fred@inuxc.UUCP (Fred Mendenhall) (11/08/84)
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
eder@ssc-vax.UUCP (Dani Eder) (11/12/84)
> I heard the end of a segment on NPR this morning where > > 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. > > 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 velocity for circular orbit at 296 km (the nominal Shuttle orbit) is 7728 meters/second. The kinetic energy of a payload moving at this velocity is (1/2)(mass*velocity*velocity). If you divide by mass, you have per kilogram energy requirements. This is 29.861 MJ/kg. Now add the potential energy of raising a kilogram from ground to 296km, which is (acceleration of gravity*height)= 2.903 MJ/kg. Total is 32.764 MJ/kg. One kiloWatt-hour(kWh)= 3.6 MJ, so we have 9.1 kWh/kg. Around here (Pacific Northwest), electric rates are 3.5 cents/kWh, so that's 32 cents/kg, or 14 cents/pound. Since you have drag losses going through the atmosphere, inefficiencies in the accelerator, and payments on the money you borrowed to build the accelerator, 65 cents/lb is in the right ballpark. Note that to make it pay off, you need to have a lot of traffic. An acclelerator is like an oil pipeline, efficient but high volume. As for acceleration required, a=(velocity*velocity)/(2*distance). So if you have 20000 meters to accelerate in (as in the west slope of Hawaii Island) and you want a muzzle velocity of 6000 meters/second, which is 3/4 orbital velocity, then a=900 m/s*s= 92 g's. You can use a small rocket to make up the remaining velocity to orbit. Going at less than orbital velocity reduces the drag problem, and launching off Hawaii gets you up to 12000 feet at the muzzle, which helps because you skip the thickest part of the atmosphere. To further reduce air drag, you make your vehicle long and thin, like a telephone pole. Dani Eder / Boeing Aerospace Company / ssc-vax!eder / (206)773-4545
menageri@mit-eddie.UUCP (The Menagerie) (11/13/84)
In article <1062@inuxc.UUCP> fred@inuxc.UUCP (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 > >
menageri@mit-eddie.UUCP (The Menagerie) (11/14/84)
In article <1062@inuxc.UUCP> fred@inuxc.UUCP (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!) ps i'm sorry about the bad try. i'm new here, please bear with me. thanks.
al@ames.UUCP (Al Globus) (11/20/84)
> > 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 > > I don't know the exact figures, but the cost of fuel for the shuttle is also very small per pound of payload. The bulk of the cost of space systems is in the engineering and manufacture, not fuel.