Leo Lewis notes that boosters at the Japan Space Elevator Association are psyched. Unfortunately, material science problems are still a challenge, albeit one that has potential to be solved quickly (say in the next 10-30 years) and economically–but it’s still only potential at this point. Kevlar is still king of industrial cabling, body armor, etc. so super strong materials will be a laboratory curiosity for some years before they will be available for Earthbound uses, much less space uses.
One oddity: electric power delivered by the elevator. That would be an electric line that would stretch around the world. Probably better to stick with power beaming by laser. With solar energy very popular, that should not have any laugh test to pass. Another oddity. They stick with the far counterweight popularized by Edwards; this may be OK for initial deployment, but once mass is coming up the cable, the counterweight should be closer and heavier and the cable shorter.
For someone who follows the advances in CNT creation, it’s amazing how quickly the many pieces are coming together. Labs are creating CNT batches with uniform characteristics, figuring out how to patch irregularities and bond multiple CNTs together, lengths of individual CNTs up to 1 meter, sheets 3’x6′ in size, and more. It’s really incredible.
That’s all just a way of saying that, while challenges remain, I believe it’s going to be sooner than most realize.
They stick with the far counterweight popularized by Edwards; this may be OK for initial deployment, but once mass is coming up the cable, the counterweight should be closer and heavier and the cable shorter.
The counterweight is already at geostationary orbit distance (22k miles which might actually be too close). I don’t see a shorter cable remaining stable without active thrust of some kind.
I remember sitting through a Space Elevator discussion, a year or two ago, where they were discussing the dynamics of the system and I came away much more pessimistic than before the session.
Lots of subtle protuberances and a very high Q potentially resonant system.
I believe that it may require active dampening along the span.
The materials issues may be addressed, but that still leaves the big issue that before you build the “real” space elevator, you are going to have to build a test model first.
Because the answer to the question “What happens when you put one of these in place” is “nobody really knows.” Think of the kinds of resonance issues we discovered the hard way when building suspension bridges…
Also, IMHO, the most likely place to build a test model space elevator would be on the moon, where it wouldn’t interfere with commercial and military terrestrial satellites. Of course, that also adds new facets to the problem…
There is a problem with Space Elevators I’ve never seen its proponents address (perhaps they have and I’m not aware of it – I haven’t followed the field closely): As the crawler moves up the tether, it will tend to pull the cable and counter-weight down. Propellant will be required to reboost the terminal station. Have they made any estimates as to how much propellant would be required, and what fraction of a crawlers’ payload, on average, would have to be given over to this? This would add to any propellant requirements for avoiding OD.
I’m sorry, but I just can’t see a space elevator being built in this century. I know you’ve discussed the issue previously and that people have considered the following criticisms, but to my mind they have not been adequately addressed …
* How much mass are we talking about? Even if we somehow capture a convenient near-earth asteroid to use as the counterweight, the rest of the beanstalk is gonna be massive. A couple of naive BOTE calculations: a tether 1 cm x 1 cm x 40, 000 km constructed of 1 g/cc handwavium will mass 4×10^8 grams, or 400 tonnes (about 20 Shuttle payloads just for the cable mass and not counting any assembly infrastructure). Is a 1-cm tether thick enough to be useful for anything? A tether 1 meter x 1 meter x 40, 000 km would mass 4 million tonnes (i.e., 200,000 Shuttle payloads).
* How massive are the individual pieces of the tether that have to be carried into orbit? How do we assemble them into a stable construct with the required tensile strength? Or is the beanstalk fabricated in space as a single unit from raw material (presumably lots and lots of carbon fibers) shipped into orbit?
* If you use the elevator to convey electrical power down to Earth surface, how massive is that additional infrastructure, and how does it affect the design of the beanstalk? How much energy would be lost over 40,000 km?
* In terms of dollars and energy and time, how much does it cost to build? At any given time, won’t people prefer to invest their careers and money in something with a shorter-term payoff, such as putting an immediately useful payload into orbit, or bringing something valuable back? If it takes 50,000 Ares 5 payloads to build the elevator, why not just fly 50,000 immediately useful Ares 5 payloads instead?
* What are the failure modes? Everything in low earth orbit is going to cross the equator somewhere twice every 90 minutes or so; how do you prevent collisions with orbiting debris? What are the vibrational instabilities? Is the structure stable against perturbations (e.g., from mass changes or lunar tidal effects)? If it does fail, what are the physical consequences? And even if it doesn’t fail, how do we get rid of it when we don’t want it any more?
* Speaking of failure modes, how much will it cost to insure the darned thing? And will there be a planetful of NIMBYs filing lawsuits in an effort to prevent you from building it?
* Given that the United States can’t seem to come up with a way to send humans back to the moon by 2020, how long will it take to design, test, approve, and construct the darned thing? (And how long will it take to capture an asteroid counterweight?) Even if all of the other problems immediately vanish, this point alone would keep us from building an elevator before 2050, in my humble opinion. OK, someone who doesn’t give a crap about optimal design, regulatory agencies, ROI, or botching the first four or five attempts *cough* China *cough* might be able to build it by 2040. Maybe if they used surface-to-orbit Orion vehicles … but then why would they care about building a beanstalk?
I think an elevator from the lunar surface to L1 or L2 might be feasible, although the shallow gravitational well and airless environment negate many of the advantages of a terrestrial elevator. But building an elevator from Earth surface to space seems like preferring the gargantuan infrastructure of Heinlein’s “The Roads Must Roll” instead of the Interstate Highway System — there are easier and more affordable ways to achieve the same results.
If you can point me to a website that resolves these problems and uses plausible numbers instead of armwaving, I will happily withdraw my concerns. The space elevator is an intrinsically neat concept, and it would be very, very cool to see it become a reality.
Martin, the key is that you can use much more efficient propulsion than chemical. For example, you could have electric propulsion (with say 5,000 secs ISP). That means that propellant would make up a small portion of the cargos that you bring up from the Earth’s surface.
Mike G, remember first that 400 tons is not that much even in today’s launch environment. It’s probably somewhere around 40 launches of the Ariane 5 (at 10 tons per launch). That’s feasible. Further, you don’t need to install the full tether at once, but can start with a much lighter starting tether and slow pull into place your bigger tether using what’s already there.
I guess my point is that if you’re already in a situation where you are piecemeal assembling your space tether, you might as well use the tether itself to bootstrap the process. As I understand it, all the more or less serious proposals out there use this trick.
As the crawler moves up the tether, it will tend to pull the cable and counter-weight down. Propellant will be required to reboost the terminal station.
No. As long as it doesn’t “pull it down” so far that the anchor is below geostationary orbital altitude, no propellant is required. If you don’t balance up mass with down mass then you’ll either increase or decrease the earth rotation period, but the elevator itself remains in tension via centrifugal “force.”
but the elevator itself remains in tension via centrifugal “force.”
The key here is that the center of mass is not in GEO – the center of mass is above GEO, so it is always exerting a force on the cable. (I mean, it has to hold its own weight up, what’s a few extra tons?)
The real problem with this is maintenance. You are building an object 40,000 km long, that has a payback period of decades. Pretend you had a road, 40,000 km long (more than twice around the Earth) that you got as a free gift from the government ;} but that you had to maintain. How much would that maintenance cost?
Earth orbit is a rough environment – there is a lot of junk out there. People say that they will play dodge ball with it, but there is a lot of junk that is too small to detect. These things will sustain a lot of damage in a decade – and if you have to replace it more often than once every few decades, the project is not an improvement over using an Altas (at least on a cost basis).
[The reasoning behind this is as follows: up mass is limited to some value, which depends on the excess strength (and therefore cost) of the cable. Velocity is also limited to some value – you cannot go mach 5 while attached to a cable. Therefore, the delivered mass is limited by these factors. Practical calculations show that it probably takes a week to get to orbit – so you can carry your “excess mass” reserve once a week.
So (playing around) let’s use Mike’s unobtainum 1 cm square cable: Let’s say that in addition to carrying it’s own mass, it can carry 1 ton. So your delivery capability is 1 ton per week. But the cable is 400 tons in mass – so to breakeven on delivering the cable you need to operate 400 weeks WITH NO REPAIRS! That with no repairs is the killer – if you only had to repair 1% of the cable per month you would send nothing but repair material up the cable. The research I looked up before says that far more repairs than 1% a month is likely – I’ll leave that as an exercise for someone else.
“One oddity: electric power delivered by the elevator. That would be an electric line that would stretch around the world. Probably better to stick with power beaming by laser.”
Maxwell’s equations show that large-scale Space power transmission by cable would create a magnetic field strong enough to make the elevator unsafe for humans. The receiving sites would be on the equator amid oceans, thousands of miles from most customers. Beaming the power by microwave or laser would far more practical.
“Rand Simberg wrote:
No. As long as it doesn’t “pull it down” so far that the anchor is below geostationary orbital altitude, no propellant is required. If you don’t balance up mass with down mass then you’ll either increase or decrease the earth rotation period, but the elevator itself remains in tension via centrifugal “force.”
Thanks, I understand that better now. Provided that the force applied by the vehicle to the cable is less than the tension in the cable, it won’t move anyway, in which case no work is done on the assembly. However that raises another question: How much of the mass is above geostationary orbit. And, by definition, anything above or below geostationary orbit is not geostationary, in which case it seems that some propellant will be required to keep it in place.
As I recall, MXER tethers ended up needing a not inconsiderable amount of propellant for attitude control, maneuvering the payload catcher, etc. That always seems to be the flaw in propellantless propulsion concepts – they end up requiring too much propellant.
And, by definition, anything above or below geostationary orbit is not geostationary, in which case it seems that some propellant will be required to keep it in place.
A space elevator is geostationary, but it is not in orbit. Any mass above geostationary altitude simply exerts tension on the tether, which is anchored to the earth. Just think of it like swinging a rock around on a rope. It will always remain vertical, once in place. No propellant is required.
Mike G,
How much mass are we talking about?
It really doesn
For dealing with orbital debris, see the Hoytether for at least a start on an answer. http://www.tethers.com/Hoytether.html
Your last couple of comments got it right Rand. Most of the designs I’ve seen call for the elevator’s counterweight to be in a much higher orbit than the station at synchronous distance. The additional tension is used to balance the weight of the crawlers and loads moving up and down keeping the whole thing rigid.
Now this means the strength of the cable needs to be greater than otherwise but also that the counterweights final altitude can be variable based on the amount of mass available to use in making it. It also is a good resting place for supplies brought up from earth with no immediate use. Crawlers would be stationed on both sides of the geo-synchronous station.
I am in agreement with Mark G. on most every point he makes. It’s going to take us how long to build an improved version of the Saturn V and get people back on the moon? And consider how long it takes to get something as relatively simple as a new military aircraft built and operational. This looks like a program that is no longer within the ability of our government to manage. In fact governmental involvements looks to be the kiss of death.
Good to see the Falcon team, in spite of their problems, ready to launch again so soon. NASA would be doing a years long review. It indicates to me that if an elevator can be built it will have to be built privately. Yet I can’t see any government keeping their hands off of something that big.
I was busy typing away when Brock made his post. I am well aware of all of the points he brings up. There are solutions for the problems mentioned I just don’t think we can get there from here so long as governments function as they do.
Brock wrote:
won’t people prefer to invest their careers and money in something with a shorter-term payoff, such as putting an immediately useful payload into orbit, or bringing something valuable back?
Ask Elon Musk and Bob Bigelow.
Unless I misread you I think they have answered the question already and are voting for rockets.
Ralphe,
You misread me. I meant that some people are clearly willing to spend $$$ to build infrastructure. Mike G. was confusing the people who make infrastructure investments with their potential clients.
Also, Bigelow is not investing in rockets. He’s investing in habitats. How you get there doesn’t really matter to him. A Space Elevator would be great for Bigelow, since it would mean cheaper access to his habitats and lower launches costs for putting them in orbit (or on the Moon).
I don’t think an elevator would ever be used for passenger traffic though. Too slow. It takes a week to get to orbit, and you need to be shielded once you’re past the geomagnetic field. I think rockets will be the way people get into orbit for some time. The elevator would be for heavy freight – rocket fuel, satellites, real spaceships, Bigelow stations, Moon bases, etc. They could also be a method for lowering down any valuables mined on the Moon or the asteroids.
Most of the designs I’ve seen call for the elevator’s counterweight to be in a much higher orbit than the station at synchronous distance.
Just to be clear, it’s not in orbit at all. None of a space elevator is in orbit. It’s simply attached to the top of the tether at a much higher altitude than geostationary altitude.
The counterweight should be above GEO, but how high? The article calls for it to have “twice the length of cable” for a counterweight. This makes sense for an Edwards-style reeling out of twenty tons of cable starting from GEO and going in both directions, but once climbers are climbing, the cost of the elevator material is probably much more than the cost of the climbers and elevator material is more likely to have manufacturing capacity constrained than climbers. That is, for the first climb, a closer-in counterweight (perhaps consisting of the empty spooling climber) should be selected that’s maybe 1.1 or 1.2 above GEO rather than 2x GEO. Depending on the tapering, the first strand could be reused once additional counterweight mass is in place at 1.2 GEO.
One trick I haven’t seen is to send up a climber with one end of the next strand leaving the spool on the ground and letting it unroll then sending up a separate “zipper” climber once the first one reaches the top, or more precisely, the other bottom.
The larger the end mass, the closer to geosynch altitude it can be. If you use an asteroid, you could use the reduced-gravity environment present at the top for mining operations. But it’s a cost tradeoff.
“there are easier and more affordable ways to achieve the same results
Such as?”
Approaches that could be cheaper* are ideas related to orbital rings with Jacob’s ladders. There is also the idea of space fountains but I’m not convinced they would be cheaper.
* Cheaper because the initial bootstrap should require far less mass and effort. A launch loop wouldn’t need any launches at all just an awful lot of space (forget about land) and maybe there exists hybrid solutions for orbital rings as well where a solution with small individual strands could pull themselves up.
Take a fully orbital ring based on Paul Birch’s proposals but nix the idea of enclosed vacuum for the Jacob’s ladders and replace that part with the work already done for space elevator tethers and you have my own favorite.
There’s something I’ve not seen addressed anywhere (possibly it has been, and I’ve missed it), Can you have two-way travel along one of these? Can ‘cars’ on a space elevator pass? can you have something like stations and sidings at anything other than the geostationary point?
If not, then it’s like a one-track tunnel under the Atlantic. Trains could go only one direction at a time and you’d have to clear the entire length of the tunnel before sending traffic the other way (Could a space elevator have two adjacent paralell cables? Can we insure their safe seperation along the entire length?)
And at anything other than the geostationary point you’d be at less than (or greater than) orbital velocity, so like the above example, you *must* get to the other end, there’s no place along the way to stop. Unless some sort of stations are indeed possible, and their only likely value would be mostly unattended communication relays (the thing would be the mother of all antenna support structures, if you could) and emergency stops…
So (playing around) let’s use Mike’s unobtainum 1 cm square cable: Let’s say that in addition to carrying it’s own mass, it can carry 1 ton. So your delivery capability is 1 ton per week.
Edwards calculates more payload per cable weight, but let’s talk about frequency. If you went to 1/2 size payloads, you could probably do 4/week as the main delivery limitation is weight in the high-g sections of the cable.
Maintenance becomes very cheap if we can get to a taper ratio of 1 (material strong enough to support it’s own weight to GEO with no taper); then we could just reel out elevator from the bottom. My guess is that would get us near the theoretical strength of single-walled carbon nanotubes, but there are other clever solutions out there.
My guess is that would get us near the theoretical strength of single-walled carbon nanotubes, but there are other clever solutions out there.
I hope you’re not suggesting there are materials with an intrinsic tensile strength greater than a carbon-carbon bond, ’cause there aren’t.
I don’t get the week to geosync travel time. It should be possible to reach 1,000 mph with the car after it is out of the atmosphere with maglev systems. That would drop time to geosync to under one day. Even 300 mph would be three days with a mechanical system.
A quicker bootstrap method starts just above LEO with one rocket launch. Deploy a 2,000 mile long gravity stabilized tether with the low end just above the atmosphere. The second rocket docks to the lower end at perigee after it has used eletrodynamic propulsion to raise its’ apogee enough to catch that mass without reentering half an orbit later. The second rocket saves a bit over 1,000 m/s delta V with serious rocket payload gain.
After the second payload is attached and deployed, the tether is about 3,500 miles long with taper. The perigee velocity is less which boosts the payload of rocket three and so on.
Starting with rocket two, reentry velocity of the returning vehicle starts dropping, which saves stress on the TPS. Also the rocket detaching from the tether raises the tether orbit which means that the energy of raising the rocket vehicle to orbit is recovered.
This is written up properly somewhere.
I doubt I will see a fullbeanstalk in my lifetime.
The second rocket docks to the lower end at perigee
Wait a sec, how do you dock with a thing (the lower end of the beanstalk) that is traveling way less than orbital velocity at that point? Seems to me your rocket is going 17,000 MPH and your beanstalk is going a mere 1,000 MPH. You need some hellacious big shock absorbers.
Brock wrote:
But how much mass can a “packing tape” tether haul into orbit? If the entire tether masses a couple of tonnes, then it’ll have to be markedly stronger than a thicker tether to support a (nominal) one-tonne payload mass. And what provides the motive force? That’ll add even more mass …
Well then, as the masses of the cable and payloads increase, you’ll need more and more of a counterweight. The “50,000 Ares 5 payloads” bit was an estimate for a half-meter-crosssection tether.
Read the effin’ post! “One oddity: electric power delivered by the elevator.”
Points 1 and 2: I think you are being incredibly optimistic.
Point 3: If you use beamed power to energize a climber, then it seems to me you’ve limited yourself to one climber at a time … because a second climber would get in the way of the first one.
“Can’t fully answer”? Hah! You want to build a 40,000 km cable (or a series of cables in your construction scenario) that’s at the theoretical limit for tensile strength and without flaws for its entire length? Yeah, that’ll take pocket change to construct.
Musk and Bigelow are smart enough to not put all their eggs into one astronomically expensive basket. If a booster fails, build another one! If a beanstalk fails, then what?
All it takes is one fatal problem to kill an elegant concept.
If a non-trivial tether (something more massive that packing tape) fails somewhere along its length, what happens to the ground station? If a massive tether fails, are you sure all the fragments burn up? And what happens to the counterweight?
Is it done by a private company in the United States? Lawyers and bureaucrats will be involved — multiply time and cost estimates by an order of magnitude.
Rockets, for the foreseeable future. Laser-launched vehicles. Hell, it might even be cheaper and more feasible to build an electromagnetic mass-driver on Earth and construct an evacuated gun barrel to take the payload out of the atmosphere than to build a beeanstalk. (I’m just talking through my hat here, because I have no freakin’ idea how difficult this would be to build … but I think it’s no less implausible than a beanstalk.)
The problem is that Googling for an hour will give me too many mutually contradictory answers.
I’ll give it a look. Thanks!
Damn. Apologies for the faulty blockquote spacing (or lack thereof).
Carl Pham wrote:
The second rocket docks to the lower end at perigee
Wait a sec, how do you dock with a thing (the lower end of the beanstalk) that is traveling way less than orbital velocity at that point? Seems to me your rocket is going 17,000 MPH and your beanstalk is going a mere 1,000 MPH. You need some hellacious big shock absorbers.
——————————————–
Orbital velocity is 7,800 meters per second while the tether end and rocket are both at less than 6,800 meters per second at docking time. The rocket has a V reduction of 1,000 meters per second, not 16,000 miles per hour. The payload mass increase is because the vehicle does not have to reach orbital velocities to dock. The propellant savings is nearly one to one increased payload.
But on the off chance you’re open to persuasion, http://www.spaceward.org/elevator is a good site.
It is, and it did answer some of my objections. Bit it didn’t answer others, and it raised some new ones in my mind.
Multiple Space Elevators can buy you redundancy, but only if the debris from a broken Space Elevator do not pose a significant threat to other Space Elevators. It is probably wisest to have only a single large Space Elevator (and a spare one in GEO as a safeguard) but from a political standpoint we’re likely to end up with multiple Space Elevators, since most major powers will want to have one of their own.
Hmm. If a space elevator fails, it probably will destroy any and all other space elevators, since they’re all sitting on the equator. This is a pretty severe consequence, wouldn’t you say?
Limiting the concept to one elevator per planet is a pretty severe problem, too. Now that you’re only building and maintaining a single system, you lose economies of scale in production costs. If I were developing and manufacturing space elevator components, i’d like to know that there’s a big, profitable market for the stuff I make. And if I were the owner/operator of the elevator, I’d like there to be a robust market for elevator parts, since I wouldn’t want to be vulnerable if the sole supplier of a key component goes out of business.
How did you arrive at the $10B price tag? how do you know how much it will cost? No one has ever even built a Space Elevator before!
Well, what we did was actually put a higher bound on what it will cost, breaking the down the cost and using rough and conservative estimates for each component:
Cost of ribbon manufacturing – even at a very conservative $1000/kg, this will be $1B.
Cost of power beaming station – this is a heavily modified telescope and laser. These components have been costed before at under $1B.
Cost of building anchor station, payload facilities, mission control – these too are almost standard facilities, costing well under $1B.
Cost of first 100 climbers – even at a very conservative $10M each, this is under $1B.
Cost of initial launches, first year’s operations – 4 large launches, well under $1B.
Cost of R&D – the Space Elevator is a very simple system in terms of the actual engineering. $1B includes one orbital technology test.
Cost of legal and regulatory work, other non-technical work – $1B.
Obviously, these items won’t cost $1B each, but we’re demonstrating here that the cost of the Space Elevator will not exceed $10B – nor even come close. For comparison, this is 10% of the cost of the International Space Station, or the cost of a single Space Shuttle.
Hmmm. How many people are employed over what lengths of time to develop the unique technologies, construct and test the equipment, deploy the elevator, and operate the system?
The baseline design calls for replacing the tether over the course of six years. That’ll cost money — you’ll need to fabricate more tether segments, pay people’s salaries, and take the elevator out of operation while you’re repairing or upgrading it.
3.9 How about magnetically induced currents?
There have been several experiments where tethers released from satellites (or the Space Shuttle) measured significant induced currents, and some were even cut by associated arcing. These satellites, however, were moving through the Earth’s magnetic field at several miles per second. The Space Elevator is a geo-stationary structure, and so does not move relative to the magnetic field, and so does not see any induced currents at all.
Three words: Coronal Mass Ejections.
The ribbons will be made from discrete segments. New segments will be introduced on a regular basis where the ribbon is thickest (in GEO) and removed at the anchor and counterweight locations.
This will address the problem of the accumulated damage and finite longevity of the ribbon material. Anecdotal damage will have to be addressed on demand, by replacing the damaged section. There are several procedures for doing this without jeoperdizing the Elevator.
So, can failure of a segment connector induce a sudden, severe stress on the rest of the ribbon?
One more (non-fatal) failure mode: What if a climber’s motor malfunctions, and the vehicle gets stuck on the tether? All elevator operations cease until the problem is resolved.
Hmm. Several italics tags turned off prematurely, making it difficult to distinguish between quoted text and my responses. 8-(
This has been an interesting discussion but essentially it means little for now other than academically. Until we have a material strong enough to make the elevator cable/stalk we are speculating on air. It will probably be developed, but as a byproduct of other research and needs. I predict it will take a while.
Even if we found a solution tomorrow morning, one that took care of all the structural details, we still could not get the thing built without affordable, reliable, access to space. That means rockets, not only now but for many years into the future. Certainly for my lifetime, excepting medical miracles.
I wish there was as much interest, and a groundswell of popular support for people looking at ways to apply nuclear power to get mass into orbit. Someway, someday, chemical rockets will become a dead end. Nuclear is the wave of the future. I do understand why no one is risking money on them today.
Maybe in twenty or thirty years, when the bad press given to nuclear electric power over the last three decades is proven false we can start a new debate. We are going to have nuclear powered rockets leaving the Earth’s surface before a space elevator gets built. At least that is my second prediction and what I would work for.
If that happens it all becomes a matter of economics, how much to put a pound into orbit. Private launch with what we have first. Nuclear power next. Elevators and fountains or something else later if it makes sense.
It’s still legible, as for the italics tags remember to make sure to tag each individual paragraph here as they don’t carry over line breaks made by the enter key.
Anyway good posts.