Japan to launch space elevator experiment to ISS
When Japan launches its unmanned freighter to ISS on September 10, it will carry a two-cubesat engineering test of some of the concepts required to build a space elevator.
In the experiment, which will be the first of its kind in space, two ultrasmall cubic satellites, or “cubesats,” will be released into space from the station. They will be connected by a steel cable, where a small container — acting like an elevator car — will move along the cable using its own motor. A camera attached to the satellites will record the movements of the container in space, according to the Japanese newspaper The Mainichi.
Each cubesat measures just under 4 inches (10 centimeters) on each side. The cubesats will be connected by a 33-foot-long (10 meters) steel cable for the “elevator car” to move along, according to the report.
I wonder if this experiment will also test some of the technology needed for generating electricity using a tether. Over the decades there have been a number of experimental attempts in space of this concept, all of which have failed for a variety of reasons, all unrelated to the concept itself.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
When Japan launches its unmanned freighter to ISS on September 10, it will carry a two-cubesat engineering test of some of the concepts required to build a space elevator.
In the experiment, which will be the first of its kind in space, two ultrasmall cubic satellites, or “cubesats,” will be released into space from the station. They will be connected by a steel cable, where a small container — acting like an elevator car — will move along the cable using its own motor. A camera attached to the satellites will record the movements of the container in space, according to the Japanese newspaper The Mainichi.
Each cubesat measures just under 4 inches (10 centimeters) on each side. The cubesats will be connected by a 33-foot-long (10 meters) steel cable for the “elevator car” to move along, according to the report.
I wonder if this experiment will also test some of the technology needed for generating electricity using a tether. Over the decades there have been a number of experimental attempts in space of this concept, all of which have failed for a variety of reasons, all unrelated to the concept itself.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Calling any cable car “a space elevator” is quite the hype. A space elevator is impossible on Earth and unnecessary on any object smaller than the Moon. And even if it would be possible on the Moon, it’s eccentric orbit causes problems for its Lunar stationary orbiting center of mass. In general a space elevator is extremely inflexible and vulnerable and has very little capacity. One still has to bring anything to and from its one and single point on the surface. Just forget about the concept!
Tethers in space however seem promising for a range of purposes. Experiments should be within reach of smaller projects like this one. So very little has been done to date. If I had the privilege of selecting a cubesat space mission for a university, I’d like to go for a tether experiment.
I read a book about the Space Shuttle Program and it detailed several different missions where this technology was tested, at a much larger scale. However, I am eager to see how these cubesats work because it is a fascinating technology if it can work.
I don’t think the tether is quite long enough to get a good static difference and thus a charge.
Jason Hillyer,
As I recall, the Space Shuttle tested a few tether concepts. Much was learned, as the behaviors of the tethers differed from expectations. I recall that a 12 km tether snapped, and another tether had a problem that required the crew to jettison it (I’m too lazy on this Sunday to look these up). A major difference between the Shuttle experiments and this one is that this one tests the concept of shuttling a container along a tether.
Localfluff,
There are quite a few problems with a space elevator on Earth. The largest one, as I see it, is the current amount of space junk in orbit. A space elevator would necessarily have to be located on or very close to the equator, and the top of the elevator would theoretically be over the equator (gravitational effects of the out-of-equatorial-plane Moon and Sun would cause a north-south instability, as they do with geostationary satellites). Every object in orbit is either on or crosses the equator, so as the Earth rotates it would cause the elevator shaft/tether/ribbon to cross the orbit of every object twice a day. There would be a low chance of collision with each object for each crossing, as the two would rarely coincide at the same place at the same time, but there are so many objects that there are bound to be collisions, over time. An elevator would have to be capable of withstanding such collisions and of being repaired. That is quite a problem to solve.
The Moon has virtually no space junk, so that is hardly a problem, there. An elevator at the Moon could save about 2 km/sec of delta V, so it may be worthwhile. However, Coriolis forces would result in vibrations and pendulum-like motions that would have to be damped or countered.
Some people propose using space elevators for small objects (e.g. asteroids or Phobos) in order to use their rotations to help “throw” spacecraft to save fuel.
Any space elevator would be long, and no matter how it was structured it would behave similar to a tether or string — buckling (string-like behavior) is a problem that must be considered even for solid columns, as well as for a space elevator. Tether experiments are a necessary step in the invention of a space elevator. There are so many problems to solve that space elevators are not yet ready for prime time.
Robert’s ponder about testing the generation of electricity may not be a priority for this team. They probably power their travelling container by battery or (less likely) solar power. However, the theory is that a conductive tether (similar to this team’s steel cable) can be used to generate electricity as it travels through Earth’s magnetic field, working similar to a generator here on Earth (rather than static difference). This method would trade speed, or rather orbital altitude, for electrical energy. Some people have thought of using tethers in the opposite way to gain or maintain orbital altitude by applying electricity to a tether.
The problem of having a space elevator come crashing down on Earth wiping out everything across thousands of kilometers, is a problem. But it is not a real problem, since a space elevator is IMPOSSIBLE to construct on Earth!
The main problem with a space elevator on low gravity objects, where it has minimal use but might be possible given enormous initial investments, is that it is a single point transportation mode. What if you want to transport something from any other location? And also the tiresome logistics of being totally dependent on one single route, waiting for a thing to climb before it van be used again. Extremely inflexible and unwanted from any transportation point of view. Already Xerxes built two bridges across the Bosporus, because otherwise it would be pretty useless. And he used it only once because he moved on.
Just forget about the concept. It is a loser technologically and economically in so many ways.
“. . . a space elevator is IMPOSSIBLE to construct on Earth!”
There are huge practical issues, but if you mean by “IMPOSSIBLE” that a space elevator requires impossible physics or impossible materials, you are wrong.
Having said that I think rotovators are far more likely as an economic tether system for very high freight volumes to and from orbit and beyond.
An elevator doesn’t act as a geosynchronous satellite and can be located some distance away from the equator. As far as capacity, there is no theoretical limit. If you can elevate a gram of material into space this way with a strand of cable, you can elevate a kilogram with a thousand strands, etc.
A space elevator from Earth is impossible because there exists no material to build it with.
One space elevator is a huge queue problem. Sure build many of them, at multiplied costs! It’s much cheaper and more flexible in every way to build more rockets instead.
Just forget about the concept!
” . . . there exists no material to build it with.”
Carbon nanotubes/graphene ribbons have the required strength/weight.
Of course we’re not talking about a space elevator any time soon, the demand for a system able to move very high volumes of freight cheaply needs to exist first, rockets are to aircraft as space elevators are to railways.
Edward: “A space elevator would necessarily have to be located on or very close to the equator, ”
MikeP: “An elevator doesn’t act as a geosynchronous satellite and can be located some distance away from the equator.”
I’ve read Fountains of Paradise and have always assumed that a space elevator would need to be on the equator, but thinking about a simple analogy – a piece of string on a spinning top, I’m not so sure. The engineering would be more complex if the base is far from the equator as each load going up would be a change in the lateral loads on the cable, with an equatorial base loads are all vertical or nearly so. Also I would expect the cable would need to be considerably stronger if anchored far from the equator.
Localfluff wrote: “But it is not a real problem, since a space elevator is IMPOSSIBLE to construct on Earth!”
In the following book, the concept that the Japanese are obviously working to is explained.
https://www.amazon.com/Space-Elevator-Earth-Space-Transportation/dp/0974651710/ref=sr_1_3?s=books&ie=UTF8&qid=1536621723&sr=1-3&keywords=space+elevator
The book’s proposed space elevator is not built as a tower from the Earth up, because that is impossible, but a strong rope or ribbon made of carbon nanotubes is proposed to be lowered from geostationary orbit as the construction mechanism. Elevators would climb and descend along this tether/ribbon allowing for transporting hardware (and allowing repair of damage).
Many people have been thinking about the problems of space elevators and working on ways to solve them. Keep calling it impossible, Localfluff, because engineers like to accomplish the impossible.
Ben Shelef used to give presentations about this topic, and he has a couple of videos. Here is one of them:
https://www.youtube.com/watch?v=_eldlKDso9o (3-minutes, Why a space elevator)
As a ribbon or tether, a severed elevator would not be a large structure falling to the ground wreaking havoc everywhere, but the lower section would be a ribbon or rope that falls down, and wind resistance would reduce the speed at which the fairly light material hits the ground. The upper section, above the break, would remain in orbit. One proposal is to anchor such elevators on platforms at sea, similar to oil drilling rigs, reducing the hazard to people and things on the ground should there be a break.
MikeP wrote: “An elevator doesn’t act as a geosynchronous satellite and can be located some distance away from the equator.”
The construction of a tether/cable elevator would start above the equator, but the anchor of a tether-type elevator could be moved to a few degrees off the equator. The counterweight would tend to stay over the equator (except for various influences that are stability problems). In fact, the anchor could be a ship that changes the latitude and longitude of the anchor, but this would have little effect on the location of the counterweight at the top of the elevator.
Andrew_W,
The engineering of a ribbon/cable type elevator is not much more complex if the anchor is a few degrees off the equator, but the initial angle of ascent would not be straight up. It could take hundreds of miles of climb before the cable gets near enough to the equatorial plane for the climb to be considered vertical. However, the anchor need not be directly on the equator.
If you get too far from the equator, though, then the ribbon/cable does not have enough upward pull to keep the climber in the air, and it will drag along the ground for miles rather than climb.
The material to build it does not exist.
Sorry but just saying that Nano tubes or ribbons would work is ignoring ALL the problems of manufacturing that much material perfectly with NO imperfections at all along a cable 200 miles long.
The strength of a nano tube a few millimeters long is in no relation to the strength of the same material 200 km long.
Plus the cable would have to be thicker in the middle than on the ends to save weight. So your elevator would have to be able to climb a variable diameter cable without slipping. EVER.
Add in winds and cross winds…..
Plus the natural spin of the planet…..
It would be better to not use and anchor and to let it spin.
The spacecraft can fly up to meet the cable as it sails through the air and latch onto it. Letting it sling the spacecraft out of the atmosphere into space.
It would only spin at the speed of the air it passes through. So at the same time another spacecraft could attach to the space side and let the cable carry it down into the atmosphere.
pzatchok wrote: “Sorry but just saying that Nano tubes or ribbons would work is ignoring ALL the problems of manufacturing that much material perfectly with NO imperfections at all along a cable 200 miles long.”
Actually, the idea is not to make horrifically long nanotubes but to spin them into strings, similar to yarn or cotton string. There are ideas for combining these strings into ribbons. This technology may be relatively easy to develop.
A rotovator has similar problems as a space elevator, plus a couple more, such as the navigation, speed matching, and timing to attach items at either end of the cable. It takes a while to attach booms or probes during midair refueling, and a little longer to dock in space. Can these attachment timeframes be reduced to accommodate a rotovator? These are two technologies that would have to be developed for a rotovator.
“It takes a while to attach booms or probes during midair refueling, and a little longer to dock in space. Can these attachment timeframes be reduced to accommodate a rotovator?”
Can fighter aircraft without any STOL capabilities land on the deck of a ship?
@pzatchok
What “200 km”? Its center of mass must be 36 000 km from Earth. An enormous space flight industry is required to build it. And then it has to compete with that enormous space flight industry. Rocketry is much cheaper and extremely more flexible.
Andrew_W asked: “Can fighter aircraft without any STOL capabilities land on the deck of a ship?”
They often are able to catch one of five cables in a 60 meter length of multi-tonne deck, stopping a great momentum with a violent but controlled crash. I’m not sure that a rotovator would appreciate that kind of treatment, being built more delicately than an tens-of-thousands of tonnes aircraft carrier.
Of course, the consequences of a missed approach are either the plane fails to land or the plane disintegrates on the deck.
The aircraft carrier is there for long periods of time, allowing for ease of location and reduced urgency of timing. A rotovator will already be heading for space, if the timing or navigation is incorrect, so there are limits on second chances at a “landing.” This type of capture system presents another set of problems to overcome.
Very few concepts for either a space elevator or a rotovator have been proven, so far, and this Japanese team is working on one proof of concept on orbit. Some ground testing has been done on the climber concept, but not at the speeds desired for climbing an actual elevator. Progress is not fast as a hare, but it is moving along more like a tortoise.
Localfluff,
I think that if you look into it, you may find that there are ideas on building a space elevator that improve on earlier thoughts. Dropping a nanotube cable or ribbon from GEO may only require one or two SpaceX BFR rocket launches, not an entire industry. Having looked into the topic, construction and cost are not the problems that I worry about. Space junk and stability are my main concerns. The other technologies, I believe, are relatively easier to develop, and the other problems relatively easier to solve.
The idea of the space elevator is to bring the price down to around $100 US per pound. This is a little more than half what SpaceX thinks they can get BFR to do, but that is also in the development phase.
Your right on my length of 200 km being wrong. I was thinking that even a short cable of 2000 km would be impossible to build and or even use.
Just how small of a diameter are some of you thinking this cable will?
If its going to be 20,000 km long how is it going to even hold itself up let alone a cargo at the end.
Like I said it would have to be tapered from the center to the ends.
Now we are talking HUGE amounts of mass. All mass moved into and re-manufactured into a cable in orbit.
Huge amounts of energy. Trillions of dollars spent.
All just to reduce the theoretical cost of getting into orbit down to under 100 bucks a pound?
None of this takes into account the upkeep and maintenance plus the cost of the lift elevator itself. Which will have to be nuclear powered and able to lift at least 100 tons at a time.
Just like i tried to explain in another thread about a Moon base for lunar water/fuel. By the time we can do this it would be cheaper and faster just to lift the cargo by rockets from Earth.
The same tech that makes it feasible makes it impractical at the same time.
I still think a rail launcher would be more practical and feasible with todays tech. From Earth or even the Moon. At least to replace some if not all of a first stage.
Edward, I was just illustrating that there are capture systems that – under direct human control – work effectively in a second or less, computer guided systems should be good for millisecond decision making, with a rotovator the difference in velocity between payload and tether end should be very low compared to the difference in speed between aircraft and ship in carrier landings.
pzatchok, for the space elevator the tether needs to extend beyond geostationary orbit. There’s a intuitive assumption that the cable would have a huge mass, after all, its 40,000 or so km long, I think that assumption is wrong, it would actually only have a mass a few times that of the payload that it can lift, you build a structure like that that can only support another 0.1 or 1% of its own weight, get such narrow margins wrong and things break, imagine a crane cable that could only lift a very small fraction of its own weight, eg, the cable weighs 10 tons and is only able to lift an additional 100 kg.
One of the reasons I like the rotovator (apart from things like it wouldn’t need to extend through the Van Allen Belts, it could all be below 2000 km, it could be built with existing materials) is that the tether is usually about the same mass as the payloads handled (the tether itself does need to be connected to a more massive object (LEO settlement?) to mitigate the loss of momentum on capture.
pzatchok asked: “If its going to be 20,000 km long how is it going to even hold itself up let alone a cargo at the end.”
The elevator holds itself up by having a counterweight several thousand kilometers farther out than geostationary orbit. It works similar to spinning a weight on a string around your head. This concept works for both the cable/ribbon/tether and tower concepts.
This video may help explain the basics of a space elevator:
https://www.youtube.com/watch?v=6Ddl55DCh-c (Space Elevator Explained, 3 minutes)
There is a huge amount of mass when a steel cable is used, and it turns out that steel is too heavy and not strong enough for the job. This is why the much lighter and stronger nanotubes are expected to be used.
An advantage of making a ribbon is that it can easily change width as necessary in order to account for the increases and decreases in tension forces over the length of the elevator. However, the climbers do not much care about how wide it is, as they wrap around only one side of the ribbon. This could also allow for climbers to pass each other, one on the “right” side and the other on the “left.”
You have made a few assumptions that are not necessarily true. The following video shows some of the thought processes and evolution of space elevators, including some math and weight estimates, with a brief but good Q&A at the end:
https://www.youtube.com/watch?v=TGfmU4eZA-w (17-minutes, Physics of space elevators)
Notice that Mr. MacDonald touches on the stability problem in answer to the first question. He fails, however, to talk about the Coriolis forces that have to be countered, but part of the solution for those forces could be similar to his stability answer. I believe that a space elevator would not be fuel free, but would need some amount of “station keeping” propellant. And, yes; this reduces some of its advantages over rockets.
“Just like i tried to explain in another thread about a Moon base for lunar water/fuel. By the time we can do this it would be cheaper and faster just to lift the cargo by rockets from Earth.”
Possibly. Various concepts are in competition with each other, including rail launchers (though this may not be as practical for launch from Earth). A space elevator may not be the solution to all of our transportation needs, for instance it may not do well for polar and sun synchronous orbits. There are still a larger number of problems to solve than rockets currently have, but rockets once may have seemed just as impractical as space elevators seem now.
Andrew_W,
I tried hard to suggest that there could be solutions for payload capture but that we do not yet have those solutions. To me it seemed as though you were offering a possible solution, which still would need some development in order to use it.
“with a rotovator the difference in velocity between payload and tether end should be very low compared to the difference in speed between aircraft and ship in carrier landings.”
Not at the upper end, where the tether end would be moving much faster than orbital speed. Capture of craft or material from space to transport to Earth would most likely occur near the center of mass, where the speed is the same as orbital speed.
There is plenty that has yet to be developed for rockets (e.g. single stage to orbit) and for alternate systems. Around the time it was 60-ish years old, aviation had reached close to the fastest, highest, and largest and has not made much progress since. We are 60-ish years into the “space age,” but we are still at the beginning of the technological advances.
Good comments everyone, Makes the mind race on the possibilities.
I had to bone up on the technology to make a basic opinion that sounds intelligent.
Wikipedia is full of information;
860 mm wide cable (6.3 inches) will weigh 750 tons with the lift capacity of 20 tons. There is currently no material that will achieve this. graphene ribbons comes close and new materials are being discovered at a surprising fast rate. (personally I had assumed that the cable would need to be 3 feet in diameter or more)
There is no lifting method that is acceptable as of yet, being self powered would require too much weight for energy (nuclear, batteries, solar panels, ect.) even carrying your fuel and ejecting the tanks would be no improvement over Rockets.
The current reasonable solution is to have a energy collector base and beam powerful lasers at it to power the craft.
There are serious problems to this, it will get very hot, lasers will lose focus after 50 miles, friction on the cable as well as using the cable as a ground conductor for the power will cause undue wear and tear. It is 22,236 miles to geostationary orbit. Even if the heavy solar panels can get you the rest the way there, there will be power loss for12 hours of night where the brakes will need to hold until the elevator can power up again. Batteries could take you all the way there, if batteries were your payload.
It will take five days to do the trip at 300 km/h (190 mph) extra food and air will be necessary for travelers. (With acceleration time, it only takes about two hours to leave the atmosphere)
Magnetic rail up the side/or inside of a mountain to low Earth orbit has too many G forces for a human to survive. Would work great for robots/food/refueling.
There are two ideas that seem feasible. First, 2 graphene ribbons with insulation between. One side electrically charged, the other side to ground.
High voltage power collected in the ionosphere between the station and the ground could power several cities. The counter balance/launching cable that passes through the station to Earths magnetic field will supply voltage and amperage to the station regulator.
With a ground cable to earth, the “potential” energy can preform more real work. The added benefit is if you reverse or pulse the polarity of the two sides of the ribbon you create an alternating current that would act as magnetic propulsion thrusters on the elevator. A rail gun type of lifting with constant acceleration. It’s speed is only limited inside the atmosphere. At 1000 mph, the trip will only take two days. Half a day to accelerate, a day in freefall, another half a day to slow down. The best part is that it is cheap and light. You can increase the payload, move up the ribbon without touching it avoiding friction and wear, putting on the brakes by reverse polarity.
The second method is similar to the first only using a circular cable in a loop inspired by the rotovator idea.
Cargo coming down from space is clamped firmly to the cable providing downward momentum. The cable speed is relatively slow so cargo will not have any heating problems on re-entry. It detaches a couple of miles up and uses a parachute to the ground.
Cargo going up are placed on the downward side of the cable a few thousand feet up. Special helicopter/or lighter than air Zepplin puts package/load over the cable and is dropped. When the load/cargo velocity matches the cables, clamps are applied before the cable rounds at the bottom and begins its journey upward. The bottom is the maximum G-force which limits the cables speed. (Acceleration machines could deliver the package on the upward side but it will be tricky. The procedure could be aborted and parachute back down)
The benefits are that the power still comes down cable, but more payloads are going up the cable. Weight of the cargo decreases with altitude allowing another load to be placed on the cable every 300 to 500 miles. If the counterbalance station is placed at 30,000 miles, that makes 60 to 100 payloads at a time slowly making their way to the drop off point.
Either detaching early with rocket motors accelerating away at 1000 miles up so it can corkscrew in to the proper Low earth orbit, or stay on the cable till it reaches geosynchronous 22,236 miles up in which it can detach and maneuver its self into a designated construction site/or customer holding area.
The counterweight/space station will need to be a little further up about 25,000 to 30,000 miles. (The details depend engineering concerns and purpose)
A cable extending beyond the counter weight can be used to accelerate payloads into higher orbit or more… 50,632 km to L1, 50,960 km to the moon, 51,240 km to L2, 53,100 km for escape velocity from earths gravity, 144,000 km (89,000 miles) to accelerate a payload to Jupiter which can then with gravity assist leave the solar system.
Once one cable is in place, in five years there will be five more cables in operation. In 20 years there will be hotels with dozens more cables.
Satellites running into the cables will be a concern, the older satellites will be decommissioned and the new ones will have refillable maneuvering thrusters.
If the cable gets hit, it will most likely happen in low Earth orbit at 200 to 400 miles up. The cable will fall straight down doing harm to the area near the space station and the rest of the cable 20,000 miles long will just dangle there until the counterweight cable is lowered down to replace the broken piece. Within a week it will be business as usual.
Countermeasures can also be taken, like A cable dedicated to protect the main cable positioned with protection devices activated. This would be a waste, because tracking devices will be plentiful and give plenty of warning. The satellites can be repositioned with robots or repairing equipment years before a collision takes place.
It’s the unplanned events that worry me, a solar storm will generate so much electricity that the cable could burn in half. In these cases the earth anchor will need to be detached and lifted up to avoid burnout until the storm passes.
If the power collected as a side effect of a conductive cable is too much for the cable to handle, an alternative system can be developed by dangling the end into the upper atmosphere above the weather where lighter than air craft like Zepplin’s can rise up to the end of the cable.
I don’t think there are any insurmountable problems that we can’t think a way through.
A cable on the moon can be done with current technology because of the low gravity. Unfortunately because the moon rotates so slowly The synchronous orbit is at 31,000 miles from the center towards the earth.
Mars cable can also be done with our current cable strength, unfortunately phobos crosses the equator twice a day.
Max, thanks for the summary, I admit I didn’t actually do any revision for my above comments.
There’s another possible variant on the circular cable in a loop idea, which is to have multiple shorter looped cables connected by pulleys, this way the cables can be thicker near GSO where the load is greatest, thinner near the Earth where the load is least, also there’s the possibility of gearing, so that the cables at the top and bottom move more slowly than those in the middle.
Max wrote: “If the cable gets hit, it will most likely happen in low Earth orbit at 200 to 400 miles up. The cable will fall straight down doing harm to the area near the space station and the rest of the cable 20,000 miles long will just dangle there until the counterweight cable is lowered down to replace the broken piece.”
Actually, because there is necessarily a tension on the cable at the anchor, a severed elevator would not be in a geostationary orbit but in some sort of elliptical orbit that probably is not quite geosynchronous, either. Assuming that the suddenly untensioned cable does not act like a spring and snap to a shorter length as well as act like a pendulum, then the end will still be moving about at the very least in the vertical direction. Recapture of the cable will take some time and effort to accomplish. Max’s point is well taken, however, that an elevator that is severed at a low altitude is likely recoverable.
I believe that there are other possible solutions to the severed cable problem. For example, a cable could have secondary and tertiary backup anchors that attach fairly high on the cable. These would not have climbers associated with them but would only act to keep the elevator roughly stationary as repairs are made. Although these increase the chance of a collision, they can ease recovery of a severed cable or take some of the tension associated with a damaged cable, perhaps preventing a brake.
Also, air drag creates a variable perturbation, over time, and is difficult to take into account for long-term prediction of satellite collision with an elevator. Since Max’s prime concern is collision with satellites that are low enough that air drag is a concern, the warning time of a future collision may not be as long as Max believes.