[ExI] Power satellites

Keith Henson hkeithhenson at gmail.com
Thu Apr 23 16:56:55 UTC 2009

On Thu, Apr 23, 2009 at 6:18 AM, Dan <dan_ust at yahoo.com> wrote:
> --- On Wed, 4/22/09, Keith Henson <hkeithhenson at gmail.com> wrote:
>> On Wed, Apr 22, 2009 at 6:20 AM, Dan
>> <dan_ust at yahoo.com>
>> wrote:
>> >
>> > --- On Tue, 4/21/09, Keith Henson <hkeithhenson at gmail.com>
>> wrote:
>> >> Even if moving cable space elevators are *never*
>> built,
>> >> they are still
>> >> useful as the gold standard for space transport.
>> >> $0.15 for the energy
>> >> and a share of the capital to put one up.
>> >
>>> I would not use a hypothetical, untested technology as
>> my "gold standard for space transport."
>> "Gold standard" in this context means, "Yah can't do
>> betta:"  I.e., it
>> is as the limit.
> I think you could: nuclear pulse propulsion from the surface.  I haven't run the numbers, but there'd be no need for the huge capital investment of a space elevator AND most of the technology for it'd be off-the-shelf.  No need to develop nanotech further.  In fact, my guess is one could do nuclear pulse propulsion with decades old tech.  (Of course, there's the problem of pollution.)

Nuclear pulse is a reaction technique.  All reaction engines are
rotten at energy efficiency--which hardly matters with nuclear energy.

Why not run the numbers?  A year at 1.5 GW is ~48 million GW-sec.  A
GW-sec is 1/4 ton of TNT, so the energy consumed by a space elevator
lifting 8700 tons to GEO in a year would be about ~12 MT.  The
literature is not very clear on the subject, but a thousand 100kt
bombs would be 100 MT.

>>> All the numbers on their cost and efficiency are based
>>> on speculation.
>> No, they are based on utterly sound physics.
> Until you've built and tested one, you can't know the costs -- which are economic -- or the physical efficiencies of an actual space elevator.  Were this not the case, there would never be any need for quality assurance and quality control; everything would simply worked as conceived.  You can, of course, make guesses, but, looking at past large scale engineering projects -- especially, ones for space travel -- it seems to me these guesses are often way off the mark.  (One can make similar claims about nuclear pulse propulsion, though it has a longer history and actual tests were done years ago with much of the underlying technology.  Certainly, nuclear weapons have been extensively tested.:)

My claim, space elevators, like common building elevators, would be
upwards of 90 % efficient in converting electrical energy into
potential energy.  If your claim is that you don't have any confidence
in this figure, why?  I.e., energy is conserved, where is going to go?

To be sure, when working on ambitious projects with a lot of R&D there
is uncertainty in the cost.  But that's not the reason for quality
control.  You need quality control on railroad axles.  For the most
part stuff does work as conceived.  But "as conceived" may include
proper heat treatment.  I remember a case of a carrier aircraft with
fold up wings where the hinge pins were not properly heat treated.
The wings fell off, fortunately not in the air.

The space shuttle/space station went way over budget, but that can
mostly be traced to political decisions that forced underestimate of
the cost.  There is a lot of commonality with aircraft design and
that's fairly well understood.

You might note that the Three Gorges dam came in under budget.


More information about the extropy-chat mailing list