Xprize and tethered space station

[Ray Toews]

I read an article about a theoretical tethered space station, where a
long cable was payed out from the surface and attached to a space
station, there are obvious technical problems to overcome but
notwithstanding them it makes sense in a logical way to attach an
object with a wire to a spinning object but would you be weightless in
this type of station.
Now a stationary object in space must travel at 25000 mph (roughly) to
stay orbital but a cable extending upward from the surface would be
stationary and subject only to local winds. where does the transition
occur?
There seems to be gap in my knowledge about how gravity works.

What I understand about Scaled and others Xprize contestants is that
they are suborbital, that is, they are lobbing a craft vertically
upwards as far as they can afford and then falling back to earth when
gravity reaffirmes it's grip.

Not to take anything away from this endeavor but it seems to me a long
way from full orbital flight.

When the X planes of the late 50's flew they came very near space and
orbital flight and if research had continued maybe they could have
acquired the extra boost to go orbital but they had the same problem
the Shuttle has, that is disipating the heat (energy) of slowing down
when they decide to come home.

I am not technically trained but have been an interested observor for
the past 40 years and I would appreciate an explanation of the
dynamics (physics) of the next step that will send the Xprize
contestants into full orbital flight.

[Ron Wanttaja]

On Sun, 14 Dec 2003 22:34:16 GMT, Ray Toews wrote:

>I read an article about a theoretical tethered space station, where a
>long cable was payed out from the surface and attached to a space
>station, there are obvious technical problems to overcome but
>notwithstanding them it makes sense in a logical way to attach an
>object with a wire to a spinning object but would you be weightless in
>this type of station.
>
>Now a stationary object in space must travel at 25000 mph (roughly) to
>stay orbital but a cable extending upward from the surface would be
>stationary and subject only to local winds. where does the transition
>occur? There seems to be gap in my knowledge about how gravity works.

Not at all. You just need a bit of background on how orbital travel works.

[Note the following is waaaay simplified.]

What is "orbit"? Simply stated, an orbit is a combination of satellite
altitude and speed that maintains the satellite at a constant average
distance from the center of the object it's orbiting. For circular orbits,
this velocity is given by the equation:

Velocity = sqrt(mu/(h+re))
(nm/sec)

Where mu is the Gravitational Constant, 62750 nm^3/sec^3
re is the radius of the Earth (3444 nm)
and h is the orbit altitude above the Earth's surface

The big thing to remember is that this altitude/velocity combination is
*inviolate*. Increase your velocity, and you climb into an elliptical
orbit with a higher average altitude or even shoot away, free of the
Earth's gravity. Decrease the velocity, and you drop into an elliptical
orbit with a lower average altitude...too much lower, of course, and you
impact the Earth.

The time it takes to go around the Earth (one orbit) is thus rigidly fixed
by the satellite altitude. The equation for the satellite period is
6.97e-6 x (re + h)^(3/2) (again, re and h in nautical miles).

So, let's look at Operation Skyhook. We can integrate every inch of the
cable, but let's look at a simplification: We have a main station at
Geosynchronous altitude (24-hour orbit) and a "way station" along the cable
at 200 nm (90 minute orbit).

Left to their own devices, the Main Station would require an orbital
velocity of about 10,000 FPS, and the Way Station about 25,000 FPS. The
Main station would float in stately grace, fixed above a spot on the
equator. In truth, though, it doesn't care about what's below it...all it
knows is that it orbits the Earth once every day. The fact that the Earth
turns to keep the same point underneath it is trivial. At the same time,
the Way Station whizzes past underneath, 13 orbits per day.

All right. Let's connect the two with a massless cable. Let's assume the
Main Station remains fixed above the equator, and the Way Station just
magically appears at its 200 nm position.

From the Way Station's point of view, it's going waaaayyyy too slow. It
wants to orbit at 25,000 FPS, but the cable fixes its speed at a lot slower
rate. It wants (has!) to fly at a speed that results in 13 orbits per day,
but is being forced to fly at a rate that only gives one orbit per day. So
it's speed is about 1/13 what it should be.

What is the Way Station going to do? Fall. Unless the Main Station can
haul up on the cable to support its weight, the Way Station will fall to
Earth, dragging the Way Station down with some 19,000-odd nautical miles of
cable. It'll wrap almost all the way around the Earth (isn't science
cool?).

So, how are we going to hold Way Station up?

We'll make the cable longer, past the Main Station, and put another station
further out. This other station will be thus be traveling *faster* than
its orbital velocity, and tugs *outward* on the cable as it tries to fly
into a higher orbit. Pick the distances right, and it balances the
downward pull of the Way Station.

>What I understand about Scaled and others Xprize contestants is that
>they are suborbital, that is, they are lobbing a craft vertically
>upwards as far as they can afford and then falling back to earth when
>gravity reaffirmes it's grip.
>
>Not to take anything away from this endeavor but it seems to me a long
>way from full orbital flight.

I'll toast to the successes and failures of the people involved in shooting
for the X-Prize. But you're right, They are *not* going into orbit. It's
the space equivalent of the Mongolofier brothers. It's not Gagarin or
Glenn, it's more akin to Alan Shepard. You can shoot straight up and reach
space, but you need about 25,000 FPS of additional delta-V to achieve the
orbital velocity that'll let you stay there.

And when you come down, you have to get rid of all the 25,000 FPS. Orbital
spacecraft take some small portion away with rockets, and scrub off the
rest in atmospheric friction. The X-Prize folks have a far simpler
problem. Hopefully, that'll be addressed in the Y-Prize. :-)

Ron Wanttaja

[Eric Miller]

"Ron Wanttaja" > wrote in message
...
>
> All right. Let's connect the two with a massless cable.

Hey! Where can I order some of this strong, massless cable?
Seems like the perfect material for lightweight composite aircraft
construction!

:-)

Eric

[Felger Carbon]

"Ron Wanttaja" > wrote in message
...
>
> And when you come down, you have to get rid of all the 25,000 FPS.
Orbital
> spacecraft take some small portion away with rockets, and scrub off
the
> rest in atmospheric friction. The X-Prize folks have a far simpler
> problem. Hopefully, that'll be addressed in the Y-Prize. :-)

Nice explanation, Ron. In a steady-state situation, with fuel going
up the tether and ore coming down the tether, the 25K fps forces
balance. Also angular momemtum.

You could have just recommended Arthur Clarke's "The Fountains of
Paradise". Since you didn't, I will! ;-)

[Felger Carbon]

"Eric Miller" > wrote in message
.net...
> "Ron Wanttaja" > wrote in message
> ...
> >
> > All right. Let's connect the two with a massless cable.
>
> Hey! Where can I order some of this strong, massless cable?
> Seems like the perfect material for lightweight composite aircraft
> construction!

Steel is much too heavy. Kevlar is _almost_ practical. Now, carbon
nanotubes just might do the trick (mass production?). If not,
tomorrow we'll have something better. Progress is wonderful, ain't
it?

[Michael Pilla]

"Ron Wanttaja" > wrote in message
...

< SNIP >

[Note the following is waaaay simplified.]

All right. Let's connect the two with a massless cable. Let's assume the
Main Station remains fixed above the equator, and the Way Station just
magically appears at its 200 nm position.

< SNIP >

I hadn't realized that you were a physicist, Ron - loved the assumptions.

Any spherical cows around your neck of the woods? :-)

Michael Pilla

[Ron Wanttaja]

On Mon, 15 Dec 2003 04:26:11 GMT, "Michael Pilla" >
wrote:

>"Ron Wanttaja" > wrote:
>
>All right. Let's connect the two with a massless cable. Let's assume the
>Main Station remains fixed above the equator, and the Way Station just
>magically appears at its 200 nm position.
>
>< SNIP >
>
>I hadn't realized that you were a physicist, Ron -

Ooooo, them's fightin' words.... :-)

Ron Wanttaja

[Orval Fairbairn]

In article >,
"Eric Miller" > wrote:

> "Ron Wanttaja" > wrote in message
> ...
> >
> > All right. Let's connect the two with a massless cable.
>
> Hey! Where can I order some of this strong, massless cable?
> Seems like the perfect material for lightweight composite aircraft
> construction!
>
> :-)
>
> Eric
>
>

Just call up Moller -- the stuff is called "balonium" and is the primary
material from which the Skycar is built.

[Larry]

> Just call up Moller -- the stuff is called "balonium" and is the primary
> material from which the Skycar is built.
And here I thought it was made from "BSium"


:-)

(¯`·._.· £ãrrÿ ·._.·´¯)






"Orval Fairbairn" > wrote in message
...
> In article >,
> "Eric Miller" > wrote:
>
> > "Ron Wanttaja" > wrote in message
> > ...
> > >
> > > All right. Let's connect the two with a massless cable.
> >
> > Hey! Where can I order some of this strong, massless cable?
> > Seems like the perfect material for lightweight composite aircraft
> > construction!
> >
> > :-)
> >
> > Eric
> >
> >
>
> Just call up Moller -- the stuff is called "balonium" and is the primary
> material from which the Skycar is built.

[Splat!]

These are the guy's that are planning to build it,
http://www.isr.us/SEHome.asp

And here is a couple of articles on their ribbon elevator,
http://www.slb.com/seed/en/watch/elevator/build.htm
http://www.sciencenews.org/20021005/bob9.asp

I remember having a Yo-yo as a kid.
The string was pretty tough stuff !
I also remember the string breaking one and a while,
with the Yo-yo spool flying away at a tremendous speed.

I would hate to be on that elevator if the ribbon ever broke,
Splat!


<Ray Toews> wrote in message ...
> I read an article about a theoretical tethered space station, where a
> long cable was payed out from the surface and attached to a space
> station, there are obvious technical problems to overcome but
> notwithstanding them it makes sense in a logical way to attach an
> object with a wire to a spinning object but would you be weightless in
> this type of station.
> Now a stationary object in space must travel at 25000 mph (roughly) to
> stay orbital but a cable extending upward from the surface would be
> stationary and subject only to local winds. where does the transition
> occur?
> There seems to be gap in my knowledge about how gravity works.
>
> What I understand about Scaled and others Xprize contestants is that
> they are suborbital, that is, they are lobbing a craft vertically
> upwards as far as they can afford and then falling back to earth when
> gravity reaffirmes it's grip.
>
> Not to take anything away from this endeavor but it seems to me a long
> way from full orbital flight.
>
> When the X planes of the late 50's flew they came very near space and
> orbital flight and if research had continued maybe they could have
> acquired the extra boost to go orbital but they had the same problem
> the Shuttle has, that is disipating the heat (energy) of slowing down
> when they decide to come home.
>
> I am not technically trained but have been an interested observor for
> the past 40 years and I would appreciate an explanation of the
> dynamics (physics) of the next step that will send the Xprize
> contestants into full orbital flight.
>
>

[[email protected]]

On Mon, 15 Dec 2003 04:50:09 GMT, Ron Wanttaja >
wrote:

:On Mon, 15 Dec 2003 04:26:11 GMT, "Michael Pilla" >
:wrote:
:
:>"Ron Wanttaja" > wrote:
:>
:>All right. Let's connect the two with a massless cable. Let's assume the
:>Main Station remains fixed above the equator, and the Way Station just
:>magically appears at its 200 nm position.
:>
:>< SNIP >
:>
:>I hadn't realized that you were a physicist, Ron -
:
:Ooooo, them's fightin' words.... :-)
:
:Ron Wanttaja

Ron ain't no physicist, he WORKS for a livin'.

[Eric Miller]

"Larry" > wrote in message
...
> > Just call up Moller -- the stuff is called "balonium" and is the primary
> > material from which the Skycar is built.
> And here I thought it was made from "BSium"
>
> :-)
>
> (¯`·._.· £ãrrÿ ·._.·´¯)

LOL... too true about the Skycar.
I believe BSium is just high-grade, refined balonium =D

Eric

[Andrew Case]

Ron Wanttaja > wrote:
>And when you come down, you have to get rid of all the 25,000 FPS. Orbital
>spacecraft take some small portion away with rockets, and scrub off the
>rest in atmospheric friction. The X-Prize folks have a far simpler
>problem. Hopefully, that'll be addressed in the Y-Prize. :-)

Actually, getting rid of that excess velocity by aerobraking is also a bit
of a trick for an X-Prize class vehicle, at least if it's going straight
up and straight down. The problem is that you end up going quite fast
before you hit sensible atmosphere, and the atmosphere is actually pretty
thin, so you have to get rid of a lot of velocity fast (which implies high
g loads and high heating) or you end up at zero altitude with nonzero
speed. This is called "lithobraking" :-)

Coming in from orbit you can decelerate higher up, and take advantage of a
bit of lift to keep you in the thinner part of the atmosphere longer. A
ship like Rutan's can also do this to a certain extent since it will have
a substantial horizontal component of velocity.

.......Andrew
--
--
Andrew Case |
|

[Rich S.]

"Andrew Case" > wrote in message
...
>
> Actually, getting rid of that excess velocity by aerobraking is also a bit
> of a trick for an X-Prize class vehicle, at least if it's going straight
> up and straight down. The problem is that you end up going quite fast
> before you hit sensible atmosphere, and the atmosphere is actually pretty
> thin, so you have to get rid of a lot of velocity fast (which implies high
> g loads and high heating) or you end up at zero altitude with nonzero
> speed. This is called "lithobraking" :-)
>
> Coming in from orbit you can decelerate higher up, and take advantage of a
> bit of lift to keep you in the thinner part of the atmosphere longer. A
> ship like Rutan's can also do this to a certain extent since it will have
> a substantial horizontal component of velocity.

Lessee here...........

When I arrive at a destination and, by cause of weather or whatever, I'm too
high - I don't dive to redline and beyond to lose altitude. I establish a
decent rate of descent and fly in circles, or out and back, to gradually
scrub off speed and altitude.

Straight down? Not me, unless I'm on fire! ;o)

Rich S.

[nafod40]

Andrew Case wrote:
> Ron Wanttaja > wrote:
>
>>And when you come down, you have to get rid of all the 25,000 FPS. Orbital
>>spacecraft take some small portion away with rockets, and scrub off the
>>rest in atmospheric friction. The X-Prize folks have a far simpler
>>problem. Hopefully, that'll be addressed in the Y-Prize. :-)
>
>
> you end up at zero altitude with nonzero
> speed. This is called "lithobraking" :-)

Nice term. Like flying through cumulo-granite. : )

> Coming in from orbit you can decelerate higher up, and take advantage of a
> bit of lift to keep you in the thinner part of the atmosphere longer. A
> ship like Rutan's can also do this to a certain extent since it will have
> a substantial horizontal component of velocity.

The easy way is to come in like a capsule, with a throwaway, ablative
shield. The engineering is infinitely easier. OK, maybe not infinite,
but lots. The next NASA ship to fly will be capsule-like, I bet.

[[email protected]]

Ron, I'm very confused... You wrote
:
:The big thing to remember is that this altitude/velocity combination is
:*inviolate*. Increase your velocity, and you climb into an elliptical
:orbit with a higher average altitude or even shoot away, free of the
:Earth's gravity. Decrease the velocity, and you drop into an elliptical
:orbit with a lower average altitude...too much lower, of course, and you
:impact the Earth.

OK, I think I understand. If you're in LEO and you want to go to a
higher orbit, you have to add not just altitude, but velocity. So you
point your self forward and up, light the rocket and climb and
accelerate.
:
:Left to their own devices, the Main Station would require an orbital
:velocity of about 10,000 FPS, and the Way Station about 25,000 FPS. The
:Main station would float in stately grace, fixed above a spot on the
:equator. In truth, though, it doesn't care about what's below it...all it
:knows is that it orbits the Earth once every day. The fact that the Earth
:turns to keep the same point underneath it is trivial. At the same time,
:the Way Station whizzes past underneath, 13 orbits per day.

And that's where I'm confused. Isn't 10,000 fps at GEO a lot less
than the 25,000 FPS at LEO?

I understand that the actual distance, the circumference, of the orbit
at GEO is a lot bigger than at LEO, and I'd always thought that
accounted for lower satellites going "faster" around the earth in
radians or orbits per day.

It's the spinning ice skater/angular velocity thing that has me
confused. Pull in the arms, you spin faster, but drag slows you down.
Put out your arms, you go slower - your hands are going the same speed
in FPS as before, but they're going around a bigger circle.

Why is it that in going from LEO to GEO you're getting rid of speed?

Maybe this will do it. Say I'm in a nice, stable, circular orbit at
GEO. I want to drop to a nice, stable, circular orbit 100 miles
lower. I don't care about the orbital period, I just want to do it.
Which way do I point my nose before I light my rocket?

[Dillon Pyron]

On Tue, 16 Dec 2003 15:39:29 GMT, wrote:

>Ron, I'm very confused... You wrote
>:
>:The big thing to remember is that this altitude/velocity combination is
>:*inviolate*. Increase your velocity, and you climb into an elliptical
>:orbit with a higher average altitude or even shoot away, free of the
>:Earth's gravity. Decrease the velocity, and you drop into an elliptical
>:orbit with a lower average altitude...too much lower, of course, and you
>:impact the Earth.
>
>OK, I think I understand. If you're in LEO and you want to go to a
>higher orbit, you have to add not just altitude, but velocity. So you
>point your self forward and up, light the rocket and climb and
>accelerate.

Just forward. Increase the velocity, increase the orbit. Just like a
plane, increase the speed, you climb, all other things being equal.

>:
>:Left to their own devices, the Main Station would require an orbital
>:velocity of about 10,000 FPS, and the Way Station about 25,000 FPS. The
>:Main station would float in stately grace, fixed above a spot on the
>:equator. In truth, though, it doesn't care about what's below it...all it
>:knows is that it orbits the Earth once every day. The fact that the Earth
>:turns to keep the same point underneath it is trivial. At the same time,
>:the Way Station whizzes past underneath, 13 orbits per day.
>
>And that's where I'm confused. Isn't 10,000 fps at GEO a lot less
>than the 25,000 FPS at LEO?

Yes. Here's the thing, the way station in LEO is attempting to be
geosynchronous, at the wrong orbit. To do so, it needs to go faster.
But, being tethered to the earth and the mass out beyond GEO keeps it
in place.

>
>I understand that the actual distance, the circumference, of the orbit
>at GEO is a lot bigger than at LEO, and I'd always thought that
>accounted for lower satellites going "faster" around the earth in
>radians or orbits per day.

Correct.

>
>It's the spinning ice skater/angular velocity thing that has me
>confused. Pull in the arms, you spin faster, but drag slows you down.
>Put out your arms, you go slower - your hands are going the same speed
>in FPS as before, but they're going around a bigger circle.
>
>Why is it that in going from LEO to GEO you're getting rid of speed?
>
>Maybe this will do it. Say I'm in a nice, stable, circular orbit at
>GEO. I want to drop to a nice, stable, circular orbit 100 miles
>lower. I don't care about the orbital period, I just want to do it.
>Which way do I point my nose before I light my rocket?

Straight back, tangential to the orbit.

Go to sci.space and ask the questions. Your head will spin with the
math they answer your question with :-)

--
dillon

Life is always short, but only you can make it sweet

[Rich S.]

"Dillon Pyron" > wrote in message
...
> >On Tue, 16 Dec 2003 15:39:29 GMT, wrote:
> >OK, I think I understand. If you're in LEO and you want to go to a
> >higher orbit, you have to add not just altitude, but velocity. So you
> >point your self forward and up, light the rocket and climb and
> >accelerate.
>
> Just forward. Increase the velocity, increase the orbit. Just like a
> plane, increase the speed, you climb, all other things being equal.
>

So this explains why a J-3 can be in a geosynchronous orbit at 1000'
altitude, sittin' in one spot over I-90 while the cars whiz past!

Rich "Rocket Scientist" S.

[nafod40]

wrote:
>
> And that's where I'm confused. Isn't 10,000 fps at GEO a lot less
> than the 25,000 FPS at LEO?
>
> Why is it that in going from LEO to GEO you're getting rid of speed?
>
> Maybe this will do it. Say I'm in a nice, stable, circular orbit at
> GEO. I want to drop to a nice, stable, circular orbit 100 miles
> lower. I don't care about the orbital period, I just want to do it.
> Which way do I point my nose before I light my rocket?

Have you ever seen one of those charity things, where you drop your
penny into the slot and it starts it spinning around and around, and
keeps getting lower into the well, until at the last it is spinning way
fast just before falling into the hole?

That is exactly what's going on in space, but bigger. While you are
going around slower in GEO/close to rim of well, you have more energy
than the penny that is near the bottom of the well. You are higher.

To get the penny to go down to a lower orbit in the well, you have to
slow it down, i.e., point the rocket engine opposite the direction of
motion.