The space elevator

[factotum]

It would also easily be capable of destroying the counterweight station itself if the flight path was calibrated for an orbital target instead of something on or near the ground.

I seriously doubt that an ICBM is capable of hitting a target in geostationary orbit. For a start, the acronym itself heavily implies that such a missile can't even achieve orbit (the "B" stands for "Ballistic", e.g. a gun-like trajectory), and getting up to 22k miles requires a lot more fuel than just hitting a target on the opposite side of the Atlantic does. So what we're talking about is essentially blowing up the ground station that must be at the bottom of the cable, which you could probably do with conventional explosives--it's going to be a lot easier to hit than the actual cable itself.

[wumpus]

I seriously doubt that an ICBM is capable of hitting a target in geostationary orbit. For a start, the acronym itself heavily implies that such a missile can't even achieve orbit (the "B" stands for "Ballistic", e.g. a gun-like trajectory), and getting up to 22k miles requires a lot more fuel than just hitting a target on the opposite side of the Atlantic does. So what we're talking about is essentially blowing up the ground station that must be at the bottom of the cable, which you could probably do with conventional explosives--it's going to be a lot easier to hit than the actual cable itself.

That depends. I wouldn't be at all surprised if ICBMs can already hit GSO orbital *altitude* (which may involve moving the ICBM near the target) without reducing their payload. Those things go pretty high, and going ~1/2 the way around the plant requires nearly orbital velocity.

Actually *hitting* the target without achieving geostationary orbital velocity is something else entirely. That counterweight would be coming very, very fast and no ICBM guidance system (officially, there might be some anti-sat mods out there that are button-lip tippy top secret) can hit that.

That other famous stick figure comic explains: https://what-if.xkcd.com/58/

[Knaight]

Most targets don't cost billions of dollars and consist of thin cables hanging in the air. We also loses tens of thousands of people to exactly your scenario a year, and we are a lot cheaper then space elevators.

Plenty of potential targets are completely irreplaceable - and not only is that tens of thousands of people dubious for my scenario (it explicitly doesn't include accidents), it's an analogy where people already have the equipment necessary and can carry out the "plan" in literally seconds. Vastly fewer people have the resources to attack a space elevator (especially if it''s out in the ocean somewhere), to the point where it's almost entirely just governments - none of whom really stand to benefit.

[pendell]

Plenty of potential targets are completely irreplaceable - and not only is that tens of thousands of people dubious for my scenario (it explicitly doesn't include accidents), it's an analogy where people already have the equipment necessary and can carry out the "plan" in literally seconds. Vastly fewer people have the resources to attack a space elevator (especially if it''s out in the ocean somewhere), to the point where it's almost entirely just governments - none of whom really stand to benefit.

Attack it from outside, yes. If I were a terrorist I'd be thinking more along the lines of internal sabotage, say, some kind of explosive cargo. 11 men turned two airliners into really huge bombs last decade, after all.

Respectfully,

Brian P.

[Mando Knight]

That counterweight would be coming very, very fast and no ICBM guidance system (officially, there might be some anti-sat mods out there that are button-lip tippy top secret) can hit that.

You definitely can hit it if the trajectory is known ahead of time (i.e. the target is a massive object in geosynchronous or geostationary orbit--exactly the parameters of a space elevator's counterweight-station) and all you need for a kill is to detonate the warhead within a couple hundred meters or so (i.e. you're using a nuclear weapon). At the least, the mission designer could remove the extra warheads to get more effective thrust--no need for a MIRV setup if you only have one target.

[Knaight]

Attack it from outside, yes. If I were a terrorist I'd be thinking more along the lines of internal sabotage, say, some kind of explosive cargo. 11 men turned two airliners into really huge bombs last decade, after all.

Respectfully,

Brian P.

This happened once in the last 17 years, yes - and that's the lowest number available for time, and you can extend it back for a good while. The vast majority of that good while had planes with laughable security, and yet for decades commercial airliners weren't being hijacked to use as missiles. Why? Because essentially nobody decided to do that, and very ordinary security measures were thus more than enough to stop it, including the basic measures of systems in place to detect said people long before they did that.

[Grey_Wolf_c]

Personally, I'm reasonably confident in this line of defense.

Agreed. If you have access to ICBMs, there are much tastier targets than a mere space elevator. Like the financial center of the economy you want to target.

Grey Wolf

[Rakaydos]

The biggest problem with a space elevator is it means removing every functional satellite in low and medium earth orbit. Every one of their tracks would intercect the elevator twice a day- it's only a matter of time until they hit it.

Those satelites need to be replaced with something. That's part of the attractiveness of the Orbital Ring concepts. Keep it low, keep it globally accessable.

[halfeye]

The biggest problem with a space elevator is it means removing every functional satellite in low and medium earth orbit. Every one of their tracks would intercect the elevator twice a day- it's only a matter of time until they hit it.

Those satelites need to be replaced with something. That's part of the attractiveness of the Orbital Ring concepts. Keep it low, keep it globally accessable.

A working space elevator would be worth taking down all the satellites not in geostationary orbit.

I'm not convinced that would have to be done, but if it did, it would be worth it.

[gomipile]

The biggest problem with a space elevator is it means removing every functional satellite in low and medium earth orbit. Every one of their tracks would intercect the elevator twice a day- it's only a matter of time until they hit it.

Those satelites need to be replaced with something. That's part of the attractiveness of the Orbital Ring concepts. Keep it low, keep it globally accessable.

No, but every satellite in those orbits would need to have redundant maneuvering capability. And every one of them would need to be removed when it was retired, yes. Doing it this way would require very good tracking and future orbit integration, but we already do that for a lot of satellites.

[Rakaydos]

No, but every satellite in those orbits would need to have redundant maneuvering capability. And every one of them would need to be removed when it was retired, yes. Doing it this way would require very good tracking and future orbit integration, but we already do that for a lot of satellites.

The problem is that the maneuvering fuel itself is an abrasion hazard. It doesnt just go away (unless it's exaust velocity puts it suborbital or beyond escape velocity, which is unlikely if it's being used to dodge sideways around a pillar), it's trapped in earth orbit just like everything else. And while it's not as much of a threat as, say, a broken washer that cant maneuver out of the pillar's way, it's goint to cause wear and tear that will drive up the eleator's maintenance costs. After a certian point, big reusable rockets are just cheaper than maintaining an elevator.

[Gnoman]

The biggest problem with a space elevator is it means removing every functional satellite in low and medium earth orbit. Every one of their tracks would intercect the elevator twice a day- it's only a matter of time until they hit it.

Those satelites need to be replaced with something. That's part of the attractiveness of the Orbital Ring concepts. Keep it low, keep it globally accessable.

The space elevator platform itself could replace most of those satellites, at least for the portion of the Earth that can see it. Since there's no reason that you could only build one space elevator once the tech exists, it would be theoretically feasible to have a platform in the sky for every point on Earth.

[halfeye]

The space elevator platform itself could replace most of those satellites, at least for the portion of the Earth that can see it. Since there's no reason that you could only build one space elevator once the tech exists, it would be theoretically feasible to have a platform in the sky for every point on Earth.

Nope, has to be approximately equatorial.

[BeerMug Paladin]

Nope, has to be approximately equatorial.

Just build a couple of really tall towers at the poles.

As long as we're talking about theoretical materials...

[hamishspence]

Just build a couple of really tall towers at the poles.

As long as we're talking about theoretical materials...

No matter how tall you build the tower at the pole, the object at the top of the tower will not be in orbit. In space, but not in orbit.

[Ravens_cry]

With existing materials tech, we could build one on the moon. Of course, doing so is another matter, but I think that actually makes more sense. The moon doesn't have a huge network of satellites around it right now, for example. Also, it could be used to deliver propellants and other materials to LEO for orbital construction and an orbital fuel depot from moon as well as goods that couldn't easily be manufactured on the moon to bases and even colonies on it.

[BeerMug Paladin]

No matter how tall you build the tower at the pole, the object at the top of the tower will not be in orbit. In space, but not in orbit.

That's why they'd be called towers.

[Chronos]

What makes me most optimistic about the space elevator is that nanofiber won't be developed for the space elevator. It'll be developed for a bunch of other applications, because it would be a really useful and practical material. Even if nobody believed in the Elevator, they'd still be funding nanofiber development. Once we have golf clubs and fishing line and suspension bridges made out of the stuff, then we can look at using it for an elevator.

The financial risk of losing it is insignificant. Sure, a space elevator costs a gazillion dollars, but most of that is for the R&D, and most of the rest is for the initial launch. Which means that, once you have one space elevator, building ten more is cheap and easy. If someone manages to destroy one, then you just rebuild it using the others. It's only a major problem if someone destroys all of them, scattered around the world (yes, all on the equator, but on many different places on the equator), before they can be replaced.

And of course it would be built small at first and then increased in size by climbers, and of course the climbers would start at the bottom. That's the whole point of a space elevator, that you can go up it.

And strictly speaking, you can't build a space elevator on the Moon (nor on Mercury): It rotates too slowly. But on an airless world like those two, you can use the same materials to build a skyhook instead, with much the same effect: Instead of anchoring your tether at the bottom, you leave it in orbit, and spin it so that as the end comes near the surface, it's momentarily at rest relative to the surface. You have to have equal masses going both ways to keep the energy balanced (which is also a good idea for space elevators), but that's not too tough: If nothing else, just send up seawater, or send down rocks, as needed. Of course, it's also possible to just rocket off of the Moon using a tiny rocket, so it doesn't matter much anyway.

[Grey_Wolf_c]

you can't build a space elevator on the Moon (nor on Mercury): It rotates too slowly.

Err, as I and Ravens_cry have pointed out, not only is it perfectly possible to put a space elevator on the moon, it can be built out of kevlar, which has the advantage of existing.

That's why they'd be called towers.

Getting to space is trivial. You can do it with a balloon. It's staying there that is the issue, and towers don't help much in that regard. Sure, they might give you a take-off platform, but that won't compensate you for the building and maintenance costs. Cheaper to use reusable rockets.

Grey Wolf

[hamishspence]

Err, as I and Ravens_cry have pointed out, not only is it perfectly possible to put a space elevator on the moon, it can be built out of kevlar, which has the advantage of existing.

Mercury at least has the problem that the elevator would need to regularly withstand large temperature extremes (Mercury's dayside gets very hot and nightside gets very cold.

The extremes are not as great for our Moon.

[factotum]

Getting to space is trivial. You can do it with a balloon. It's staying there that is the issue, and towers don't help much in that regard.

Yeah, I agree. The regular equatorial space elevator has the advantage that the upper end is in geostationary orbit, so once you've got your payload up there you can easily manoeuvre it into more or less any other orbit you like (albeit LEO would require quite a bit of delta-V). A tower at the Pole has no such advantage, so you need to ensure that anything you put up there has enough rocket power to get it into a standard orbit before it crashes back to Earth.

[Algeh]

Mercury at least has the problem that the elevator would need to regularly withstand large temperature extremes (Mercury's dayside gets very hot and nightside gets very cold.

The extremes are not as great for our Moon.

I would also argue that a space elevator on Mercury would have roughly the same problems as a large shopping mall with attached water park would have in the middle of Antarctica: not only would it be a giant engineering hassle to build, it also wouldn't get enough traffic to be useful afterward. I mean, in both cases that could change someday, but in terms of "things we as a species should probably be getting around to soon" I really wouldn't put either of them on the to-do list.

The moon makes a great deal more sense than Mercury, since it's relatively nearby and easy to get to. I suspect we'd need a particular goal in terms of getting stuff off of the moon to build something else in space before it would really make sense, but there are lots of cool things I'd like to see us build in space, so that seems more like it could be part of a relatively near-term plan (near-term meaning the next 50 years or so, if we decided to make a go of doing neat stuff in space).

[halfeye]

Getting to space is trivial. You can do it with a balloon.

While I'm not sure the current definition of space isn't so wonky that it allows it, I really have a problem with the idea that you can get up to hard vacuum with a balloon. A balloon rises by displacing it's own mass and the mass of its payload. There is no way is no way a gas dense enough to lift a balloon ought to count as hard vacuum.

Yes that means that in my view the x15 folks shouldn't have astronaught certification, they were brave and good and ought to be honoured for it in some way, but they weren't in vacuum.

[hamishspence]

There is no way is no way a gas dense enough to lift a balloon ought to count as hard vacuum.

It might not be hard vacuum, but it's still lethally deadly vacuum. When you're over 40km up (the record, for highest skydive from a balloon), and all you have is a breath mask and oxygen - you will die. You need a pressure suit at about 20km (ideally, 18 km).

100km is the usually-accepted boundary between "near-space" and "space". Balloons have never gone that high, true.

Yes that means that in my view the x15 folks shouldn't have astronaught certification, they were brave and good and ought to be honoured for it in some way, but they weren't in vacuum.

At the time the X-15 flights were made, 80km was considered the boundary by some groups. They did go that high. Two of them exceeded 100km, which is where the boundary is usually placed now.

[BeerMug Paladin]

I would also argue that a space elevator on Mercury would have roughly the same problems as a large shopping mall with attached water park would have in the middle of Antarctica: not only would it be a giant engineering hassle to build, it also wouldn't get enough traffic to be useful afterward. I mean, in both cases that could change someday, but in terms of "things we as a species should probably be getting around to soon" I really wouldn't put either of them on the to-do list.

The moon makes a great deal more sense than Mercury, since it's relatively nearby and easy to get to. I suspect we'd need a particular goal in terms of getting stuff off of the moon to build something else in space before it would really make sense, but there are lots of cool things I'd like to see us build in space, so that seems more like it could be part of a relatively near-term plan (near-term meaning the next 50 years or so, if we decided to make a go of doing neat stuff in space).

If there's going to ever be any sort of colony (not an outpost, the logistics of the supply chain is unlikely to ever be justifiable, even with space elevators) on another planet, Antarctica provides us an easy training mode to work through first. It might not seem as cool as getting off of Earth, but it has many similar problems another planet's colony would need to have solutions for.

Nobody's even close to trying on easy. It might not be terribly interesting, but something like that is probably the most sensible next step for space travel. Unless scientists invent magic far ahead of schedule.

I think there's been a little bit of confusion regarding my statements about towers at the poles. I'm going to stack some quotes in the hopes that clarifies my meaning.

The space elevator platform itself could replace most of those satellites, at least for the portion of the Earth that can see it. Since there's no reason that you could only build one space elevator once the tech exists, it would be theoretically feasible to have a platform in the sky for every point on Earth.

Nope, has to be approximately equatorial.

Just build a couple of really tall towers at the poles.

As long as we're talking about theoretical materials...

No matter how tall you build the tower at the pole, the object at the top of the tower will not be in orbit. In space, but not in orbit.

That's why they'd be called towers.

TL;DR yes, it was a joke method to provide additional ground coverage for absent satellites.

[hamishspence]

How would a tower at the pole, replace a satellite, the way a geostationary platform might?

[Gnoman]

Nope, has to be approximately equatorial.

I'm not certain how to calculate it, but even assuming that the elevator platform isn't high enough for an entire hemisphere to see it, a chain around the equator would provide coverage to a huge percentage of the human population. I see no reason why relay satellites in higher orbits couldn't handle the remaining percentage.

[BeerMug Paladin]

How would a tower at the pole, replace a satellite, the way a geostationary platform might?

I'm not certain how to calculate it, but even assuming that the elevator platform isn't high enough for an entire hemisphere to see it, a chain around the equator would provide coverage to a huge percentage of the human population. I see no reason why relay satellites in higher orbits couldn't handle the remaining percentage.

Trigonometry is useful here. So are these links, which provide all the data needed in order to calculate an answer. There's also google.

[Mechalich]

If there's going to ever be any sort of colony (not an outpost, the logistics of the supply chain is unlikely to ever be justifiable, even with space elevators) on another planet, Antarctica provides us an easy training mode to work through first. It might not seem as cool as getting off of Earth, but it has many similar problems another planet's colony would need to have solutions for.

Nobody's even close to trying on easy. It might not be terribly interesting, but something like that is probably the most sensible next step for space travel. Unless scientists invent magic far ahead of schedule.

They actually do Mars mission simulations in a habitat on the top of Moana Loa in Hawaii, which for various reasons works better than Antarctica for this purpose. But yes we're a long ways from actual colonization of another planet and it is difficult if not impossible to imagine a scenario in which planetary colonization (as opposed to asteroid mining) makes economic sense. A space elevator offers vast economic benefits in the asteroid mining case, however, which is really the principle reason to build one.

[halfeye]

They actually do Mars mission simulations in a habitat on the top of Moana Loa in Hawaii, which for various reasons works better than Antarctica for this purpose. But yes we're a long ways from actual colonization of another planet and it is difficult if not impossible to imagine a scenario in which planetary colonization (as opposed to asteroid mining) makes economic sense. A space elevator offers vast economic benefits in the asteroid mining case, however, which is really the principle reason to build one.

Yeah, going to other planets is silly, it's way too hard to get off them again.

Space habitats are what's needed. At the top of a space elevator will do for one, but that can't be the first big one, we'll need one to build the space elevator.