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Space elevator a reality soonish

daver said:


The ribbon is under tension--if you blew up the ground base the lower end of the ribbon would snap up a bit; the ribbon as a whole would wander slowly westwards. After rebuilding the ground base, you'd have to launch a suborbital craft to dock with the remnants of the tether; this would splice the cable and eventually redock with the rebuilt ground base. The rebulit ground base would haul the tether back down and you're back in business.

The ribbon is probably going to be black--i don't imagine it would fare very well in a laser battle.
Click to expand...

For the best description of such an event, read Red Mars by Kim Stanley Robinson - the 'greens' perform a terrorist act where a Martian elevator is blown up at the top. The whole elevator falls to the planet below, pulled along by Mars' orbit, and slams into the surface. Big bang!

so cool...

Athon
 
I am skeptical of the $7 billion price tag, among other things. That seems way too cheap, especially when factoring in R&D (disclaimer: I am not , nor am I anywhere near being, a scientist).

I didn't see in the article how they intend to get the uppermost part of this thing moving. Obviously a geosynchronous orbit would have to be maintained or the thing would wrap itself around the Earth as the planet spins, like an Earth yo-yo. I do, however, see where someone above mentions them moving it around to avoid satellites. Oh brother!

Is this for real? Seems extremely ludicrous. Can a cable that long really support its own weight (I know they claim it can..)? Hey, I'm just a computer geek, but I think it's hogwash.

I like the part where they compare the debris falling to Earth from a disaster to a ticker-tape parade.

What if space aliens hitch this thing to the back of their UFO and drag us out of orbit? Prediction: this "elevator to heaven" will never happen.
 
Um. . . impossible.

Think of two things that would prohibit this.

1. Materials: THOUSANDS and thousands of miles of steel, iron, plastic, glass, etc to create this.

2. STRESS and STRENGTH: Just try ot think, ofr one second, about the unimaginable stress placed on the elevator over that great distance, with the speeds and strains placed on it.

Come on, people! Get real!

www.badastronomy.com
Phil already tore this idea apart.
 
schplurg said:
II didn't see in the article how they intend to get the uppermost part of this thing moving. Obviously a geosynchronous orbit would have to be maintained or the thing would wrap itself around the Earth as the planet spins, like an Earth yo-yo.
Click to expand...

You launch the cable on a spool via a conventional launch vehicle. Once the spool is at geosychronous orbit, you unspool the cable (in both directions) until one end of it reaches the ground. Tidal forces will keep it (relatively) straight as it extends. You have to make sure that the center of gravity of the system remains at geosych orbit, which might be slightly tricky to do.

There are a number of problems with the space elevator idea, but I don't think "getting the counterweight going round fast enough" is one of them.

--Terry
 
c0rbin said:
Link in BA to space lift

Diogenes, don't forget to eat!
Click to expand...
Originally posted by Larspeart

Phil already tore this idea apart.
Click to expand...

That article is about 7 years old, and I would hardly say it dismisses the idea as nonsense..

It includes this link added in 2002..........

Space Elevator Gets Lift

Although much of the technology already exists, or is in advanced stages of development, the space elevator's primary component is still far from perfected, and is the main impediment to moving ahead on the concept.
Edwards says he believes the timetable depends on the carbon nanotubes and the epoxy composite material that will hold it together.
"That's essentially the last raw technology that we need before we can do this. When that's done, if a concerted effort is put together, we could have the first operational space elevator 10 years after that," Edwards said.
Pearson said once the carbon nanotubes are acquired, "I don't see why we couldn't build one in the next 30 or 40 years
Click to expand...
 
Larspeart said:
Um. . . impossible.

Think of two things that would prohibit this.

1. Materials: THOUSANDS and thousands of miles of steel, iron, plastic, glass, etc to create this.

2. STRESS and STRENGTH: Just try ot think, ofr one second, about the unimaginable stress placed on the elevator over that great distance, with the speeds and strains placed on it.

Come on, people! Get real!

www.badastronomy.com
Phil already tore this idea apart.
Click to expand...

The dynamics behind the space elevator are pretty straightforward; if you know differential equations you can solve them yourself. It turns out that you can build one from "conventional" high tensile strength steels, but that the taper factor (the ratio of the thickest portion (at GSO) to the thinnest (at ground)) is enormous, as is the total volume of steel.

The elevator would be made out of some carbon fiber, not thousands of miles of steel and plastic and glass. You're going to need hundreds of thousands of miles of carbon fiber. That's a big number, but not on the face of it an outrageous number.
 
athon said:


For the best description of such an event, read Red Mars by Kim Stanley Robinson - the 'greens' perform a terrorist act where a Martian elevator is blown up at the top. The whole elevator falls to the planet below, pulled along by Mars' orbit, and slams into the surface. Big bang!

so cool...

Athon
Click to expand...

I'm not sure if it's realistic, though. You can blow off the bottom couple thousand miles of the tether, and you end up with a shorter tether in an elliptical orbit.

Even without a safety charge, i don't think the entire tether would wrap itself around the planet like a string around a yoyo. It might make it part way around, but then it's going to snap. Damage on the ground is going to be very localized. I'd expect more dealths on the beanstalk than on the ground.
 
DanishDynamite said:
In the article, they relate how the ribbon will be some 100,000 kms long, way past the altitude of the geosynchronous orbit. I'm somewhat puzzled in regard to why the ribbon should be longer than the 36,000 kms or so of geosynchronicity.

Suggestions?
Click to expand...

Some designs put a large mass at GS orbit to counter the mass of the part extending to the surface. The design mentioned above instead has the mass extend past GS orbit as a counterwieght. This has the advantage of allowing you to use the outer part to sling spacecraft or whatever into space at high velocities. Doing this could shorten the trip to say Mars to only a few weeks rather than the many, many months it would require otherwise.

As for the other satellites getting in the way, GS satellites are orbiting at the same speed as the tower top and others, lower satellites can vary the plane of their orbit to avoid the tower. Coverage of the area around the tower can be accomplished by sensors placed on the tower itself.

The tower doesn't have to be very wide. A tower that could lift 50 mt would probably only need to be a few centimeters in diameter so its not like the tower is a significant obstacle for orbit craft.

The tower will be under tension, but probably won't be elastic and so wouldn't snap back if severed. As an example of what I mean - some ships use nylon mooring lines. Nylon is very stretching and if these things are loaded until they break the ends whip back at supersonic speeds. Newer mooring lines are made of kevlar/aramid. These guys can take a lot more tension that an equal diameter nylon line before breaking and when they do the two ends just drop. They aren't elestic so they don't stretch.
 
Learspeart :"Phil already tore this idea apart."

I read BA's critique and would offer this rebuttal.

His judgement relies of three main points

!. The materials question
2 The deployment question
3 The differential orbital speed

On question one , the date of the inquiry is 1996, meterials science has moved quite far in the preceding 7 years to exotics like carbon nano tubes and ultra light weight ceramics that not only incredible strength but thermal property's that make them seem magic. They are both constructed of materials that are mostly space, hence the weight problem is modified.

The deployment, I cant really address this question as it would just be a stew of ideas and would rely on the characteristics of the "cables", but this appears to me to be a practical problem that engineers could work out . There need be no "Hiesinburg Compansator" for the problem to be solved.

Number three has me positively flummoxed, ether I'm missing something or BA is , I'll proceed on the assumption that I'm trying to understand his explanation.

BA:"Worse, each part of the cable will want to orbit at its own speed. The tip will want to move fastest, and the part near the satellite slowest. This will increase tension on the cable, meaning you'll need a stronger cable. Actually, applying a series of thrusters every mile or two along the cable may ease this situation, much like having a telephone pole every few tens of meters along a telephone wire to help support the weight of the wire.

Ok the system I understand requires no counter weight, it dead ends at geosync orbit (22,000 Miles, 40,000 Km), anything we put there is relatively static as it is at the null point between gravitational attraction and centrifugal force. Now the proclamation of differential orbital speeds ( a little relativity on a Newtonian scale ). What BA is describing is a speed relative to a neutral gradient..a Linear force description, but the system cannot be examined or explained that way this system functions and can be explained by CAV..constant angular velocity. I was gonna bring up records as a demonstration but half of you probably don't know what they are =)...so how about hard disks?? That'l work. ....na lets talk bicycles The linear component here is how much chain will travel on the gear your in as you shift gears the linear component changes. more chain travels thru the pair of gears. The angular component is evident in the primary crank, the rotational speed doesn't change from the inner crank axal to it's outer gear at any point in the gear relative to it self. So the tidal force ascribed to by BA to the orbital forces at different heights doesn't exist ( to a high degree). All points are moving at stasis relative to the earthside station. Any given point along the line is traveling at zero speed in relation to the ground station. Not only that but the linear velocity relitive to the neutral gradient is FASTER ( not slower as stated) at the satilitte then at the base of rotation the earthside station So...blown away? This is so basic mistake I believe I must have misunderstood or I'm just a dullard.
 
TillEulenspiegel said:
[...]
Ok the system I understand requires no counter weight, it dead ends at geosync orbit (22,000 Miles, 40,000 Km), anything we put there is relatively static as it is at the null point between gravitational attraction and centrifugal force.
Click to expand...

The system with no counterweight has the cable extend considerably past geosych. The simplest case would be a symmetric cable, which would extend as far out from geosynch as it does down towards the earth. (Actually, there might be a correction for the gravity being less at that great a distance, I'd have to think a bit about that. Is it weight or mass that matters?)

Geosynch is not "the null point between gravitational attraction and centrifugal force", at least no more than any other orbit. There's nothing special about geosynch. except it just happens to be synchronous to the turning of the earth.


Now the proclamation of differential orbital speeds ( a little relativity on a Newtonian scale ). What BA is describing is a speed relative to a neutral gradient..a Linear force description, but the system cannot be examined or explained that way this system functions and can be explained by CAV..constant angular velocity. I was gonna bring up records as a demonstration but half of you probably don't know what they are =)...so how about hard disks?? That'l work. ....na lets talk bicycles The linear component here is how much chain will travel on the gear your in as you shift gears the linear component changes. more chain travels thru the pair of gears. The angular component is evident in the primary crank, the rotational speed doesn't change from the inner crank axal to it's outer gear at any point in the gear relative to it self.
Click to expand...

sorry, you lost me there.

So the tidal force ascribed to by BA to the orbital forces at different heights doesn't exist ( to a high degree). All points are moving at stasis relative to the earthside station. Any given point along the line is traveling at zero speed in relation to the ground station. Not only that but the linear velocity relitive to the neutral gradient is FASTER ( not slower as stated) at the satilitte then at the base of rotation the earthside station So...blown away? This is so basic mistake I believe I must have misunderstood or I'm just a dullard.
Click to expand...

Tidal forces certainly do exist, and most definitely would be important in the dynamics of the space elevator. Tidal forces arise due to the fact that gravitational forces vary inversly with distance (square of, to be more accurate). Therefore, for an extended object, the force (per unit mass) on the part furthest away from the earth is less than the force on its center of gravity, which is in turn less than the force on the bit closest to the earth. If you cancel out the "bulk" force of gravitational attraction (say by being in orbit), there is still the tidal component, which "looks like" it is stretching the object along the line between the center of the earth and the center of the object.

--Terry.
 
"Geosynch is not "the null point between gravitational attraction and centrifugal force", at least no more than any other orbit. There's nothing special about geosynch. except it just happens to be synchronous to the turning of the earth."


I'm sorry but the geostationary orbit is precisely that. The Clarke orbit is special as it is the point not only that matches the rotational speed of the earth, but also it is the point that requires minimal fuel for positional maintainance.You can go lower but that takes fuel to keep the speed of the object synced and aloft.
http://home.alltel.net/nelpi/nelpagec.htm
http://www.leydenscience.org/physics/gravitation/satspeed.htm

"sorry, you lost me there."
What I was trying to demonstrate is the difference between linear velocity and angular velocity. On an arbitrary grid, a point on the rotational body (closest to the axis of rotation ) say on the surface moves slower than a tower 10 miles tall has no relevance to our elevator. ( I don't think) The difference in the angular velocity relationship of the top of the tower and the point directly on the ground is ~0. so theres no shear force except in accounting for inertial and atmospheric drag . The inertial being overcome in the first few hours of completion, the atmospheric being a slow cyclical problem being dampened by the size and mass of the thing. Like a long spring.
A tower at the equator at ~sea level travels at 1K Mph, a satellite that travels directly over head fixed in the Clarke orbit clocks in @ 6,868 Mph.But the fact is as I understand it the system in unaffected by that linear differential.

"Tidal forces certainly do exist"
That was stupidity on my part I was thinking of shear force perpendicular to the cable and not tidal along its length . I stand corrected.
Like a dumbass I looked at the site Dave mentioned after posting and realized that the complex studies had been done by experts.. The gravitational and centrifugal gradient effecting the cables, the mechanics of treating the whole cable as a body in regards to gravity rather then a point mass. So I've been gibbering like a baboon
I still , tho, disagree with BA's assessment.
 
TillEulenspiegel said:
"Geosynch is not "the null point between gravitational attraction and centrifugal force", at least no more than any other orbit. There's nothing special about geosynch. except it just happens to be synchronous to the turning of the earth."


I'm sorry but the geostationary orbit is precisely that. The Clarke orbit is special as it is the point not only that matches the rotational speed of the earth, but also it is the point that requires minimal fuel for positional maintainance.You can go lower but that takes fuel to keep the speed of the object synced and aloft.
Click to expand...


It doesn't take fuel to stay aloft in an orbit lower than geosychronous. Of course if you are so low that you are in a noticable amount of atmosphere, that's a different matter...
http://home.alltel.net/nelpi/nelpagec.htm
Click to expand...

Doesn't say anything about geosynch being some magic null point so far as I can see...

http://www.leydenscience.org/physics/gravitation/satspeed.htm
Click to expand...

This just says a satellite's orbital speed varies with it's orbital radius (and gives the equation). No help there either.

So unless your point was that a powered earth-synchronous trajectory is possible at a different radius than the Clarke radius, I'm still not following you.

--Terry.
 
Wow, I go on holiday for a couple of days and look what happens.

There are some good questions, I will explain things as I understand them to help answer some of the questions.

The space elevator should in the end be little more than a really long but really thin carbon nanotube rope, attached to an oil rig in the ocean at the equator, with a small satellite at the other end way up. Now in order to dodge storms, and other satellite's, the oil rig thingy just motors around on the ocean. That makes it easy to move the elevator, if there is one thing that couldn't get more established about this, it's the moving of an oil rig.

If terrorists or an accident did break the rope, it could not cause any damage to anything, the rope is too thin to survive falling through the atmosphere at any decent speed. Any cargoe or people in a lift as it was climbing up when the rope broke would either end up in orbit, or float gently to earth with a parachute. Then you could retreive the end of the rope and epoxy it back together using the same stuff you used to build the rope.

The building of the first elevator is the really nifty part, what you do is send up a satellite to geosynch orbit, on board this satellite is enough carbon rope to stretch from earth to really far, can't remember how far, but I think more than twice geosynch orbit. Keep in the mind the rope is ribbon shaped, really flat and wide, so you could roll up a huge amount.

This first line is really thin and is rolled up in the satellite, as it deplys the rope down, it travels up, at the right rate to keep the centre of gravity at geosynch, once the rope is fully deployed and attached to the sea platform, you send up robot after robot with it's own coil of carbon rope, which is then epoxyed on to the current one, making it stronger, now remember the rope is actually a ribbon, so the robots climb by a simple wheel arrangement that clings on to the flat of the ribbon. The robots make the ribbon wider and also thicker, but not too much. Then once you have this all epoxyed up, it's ready for cargoe, and the beauty is, it is then even cheaper to make another space elevator, using the same method, but launching from the elevator to make it cheap.
 
Originally posted by daver
The dynamics behind the space elevator are pretty straightforward;
if you know differential equations you can solve them yourself.
Click to expand...
Okay.

The cable has tension in the form of negative pressure from two directions
inward from gravity and outward from the rotation of the cable in the same
direction as the planet.

First I derive the gravitation pressure on the cable.

Pg = F / A
F = (m M G) / (r r)
m = p A d[r]
Pg = (p M G) ? (d[r] / (r r))
Pg = (p M G) | (-1 / r)

Next I derive the rotational pressure on the cable.

Pr = F / A
F = (m V V) / r
V = 2<pi> r / t
m = p A d[r]
Pr = (4 <pi> <pi> p / (t t)) ? (r d[r])
Pr = (4 <pi> <pi> p / (t t)) | (r r / 2)

Total Pressure is therefore the sum of these two.

Pt = Pg + Pr

Now, what do I need?
Earth Time = 86400 seconds
Earth Radius = 6.378E+6 meters
Earth Mass = 5.98E+24 kilograms
Gravitational Constant = 6.67E-11
Density of Carbon Fibers = 1300 grams per cubic meter
Oh and of course, geosynchronous orbit.

a = (M G) / (r r)
a = (V V) / r
V = 2 <pi> r / t
4 <pi> <pi> r r r = M G t t
r = 42.174E+6 meters

Okay.
So the pressure at earth radius is -81.157 gigapascals, and at
geosynchronous orbit it's -6.181 gigapascals resulting in a total
pressure of -74.968 gigapascals on the cable. I wonder how long
the cable has to be past geosynchronous orbit to balance this pressure.

Hm.

Well, I leave that as an exercise for the readers of this message.
 
Just set pressure for +81.157 GPa and solve for r. Assuming I can do the math correctly (a fairly poor assumption, admittedly), it would be around 240 000 km, or 240E6 m, about 200E6 m beyond geosynchronous.
 
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