Perhaps it would be possible to build a structure which encircles a
planet (such as Earth), but only rotates at orbital speed. This would
make the structure essentially weightless. GEO is probably a good
orbit. The structure could be made very robust. It would not, of
course, be able to support its own weight if spun up to one G, but
then it doesn't have to.

The inside would be, basically, a huge tunnel, perhaps one hundred
kilometers wide and one kilometre high. It wouldn't contain any
atmosphere, and would not be airtight. The inside would be coated
with aluminum.

And maglev vehicles, themselves airtight, would zip around inside the
ring. These vehicles would be one hundred kilometres wide, one
kilometre high, and 264,924 kilometres long, basically filling the
tunnel. This vehicle does rotate fast enough to provide one G, and
cannot support its own weight while doing so. But then it doesn't
have too. The tunnel structure itself does that. As robust as this
structure is, it is also thick enough to serve as a
radiation/micrometeoroid shield.

26,492,400 km of living space, as compared to 148,939,100 km land
area of the Earth itself. So around a fifth of Earth. Not bad.

Would this work, and without unobtainium?

Uh... If I understood correctly your explanation, the "railring" works
as a kind of "counterweight" against the maglev ring. The maglevring
would tend to rip itself apart outward, but the static (it would work
better at zero speed instead of orbital speed) ring being attracted by
Earth would press the thing inward.

Yes, I think that would work without unobtanium. There would be moon
and sun tides and stuff, by I guess that you can compensate that doing
structures slightly flexible and with the orbital mechanics equivalent
of "dilation gaps".

By the way, if that ring is constructed not at GEO but rather LEO, it
would have an interesting property: the outer side of the "railring"
would have natural gravity, close to 1g (say, 0.9 g or something), and
pointing to the center of Earth. Both the outer and inner sides could
be inhabited.

On 1/3/07, Xenophile wrote:

--- In spacesettlers, "Lucio de Souza Coelho" wrote:

> Uh... If I understood correctly your explanation, the "railring"
> works as a kind of "counterweight" against the maglev ring. The
> maglevring would tend to rip itself apart outward, but the static
> (it would work better at zero speed instead of orbital speed) ring
> being attracted by Earth would press the thing inward.

Not exactly, though if that works, then I'm happy. The idea is that,
since the railring doesn't rotate (or at least doesn't rotate fast
enough to generate significant G's) you can make it as massive as you
like, until it's simply strong enough to resist the maglev ring's
efforts to rip itself apart.

You couldn't just rotate the whole thing, because as you beef it up to
make it stronger, you also beef it up and make it more massive. But
in this case, it can be as massive as you like.

> Yes, I think that would work without unobtanium. There would be moon
> and sun tides and stuff, by I guess that you can compensate that
> doing structures slightly flexible and with the orbital mechanics
> equivalent of "dilation gaps".

At this size, I suspect that a degree of flex is unavoidable.

> By the way, if that ring is constructed not at GEO but rather LEO,
> it would have an interesting property: the outer side of the
> "railring" would have natural gravity, close to 1g (say, 0.9 g or
> something), and pointing to the center of Earth. Both the outer and
> inner sides could be inhabited.

Now THIS is interesting! Cuts down on the living area, but...

But could it hold itself up at 0.9 G? That's why I had the thing at
orbital speed. But even if it is at orbital speed, why not have the
maglev ring inside zipping around in the direction opposite the
orbital? Then when it gets to exactly orbital speed in the opposite
direction, the maglev ring is stopped, and you have that 0.9 G for the
people living on it.

On 1/3/07, Xenophile wrote:
(...)
> But could it hold itself up at 0.9 G? That's why I had the thing at
> orbital speed. But even if it is at orbital speed, why not have the
> maglev ring inside zipping around in the direction opposite the
> orbital? Then when it gets to exactly orbital speed in the opposite
> direction, the maglev ring is stopped, and you have that 0.9 G for the
> people living on it.
(...)

In the proposed LEO scheme, the outer ring would still be static
relatively to Earth - well, in fact it would rotate once in 24 hours
accompanying Earth, but at just, say 200Km of altitude, its speed
would be far lower than orbital. The inner ring, however, would rotate
*much faster* than orbital speed (in order to fake 1g gravity pointing
outward). Therefore it would press the outer ring outward,
counteracting the inward pressure of the outer ring weight; thus the
outer ring would not fall over Earth and the inner ring would not
centrifuge-rip itself apart. Of course the masses of the rings would
have to be precisely matched so that those effects would cancel
themselves exactly and the structure would be static around Earth.

I guess I need to draw a diagram of the forces involved to make the
idea clearer... Perhaps at night.

--- In spacesettlers, "Lucio de Souza Coelho" wrote:

> In the proposed LEO scheme, the outer ring would still be static
> relatively to Earth - well, in fact it would rotate once in 24 hours
> accompanying Earth, but at just, say 200Km of altitude, its speed
> would be far lower than orbital. The inner ring, however, would rotate
> *much faster* than orbital speed (in order to fake 1g gravity pointing
> outward). Therefore it would press the outer ring outward,
> counteracting the inward pressure of the outer ring weight; thus the
> outer ring would not fall over Earth and the inner ring would not
> centrifuge-rip itself apart. Of course the masses of the rings would
> have to be precisely matched so that those effects would cancel
> themselves exactly and the structure would be static around Earth.
>
> I guess I need to draw a diagram of the forces involved to make the
> idea clearer... Perhaps at night.

Ah, I begin to see. But if the the forces are to be balanced, and one
ring is moving much faster than the other, then the faster-moving ring
needs to be LESS massive than the slower-moving ring. How much less
massive? How Fast?

There is no way in Heaven, Hell, Earth or Space that I could do the
math for this. But the idea does seem doable.

On 1/4/07, Xenophile wrote:
(...)
> Ah, I begin to see.

That's good, because I still have no drawing. :)

(...)
> But if the the forces are to be balanced, and one
> ring is moving much faster than the other, then the faster-moving ring
> needs to be LESS massive than the slower-moving ring. How much less
> massive? How Fast?
(...)

Well, lets put some numbers in an hypothetical case. Suppose a ring
circling Earth at an altitude of 200Km (Shuttle/ISS-like altitude). At
that altitude the outer, static ring would experience a surface
gravity of around 0.93g. Then in order to counteract that gravity and
produce 1g outward, the inner ring would have to spin at 11.2 Km/s .
And the mass of the outer ring would have to be around 8% higher than
that of the inner ring.

Conversely, if you put the gravity of the inner ring also at 0.93g,
then the outer and inner rings will have exactly the same mass.

Another Ringworld-related problem that I forgot is dynamic
stabilization. Since this structure would not be in orbit, behaving
instead like a "solid" ring around Earth with the center of mass
matching that of Earth, some portions of it could be slightly closer
to Earth than the others; and as a result the ring would be
irrevocably pushed toward Earth from some side and be destroyed. In
order to avoid that, the ring has to be dynamically stabilized, ie,
sensors have to constantly monitor if the ring is tending to "fall" in
some point and push the structure a little bit accordingly. The
obvious way to do such corrective pushes would be using giant
thrusters, but since those are very inefficient I am thinking about
something more elegant: magnetic attitude control. By using
electrodynamic tethers, the ring could interact with Earth's magnetic
field and use the forces thus obtained to keep itself correctly in
place.

Of course I have no idea of the order of magnitude of magnetic fields
required by that. I would need restart the little knowledge of
magnetism that I have...

--- In spacesettlers, "Lucio de Souza Coelho" wrote:

> Another Ringworld-related problem that I forgot is dynamic
> stabilization. Since this structure would not be in orbit, behaving
> instead like a "solid" ring around Earth with the center of mass
> matching that of Earth, some portions of it could be slightly closer
> to Earth than the others; and as a result the ring would be
> irrevocably pushed toward Earth from some side and be destroyed.

Well, I've got a simple solution to that, but it strays into
unobtainium territory. Not by much, though.

Since the ring is geostationary (despite being at Shuttle height), you
could have a bunch of space elevators connecting it to the ground.
Then, if one side drifts closer to Earth, the other side has to drift
farther away, and the elevator ribbons won't allow that. You could
position one, say, every thousand Km around the equator, giving you
forty of them.

And a tether that can support itself for 200 Km is probably more
"obtainium" than one which can support itself for 35,792 Km.

On 1/5/07, Xenophile wrote:
(...)
> Well, I've got a simple solution to that, but it strays into
> unobtainium territory. Not by much, though.
>
> Since the ring is geostationary (despite being at Shuttle height), you
> could have a bunch of space elevators connecting it to the ground.
> Then, if one side drifts closer to Earth, the other side has to drift
> farther away, and the elevator ribbons won't allow that. You could
> position one, say, every thousand Km around the equator, giving you
> forty of them.
>
> And a tether that can support itself for 200 Km is probably more
> "obtainium" than one which can support itself for 35,792 Km.
(...)

Heck, why in hell I started to think about electrodynamic tethers when
there is a solution SO much simpler, and completely passive, like
yours!

I am not that good with materials science, but I guess that you don't
need any sort of unobtanium at all. AFAIR, some projects of rotovators
tens or even hundreds of kilometers long use polymers commercially
available now.

Greetings,

I don't think you need that strong a material, a
tapered Kevlar ribbon would do. If any of those
reading about these "Orbital Ring Systems" as Paul
Birch described them in his (JBIS, 1983) article, are
in the Space Elevator Group, they might want to pass
this info to there group.

This system is about 100 time more useful that the
space elevator to GEO, and would cost about
1/1,000,000th the amount a space elevator to GEO would
cost, assuming it were possible to obtain the Carbon
Nanotube fiber material for the ribbon. Furthermore
this ring system could be built now with existing
materials. More useful in that it could take more
material to orbit faster and cheaper.

The amount of mass that must be launched for this is
still pretty sizable, even for the start up ring from
which the full-scale ring could be eventually lifted.
Sizable means 1,000s or 10,000s of tons, so it's cost
(just for launch) would be in the $100B range.

Clearly massive space projects like this require a new
Very Low cost launch system. The best one that may
fit the bill is called "the Telephone Pole Launcher"
invented by By Henry Kolm (L5 News, September 1980),
see
http://www.nss.org/settlement/L5news/1980-massdriver.htm
But even this launcher would cost $3B-$5B today.
Maybe a scaled down version of the TPL could be built
for $2B to $3B, but who has that kind of money? Even
if it came from our taxes, that amounts to $10.00 to
$15.00 from every man, woman and child in the U.S.!

Regards,

Dave Handwerk

--- Xenophile wrote:

> --- In spacesettlers, "Lucio de Souza Coelho" wrote:
>
> > Another Ringworld-related problem that I forgot is
> dynamic
> > stabilization. Since this structure would not be
> in orbit, behaving
> > instead like a "solid" ring around Earth with the
> center of mass
> > matching that of Earth, some portions of it could
> be slightly closer
> > to Earth than the others; and as a result the ring
> would be
> > irrevocably pushed toward Earth from some side and
> be destroyed.
>
> Well, I've got a simple solution to that, but it
> strays into
> unobtainium territory. Not by much, though.
>
> Since the ring is geostationary (despite being at
> Shuttle height), you
> could have a bunch of space elevators connecting it
> to the ground.
> Then, if one side drifts closer to Earth, the other
> side has to drift
> farther away, and the elevator ribbons won't allow
> that. You could
> position one, say, every thousand Km around the
> equator, giving you
> forty of them.
>
> And a tether that can support itself for 200 Km is
> probably more
> "obtainium" than one which can support itself for
> 35,792 Km.
>

Never Miss an Email

Hi,

Have you read the 3 part article by Paul Birch,
"Orbital Ring Systems and Jacob's Ladders," in the
Journal of British Interplanetary Society (part I,
Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
ff; part III, pp. 231 ff (1983))? It gives a very
through explaination and all the needed physics. Plus
some other very interesting applications that are just
now starting to become of practical importance.

regards,
Dave

--- Lucio de Souza Coelho wrote:

Hi,

Have you read the 3 part article by Paul Birch,
"Orbital Ring Systems and Jacob's Ladders," in the
Journal of British Interplanetary Society (part I,
Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
ff; part III, pp. 231 ff (1983))? It gives a very
through explaination and all the needed physics. Plus
some other very interesting applications that are just
now starting to become of practical importance.

regards,
Dave

--- Lucio de Souza Coelho wrote:

> On 1/4/07, Xenophile
> wrote:
> (...)
> > Ah, I begin to see.
>
> That's good, because I still have no drawing. :)
>
> (...)
> > But if the the forces are to be balanced, and one
> > ring is moving much faster than the other, then
> the faster-moving ring
> > needs to be LESS massive than the slower-moving
> ring. How much less
> > massive? How Fast?
> (...)
>
> Well, lets put some numbers in an hypothetical case.
> Suppose a ring
> circling Earth at an altitude of 200Km
> (Shuttle/ISS-like altitude). At
> that altitude the outer, static ring would
> experience a surface
> gravity of around 0.93g. Then in order to counteract
> that gravity and
> produce 1g outward, the inner ring would have to
> spin at 11.2 Km/s .
> And the mass of the outer ring would have to be
> around 8% higher than
> that of the inner ring.
>
> Conversely, if you put the gravity of the inner ring
> also at 0.93g,
> then the outer and inner rings will have exactly the
> same mass.
>
> Another Ringworld-related problem that I forgot is
> dynamic
> stabilization. Since this structure would not be in
> orbit, behaving
> instead like a "solid" ring around Earth with the
> center of mass
> matching that of Earth, some portions of it could be
> slightly closer
> to Earth than the others; and as a result the ring
> would be
> irrevocably pushed toward Earth from some side and
> be destroyed. In
> order to avoid that, the ring has to be dynamically
> stabilized, ie,
> sensors have to constantly monitor if the ring is
> tending to "fall" in
> some point and push the structure a little bit
> accordingly. The
> obvious way to do such corrective pushes would be
> using giant
> thrusters, but since those are very inefficient I am
> thinking about
> something more elegant: magnetic attitude control.
> By using
> electrodynamic tethers, the ring could interact with
> Earth's magnetic
> field and use the forces thus obtained to keep
> itself correctly in
> place.
>
> Of course I have no idea of the order of magnitude
> of magnetic fields
> required by that. I would need restart the little
> knowledge of
> magnetism that I have...
>

You snooze, you lose. Get messages ASAP with AutoCheck

Hi,

Have you read the 3 part article by Paul Birch,
"Orbital Ring Systems and Jacob's Ladders," in the
Journal of British Interplanetary Society (part I,
Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
ff; part III, pp. 231 ff (1983))? It gives a very
through explaination and all the needed physics. Plus
some other very interesting applications that are just
now starting to become of practical importance.

regards,
Dave

--- Lucio de Souza Coelho wrote:

Hi,

Have you read the 3 part article by Paul Birch,
"Orbital Ring Systems and Jacob's Ladders," in the
Journal of British Interplanetary Society (part I,
Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
ff; part III, pp. 231 ff (1983))? It gives a very
through explaination and all the needed physics. Plus
some other very interesting applications that are just
now starting to become of practical importance.

regards,
Dave

--- Lucio de Souza Coelho wrote:

On 6/14/07, Dave Handwerk wrote:
(...)
> Have you read the 3 part article by Paul Birch,
> "Orbital Ring Systems and Jacob's Ladders," in the
> Journal of British Interplanetary Society (part I,
> Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
> ff; part III, pp. 231 ff (1983))? It gives a very
> through explaination and all the needed physics. Plus
> some other very interesting applications that are just
> now starting to become of practical importance.
(...)

No, but somehow I felt that many people probably thought of the same
concept long before us. :)