Re: beanstalks (was Re: Metallic hydrogen ...)

From: Henry Spencer (henry_at_spsystems.net)
Date: 06/09/04 

Date: Wed, 9 Jun 2004 23:14:45 GMT

In article <40c7645a$0$551$ed2619ec@ptn-nntp-reader02.plus.net>,
Ian Stirling <root@mauve.demon.co.uk> wrote:
>Rockets are currently higher than $1000/Kg.

And beanstalk launch costs are currently infinite (can't get there from
here using that technology). A proper comparison is apples to apples; for
example, if you propose to spend several billion on beanstalk development,
you should compare to spending the same amount on rocket development, and
if you propose a lean, efficient organization which doesn't have Boeing's
overhead rates, you shouldn't compare the results to Boeing-made rockets.

There are lots of people who think they can get to $1000/kg -- the current
guess for first-generation beanstalk payload costs, probably somewhat
optimistic -- for less than a billion dollars of development money.
That's an order of magnitude less than current estimates for the first
beanstalk. You could fund five of them for less than a beanstalk, and at
least one would probably succeed. (How credible are their estimates?
Well, as Jordin Kare put it a year or two ago in a slightly different
context: "they aren't Lockheed Martin, but neither are you".)

>There seems to be no theoretical reason why they can hit $1000/Kg (NASA
>seems to disagree, and hold it as one of their sacraments.

There is no theoretical reason why rockets cannot get stuff into orbit for
$5-10/kg. The only fundamental limit is that you need $3-4 worth of LOX
plus a cheap hydrocarbon (kerosene, propane, whatever) to get a kilogram
of dry mass into orbit, and some of the dry mass will be hardware rather
than payload, and there will be some overhead for wear and tear on the
hardware.

>$100/Kg is more or less the fuel cost for optimistic assumptions.

Not unless you use unnecessarily expensive fuels. Even today's designs
for SSTO RLVs -- SSTOs are fuel hogs, and current designs are only 15-20%
payload at orbit injection -- shouldn't cost more than $20-30/kg if they
burn LOX/hydrocarbon. Liquid hydrogen costs more but I don't think it
would push them to $100/kg. To go that high you'd need to resort to
hypergolics.

>For a tether, it can go to $.1 for optimistic assumptions.

Amortized over huge traffic volumes, yes, beanstalks unquestionably beat
rockets. (And the crossover point occurs somewhat earlier if you figure
in a cost for rocket emissions, like stratospheric water vapor during
ascent and nitrogen oxides during reentry, both of which are bad for the
ozone layer if flight rates get really high.) 

-- 
"Think outside the box -- the box isn't our friend."    |   Henry Spencer
                                -- George Herbert       | henry@spsystems.net

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