[extropy-chat] Space elevator numbers III

[Keith Henson]

At 04:25 PM 2/15/2007 -0800, you wrote:
>On Thu, 2007-02-15 at 17:13 -0500, Keith Henson wrote:
> > Yep.  Prices have to come down to cents per kg from thousands of dollars a
> > gram.  But nobody has yet given a serious look at the iron process, which
> > looks like (if it works) would cost a few cents per kg to make nanotubes.
>
>How well does the iron process do in terms of flaws in the fiber? The
>last presentation I saw on carbon nanotubes was that this was the crux
>of the problem.

Who knows?  It looks good but has not been tried yet.

> > This puppy is sized at 2000 tons per day capacity to GEO, with the ability
> > to double that in 100 days.  The Saturn 5 could put maybe 50 tons in
> > GEO?  You thinking about 40 of those a *day*?
>
>Sure, the only why not is $$. If the rocket industry can deliver
>reusable once-around launch vehicles (like the USAF is asking for), you
>are looking at 10 tons/vehicle per mission to LEO, mission duration plus
>turnaround at 4 hours, so 6 per day (3 shifts).

Ok, 200 launches a day for the SPS parts.  Ignoring mass for the tugs, 1000 
launches, 10,000 tons will build a 5 Gw power sat.

LOX-Hydrogen for the fuel I presume?  What mass ratio?  Let me assume 95% 
and that the payload fraction is half the dry weight.  So lifting ten 
thousand tons will take 400,000 tons of propellant.  Give me real numbers 
and I will recalculate.

Ignoring liquefying the gases, what does it take to electrolyze 400,000 
tons of water?

http://www.stardrivedevice.com/electrolysis.html

(a) 1 kWh (kilowatt-hour) equals 1,000 J/sec x 3,600 sec = 3.6 million 
joules;

(b) 237.13 kJ/mole ÷ 3.6 MJ/kWh = 0.06587 kWh/mole;

400,000 tons of water Google tells me is 362 873 896 000  grams or 
20159660889 moles.  Which would take 1,327,916,863 kwh to electrolyze.

or 1,328 Gwh or 55 Gw days.  Given various factors like electrolysis 
efficiency it would probably take about 100 Gw days (20 days for a 5 Gw 
power sat) to pay back the energy lift cost.

That's not actually bad, but you are up against a *one* day energy payback 
for the space elevator.

>Allow a few vehicles out
>at any time for maintenance, so say 40 launchers. Probably 120 LEO-GEO
>tugs. I think that puts the whole operation on par with an airline.
>Launchers and tugs have a cost to build in line with airliners. So, the
>capitalization required is doable, now. That leaves us with a practical
>technology problem, which I would submit is much easier than the
>practical technology problem(s) of a tether.
>
> >  This thing runs on electric
> > power in the high 90 percent efficient.  Is there any way for rockets 
> to do
> > that?
>
>I have always been under the impression that electric motors are much
>less efficient than chemical motors. Am I not recalling correctly, or
>are you talking about a different efficiency rating, or something else?

Electrical power in to mechanical power out is typically 95 % or better for 
large electrical motors.

http://www.energyexperts.org/energy_solutions/res_details.cfm?resourceID=3823&keyword=cheap&sector=All

Keith