net> wrote:
> >
> > >
> > >Many gun/catapult schemes run into a fundamental difficulty:  it's
> > >hard to fire something out of the atmosphere with enough horizontal
> > >velocity that it only needs one rocket kick stage,
> > >
> >
> > An excellent point that needs to be FAQified for those who are
> > learning about launchers: most of the velocity an ordinary satellite
> > launcher needs to attain is *horizontal* (parallel to the ground).
> > Going up is only needed to get out of the draggy air. Getting into
> > orbit needs 7500 m/sec of horizontal velocity; just getting above the
> > sensible atmosphere isn't nearly as hard, as witness the bigger
> > sounding rockets, which don't put anything into orbit but do reach
> > orbital altitudes.
> > 
> > There are various somewhat academic exceptions and qualifications to
> > the above, but it's good enough to start with.
> >
> Balloon floats up to 135,000 feet or as close to the edge of the
> sensible atmosphere as possible. Attached cannon fires projectile up a
> bit and horizontal. Shaped charge on projectile explodes sending
> sub-projectile payload into orbit. If you don't think this quite gets
> the velocity there, than a sub-sub-projectile is used.
>

A shaped charge is easily capable of launching a projectile to
orbital velocity.  Conventional shaped charges have jet velocities
of 10 km/s, and I have seen some recent Russian work on ceramic-
lined cylindrical shaped charges with velocities up to 12 km/s,
with potential theoretical velocities from using alumina or boron
nitride of 20 - 30 km/s.

Unfortunately, there are no good ideas for making a useful satellite
out of a jet of liquid metal (or ceramic).  These are very useful
devices, however, for simulating orbital debris and micrometeoroid
impacts on real satellites.
--
   Andrew J. Higgins            Department of Mechanical Eng.
   Assistant Professor          McGill University
   Shock Wave Physics Group     Montreal, Quebec CANADA
   higgins@mecheng.mcgill.ca