Space elevator now possible?

On Sat, 26 Jul 2003 07:15:57 -0700, "Richard Henry"
wrote:

"Cardman" wrote in message
.. .

Also just how fast would a trip to 37,000 km take? I guess that
depends on how fast you want to go, where 2 to 3g seems about as fast
as some passengers could handle. Although it could go faster higher
up.

Please expand.

The faster this space elevator goes up and down the more people and
goods it can move. However, for passengers this would have to be kept
within comfortable levels.

Due to a decrease in the pull of gravity at higher altitude, then so
can you increase the travel speed over time.

Also space elevators would not go up to LEO, like where the ISS is,
when this station goes around the Earth. Instead you would have all
your buildings up at geo-stationary orbit in the clarke belt, even if
the radiation here is not too good.

You can always go up higher I guess, but then you would float away
when you climbed out.

And how high could you go if you are running a cable up to about
91,000 km? As of course near the top it would start bending.

Please expand.

This elevator cable remains taunt due to itself, when either end is
pulling away from each other. There would be weights on either end,
but these only would be small.

So if you traveled all the way to the top, then the weight of your
elevator would bend the cable due to not enough cable and weight being
above you to keep it taunt.

Cardman.

"Joe Strout" wrote in message ...
In article ,
DrPostman wrote:

Can anyone explain to me why you would HAVE to have mach 16
speed vehicles to mate up with non-fixed tethers?

Well, here's the thing: if you want a non-rotating tether to be
stationary with respect to the surface of the Earth, then its center of
mass has to be in geosynchronous orbit -- that is the definition of
geosynchronous orbit, after all.

But GEO is really really high. About 36000 km high in fact. That means
you need a REALLY long tether. And since it has to hold up its own
weight over 36000 km, it has to be really strong too. This is why it's
hard.

So, you think, put it closer to Earth so it doesn't have to be as long.
But something closer to Earth has two choices: (1) move faster, so as to
stay in orbit, or (2) fall. The closer you get to the Earth, the faster
the orbit is. This just results from basic laws of physics.

So, there are an infinite number of compromises to choose from, but I
presume the one in question is at an altitude such that the velocity
(relative to the surface of the Earth) is about mach 16. That's how
fast the tether is moving in its orbit around the Earth, so that's how
fast you have to go to catch it.

The trouble with that of course is atmospheric drag. You start
at Mach 16 but pretty soon you are down to Mach 15 and falling.

Note that there is a clever way to improve things about: rotate the
tether, something like a giant wheel. Then the lower end of the tether
is moving opposite the tether's orbital direction. You can then
subtract the linear speed of the tether tip from the orbital speed of
the tether, thus making it easier to catch. As a bonus, the tether can
then drag you up and launch you into a higher orbit than itself.

But these dynamic tether systems, while very interesting, may be a lot
more complicated than the GEO tethers being studied now. If the latter
work out, I think we'll never need the faster-moving ones.

It would be interesting to look at the stability of a geosync
tether in the case of the anchor becoming detached. If the
bottom was normally under excess tension, the zero-g point
on the cable would presumably start to move away from Earth
and the location at release would be the perigee of an
elliptical orbit. Would atmospheric drag gradually change the
orbit to circular or would it increase the eccentricity until
the cable hit the ground or left the atmosphere?

"DrPostman" wrote in message
...
On 25 Jul 2003 08:59:34 -0700, (Robert Clark)
wrote:

Space Elevators Maybe Closer To Reality Than Imagined
by Richard Perry
Los Angeles - Jul 22, 2003
http://www.spacedaily.com/news/materials-03w.html


Bob Clark


Can anyone explain to me why you would HAVE to have mach 16
speed vehicles to mate up with non-fixed tethers? I have always
seen that as a better idea to the space elevator attached to the
Earth, but I never knew it would require such great speeds to
work. I even thought the idea of a set of these between worlds,
wipways, if you will, to be a interesting way of spacecraft propulsion
through our system. I am not an engineer or a scientist, so if you
could keep the explanation dumbed down a bit I would appreciate it.



Well, if the tether was rotating you could match the rotation to some very
low speed for docking. I know nothing about the stability issues involved.

Blurrt








--
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On Sun, 27 Jul 2003 08:19:08 +0100, "George Dishman"
wrote:

"Cardman" wrote in message ...

The faster this space elevator goes up and down the more people and
goods it can move. However, for passengers this would have to be kept
within comfortable levels.

Speed doen't matter for comfort, you are thinking of
acceleration.

Yes, where I will remember to use the correct word next time.

Aircraft travel at 1000kph so 37000km could
take 370 hours.

Sounds like a little too long to me.

I should do a calculation to see how long the trip would take with a
constant acceleration of 3g. As Earth gravity can be fixed as 1g, then
I will do it the easy way, when it is 2g acceleration up to 18350 km,
then 3g acceleration up to 36700 km.

Due to a decrease in the pull of gravity at higher altitude, then so
can you increase the travel speed over time.

The limiting factor would most likely be friction with the
cable.

And a very good point that it, when your elevator should be designed
for ultra fast cable streaming. Yet here of course you have to grip
this cable hard to give friction and to stop you slipping.

Shame that you cannot bend the cable, when that would have helped out,
but due to the stresses that is impossible, or more correctly one step
below impossible.

Well have a large elevator that goes both sides of the cable and
balances on it. Then use four large wheels (two below the elevator and
two above) to push against the cable, then to use powerful springs to
give a very strong grip on the cable.

You can set the grip as required, but I was thinking that some
computer control could help. As say when moving upwards rapidly, then
the grip can be loosened slightly to allow the cable to be fed though
faster.

Then again maybe there is some optimum setting already, but I suspect
this has to do with the mass that the elevator has to move. So
computer control would provide the best speed.

You can always go up higher I guess, but then you would float away
when you climbed out.

Zero-g gives health problems.

Yes, but people still do it.

Having production facilities
and labs at zero-g and accomodation and launch at the cable
end also provides the counterbalance weight.

Well the counter balance weight is up at 91,000 km.

Also you have to be a bit careful here, when attaching your 36,700 km
hotels and shops to this cable would strain the cable. As if all the
buildings pushed against the cable, then so could the cable bend.

Or you would break your building...

Maybe it could work out, but I would be more happy having a little
space between the arrival platform and the buildings. As just let the
buildings balance themselves around the cable without directly
touching it.

So if you traveled all the way to the top, then the weight of your
elevator would bend the cable due to not enough cable and weight being
above you to

The elevator itself would be adding to the weight and
keeping taut.

Yes below it, but above I could still see the cable bend slightly as
it is fed through. Hardly an issue though.

91,000 km. Last stop, everybody off.

Watch that first step...

keep it taunt.

As you wish: "Your father smelled of elderberries!"

And... "Your Mother was a Hamster".

Who worked in Castle Anthrax...

Cardman.

In sci.space.policy Devlin wrote:
In article , David M. Palmer
wrote:

Right. Carrying your energy up with you in the form of e.g. batteries
or gasoline+LOX is the wrong way to do it. Beaming the power up (or
down) to the car in the form of light onto solar panels, or microwaves
onto rectennas, is the way to go.

I came to the same conclusion, but the question then becomes how to
recover energy from descending cars as they propose. I haven't read the
paper, so have they addressed this? Using the tether as a conductor
would be dangerous with the change in electric potential at various
altitudes.

You either need superconductors that can cope with very high magnetic
fields (you want tiny conductors) as well as maybe 500K, or to make
the tether so huge it's not possible to launch it with anything close
to near-term launchers.

(if the resistance of the camels is an ohm a kilometer, then that's
80K in total. It'd need at least 100Kv to get any sort of power
to the end of such a cable. For copper, you'd need around 18mm^2 cables,
so that's around 300g/m, and probably equal to that for insulation.
Adding tens of thousands of tons to the mass of the cable is insane
to save $few worth of electricity per trip)

The energy needed to get the thing to GEO is much higher than chemical
fuels can provide, unless you practically fill the car with them, and
use stages.
So, you'r left with nuclear, solar, or something else.
Nuclear isn't well suited to the few tons/100Kw range that the first cars
will likely be.
Solar has serious problems with day/night, and lousy specific power.
I think probably the easiest way is microwave beaming for the first
50Km or so, and then laser powered from the top of the beanstalk
for the rest of the way.
40000Km is a bit long for microwave reception on a small object.

Initially, you can't share the power between cars close on the cable,
as you want the cable to be very very light.


This implies that you only want around 1.4 cars weight (not mass) on the cable
at once, which implies that you have to have them initially spaced around
4000Km or so.
Efficiant (50%) lasers don't yet exist, so it's probably not worth
trying to capture this wasted energy, just dump it into a heater or
something.

Eventually, maybe, but not soon.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
Tad Williams has an interesting new fantasy: http://www.shadowmarch.com/

"George Dishman" wrote in
:


"Cardman" wrote in message
...
On Sat, 26 Jul 2003 07:15:57 -0700, "Richard Henry"
wrote:

"Cardman" wrote in message
.. .

Also just how fast would a trip to 37,000 km take? I guess that
depends on how fast you want to go, where 2 to 3g seems about as
fast as some passengers could handle. Although it could go faster
higher up.

Please expand.

The faster this space elevator goes up and down the more people and
goods it can move. However, for passengers this would have to be kept
within comfortable levels.

Speed doen't matter for comfort, you are thinking of
acceleration. Aircraft travel at 1000kph so 37000km could
take 370 hours.

That would seem to be an excessive amount of time spent in the Van Allen
belts, so I hope your mass budget accounts for the shielding required.
--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Cardman wrote in
:

You can always go up higher I guess, but then you would float away
when you climbed out.

Zero-g gives health problems.

Yes, but people still do it.

For extended periods in micro-G, you need 1-2 hrs of vigorous exercise per
day to avoid the health problems. Astronauts do this willingly - it's their
job and many of them are exercise freaks anyway - but it might be a bit
much to expect of passengers.

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
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In sci.space.policy George Dishman wrote:

"Ian Stirling" wrote in message ...
(if the resistance of the camels is an ohm a kilometer, then that's
80K in total. It'd need at least 100Kv to get any sort of power
to the end of such a cable.

If you stick 100kV up a camel, it'll be in space before
you can saddle it!

(Sorry Ian, but that's the best typo I've seen in ages.)

Oh dear
I blame my new laptop, which has a slightly undersized keyboard.
Most of the time I can touch type, apart from the times when I can't.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
"Looks like his brainwaves crash a little short of the beach..." - Duckman.

nightbat wrote

"Jorge R. Frank" wrote:

Cardman wrote in
:

You can always go up higher I guess, but then you would float away
when you climbed out.

Zero-g gives health problems.

Yes, but people still do it.

For extended periods in micro-G, you need 1-2 hrs of vigorous exercise per
day to avoid the health problems. Astronauts do this willingly - it's their
job and many of them are exercise freaks anyway - but it might be a bit
much to expect of passengers.

--
JRF

nightbat

Ha, ha, haven't you ever heard of motel guest magic fingers?
Sure zero gravity hotel and spa in the stars. Where displaced vacuum
engine power is used to run everything. Velcro, orange Tang, and
metallic gravity boots are the thing. The Madison Ave. stocks on hip
lounge around space wear go through the roof. 50 US billion initial
investment and counting with a predicted research and development boom
never seen on Earth. Las Vegas can't wait, Moon over Miami wouldn't be
able to compete. Brazil nuts and plastic sippy bag coke for second class
folks with steak, champagne, and caviar for first class. Don't fight the
sky hook, get on it, and later get to ride to Mars and Venus. Float or
ease to your lover, breakfast, and tv. Von Braun wanted that space
station done right, 2001 or 2 or 3 or maybe 10. Can we live with a
possible 5% sky elevator nano tube tape failure rate 'til they get it
right if the accumulated sky hook free miles are there? Didn't everyone
love the Concord 'til a little garbage got on the runway? Did the
Indians stop the wagon trains, or it can't be done stop the Wright's?
What's a few billion here or there to watch " I love Lucy " reruns on a
thin plasma wall tv with your cutie out in space? Just think of the
views, the stars, the thought of really getting away from it all. Are
there really any taxes in deep space and who collects them, Space IRS?
Ha, ha, what if you have a dummy moon address like some of those Earth
Corporate island big boys, na, there will always be sky elevator highway
tape tax. Or how about investing in water futures on Mars, it could
happen. If taxpayers didn't invest in silly putty, holahoops, or, Nasa
Tang, could we have gone to the moon? Hey, the science equivalency
parity book rights should be worth more then the cost of doing the
experiment itself. Or a few inches of deferred projected cable nano tape
cost could help them look. A sky elevator to the stars, what will they
think of next? Space college, rent time shares on Mars, Milky Way punch?
Who says science doesn't march on?


the nightbat

DrPostman wrote in message . ..
Can anyone explain to me why you would HAVE to have mach 16
speed vehicles to mate up with non-fixed tethers?

It's just a question of how fast you can spin a tether. In principle
there's no limit, but as the spin speed goes up you have to build the
tethers heavier and heavier to take the stresses; so there is a limit
in practice.

A tip speed of about 2.5km/s is considered about the practical limit
(compared with the orbital speed of 7.8 km/s); unless you can use
carbon nanotubes (but they aren't long enough yet).

I have always
seen that as a better idea to the space elevator attached to the
Earth, but I never knew it would require such great speeds to
work.

Well, low earth orbit is about mach 25 so consider yourself well
blessed if you only need mach 16 to reach orbit.

(Rockets get exponentially bigger with the speed they have to reach,
so although mach 16 sounds high, rest assured it's a walk in the park
compared to what the Shuttle has to deal with.)

--
Dr.Postman USPS, MBMC, BsD; "Disgruntled, But Unarmed"