Space Elevators, was Re: [extropy-chat] good space shuttle article

[Jay Dugger]

On 8/3/05, Mike Lorrey <mlorrey at yahoo.com> wrote:
> 
> 
> --- Jay Dugger <jay.dugger at gmail.com> wrote:
> 
> > Probably time to change the subject line...
> >
> > On 8/3/05, Mike Lorrey <mlorrey at yahoo.com> wrote:
> > > Actually, I wouldn't mind riding a real bomb propulsion system.
> > Orion
> > > needs doing. Five moderate sized nukes could put an aircraft
> > carrier
> > > worth of cargo and spaceship into orbit. I think the trade off is
> > worth
> > > it.
> > >
> >
> > The statistic I remember from "Project Orion" is something like more
> > mass to orbit in the first flight than in every shuttle flight
> > combined.
> 
> Depends on the scale. Project researchers came up with several
> spacecraft sizes ranging from a few thousand tons up to 8 million.
> 

Good point. My copy's out on loan--this might have gotten covered there.

> >
> > > Space elevators are a penultimate system to develop, but we've got
> > to
> >
> > Next to last? What trumps an elevator?
> 
> Well this is open to debate. They say that ten bucks in electricity
> will get a person in orbit on a space elevator. Orion was estimated to
> be able to orbit cargo at 5 cents per lb (in 1957 dollars).
> 
> The ultimate is of course teleportation... ;)
> 

Okay, smart guy. ;)

> 
> >
> > Just how destabilizing would an SE prove? The first group to do it
> > gets a big advantage. See Edwards and Westling [152-155]. This seems
> > to depend on surprise applications. Deployment of a ribbon to Mars,
> > while long-term, (first SE + ~8 years), gets predicted. What
> > inevitable surprises do you all think might happen?
> 
> The problem with a space elevator is that it eliminates the ability to
> orbit anything in orbit below its center of mass for a long term. No

I don't think so. It rules out any orbits that cross its' exact
location; those get called collisions. If you've a mobile Earth-side
platform like a Sea Launch or a large oil platform, you get the chance
to avoid such strikes and purely terrestrial hazards such as
hurricanes. What effect motion might have on cable dynamics requires
math skills beyond mine. Remember the cable is long, but thin.

Stick a pin on the equator of a Mercator projection of Earth. Call the
whole shaft of the pin "restricted space." Look at what you have left
over. Yes, the pin goes outward a very long way, about 10E5 km. If
your scale gets big enough, this starts to look one-dimensional.
Enough hand-waving on that. I don't know orbital dynamics well enough
to argue this. (Where's Szabo?)

Ocean basing allows its own advantages. For instance, transfer cargo
directly from container ships to SE and vice versa. If the economics
work out you might even see super-container ships far too large for
any canal that transfer to go up a Pacific SE, orbital transfer to an
Atlantic SE, down that SE, and transfer back to a container ship.
Totally speculative, I admit. No worse than teleportation, however. :)

> ISS. No Hubble, No Bigelows Budget Suites, and IMHO it puts access to

I see your point and agree with it, but I think your counter-examples
lack strength. Each of these precedes or likely precedes a SE. The SE
would also enable superior replacements in each case. You don't need
ISS if you can build space stations that take advantage of the SE. See
Edwards and Westling [176-188]. Inflatables get a little discussion in
that section. Who cares about Hubble if you can also cheaply build
telescopes at L1 or out of the ecliptic altogether?

> space in a monopoly position for those with the capital to build one

Yes, it sure does. I don't think this makes a fatal problem. Again,
Edwards and Westling [144] estimate the first ribbon might cost
US$6.1E9. The second, about US$1.9E9. E&W[166] assumes an eleven-fold
improvement in cargo capacity for the third and fourth SEs: 13T to
140T. Costs still drop to US$5E9 and US$4E9. Eighteen billion dollars
is much money, but within the reach of large private companies. Heck,
double the numbers if you want. What do those new big oil platforms
cost? I want to make the point that the required capital drops over
time into the range affordable by large companies, not nation-states.

> and creates a massive barrier to entry for medium to small operators
> wanting private or commercial passenger space shuttles to LEO. SE is a

I disagree. The first few SEs would get built near the equator for
various reasons. Ballistic hoppers or spaceplanes would prove very
valuable in an air-transportation system that incorporates a SE.
Suppose you go up the SE a little ways, release, brake, and steer. How
long does it take you to get anywhere on Earth's surface? If it turns
out less than eight hours, then long-range air travel dramatically
changes: Origin to SE, SE up, release, de-orbit to Destination.
Spaceplanes might cover the "origin to SE" part.

I admit this does nothing for concentration of the system at a SE
choke point. If it turns into a problem, market forces might encourage
multiple elevators. You still end up with a concentrated system, more
like railroads than privately owned cars on highways. I hadn't
considered the effects on personal freedom. Does opening up the solar
system compensate for it? I could say so, but the physical arguments
for elevators apply to other planets too. So long as one goes down a
planet's gravity well for mass, an elevator offers some advantage. If
you stay in wells too shallow for economic elevator operation then you
avoid that concentration, and all its dangers. What remains for real
estate? The Trojans, the belt, the NEAs, perhaps some of the rest of
the Jovian system.

> statist solution, not just because of this, but because disposing of

Inherently statist? It requires a large concentration of capital, and
the first one might only happen through public-private partnership.
Nationalization seems a bigger risk, though.

> them once teleportation becomes reality will be problematic. I suppose

I don't think teleportation lies in the near-term, or possibly ever.
At least you seem to think it more likely than I do. Please give
references.

For argument's sake, let's assume Niven-style transfer booths. The
difference between any two cities on Earth turns into fifty cents
worth of energy. That's a big inivitation for governments to crack
down on the technology--free movement of people so fast that it
resembles an ideal gas expanding to fill a container. That aside, you
don't have interplanetary transport. A SE still lets you do momentum
transfer. [B&W94--Figure 7.1] Varying the release height of a payload
on the SE, you can fire it off for various destinations, just like
using a sling.

> simply detaching them from earth and adding mass to the counterbalance
> end would do to get it off earth? Where do you put it? You'd need to
> disassemble it in situ.
> 

What? Are you suggesting design for disassembly? :) You've got some
green tendencies, after all. Just good sense, really.

If you had to dispose of one, and I don't think you would for the
reasons above, I guess you could detach the ribbon's terrestrial
anchor first. Then, from a midpoint at GEO, start reeling in both
ends. Once done, deorbit the reels for atmospheric incineration. No
counterweight to dipose of--an extension of the cable is its own
counterweight, and that gave you a longer moment arm for momentum
transfers. Would this work? Perhaps you could do something clever,
like electrodynamic braking for the deorbit, or just reel in from a
spot other than the midpoint. Would you send a reeled-up SE into deep
space if you moved its center of mass above GEO? I just don't know.

Heck, just sell it to those folks too superstitous to teleport.

-- 
Jay Dugger
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