Conference 7.286::space

24.0. "Electromagnetic Launchers" by PYRITE::WEAVER () Thu Nov 15 1984 10:05

Path: decwrl!decvax!genrad!mit-eddie!menageri
Subject: Re: Sixty Cents a Pound?
Posted: Tue Nov 13 19:19:54 1984

Keywords: mass drivers,electromagnetic launchers

In article <[email protected]> [email protected] (Fred Mendenhall) writes:
>
>	I heard the end of a segment on NPR this morning where
>someone was making the following claim:
>
>	It costs about  $1000.00 to accelerate a pound of material
>	to escape velocity today. However if we were to switch to
>	electromagnetic launchers (mass drivers?) the cost of
>	electricity required to accelerate a pound of material to
>	escape velocity would be $0.65.
>
>	I have no idea who was talking, but the economics, if they are
>even close to being right , are interesting. Do these numbers sound
>reasonable to the space wizards on the net or are they science fiction.
>What are the problems with electromagnet launches, i.e. payloads must
>be designed to withstand 3000000G and must be launched in a restricted
>direction, etc.etc.?
>
>
>					Fred Mendenhall
>
>


the figure of about $.60/lb is accurate for the cost of the electricity
alone, but will not pay for the necessary machinery to make it work.
studies have been done, however, that indicate that it could be
practical to build an EM launcher IF we want to send large masses of
material into space (thousands of tons per year for several years). an
article by henry kolm, peter mongeau, and fred williams, then of the
francis bitter national magnet lab here at mit gives the following
numbers:(actually calculated by peter mongeau and presented at the
annual propulsion meeting of the american institute of aeronautics and
astronautics in las vegas in june 1979)

initial velocity		12.3 kilometers/sec
final velocity			11 km/s (escape velocity)
vehicle mass 			1000 kg
ablation loss (carbon nose)	3%
acceleration			1000 gee
accelerator length		7.8 km (4.85 mi)
average power (for 1.26 s)	60 gigawatts (6e10 watts)

the costs for the launcher were listed as:

accelerator:
	cu drive coils ($4/lb, 1.4 million lbs)		5.6 M$

	steel restraining shell
	($4/lb, 4.2 Mlb)			       16.4 M$

	reinforced concrete foundation
	(4 cu. yards/meter, $50/cu. yd, 31,000 cu.
	yds)							1.2 M$
						      _________
						       23.6 M$

energy storage costs:

	fast discharge units including switching
	at $0.15/joule for 76 gigajoules (the initial
	kinetic energy of the projectile)		11.4 G$

operating cost:

	100 GJ/launch at $.05/kW-hr		   $1400/launch
						    (about $.63/lb)

amortization schedule

	$12,000,000,000 loan at 5% over 20 year
	write-off				   $1 billion/yr

	at $10/lb launching fee, 121 launches/day are required, or one
launch every 12 minutes.

as an example, building one solar power satellite per year would take
about 200 launches per day (~75,000 tons per year) if all materials
weere to come from the earth.

the above was proposed as a reference design only. it is possible to
scale the launcher to fit other design goals, if you want. here are some
relationships (from basic physics, so they are the ideal case, season to
taste depending on how optimistic you are):

acceleration	a = v**2/2l

force		F = mv**2/2l

energy 		U = mv**2/2

duration	t = 2l/v

power
	average	P = mv**3/2

	maximum	P = mv**3

where
m = mass
v = launch velocity
l = launcher length
these assume a constant acceleration launcher


as you could tell from some of the numbers above, the launcher is going
to be BIG and thus won't move, thus restricting our choice of initial
orbits. it is of course possible to put rockets on each payload to move
it into another orbit, but i am not sure if this is practical (i'm not
an aero/astro major.) if it isn't, i'd be happy to be told this.

it has been suggested that the launcher be built on an east-facing slope
of a mountain near the pacific intertie in northern california (the
largest existing dc power line in the us.) this suggests the use of one
or more of the following mountains for the site of the launcher:

name		height		distance to intertie
hood		11,325 ft	30 mi
whitney		14,500		50
st helens	 9,670(?)	70	[i don't think so - gem]
shasta		14,162	       120
lassen		10,457		90
ingall		 8,370		70

a bit of history before i leave: the first EM launcher to have been
built seems to have been professor edwin northrup's (then of princeton
university) in 1937. it threw projectiles across the princeton campus.

the germans apparently built one to launch guided missles, but because
it used induction badly, the missles melted from current induced in
their skin before they reached usable velocities.

arthur c. clarke first proposed using EM launchers for space
applications in 1950, and robert heinlein used them in his stories "The
Man Who Sold The Moon" and "The Moon Is A Harsh Mistress" (1951 and
1968)

i have more information from a class in EM launchers that i took last
year, if anyone is interested, and i have the time.

					greg

usenet:		!genrad!mit-eddie!menagerie
arpanet:	i'm not sure to this account, but
		g.mcmullan%mit-eecs@mit-mc should work, i'm told.
		(that is better for me, as i log on there more often)
us mail:	500 memorial drive
		cambridge, ma, 02139
phone:		(617) 225-8942 (good luck!)

    Has anyone looked into the economics of laser-launch ?
    This is a simple ablative cone, with a payload on top, with a large
    ground-based laser firing pulses into the cone. While the target
    is in atmosphere, the system works like a pulse-jet, when in vacuum,
    there is enough ablation from the "BELL" or "cone" to provide reactive
    mass.
    On the MASS Driver, it's feasable, but you need a long, high ridge
    (as close to the equator as possible), facing east, and as high
    as possible to lessen losses by air resistance.
    
    By the way, I wonder if it's more possible using the new
    superconductors as either the driver coil or in the target. 
    It'd be more efficient, but more expensive to build.
    
    David Otten, UCG (U.K)
    

    	See Topic 247.