knudsen@ihnss.UUCP (11/09/84)
<meteorite dust> Subject: Re: Sixty Cents a Pound? References: <1062@inuxc.UUCP> The main restrictions on electromagnetic mass drivers are: (1) the object must contain quite a bit of iron (of course) (2) you really should launch above/outside/without an atmosphere. On Earth, the projectile would have to survive 3+ miles of our air, much more if not launched straight up, and EXIT our air at escape velocity, meaning a tremendous initial velocity. Aside from the ablative heat shielding required (which you have to accelerate along with the rest of the load, even tho it never leaves our planet), the G forces of DEceleration encountered after leaving the electro-gun would be almost as bad as the acceleration inside the launcher. Of course, if the object is all iron, the parts are accelerated evenly and little stress occurs during acceleration. Anyway, most advocates of mass drivers are talking about installations on the Moon, asteroids, L5 space colonies, etc. A GOOD possibility: a mass driver in low earth orbit, to shoot things up to geo-synch, to moon, Mars, .... mike k
henry@utzoo.UUCP (Henry Spencer) (11/11/84)
> The main restrictions on electromagnetic mass drivers are: > (1) the object must contain quite a bit of iron (of course) > ... You are thinking of induction motors, which are essentially obsolete as electromagnetic accelerators. Nowadays the favored accelerator technology is the linear synchronous motor, which requires magnetic coils on the accelerated object. And by the way, a "mass driver" is a specific type of accelerator in which the payload is carried by a bucket for acceleration, and the bucket is then decelerated for re-use while the payload continues on. This permits accelerating small payloads without throwing away a costly magnetic-coil system for every payload. "Mass driver" is **NOT** a generic synonym for "electromagnetic catapult". Electromagnetic catapults have been around for quite a while. The mass driver, with its recirculating buckets, was invented by a specific man: Gerard O'Neill. He could have patented it, and perhaps should have. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
ems@amdahl.UUCP (Edward Michael Smith) (11/12/84)
> The main restrictions on electromagnetic mass drivers are: > (1) the object must contain quite a bit of iron (of course) I thought that only the mass driver bucket had to be metalic and that one could use induced electromagnetic force to create a magnetic field in the bucket. No need for iron... Was I mistaken? I remember a demonstration from high school physics where a coil induced a magnetic field in an iron rod. Aluminum rings stacked on the iron rod would head for the ceiling. Required a fluctuating magnetic field though. -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems The opinions expressed by me are not necessarily those of anyone. (How can a company have an opinion, anyway...)