From: jdunning@picasso.Princeton.EDU (John Alan Dunning)
Subject: Re: Potential Launch Technologies (was Re: Wrecking a Planet)
Originator: news@nimaster
Organization: Princeton University
Date: Wed, 20 Jan 1993 00:32:17 GMT

In article <1993Jan19.182118.29076@julian.uwo.ca> jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll) writes:
>In article <rwallace.727448294@unix1.tcd.ie> rwallace@unix1.tcd.ie (russell wallace) writes:
>>Having a high muzzle velocity isn't the problem; the problem is the
>>atmospheric friction at 8 km/sec. What exactly are gas guns and laser
>>propulsion, BTW?
>
>	One of the sci.military folks could give a detailed description,
>but as I understand it, a light gas gun uses (I think) hydrogen as the
>propellant, to get fairly gross muzzle velocities. Using Big Guns to lob
>material to orbit is an old, if usually ignored idea. Back in the 60s,
>Gerald Bull worked on the HARP project, whose goal was to build a gun
>which  could fire shells into orbit (Where their orbit would be circularised
>using on-board rockets). At the time, Bull claimed he could cut launch
>costs to  15% of the rockets then used.

Bull also started working on a supergun for George Bush's favorite
person in the whole world, Saddam Hussein.  He wanted to rain chemical
weapons on Israel while sitting in Baghdad.

>	Actually, the HARP project makes for interesting reading. Fairly
>delicate equipment was lofted at least 80 km, and on Nov 18, 1966,
>HARP set the record (which I don't believe has been broken) for a
>shell fired  from a cannon  (180 km). Neat stuff, and one has to wonder
>what the ultimate technical limits of cannon technology  are (As opposed to
>political  and funding limits, which is what killed HARP). 

Politics is also what killed Gerard Bull. 8-)  As to exactly who put a
bullet in the back of his head as was leaving his apartment, there are
plenty of theories....

Another type of gas gun-type launching system I've read about consists
of two long pipes joined at a right angle.  The payload sits at the
junction of the pipes, in front of a piston.  The payload's pipe is
evacuated (not a very hard vacuum, but enough to reduce air friction
inside the pipe).  The other pipe is filled with some sort of gas
(hydrogen? air? not sure).  A large plug is fired down this pipe
towards the right angle joint, compressing the gas and accelerating
the payload.  The payload breaks through a thin plastic covering on
the end of the pipe (which is maintaining the vacuum) and is then up,
up and away.  At least in theory.  The system works now, but to reach
orbit they need much longer muzzles, which are very difficult to keep
perfectly straight, especially with repeated firings.  

The friction at 8 km/s is certainly going to be tricky to handle, 
but if you've got the materials to build a gigaton habitat, is air
friction really going to be much of a problem for you?

>	Both methods are old news. Perhaps if you were more familiar
>with such ideas, your view on long term launch costs might change. Given
>that you  *are*  unaware of two fairly old  ideas makes it  difficult 
>to  place much  faith in your conviction that launch costs from Earth
>are bound to be relatively high forever.

Before you can really start building habitats, you've got to have a
launch system which is capable of putting payloads into earth orbit
cheaply, regularly and safely.  Not that you're going to haul the
building materials up from the ground, but by the time you're
seriously thinking about building huge space colonies, you're going to
have a very large and well-established space industry.  And you won't
achieve that until you've got a relatively cheap earth-to-orbit launch
system. 

John