Science: Space: Satellite
An Earth Ring   (+3, -1)  [vote for, against]
Make a ring around the Earth

The long-term objective is to build a complete ring around the equator at geostationary orbit distance.

To this end, a treaty and set of standards would be drawn up, dictating that all new satelites should have docking capabilities. Where practical satelites could be joined to existing satelites to extend a fragment of the ring. The International Space Station, Hubble Telescope and anything else we put up there would all form part of the (at this point virtual) ring.

Then international projects could begin to fill in the gaps between satelites until a complete ring is formed.

Ideally, an automated construction device would sit at the end of a fragment of the ring, catch floating debris and connect it to the ring. We can start being picky about how nice the ring looks once it's finished, until then it will be like a shanty town.

(there is already an idea called Earth Ring, which is an aesthetic ring of rocks not joined together)

GEO Ring: radius = 42000km, circumference = 265000km, weight @ 1kg per 1m = 265000 tonnes, cost to launch materials @ $200 per kg = $53 billion, current cost @ $20000 per kg = $5.3 trillion

LEO Ring: radius = 15000km, circumference = 47000km, weight @ 1kg per 1m = 47000 tonnes, cost to launch materials @ $200 per kg = $9.4 billion, current cost @ $10000 per kg = $470 billion
-- marklar, Jul 18 2007

a smaller ring http://www.unfeign....capes/earthring.htm
one of many artists depiction of this idea [the great unknown, Jul 18 2007]

Launch Ring http://space.newsci...tes-into-orbit.html
A good way to launch building materials [marklar, Jul 18 2007]

Hohmann transfer orbit http://liftoff.msfc...llites/hohmann.html
It takes energy to change orbits. [Freefall, Jul 18 2007]

Would a ring system remain stable? http://www.astrosci...h-ring-dynamics.htm
(Doesn't much matter if it's initially connected, because it will break up almost immediately.) [ldischler, Jul 19 2007]

GEO ring http://home.comcast...cker/Earth_Ring.jpg
Alright, a better pic in my collection of *your* idea [the great unknown, Jul 19 2007]

Would sun activity push this ring in any direcction at all? Having a ring attatched together, if the ring were moved slightly out of orbit, would move one part closer to the earth and the opposite part further away, causing the ring to fall on one side towards the earth
-- miasere, Jul 18 2007


Kinda baked. this idea has been bounced around for awhile. But this is a good forum to discuss the good/bad of this idea.
-- the great unknown, Jul 18 2007


[miasere] It would be no more unstable than any other object in orbit, but would require boosters for stablisation. The ring would be better than individual satelites because if one of them fails, it either needs someone to fly to it and fix it, or it re-enters/floats away.

[the great unknown] I think baked is used to refer to things which have been done, rather than things that have been thought of. The ring you linked is in a lower orbit so shorter, but certainly not smaller. My idea is basically orbital scaffolding and IMHO feasible.
-- marklar, Jul 18 2007


A couple of factors.

First, the ISS and Hubble are not in geostationary orbit. Hubble is at 600km/28.5deg and the ISS is at 330km/51deg. Clarke orbit is 35000km/0deg.

Second, $10,000/kilo is cost to LEO. Cost to GSO is more like $22,000/kilo.

But hey! Why not, this is the halfbakery!(+)
-- Galbinus_Caeli, Jul 18 2007


I like it but, why "around the equator" as opposed to crossing it?
-- 2 fries shy of a happy meal, Jul 18 2007


[Galbinus_Caeli] I don't understand why LEO is cheaper than GEO, if you apply any outward force to something in LEO, it will end up at the GEO distance but moving too fast to stay in orbit. My conclusion is therefore that it requires more energy to reach LEO. Does that make sense?

I noticed that other stuff is in LEO, why is that? quicker & easier to get to?

The Earth Ring could be in LEO, it would be a lot shorter, but it would then be of no use for GEO satellites, but would be handy for the few GPS satellites that happened to be covering that loop of the Earth. I guess we'll just have to build 2 rings.
-- marklar, Jul 18 2007


Well, orbital velocity at GSO is a bit over 3km/sec, LEO is 8.5km/sec. But if you are traveling at GSO speed at LEO altitude, it is called falling (as in "falling to earth"). What you need to do is kick your object out to GSO, then change vector to 3km/sec in the right direction. All this requires fuel.

The numbers I took are NASA's numbers, (just like you did).
-- Galbinus_Caeli, Jul 18 2007


//if you apply any outward force to something in LEO, it will end up at the GEO distance but moving too fast to stay in orbit//

?

If you apply an outward force to something in LEO (let's assume circular orbit to start), the orbit of the object will become elliptical, but will still return to that original point as it completes its orbit. In order to reach GEO, you have to impart enough energy to the object at LEO that the new elliptical shape of the orbit will intersect the GEO orbit.

If you've applied just the right amount of energy, your elliptical orbit will be exactly tangential to the GEO orbit, but will be at its farthest point from Earth ("apogee"), which is also its slowest point. Its velocity will be less than what's required to remain in GEO, and will therefore be accelerated back towards Earth until it reaches its closest point ("perigee") and heads outwards again.

If you want your object to remain in GEO orbit, you need to apply additional thrust when your object is at or near apogee, so that it achieves GEO velocity.

This type of orbital transfer is called a "Hohmann transfer", for the scientist who determined that this is the most efficient way to change orbits in a two-body system. See link.

That you think a connected ring will be //no more unstable than any other object in orbit// merely reflects your lack of understanding of orbital mechanics. If this ring moves off-center, the portion of the ring closer to the Earth will have a velocity lower than what's required to maintain that orbit altitude, and will be drawn closer to Earth. The portion on the opposite side of the planet will have a velocity too high to maintain that orbital altitude, and will move away. Such a structure would be very unstable, and would quickly lose orbit.
-- Freefall, Jul 18 2007


I've been playing with this idea for a few years now, and even wrote a short story that features an Earth ring, but mine is a couple hundred meters across for convenient spacecraft launch and retrieval outside of the atmosphere, and low enough for elevators to the surface without exotic materials.

Yours weighing only one kilo per meter of length makes me think it must be very, very narrow - like a few cm - and is up there mostly just for mounting of instrumentation and comm relays.

The upside of yours is that if it falls it's small enough to not destroy entire towns on impact.
-- elhigh, Jul 18 2007


I admit to having only a passing knowledge of orbital physics, most of my assumptions are based on (probably incorrect) logic.

I see an orbit as a ratio of speed/distance. If you decrease either or both, the object will get closer to Earth, if you increase, it will move further away.

If you imagine the ring as a load of 100m panels not joined together, just floating next to eachother, each one has to correct its orbit occasionally. Now imagine that you tie them together with string. As one moves slightly out of orbit, it will tend to move the others, but it will move less because of that, so changes in orbit will be more gradual and require less drastic corrections.

I picture the ring as basically ladder shaped, reasonable stiff to 20m or so, with elastic flexibility over long distances.

A GEO ring has to be over the equator. I think the best orbit for a LEO ring would be over the poles, with one side always facing the sun.

In case anyone was starting to worry that this idea is not halfbaked enough, I've been considering the merits of having 2 LEO rings next to eachother, spinning in opposite directions, connected by an electromagnetic rail. This would allow launches from the ring using solar power for the motive force. Instability in the orbit could be corrected by moving masses around the ring. This is of course much more ambitious but should be taken into consideration as an upgrade when building version 1.
-- marklar, Jul 19 2007


2 fry, the reason GEO sats are around the equator is so it's orbit matches the earth's rotation. From earth they appear to just hang in space. This is why you don't have to keep moving your TV dish all the time. Also the reason why space elevators have a good chance of working. If the ring has these elevators, like spokes on a wheel, it may help keep it stablized. I also heard that having water on the "bottom" of the classic wheel space station would keep it stable as the crew & stuff shift around. There's not much advantage of having a polar GEO ring. One thing I notced is that the ring will cast a shadow across the earth. Saturn has such a shadow from it's rings. It would move slowly over the tropical zone as the seasons change. This may cause a more environmental impact than global warming.
-- the great unknown, Jul 19 2007


Ahh, of course. Thanks.
-- 2 fries shy of a happy meal, Jul 19 2007


May I ask why? You state the long-term objective is to build the ring, but then what? We have a shiny ring to show off to Saturn and Jupiter, but what do we do with it then? Or is the aesthetics the goal and nothing more?
-- Noexit, Jul 19 2007


//One thing I notced is that the ring will cast a shadow across the earth.// At one kg/meter? Not very likely you'd ever see it. Like trying to see a spiderweb a mile away.
-- ldischler, Jul 19 2007


// Doesn't much matter if it's initially connected, because it will break up almost immediately //[ldischler] Here's an extract from linked page "... perturbing influences of the Sun and the Moon cause these satellites to drift within a belt of approximately +/- 15 degrees geocentric latitude either side of the equator with an oscillation period of 54 years."

Non-connected objects next to eachother will be subject to the same forces, the article is talking about objects at GEO at various times and how they drift off over years.

The force acting between adjacent sections would be minimal, the ring is actually continuous, not really panels held together with string, that was just to illustrate a point. The ring would have stabilising thrusters. The idea of them being movable is that the ring will not be strong enough to support movement over hundreds of kilometres, so there would need to be thousands of them otherwise.

[great unknown] Saying, let's out a big ring round the earth is IMHO quite different to suggesting its size, method of construction, cost and how it would work (although I haven't really come up with a very convincing cost/benefit arguement). Otherwise it should get an MFD for WIBNI or magic.

I stumbled across an article suggesting a big reflective ring to counter global warming. I think my ring would be too small to cast a shadow due to particle scattering in the atmosphere (I'm guessing, I assume the ISS doesn't cast a shadow).

<pedant> GEO is by definition over the equator, if it was over the poles it would not be geostationary.</pedant>

Thanks to everyone for the links and criticism, I'm learning more about it every day.

Edit: (after seeing new posts) The main benefit I originally thought of was to increase the lifespan of satellites by removing the need for them to carry fuel and be refueled. You could just have a central refueling point for the ring, that the roving thrusters use.

Re: the shadow - on second thoughts, it doesn't matter whether you can see it, the fact is that (if it were solid rather than a framework) there would be 1m x 10,000km(ish) of shade. The sun's power is around 1kW per square meter so you'd be removing 10GW of heat.
-- marklar, Jul 19 2007


[ldischler] I saw your comment about the stresses on the ring but i think I might have clicked delete instead of annotate, sorry.

Anyway, although I don't think I could make the ring stretchy, I had pictured it being deformed by lunar/solar forces and I'd assumed (I have no idea how to calculate it) that the deformation would be slow enough for the structure to cope with it.
-- marklar, Jul 19 2007


I see how this ring can serve as a giant shared fuel tank, but I see other benefits: a platform for space elevators, a launch site for space vehicles, repair station for satellites, etc., space factories, habitation for an overcrowed planet and other uses.
-- the great unknown, Aug 03 2007


(chant) "The Ringworld is unstable! The Ringworld is unstable!"
-- normzone, Aug 03 2007


C'mon [normzone], how many people do you think will get that reference?

I seem to recall that, following the revelation of instability, that Larry Niven added stabilizing thrusters to the ringworld in "The Ringworld Engineers". (or was it "The Ringworld Throne"? I don't have the books handy to check)

man, what I wouldn't do to get my hands on some scrith.
-- Freefall, Aug 03 2007



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