Space Elevator
Space ElevatorHow can the SpaceElevator be built? ("deployed", "initial deployment").
The real reason why the Space Elevator couldn't possibly work
I know when I first heard about this, I thought "that can't possibly work". I thought of 3 obvious reasons why it wouldn't work:
Perhaps there's some not-so-obvious reason why it is impossible. Please list any you think up. I would be very, very interested in any reason why the NIAC proposal couldn't possibly work. I couldn't care less about reasons why some other, inferior proposal couldn't possibly work.
false reason #1 why it is impossible: How do we get the asteroid counterweight into exactly the right place?
There is no asteroid in the NIAC proposal.
The NIAC report proposes lifting every part of the Space Elevator from Earth, using standard, ordinary rockets to put the initial counterweight and 19 800 kg of cable (a single cable long enough to reach from the counterweight to the ground) into geosync orbit, using exactly the same rockets that have been used to put (many) 22 000 kg communications satellites into geosync orbit. The rocket engine, the empty propellant tanks, and the empty spool are used as the initial counterweight.
tangential discussion about asteroids
Using an asteroid as counterweight would save a few million dollars - we could ship up less counterweight mass and use a shorter cable. The savings might be more than enough to pay for a mission to some asteroid to bring it to Earth orbit.
A rock, big enough, arriving JustInTime to just the right place to connect to a cable made to stretch to it somehow from the surface of the earth at the same instant, with all the proper connection points already in place, at both ends by people or robots also present at the same instant. (Where does this rock come from, and how does it have all of the qualities required? How is it slowed down, or speeded up so that it maintains a synchronous position in a previously non-synchronous orbit at the precise moment of its connection to the cable?) [When asked for an estimate of when the SpaceElevator would be built, ArthurCeeClarke replied, "Fifty years after everybody has stopped laughing."]
The rock can come from anywhere: the earth, the moon, it doesn't matter. It is placed in geosynchronous orbit the same way any human made satellite is. The cable is extended from the rock to the surface of the earth.
Properties of the counterweight
The counterweight must have sufficient mass to act as a counterweight. It must be beyond synchronous orbit to keep the mass center of the system at geosynchronous orbit altitude. It must somehow be attached to a point on the earth, and remain in equilibrium before, during and after attachment. It must have a consistent and constant force applied to it to cause it to remain geosynchronous in a beyond synchronous orbit. After attachment, that force will be the cable.
Then it seems that there is your view, (http://www.chaos.org.uk/~eddy/project/space/ladder.html#Theory)'s view, and several other views. How many others? Which of these is the real SpaceElevator, and who is designing/researching into what it will be?
Dr. Brad Edwards wrote the NIAC report. It is a proposal for a real SpaceElevator. Is it OK if we discuss that proposal? I think his proposal is viable as-is, but by the time "we" get around to building it, people will have thought up small improvements in various parts of his design.
What is the timetable?
The timetable is 50 years after everyone stops laughing.
Who will pay for it?
Ah, now that is a good question.
Since it seems that everything in space today is funded by NASA and the European Union, it seems logical to guess that perhaps they would fund the SpaceElevator as well. (They have already paid for several other projects that were more expensive). Some people suggest that perhaps the ROI and positive publicity is enough to attract private companies.
How will space loads made in the UK, Europe, Sweden, Russia, Egypt and other such places make their way to to the marshalling point at the elevator base? Said to be in the middle of the Pacific Ocean? Will the cost of that part of the transport be negligible?
The cost of moving cargo from the UK to the middle of the Pacific Ocean is negligible compared to the cost of lifting cargo from anywhere to orbit.
And what about the time required for that part of the journey (which in some cases may exceed 15,000 kilometres?
The NIAC design has 200 km/hr climbers; taking 7.5 days to get to about 35 800 km altitude (geosync orbit) and 20 days to travel the full 100 000 km length of the cable. But why do you care? How would it change anything if it was so slow that it took several days just to lift something to the typical space shuttle altitude of 300 km?
I wasn't referring to the climbers, but the transport time and effort from manufacturing point to half way round the world.
What's the problem with transporting anything anywhere around the surface of the Earth?
This complaint is particularly amusing when you consider that most conventional launch-to-geosynchronous orbits are best done from as close to the equator as possible - UK satellites are frequently launched from French Guyana. There is already a company that provides conventional launches from the middle of the sea. (See http://www.sea-launch.com/) The reason for this? It's cheaper to move your payload to close to where you want it along the surface than it is in space, because you don't have to lift as much fuel.
Questions about Initial Deployment
Then how will the cable reach the earth? Some parts of the system must be earthward (cable and transferable loads) How will part of the orbital mass descend straight down, losing precisely the amount of velocity to keep it directly below the geosynchronous point? There is a force called gravity which is zeroed out at geosynchronous orbit. It cannot cause it. Some other force is necessary.
Again, rockets. They can lift things and lower them. I'm not saying the math will be simple, but the principle is.
[At the geosynchronous point, the rock is stationary with respect to the ground, the centripetal force just compensated for the gravity (i.e., the orbital speed at that height is the same as the Earth's rotation speed). The rock lowers a rope towards the ground. Since the rope is rotating Earth at the same speed as the rock, which is slower than the orbital speed of the now lowered altitude of the rope, the rope will be pulled towards the ground*. Meanwhile, on the other side of the rock, you "lower" another rope. That 2nd rope will "fall" away from Earth due to centripetal force. So it acts as a "counterweight" to balance pull of the first rope on the rock, you can attached some weight to the 2nd rope so it won't need to be as long. Some rockets on the rock can deal with any remaining imbalances to keep the rock at the right place. Theoretically, the first rope can lowered all the way to the ground this way, although you might have to compensate for the additional pull due to winds with rockets on the rock. After the first rope is tied to the ground, you can extend the 2nd rope to over-compensate, so you get a more outward pull on the rock and pull the first rope tight, the tension can be adjusted by the length of the 2nd rope.]
[*While the rope is being lowered, the rope will be slanted slightly eastward initially. But since the rope is being pulled towards the ground all the time, just stop lowering the rope, and it will eventually swing back to being vertical. Similarly for the 2nd rope going the other way (will be pushed westward).]
Before attachment where will the force come from (to get it from the Earth, the moon, or (it doesn't matter) location -- to that stable, precise location)?
Probably rocket fuel, just like any other object we put in orbit.
And just where will the equal and opposite force come from to lift the cable to the attachment point at the precise location to complete a stable, strong connection. ---- IstillWantToKnow? (for I am afraid (it doesn't matter) and (The entire system will be in geosynchronous orbit) are both imprecise and incomplete answers)
Again, probably rocket fuel. The cable will probably be lifted on a spool, then lowered to earth from the object.
A spool with over 35,000 meters of cable strong enough to support itself and the hook on its end? What is the inside and outside diameters of that spool, and who or what will account for it being "lowered to earth from the object?"
Most of the accounts I've read will use a winch to lower it.
The NIAC proposed "initial cable" design is roughly 100 000 km long, 1 um (1e-9 m) thick, and tapering from 0.115 m wide in the middle to 0.05 m wide at the ends. That gives it a volume of less than 11.5 m^3. It should fit on a spool with an inside diameter of 1.1 m, outside diameter of 2.2 m, and a width of 1.1 m. The "initial cable" has a mass of 19 800 kg, slightly less than a Russian geosynchronous communication satellite. DeleteWhenCooked: This paragraph has a significant typo. Is this 1 um (1e-6 m) thick, or 1 nm (1e-9 m) thick? 1 nm is about 2-4 atomic diameters.
Would it help if we listed all the steps in the NIAC plan?
Yes indeed: the part called
The cable can be lowered as slowly as it is safe, just stop turning the wheel on the far side and cable stops. Read somewhere above in this page. We are talking 7-20 DAYS of ascend here, which is 20-60x longer than your number. And if a couple jet engines and rockets cannot provide the horizontal thrust at that rate, what's the problem with letting the ascend take a month or two? Why create artificial requirements that make the system impossible? Who needs the load to go up in 6 hours instead of 1 month? Why must it travel at supersonic speeds? Why can't the load move up at a speed limited by the most limiting factor, such as climber power, horizontal thruster power, cable tension, etc?
As the climbers pull themselves up the cable, they do deflect the cable sideways. Steven Den Beste http://denbeste.nu/cd_log_entries/2003/10/GreatChipmunkSpaceshipRac.shtml has a good introduction to the physics of the space elevator -- especially the counter-intuitive fact that a climber pulling itself *up* the elevator also pushes it sideways. (This is sometimes called the "Coriolis Force" http://scienceworld.wolfram.com/physics/CoriolisForce.html )
A 1000 kg climber (at 200 km/hr) exerts 190 N = 43 pound of force sideways on the ribbon (and, of course, 9 800 N of force downward on the ribbon). This horizontal force causes the part of cable below the climber to tilt a fraction of 1 degree from vertical. This causes the boat attached to the bottom of the cable to be pulled to the west. Jet engines or rockets could hold the boat in position, but you can probably think of a more cost-effective technology.
I mean thrusters on the climber itself to counter the horizontal thrust. The Earth bound part is probably anchored tightly to the ocean floor, but orbital part has nothing to anchor on, so we will need thrusters somewhere anyway, so might just as well put one on the climber to reduce tension on the rope. [No, we won't. The orbital part is constantly trying to get away from earth, and the furthest from earth it can get is directly above the bottom anchor.]
I agree that we could put rocket thrusters on the climber to counter the horizontal thrust. But I also think that the climber can go up the space elevator just fine without them. Without rockets, the section of the space elevator below the climber merely tilts some fraction of 1 degree; the section of the space elevator above the climber merely gets pushed sideways into a new stable position a few kilometers to the west. As soon as the climber stops, the space elevator returns to its original position. Unless, of course, I've messed up my calculations.
If the cable is anchored then the section above the climber is pulled down as well as westward. I don't understand what will return the elevator to its original position.
Perhaps when initially explaining the SE to someone, "rockets on the climber" and "big rock at the geosync point" can help people understand that it's even possible. I fear that trying to explain why the rockets aren't necessary, and why the big rock isn't necessary, may confuse people who are not yet convinced it's possible at all. Is there a name for this sort of "mental scaffolding" used to help explain new concepts to people? WittgensteinsLadder?
What will return the elevator to its original position ? is a very good question. [Centrifugal force does.]
An important part of the SE is the mass of the counterweight at the far end of the cable, far beyond geosynchronous orbit. Just like when you swing a weight on the end of the string, the further out you place that weight, the more force it pulls out. The position of the counterweight is adjusted so that it not only holds up the entire weight of the cable "hanging" below geosync, but also has an "extra" 400 000 N (is this right?) or so force pulling up at the anchor point (when no climbers are attached).
Since climbers have a mass of about 33 000 kg, below LEO they pull down on the SE with a force of about 320 000 N, relieving the vertical force on the anchor point to "only" 80 000 N. (If the counterweight isn't far enough out, there may not be enough "excess tension" to hold up the climber. If the climber is much too far out, the cable will break from the excess tension -- the NIAC report only has SafetyFactor? of 2).
As the climbers go up, they typically push the cable sideways with a force less than 200 N (45 pounds of force).
If I take a piece of ribbon and tie it to a large boat, pulling up with a force of 80 000 N and sideways with a force of 200 N, the ribbon leans over at an angle of less than 0.15 degrees from vertical. As soon as I stop pushing it sideways, the vertical force pulls it back to straight up (possibly with some oscillation).
Even if the entire ribbon leaned over 0.15 degrees, the counterweight would be displaced towards earth less than 500 meters. So the part of the ribbon above the climber still has the "extra" 399 999.93 N of tension out to the counterweight, which is still thousands of kilometers on the other side of geosync orbit.
There's no east-west force holding the counterweight in position over the anchor, so it would get pulled sideways by any non-vertical ribbon until it is directly "over" the climber (making the ribbon vertical from the climber up to the counterweight).
Is there a better way to explain this?
Is it just me, or is no-one taking into account that as the climber moves up the ribbon, that it would start generating larger and larger amounts of centrifugal force itself? Think of twirling a string with a rock on the end, then sticking a washer on the string at the origin point, it's going to get to the end just through centrifugal force isn't it?
Yes, that's exactly what would happen if you put a washer around the ribbon about halfway up and just let go. When you stand on the equator, there is a (small) centrifugal force associated with your circular motion around the center of the earth. Unfortunately, earth's gravity is almost 300 times as strong as that small centrifugal force. You need to start far enough out that the centrifugal force has increased enough to be equal to earth's gravity. That's such a useful starting point that various space agencies have already put tons of equipment at that altitude.
Another consideration is that there would probably be thousands of climbers moving up and down simultaneously. So a climber moving down would counteract another that is moving up.
questions about maintenance The cable as proposed is one monolithic carbon-nanotube/epoxy composite. Is it possible to repair it if it becomes damaged? Can it be made and assembled in replaceable segments, or does it have to constructed in 24000 mile spool increments? Can a segment be replaced after the elevator is deployed?
A SpaceElevator is a type of geosynchronous satellite. A SpaceElevator is also a type of SpaceHook or SkyHook?, which is a type of MegaStructure.
A SpaceElevator consists of a cable stretching from the surface of a planet to a mass far beyond geosynchronous orbit.
Satellites at geosynchronous orbit around Earth are at an altitude of about 35,786 kilometers (19,323 nautical miles or 22,241 statute miles). One proposed SpaceElevator design is about 100 000 km long, reaching about 1/4 of the way to Earth's moon.
A space elevator could get stuff into space and back much more cheaply and with far less stress than any other method (rockets, SuperGun?). Unfortunately, the start-up cost is huge (BigDesignUpFront). Some people estimate $40,000,000,000 . (Is that all? That's cheaper than invading a modestly-sized country on the other side of the world.) (SelfReplication: you can make space elevator number 2 for far less than that, by using the first one to send up the materials). (The InternationalSpaceStation? ISS has an estimated total cost of more than twice that, but it was/will be put up a little at a time).
The SpaceElevator was first conceived by YuriArtsutanov?, later popularized by ArthurCeeClarke, in his book The Fountains of Paradise. On the likelihood of its construction, he said: "The space elevator will be built about fifty years after everyone stops laughing".
KimStanleyRobinson put space elevators in the Mars trilogy (see RedGreenBlueMars), at both Mars and Earth. The anchor mass/station for the first elevator, built at Mars, was named "Clarke". In both Clarke and Robinson's stories, the Mars elevators had the problems of avoiding one or both of Phobos and Deimos, which was done by inducing carefully timed oscillations in the cable. At Earth we might have a problem with smaller man-made space junk.
Charles Sheffield a former president of the American Astronautical Society wrote The Web Between the Worlds, a novel about the first SpaceElevator. The book came out at the same time as The Fountains of Paradise. It holds up quite well in comparison with Clarke's book. Clarke wrote an introduction to Sheffield's book.
The Mars trilogy by KimStanleyRobinson also explores what would happen if the cable fell down. (I'd like to hear more about what happens WhenSpaceElevatorsFall?. From the FAQ at http://www.liftport.com/faqs/index.php?fuseAction=faq&faqID=21#92: "The ribbon is light (7.5 kg/km) so, any pieces that fall to earth will slow down, in the air, to about the same terminal velocity as that of an open newspaper page falling.")
The cable is sabotaged and falls in Mercury by BenBova? (ISBN 0765304120 ).
operational costs compared to rockets
So, what is the cost advantage (if any) of the space elevator compared to rockets? Does anyone have any actual data and/or projections?
How much less energy does it take to put stuff in orbit using the elevator compared to using rockets? You still have to overcome the same gravitational potential.
You're right. It is unavoidable that it takes 57e6 N*m = 16 KWh of energy, per kilogram, to move any mass from the ground to geosynchronous orbit (allow me to call this "orbit energy").
It seems that the Space Elevator would be at least 1% efficient at converting wall plug electricity to "orbit energy". My last electric bill gives a "fuel rate" of less than $0.10 per KWh. (I misread this number before -- I hope I got all the re-calculations right this time). This gives $0.10/KWh * 100 * 16 KWh per kilogram = $160 per kilogram = $80 per pound. (Imagine if we could bump that to 2% efficient !). ISR (http://isr.us/SEHome.asp?m=1) claims that after factoring in the cost of the first elevator, depreciation, staff, security, etc., "The first space elevator would reduce lift costs immediately to $100 per pound, as compared to current launch costs, which are $10,000-$40,000 per pound".
(http://www.isr.us/spaceelevatorconference/) claims it will reduce lift costs to $100 per pound, compared $10,000-$40,000 per pound for rockets.
The cost advantage of a space elevator doesn't come from using less energy, but dispensing it using a cheaper mechanism (a cable and laser/microwave beaming rather than rocket fuel).
You also get a few percent savings because SE can spread out that energy over a longer period of time (days instead of minutes) means don't need to pay (at $10,000 per pound) for padding you otherwise would need to protect fragile cargo from launch vibration.
My guess is that after you factor in depreciation and the cost of security, that the cable isn't really going to wind up any cheaper than rockets.
You may be right. What did ISR neglect when they calculated that a price of $100 per pound was enough to pay for all the security they needed and still be profitable?
The $10000/pound figure for rockets is the rate the government pays. :) See Scaled Composites orbital plane effort (http://www.scaled.com/projects/tierone/index.htm). They are talking about affordable space tourism. If that means, say, a $10000 per ticket for Joe Average who weighs in at 150 pounds, they've already beaten the ISRs $100/pound deal. Careful - the Scaled Composites rocket does not achieve orbit - it is suborbital, and conceptually like the X-15 rocketplane. That's true, but of the 35000 km to geosyncryonous orbit altitude, it's the first 150 km (getting out of the atmosphere) that are the problem. No, the problem is achieving orbital velocity and angular momentum vs a ride straight up to 60 km altitude and back down. The energy required is far greater, about a factor of 10 to 100. One factor of ten because the payload needs this much energy to achieve orbit. Another factor of 10 because you need to fly the engines and propellant that puts that energy into the payload. This is why rockets are hard. Only a few percent of the mass of a rocket at the moment of launch reaches orbit.
It depends on where you're going, doesn't it? If you want to get into orbit, the elevator can do it for you. If you want to go to the moon, or to Mars, or to orbit in the other direction, or to any of the Lagrange points, you don't want the angular momentum you get from the elevator.
Huh? Angular momentum is a problem? Please explain. Compared with starting from ground level, it is trivially easy and orders of magnitude cheaper to launch yourself from geosync orbit to any destination you mentioned. Yes, but the comparison is not between ground and geosync, but between altitude 150km and already pointing where you want to go (space plane) and geosync. If you want to go to Mars for example, and you are already at 150km on the SE, why not climb all the way before firing your own rockets? Still, what's the problem with the angular momentum? You let go of the SE and fire your rockets at the right time, and there you go.
Removed chart that was put here by DonaldNoyes some time ago - to:
I think the NIAC proposal just has raw cable from the anchor to the counterweight at the far end -- there doesn't need to be anything at GEO. The initial proposal is more-or-less completely unmanned.
Why do I think of the Pony Express when I look at this? -- IStillWantToStopLaughing
For perhaps more scholarly and vetted information on this subject, refer to:
Investors please form a Queue
This is an example of BigDesignUpFront and You'reNotGonnaNeedIt which supposes a continuing interest in and a will to put stuff up and bring stuff down and pay for the SpaceElevator's maintenance, will exist in the future.
Questions continue
Does anyone know of any ventures to make money in space that is built around the idea of moving what we have here up there, and bringing down what is already up there down (past, present and future)?
The moon is already there, a big rock, beyond GeoSynchronous? orbit, why not tie the other end to it? Are there related scientific reasons why any rock of any size which is to remain geo-synchronous in an orbit beyond that at which it will naturally remain stationary above a point on earth, will somehow do so without the application of some kind of force?
You do realize that the asteroid you tie to the end of the space elevator is going to be dragged along with it, right? And that if you tied the moon up, and it didn't break the tether, then it would completely fuck up its orbit, right?
Let's break the moon in half so we can get at what's inside it
To answer your next question, no mysterious forces or magic are required, the tether provides the force needed.
IonThrusters are proving useful for pushing and pulling things about in space using little power and varied power sources. Xenon, solar, blueberries, etc. (could be wrong about the blueberries, maybe it was strawberries) anyway, for sure the xenon and solar are correct. So IonThrusters could prove a useful part of the SpaceElevator developmental suite brought in from existing field-tested technology.
See SpaceElevatorTerrorism for more about space elevators and terrorism.
For a long time, the SpaceElevator (like the cellular phone) was in CategoryScienceFiction ... but some people think it could soon be made reality.
-- yeah, that's what they said about waterbeds.
These kinds of Projects, while obviously containing some ElementOfRisk?, outsourced internationally, might inspire global cooperation, and cohesion. SpeakingInDeath? (planned before the fact, with all due respect to AndyWarhol?), dividing cities into DemilitarizedZones?, punishing targets exercising their FreedomOfMobility? via SurveillanceAbuse? retributions, or physically, does nothing to enhance GlobaPeace?.
Dave Barry has written about this idea - http://www.the-equilibrium.com/id78.html.
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