Space Elevator

On Sat, 26 Jun 2004 23:15:26 GMT, "Bill Daniels"
wrote:


"Howard Eisenhauer" wrote in message
news
On Fri, 25 Jun 2004 22:42:15 -0700, Richard Riley
wrote:

On Fri, 25 Jun 2004 20:47:03 -0500, Big John
wrote:

:Scientist Sees Space Elevator in 15 Years
:
*Snip*


H.

This space elevator thing is elegant in a Newtonian sort of way but I
suspect that there is a lot more to it that hasn't been completely thought
out.

You may well be right- not really my field but I've heard the math is
the same as applies to suspension bridges, thats to say well
understood.

They say put it on the equator where the winds are low. Well, they are low
most of the time but there is always the occasional typhoon.

True, but anything with the kind of strength we're talking about here,
under that amount of tension ain't gonna be much bothered by the
occaisional blow.

Then there are the electrical effects. A carbon nanotube cable will conduct
electricity pretty well. Some claim it's a room temperature superconductor
candidate. A tropical lightning strike can be several million amps and this
cable will be a pretty good lightning rod. There's the induced voltages
too. The normal atmospheric potential gradient is several million volts per
meter.

Last I checked deltaV/m was more liket ~200V. I heard the speculation
about nanotubes being superconductors a few years ago back before they
were able to produce them in decent quantities but haven't heard
anything since, If they really are I think somebody would have noticed
by now. To bad though, a superconducting space elevator would be a
neat way to generate "free" power, a-la the NASA/Italian experiment
with a tether a few years back. .

What about tidal effects? Twice each day the Moons gravity will pull on the
structure.

Bill Daniels

Yes, it will. Geosync satellites get pulled around quite a bit by the
moon (& sun's) gravity. Then they get pulled back again., Not a
biggie.


H.

"Tim Ward" wrote

I dunno, but this seems as good a time as any to bring up a stupid,
complicated idea of mine for access to space.

First, you should be familiar with the Kelly Aerospace idea of towing the
spaceship to altitude. If not, Google for "Eclipse project", NASA, and
perhaps F106.

They towed an idling F106 behind a C141 as a proof of concept project.

Second, you should be aware of the "payout winches" used to ground launch
hang gliders. These just pay the line out at a constant tension, rather
than reeling them in at a high rate of speed, as in sailplane launches.

So here's the scheme:
You build a tow plane about the size of a 747. The payout winch is mounted
such that it "pays out" from the CG of the airplane, on top. You have
somewhere around 100,000 lbs of Vectran tow rope (several tens of
kilometers) on the payout device. This is within the cargo capability of a
747, though you may want to throw on a couple of extra engines because of
the additional drag.

Pac sez:
I like this idea. A 747-200F can carry 250,000 lbs of fuel and 250,000
of cargo at the same time. But at that weight 820,000 lbs it could
only make ~FL280. It would have to leave most of the gas behind: no
sweat there. Since it burns a rough average of 25,000 lbs an hour a
t/o fuel load could be as low as around ~50,000lbs of fuel for
twenty-nine minutes of ascent plus return and skinny reserves so, you
would have good rate of climb to the service ceiling of FL450 (45,000
ft.) The combined tow weight of OrbitOne plus fuel and Colonauts
could be easily be greater than 200,000 lbs if all your tow apparatus
could handle it. So figure a total Mojave t/o weight of ~650,000lbs.
These numbers are off the top of my head, I could look up the exact
ones if you want me to. Don't know if this would be cheaper than a
Vandenberg launch, but Rutan would control it all, and stay away from
gov turd interference. **** I like it. You should email this idea to
Scaled Composites Tim. Bet you a nickle Burt is already considering
it. Evergreen in Oregon is already using 74's for fire fighting.
This might be the next great role for that old queen of the sky.

pacplyer


The spacecraft has a CG hook on the bottom.

You take off, and climb as high as you can, while paying out the tow line.
The spacecraft pilot basically controls the pay out. Pitch up, and a little
more line pays out. Pitch down, and it stops.

If the spacecraft can maintain a 45 degree angle behind the towplane, it
will be 70% of the towrope's length higher than the towplane.

At some point, the true airspeed of the tow plane will not provide enough
airspeed for the spacecraft to continue to climb. So the towplane starts to
turn, and the spacecraft maneuvers to the outside of the turn. Now it's
just like playing "crack the whip". The air-breathing booster is down in
the (relatively speaking) thick atmosphere at 50,000 feet, while the
spacecraft is above most of the atmosphere at say, 100,000 feet.

That's when the spacecraft releases and fires its rockets.
Because the atmosphere is so much thinner, and the spacecraft is going
faster than it would be at lower altitudes, the increase in peak altitude
achievable should be much higher than just the 50,000 ft altitude difference
between the tow plane and the spacecraft.

After the spacecraft releases, the towplane also releases the towline, and
it descends under a parachute, separately.

There, I feel better.

Tim Ward

p.s. I wonder what Dr. "Moonraker" (Ron W.) thinks of this idea? Too
revolutionary? Not expensive enough? ;-)

pac

On Sat, 26 Jun 2004 09:03:02 -0700, "Tim Ward"
wrote:
//
I dunno, but this seems as good a time as any to bring up a stupid,
complicated idea of mine for access to space.
///
somewhere around 100,000 lbs of Vectran tow rope (several tens of
kilometers) on the payout device. This is within the cargo capability of a
747
//
There, I feel better.

Tim Ward

Possible practical objection:
there is a limiting length of a line hanging freely downwards.
For the strongest engineering material per unit mass known it's
about 15 miles as I recall. That just to carry its own weight: thick
at the top, thin at the foot.

So less than 24 km. But you want it to tow a spaceplane
so that limiting length goes way shorter....

Feel free to correct this....

Brian W

"Tim Ward" wrote in message
...

I know Niven & Pournelle had something
like that in Lucifer's Hammer, but that was an effort to throw off
alien
conquerors.

The book was "Footfall", not "Lucifer's Hammer". In the fictional
account, the city of Bellingham WA was scragged by the Orion-engined
takeoff.

BTW, "Orion spacevehicle" and "aviation.homebuilt" are not a close
match. ;-)

"pacplyer" wrote in message
om...
snippage
Pac sez:
I like this idea. A 747-200F can carry 250,000 lbs of fuel and 250,000
of cargo at the same time. But at that weight 820,000 lbs it could
only make ~FL280. It would have to leave most of the gas behind: no
sweat there. Since it burns a rough average of 25,000 lbs an hour a
t/o fuel load could be as low as around ~50,000lbs of fuel for
twenty-nine minutes of ascent plus return and skinny reserves so, you
would have good rate of climb to the service ceiling of FL450 (45,000
ft.) The combined tow weight of OrbitOne plus fuel and Colonauts
could be easily be greater than 200,000 lbs if all your tow apparatus
could handle it. So figure a total Mojave t/o weight of ~650,000lbs.
These numbers are off the top of my head, I could look up the exact
ones if you want me to. Don't know if this would be cheaper than a
Vandenberg launch, but Rutan would control it all, and stay away from
gov turd interference. **** I like it. You should email this idea to
Scaled Composites Tim. Bet you a nickle Burt is already considering
it. Evergreen in Oregon is already using 74's for fire fighting.
This might be the next great role for that old queen of the sky.

pacplyer


I think the mission might turn out to be longer than a thirty minute climb.
It's going to take some time to pay out all that tow line -- payout winch
launches are slower than auto tows, and much slower than regular winch
launches.
OTOH, the tow plane doesn't have to _lift_ the spacecraft -- it just has to
overcome the drag.
In fact, once the spacecraft is in high tow, it should be pulling up and
back (or up and out, in the slingshot portion of the flight). If things are
going right, in high tow, the spacecraft is always lifting the weight of the
tow cable that's extended, so as the tow line gets longer, the payload that
the 747's wing is lifting gets smaller. At peak altitude, the 747's wing
should only "see" the remaining fuel as a load. If the tow cable is pulling
down, then you haven't got enough tension in the tow cable. If you can't
increase the tension, then you've got too much line out.
But I expect the drag is going to be considerably higher than a stock 747.
20 km of cable an inch or so in diameter is going to be quite a bit of drag,
even at altitude. Thus my suggestion that some more engines (and higher
fuel burn) might be in order. Or do you need to throttle back a 747 at
altitude to keep the speed in limits?

I'm sure that after the publicity of the SpaceShip1 flight, Rutan is getting
all the hare-brained ideas that he can use via email, snail mail and
telephone. As I mentioned in the first post, Kelly Aerospace is working on
a tow-to-altitude and launch scheme, so some of the idea isn't new, anyway.

I wonder about the flight dynamics of a 20 km tether. I don't think anyone
has modeled anything like that. Why would they?

But a reusable 747 "first stage" that could get the "second stage" to
100,000 feet, albeit only at a little below Mach 1 (I think the drag would
go WAY up if the tether went supersonic!) is certainly cool to think about.

Tim Ward

On Sat, 26 Jun 2004 09:03:02 -0700, Tim Ward wrote:


"Ron Wanttaja" wrote in message
...
Space Elevators are obvious, but how does a Space Trim Tab work? :-)

Ron Wanttaja

I dunno, but this seems as good a time as any to bring up a stupid,
complicated idea of mine for access to space.

First, you should be familiar with the Kelly Aerospace idea of towing the
spaceship to altitude. If not, Google for "Eclipse project", NASA, and
perhaps F106.

They towed an idling F106 behind a C141 as a proof of concept project.

Second, you should be aware of the "payout winches" used to ground launch
hang gliders. These just pay the line out at a constant tension, rather
than reeling them in at a high rate of speed, as in sailplane launches.

So here's the scheme:
You build a tow plane about the size of a 747. The payout winch is mounted
such that it "pays out" from the CG of the airplane, on top. You have
somewhere around 100,000 lbs of Vectran tow rope (several tens of
kilometers) on the payout device. This is within the cargo capability of a
747, though you may want to throw on a couple of extra engines because of
the additional drag.

The spacecraft has a CG hook on the bottom.

You take off, and climb as high as you can, while paying out the tow line.
The spacecraft pilot basically controls the pay out. Pitch up, and a little
more line pays out. Pitch down, and it stops.

If the spacecraft can maintain a 45 degree angle behind the towplane, it
will be 70% of the towrope's length higher than the towplane.

At some point, the true airspeed of the tow plane will not provide enough
airspeed for the spacecraft to continue to climb. So the towplane starts to
turn, and the spacecraft maneuvers to the outside of the turn. Now it's
just like playing "crack the whip". The air-breathing booster is down in
the (relatively speaking) thick atmosphere at 50,000 feet, while the
spacecraft is above most of the atmosphere at say, 100,000 feet.

That's when the spacecraft releases and fires its rockets.
Because the atmosphere is so much thinner, and the spacecraft is going
faster than it would be at lower altitudes, the increase in peak altitude
achievable should be much higher than just the 50,000 ft altitude difference
between the tow plane and the spacecraft.

After the spacecraft releases, the towplane also releases the towline, and
it descends under a parachute, separately.

There, I feel better.

I'm fascinated by this idea, but I'm still not sure if I've got my head
round it.

One thing that worries me, is that stubby little planes like the
space-shuttle or spaceship 1 need to be flying very fast in order to stay
up at high altitudes. For example, the U2 cruised at this speed near
100,000 feet (unladen). If the 747 was to tow a spaceplane up to this
altitude in straight and level flight, I expect it would need to look like
an U2 and might have problems during re-entry.

Imagine the 747 was flying in 1km (radius) circles; if the spaceship flew
concentric 4km circles the ratio of its speed to that of the 747 would be
4:1. At it began to approach this speed maybe it could ascend above the
747? If the 747 could reduce the turning circle down to 0.5km radius,
you'd be up to 8 times its velocity - well on the way to orbit. I think
this is a fair simplification of your 'crack the whip' - but this is what
I'm not sure of.

3KM of 1cm wide costlium wire would have 30M^2 of frontal area which
doesn't sound unmanageable, but perhaps it would cause more drag than
that suggests. But presumably it would get quite toasty...

If our 747 is flying 0.5km radius circles at 500kph, acceleration on it
will be V^2/r = (500000/3600)^2/500 = 38.5 M/S - about 4 G's

If our spaceship is flying 4km radius circles at 8*500kph it will be
pulling (8*500000/3600)^2/4000 = about 30 G's.

Hmm...

To keep that down to 7G's at 4000kph I get 20km of cable required
80KM for 8000kph

Escape velocity is about 40,000kph

If people are seriously considering cables strong enough for
space-elevators, maybe there could be something in this. If you can
tolerate higher G-forces then you can use much more feasible lengths of
cable - perhaps it would be a practical way of launching freight into
orbit, even if it wasn't suitable for people.

Maybe you could fix one end of the cable to a mountain-top, and send
electrical power through the cable to a prop-unit mounted part of the way
along it.

AC

They ran this all over the sci.space groups for a while.

Somebody made up a neato web site with clever animations
showing how well it worked.

When people started pointing out some of the more obvious
problems, thing got a bit heated.

It's BAAAck...

One of my posts from back then.......................................


All you have to do is demonstrate that this thing _can_ actually work.

I'd settle for a simple math description of the transfer mechanics
and mechanical reactions, but a couple of small tethers playing catch
with a base ball would convince almost everybody.

(Mom is a die hard skeptic)


Animations are useful for visually describing something.
Ok, you've got that.

Next step up the ladder is a 'simulation'.
A 'scale model'.
Either physical - or computer code.

It will take EVERYTHING into account.

How the ractions occur when you release mass.
What happens (and how?) when you capture mass.

(Including such minor problems as rotation of the mass you
intend to capture? That's energy too.)

How the C.G. of the whole thing changes during capture and release.
Or, while 'hauling' something 'up' the tether?
(that's where I have my own doubts.)

How the tether structure will react to all that...

What the orbital reactions are when gaining and expending energy?

Get a good SIMULATION up and running, you'll get R&D money and a
launch schedule.

And we'll just put a couple of small test toys in orbit and toss a
baseball back and forth...

Until then?

All you have is an idea that can't be tested.

Or a LOT of work to do...

"Tim Ward" wrote in message
...

Why not resurrect project Orion and ride the wake of nuclear blasts into
space.

Tony

Cost?
Even if the hardware was free, the infrastructure to support a surface
launch would be awfully expensive. I know Niven & Pournelle had something
like that in Lucifer's Hammer, but that was an effort to throw off alien
conquerors.

I thought Orion was space-to-space transportation.

The system I've proposed wouldn't be cheap, but it could conceivably take
off and land from a regular airport.

Tim Ward

You really need to see the history channel show on Project Orion. I can't
do it justice here. The team on the project expected to be to Mars buy 1965
if their funding hadn't been dropped.

Tony

On Sun, 27 Jun 2004 05:38:59 +0000, Anthony wrote:


"Tim Ward" wrote in message
...

Why not resurrect project Orion and ride the wake of nuclear blasts into
space.

Tony

Cost?
Even if the hardware was free, the infrastructure to support a surface
launch would be awfully expensive. I know Niven & Pournelle had something
like that in Lucifer's Hammer, but that was an effort to throw off alien
conquerors.

I thought Orion was space-to-space transportation.

The system I've proposed wouldn't be cheap, but it could conceivably take
off and land from a regular airport.

Tim Ward

You really need to see the history channel show on Project Orion. I can't
do it justice here. The team on the project expected to be to Mars buy 1965
if their funding hadn't been dropped.

There's a good book on it by Dyson too.

AC

On Sun, 27 Jun 2004 01:32:51 GMT, "Felger Carbon"
wrote:

"Tim Ward" wrote in message
...

I know Niven & Pournelle had something
like that in Lucifer's Hammer, but that was an effort to throw off
alien
conquerors.

The book was "Footfall", not "Lucifer's Hammer". In the fictional
account, the city of Bellingham WA was scragged by the Orion-engined
takeoff.

Jerry later said that, had he known what the future would bring, they
would have chosen Redmond. :-)


BTW, "Orion spacevehicle" and "aviation.homebuilt" are not a close
match. ;-)



I've seen video of a proof of concept vehicle. Esentially a large
hemispherical plate of steel, maybe 200 kilos. They had some sort of
device to load the explosives into the fireing chamber. They used
half sticks of dynamite and lofted it to over 1000 feet. Really quite
impressive, although I think RUN would be the order of the day when it
quit being a flying machine and turned into a heavy slab of metal.
--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.