fred@inuxc.UUCP (Fred Mendenhall) (11/16/84)
I would like to thank those of you who responded to my mass driver
question. The reply that I found the most interesting was from
Keith Lofstrom. His analysis clearly ignores atmospheric friction and
conversion losses, yet I'm sure that is how the 60 cents per pound
number was originally calculated. (AT that price even I could afford
to get away from it all)
Fred
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
In reply to your news message ---
Cost to escape:
One pound = 0.454 Kg
Escape Velocity = 11,000 m/s
Energy per pound = 1/2 * m * v^2 = 0.5 * 0.454 * 11000^2 Joules
= 27.4 M Joules
1 Kilowatt-Hour = 1000 Watts * 3600 Seconds = 3.6 M Joules
Energy per pound = 27.4 M / 3.6 M KWHr = 7.63 KWHr
At 4 cents per KWHr (Pacific Northwest) that's 30.5 cents per pound to escape.
At 8 cents per KWHr (NYC?) that's 61 cents.
The how, of course, is just an engineering detail...
Keith Lofstrom
uucp: {ucbvax,decvax,chico,pur-ee,cbosg,ihnss}!tektronix!vice!keithl
CSnet: keithl@tek
ARPAnet:keithl.tek@rand-relayarlan@inuxd.UUCP (A Andrews) (11/16/84)
[A wee line for the wee folk...] Fred & et al: Keith Lofstrom's article about the electromagnetic launcher appeared, I believe, in the mid-December '83 ANALOG. He is now looking for backing and interested/competent folks to help build a working model. I met him at LaCon II and he's quite sincere. (Have a go at it Fred; just drop me a [long, strong] line when you guys get away from it all...) --arlan andrews
jlg@lanl.ARPA (11/21/84)
There were two estimates of the acceleration necessary for an EM launcher to work: 92 g and 1000 g. I'm not going to argue which is right since I can't think of subjecting any object to those forces except raw materials. To manufacture something which could take that kind of acceleration would either cost too much or add weight to the object just to strenghthen it. Sending only raw materials into space would solve this problem (manufacture what you need in space). I still don't know what kind of vehicle (to put the raw materials into) could withstand the forces. Seems like the vehicle itself would account for the lions share of the launch weight.
henry@utzoo.UUCP (Henry Spencer) (11/27/84)
> There were two estimates of the acceleration necessary for an EM launcher > to work: 92 g and 1000 g. I'm not going to argue which is right since > I can't think of subjecting any object to those forces except raw materials. > To manufacture something which could take that kind of acceleration would > either cost too much or add weight to the object just to strenghthen it. > Sending only raw materials into space would solve this problem (manufacture > what you need in space). I still don't know what kind of vehicle (to put > the raw materials into) could withstand the forces. Seems like the vehicle > itself would account for the lions share of the launch weight. Not at all. This sort of acceleration may sound formidable, and there are a good many things which could not travel via such a launcher, but it's not as bad as you suggest. Back ten or fifteen years ago, there was a small research project called HARP (High Altitude Research Project), a joint US-Canada effort. It was doing upper-atmosphere studies, using a most unusual method to get its instrument packages to high altitudes: firing them out of cannons! I believe HARP reached an altitude of 75 miles with one package, fired out of a 16-inch gun with a tremendously long barrel (two WW2 battleship guns end-to-end, I think). The packages had to be, uh, sturdily built, but there were no insuperable difficulties involved. The accelerations involved were tens of thousands of Gs. If you want a more modern example, the Copperhead missile is fired from a six-inch gun. It has non-trivial laser-homing electronics and optics on board. My recollection of the articles I've seen on its design is that care was necessary, but the result doesn't look overly outlandish. Remember that human beings, one of the more fragile payloads of interest, have taken 50+ Gs briefly without serious injury. The accelerations ARE probably too high for humans, but should not be a serious problem for many types of cargo. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
jlg@lanl.ARPA (12/01/84)
> > If you want a more modern example, the Copperhead missile is fired from > a six-inch gun. It has non-trivial laser-homing electronics and optics > on board. My recollection of the articles I've seen on its design is > that care was necessary, but the result doesn't look overly outlandish. > > Remember that human beings, one of the more fragile payloads of interest, > have taken 50+ Gs briefly without serious injury. The accelerations ARE > probably too high for humans, but should not be a serious problem for > many types of cargo. The key word in the above message is 'briefly'. The longer an instrument, device or person is subjected to the high loading, the more likely that permanent damage will occur. Humans may indeed be able to survive very short encounters with ~50 Gs, but long (10-60 seconds) exposure to just 15 Gs usually results in long term disability or worse. Even well built equipment would break down fairly quickly under the proposed 100 to 1000 Gs of these E/M mass drivers. Remember, the proposals are for tens of seconds at 100 Gs or several seconds at 1000 Gs. The cannon launched equipment previously mentioned only had to withstand the accelerations for times on the order of microseconds or at most milliseconds. I once had a fairly high quality 'shock resistent' mechanical watch which was advertised to be able to take shocks of up to 100 Gs (which corresponded to dropping it on concrete from ceiling level). I'm sure it couldn't really have survived 100 Gs for any period exceeding a few milliseconds though. 100 Gs is zero to 60 mph in .028 sec, during which time the unfortunate race driver would travel two and a half feet (He's really plastered on the seat). 100 Gs accelerates an object to 200 mph in less than .1 second, during which time the object travels about 27 feet. Anyone who has ever seen the results of an aircraft hitting trees and stopping within 27 feet knows the type of damage this kind of acceleration (or deceleration) can cause. And the longer something is subjected to these forces, the worse it gets.
jlg@lanl.ARPA (12/01/84)
> > 100 Gs is zero to 60 mph in .028 sec, during which time the unfortunate race > driver would travel two and a half feet (He's really plastered on the seat). > 100 Gs accelerates an object to 200 mph in less than .1 second, during which > time the object travels about 27 feet. Anyone who has ever seen the results > of an aircraft hitting trees and stopping within 27 feet knows the type of > damage this kind of acceleration (or deceleration) can cause. And the longer > something is subjected to these forces, the worse it gets. My mistake! This distances in the example above are off by a factor of two. Zero to 60 at 100 Gs is only ~1.25 feet, 0 to 200 mph is ~13.5 feet.