Re: More Space Elevator news

From: Pete Lynn (pete_at_peterlynnkites.com)
Date: 07/13/04 

Date: Tue, 13 Jul 2004 22:04:55 +1200

"John Schilling" <schillin@spock.usc.edu> wrote in message
news:ccv5r7$69o$1@spock.usc.edu...
>
> Did you really just use "mature industry" and "quickly approach" in
> the same sentence? Try again.

Yes I do, why should I try again?

Given reasonable flight rates, I expect it would only take a couple of
years for rockets to achieve $100/kg, a couple more to reach the around
$10/kg fundamental limit. A couple of years being the natural
development time and generation spacing of such private space
transports. Once the high flight rate hurdle has been passed, (a
seriously big hurdle), I would expect this to almost become an economic
certainty. I can not really see how such a free market could go any
other way, those are the base costs, and the only thing that could hold
it back would be external regulation, (the technology is not, nor would
the economics).

> Or not, but *do* recognize that however popular the whole, "three
> times fuel cost", mantra is here, it is an *extremely* crude and
> simplistic sort of analysis, that is really only relevant on a
> generational timescale and bound to disappoint anyone here
> expecting to see such costs in their own natural lifetime. For that,
> you add another zero or so.

Yes it is somewhat simplistic, though actually relatively accurate,
would you prefer I used the highly detailed cost estimation methods of
the shuttle? Placing the cart along way before the horse? In such
unknown circumstances comparative cost analysis tends to be of some use,
as in some regards it is more directly based on real world figures.

A mature space transport, compared to a half way round the world
passenger jet, has similar drymass as a proportion of payload, but
probably requires around ten times the fuel per trip. However, assuming
similar turn around times, can make almost ten times as many trips in
the same time, hence only a tenth the drymass is required for the same
payload flow rate. Now drymass cost per kilogram for the space
transport is probably a bit higher, as would be maintenance costs and
the like. All up, I expect the costs of the space transport and
aircraft to be similar, excepting the different fuel costs.

If memory serves, a common metric for passenger aircraft is 20% fuel,
20% cost of capital, 20% maintenance, operating, etc., the rest
passenger related costs. Similarly applying this metric to the space
transport, accounting for the tenfold increase in fuel, (say $5/kg),
gives a total cost of $7/kg to LEO. Obviously this is just a rough
ballpark figure.

> Yes, in the same way and for the same reason that cable dry mass
> is orders of magnitude cheaper that airplane dry mass even when
> they are made of the same basic materials.

Passenger aircraft drymass typically costs around $1000/kg, A mature
space transport might be a couple times this, but no more. Somehow I do
not see a CNT beanstalk costing much less than this, though I am willing
to be convinced otherwise.

> But why are we talking about dry mass? Your formula for cost
> analysis is based on energy cost and a concept-of-operations
> multiplier. Which, as I have said, is crude and simplistic but
> perhaps reasonable in the long run.

Fuel cost serves to set a fundamental base cost, it reveals that energy
cost is not a major cost determinant until around $10/kg to LEO. Hence
the beanstalk has to come in at less than this to be competitive. A
$100/kg beanstalk would not be competitive with similarly advanced space
transports, it would not be viable on a level playing field. The point
I was originally trying to make.

> OK. The energy requirement to lift a kilogram to GEO along a
> beanstalk is a hair over 48 megajoules/kilogram. Assuming 50%
> efficiency in the power beaming and 50% efficiency in the drive
> system, that's 53 kW-h/kg at the wall plug.

A rotating tether does not necessarily have to sustain any of these
inefficiencies, hence they can be far more energy efficient than a
beanstalk, (not to mention much easier, lighter and lower cost).

>Wholesale price of electricity in Brazil, one reasonable location for a
> beanstalk terminus, is $0.024/kW=h.
>
> A mature beanstalk launch industry will eventaully approach 53 *
> 0.024 * 3 or $3.82/kg to GEO (based on energy cost and railroad
> type operation).

This makes a great many assumptions on the cost and operation of a CNT
beanstalk that I would not be in the least bit comfortable with. A CNT
beanstalk is like a transcontinental railway made entirely of gold which
only operates once a month. Sure it would be more energy efficient than
a 747... Aircraft cost metrics are not even close.

> If GEO is accessible at $3.82/kg by beanstalk and LEO costs
> $20/kg by rocket, or for systems you and I might live to see
> $38.20/kg to GEO and $200/kg to LEO, who on Earth do you
> think is going to be paying the extra 423% for the LEO service and
> why?

Sure you do not wish to place a decimal point after that 423%?
I can not agree with any of this. How much do you think CNT will cost?

Pete.

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