Space Elevator cars' shielding

Hi all

A major objection raised time-and-time-again (like a struck record really)
about humans going either up or down a space elevator is the radiation of
the Van Allen belts.

How much shielding do you need? Is the Mars Direct scheme of using your food
and water consumables as Rad-shielding going to be enough? Or do you need to
pack an iceberg?

How about doing what Mother Earth does and take along a Magnetic field? That
is why the VA belt is there in the first place right. They're charged
particles trapped by the Earth's magnetic field. Well take a couple of hoops
of reasonably decent conductors and spread them out at a couple of car
diameters once you're clear of the atmosphere and power up. If one magnetic
field can attract particles another (of the reverse polarity) can repel
them. It might be bad for a satellite 'downwind'.

Is this completely insane?

On a completely different subject:

How many people have you spoken to whose first reaction to hearing about the
elevator concept is: 'If this cable is strong enough to hold the station at
the top in place then I should able to bungee jump from there, right? How
long would it take me to reach the bottom?'

I know, I work with some REAL adrenaline junkies.

Regards
Frank Scrooby

"Frank Scrooby" wrote in message ...

How much shielding do you need? Is the Mars Direct scheme of using your food
and water consumables as Rad-shielding going to be enough? Or do you need to
pack an iceberg?

You would need quite a bit of shielding but the extra mass is not such
a problem for a space elevator car because (1) they are supported by
structure (wheels and the cable) and (2) they can be externally
powered. Moreover energy recovered from descending cars can be used to
power ascending cars (with a bit of extra energy fed in from an
external source) so the additional mass would only increase energy
requirements by a small amount.

How about doing what Mother Earth does and take along a Magnetic field? That
is why the VA belt is there in the first place right. They're charged
particles trapped by the Earth's magnetic field. Well take a couple of hoops
of reasonably decent conductors and spread them out at a couple of car
diameters once you're clear of the atmosphere and power up. If one magnetic
field can attract particles another (of the reverse polarity) can repel
them. It might be bad for a satellite 'downwind'.

I have heard it said that the massive hardware required to generate
the shielding field would itself be a good shield. I think the short
answer is that 100mm or so of water in a shell is sufficent.

How many people have you spoken to whose first reaction to hearing about the
elevator concept is: 'If this cable is strong enough to hold the station at
the top in place then I should able to bungee jump from there, right? How
long would it take me to reach the bottom?'

Jumping from the cable over most of its length will only leave you in
Earth orbit. There is a point (less than 10 thousand km up) where your
new orbit will intersect the earth. More like skydiving than bungee
jumping, I suspect.

I know, I work with some REAL adrenaline junkies.

No Kidding!

On Wed, 07 Jul 2004 21:09:36 GMT
Ian Stirling wrote:

Energy recovered from descending cars can be used to
power ascending cars (with a bit of extra energy fed in from an
external source) so the additional mass would only increase energy
requirements by a small amount.

Only for really, really large elevators.
For small (near term) ones, the mechanisms to beam the power around
are simply too expensive, and not very efficient.

I was thinking more in terms of conducting tracks, like a conventional electric train.

It's cheaper just to burn the power off as you come down on a heater, than to have the large payload reduced significantly.
Lasers/optics/cooling systems are heavy, not particularly efficiant
and power conversion from the motors is also not free.

It's going to be a long, long time until the electricity cost becomes
the dominant cost for an elevator.

True, but the distrbution cost is substancial over the distances involved in a space elevator. I am assuming that it is still expensive for ascending cars to carry all the energy they need for the trip to GSO, in which case some sort of external power source would be an advantage.
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

Michael Smith wrote:
On Wed, 07 Jul 2004 21:09:36 GMT
Ian Stirling wrote:

Energy recovered from descending cars can be used to
power ascending cars (with a bit of extra energy fed in from an
external source) so the additional mass would only increase energy
requirements by a small amount.

Only for really, really large elevators.
For small (near term) ones, the mechanisms to beam the power around
are simply too expensive, and not very efficient.

I was thinking more in terms of conducting tracks, like a conventional
electric train.

With conventional conductors, that's even worse.
The conductors end up vastly outweighing the rest of the cable.
Even room-temperature superconductors, with current carrying abilities
similar to liquid nitrogen ones won't really work, as they need to be
comparatively large.

The voltage can't be that high, or you risk arcing, which means the current
is very high.



It's cheaper just to burn the power off as you come down on a heater, than to have the large payload reduced significantly.
Lasers/optics/cooling systems are heavy, not particularly efficiant
and power conversion from the motors is also not free.

It's going to be a long, long time until the electricity cost becomes
the dominant cost for an elevator.


True, but the distrbution cost is substancial over the distances involved in
a space elevator. I am assuming that it is still expensive for ascending
cars to carry all the energy they need for the trip to GSO, in which case
some sort of external power source would be an advantage.

It's currently impossible for ascending cars to carry enough energy
(without using stages, or very high amounts of fuel (lots more than
payload)) without using nuclear.

"Frank Scrooby" wrote in message
...
Hi all

I don't think there is any chance of one actually being built. One major
storm, terror attack, or accident, and the whole thing comes tumbling down.

"Renee Keller" :

"Frank Scrooby" wrote in message
...
Hi all

I don't think there is any chance of one actually being built. One major
storm, terror attack, or accident, and the whole thing comes tumbling
down.

Please think carefully before posting, S.E. tend to fall up when broken near
the Earth end.

Earl Colbt Pottinger
--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

"Renee Keller" writes:

"Frank Scrooby" wrote in message
...
Hi all

I don't think there is any chance of one actually being built. One major
storm, terror attack, or accident, and the whole thing comes tumbling down.


Strangely, you are not the first person to think of this. A lot of good
work has been done on fault-tolerant tether design, the dynamics of the
system are such that if it is nontheless completely severed most of the
thing falls *up*, and the small fraction that falls down is too "fluffy"
to hurt anyone.

Retrieving the part that fell up and tying it back down would be an
operational nuisance, of course, but then that's why all the work on
fault-tolerant designs where cutting one cable doesn't break the
system.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

"Renee Keller" wrote in message hlink.net...
One major
storm, terror attack, or accident, and the whole thing comes tumbling down.

Uh, no it doesn't. It's hanging down from geostationary orbit, not
built up from the ground, so if it was broken only the part below the
break would fall (and then, only if it wasn't rigid enough to support
its own weight). It's possible that some terrorist could plant a bomb
high up and destroy the elevator that way, but it would be hard to do
with decent design safeguards and security precautions.

That's not to say that I think an elevator will be built in the near
future, but in the long run it seems highly likely, particularly if
there was ever a reason to want to get most of the population off the
planet in a decade or two (e.g. advance warning of a planet-killing
impact that couldn't be stopped).

Mark

On Mon, 02 Aug 2004 04:24:44 GMT, "Renee Keller"
wrote:

I don't think there is any chance of one actually being built. One major
storm, terror attack, or accident, and the whole thing comes tumbling down.

That's why we'll build two. Or six. The second one, built using the
first, will only cost 40% as much as it did. The sixth will be about
the cost of a B-2 bomber.

And, of course, it won't tumble down. At worst, it'll flutter down
in bits and pieces. At best, it'll just hang there, drifting vaguely
to the east.

Bob Munck

"Perplexed in Peoria" wrote in message . com...
"John Schilling" wrote in message ...
"Renee Keller" writes:
I don't think there is any chance of one actually being built. One major
storm, terror attack, or accident, and the whole thing comes tumbling down.

Strangely, you are not the first person to think of this. A lot of good
work has been done on fault-tolerant tether design, the dynamics of the
system are such that if it is nontheless completely severed most of the
thing falls *up*, and the small fraction that falls down is too "fluffy"
to hurt anyone.

I think that you are assuming that the break happens in the portion of the
cable below geo-synch. But what happens if the beanstalk is severed in the
"counterweight/earth-escape-thrower" portion of the beanstalk above geo-synch?
I've never seen an analysis of that possibility. Granted, a storm is unlikely
to result in that failure mode, and it would be comparitively difficult for
terrorists to accomplish it too. But it is a possible failure mode. What
would happen?

It would depend where, and also on the mass at the GEO point. Near the
GEO point, the cable should be fairly thick and well protected.
Further up, it'll be thinner. However, a break further up might be
easy to repair, as the tower will descend slowly, and there may be
time to retie the cable.

It would also make sense to have movable weights in the 1,000 km or so
either side of GEO, to enable the centre of mass to be reset. Of
course, after a while, the GEO mass might be significantly greater
than the cable mass, which would slow down any altitude loss
significantly.

If all else fails, then the tower management company would have to
sever the tower at the opposite point to the original sever (below
GEO), and hope to save the majority of the tower.