Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.space Subject: Re: Terraforming vs. Space Stations --> - (nf) Message-ID: <3501@utzoo.UUCP> Date: Tue, 31-Jan-84 17:56:20 EST Article-I.D.: utzoo.3501 Posted: Tue Jan 31 17:56:20 1984 Date-Received: Tue, 31-Jan-84 17:56:20 EST References: <2319@fortune.UUCP> Organization: U of Toronto Zoology Lines: 17 Heinlein's catapults in "The Moon Is A Harsh Mistress" are properly and correctly called "catapults", not "mass-drivers". The distinction is that a mass-driver uses recirculating buckets, so that the moving part of the magnetic system is not ejected along with the payload. This was O'Neill's key invention, which nobody had thought of before. Heinlein's catapults are probably unworkable, in fact. The problem is that they are linear induction motors. An induction motor is about the best you can do if the moving part of the magnetic system can't include things like coils, but induction motors do not scale well to large sizes and high accelerations. Nobody is seriously considering induction motors for space propulsion nowadays. O'Neill mass-drivers are linear synchronous motors, which work *much* better but do require the moving part to have a strong magnetic field that they can push/pull against. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry