I should probably qualify my earlier use of the term “extremely slender” as relative. Compared to ‘mountain sized’ I would think a cable a few meters or so in diameter would be slender compared to the base of say… a beanstalk type tower going into space or even the middle of the elevator cable itself.
This is a stupid question, but what about the atmosphere? You hear about things “burning up in the atmosphere” and isn’t that what happened to the space shuttle? What happens in the area between the earth’s atmosphere and space itself to cause problems, and how would the space elevator protect itself?
because the space elevator isnt going 12,500mph like the shuttle
was…
So it’s the speed something is traveling relative to the earth? When asteroids, meteorites and space junk “burn up” it’s because they’re moving fast, but the space elevator will be moving with the earth?
This isn’t something I’ve thought about before, but it’s interesting to me.
There have been a few comments speculating on the size of the cable. The Highlift Systems proposal, at least, is for a ribbon-shaped tether 100,000km long, 1m wide and 2um (microns) thick, with a 2 square milimeter cross section. It’s so small, that from the right angle, I guess this thing would actually be invisible.
Others have recommended the Highlift Systems website as interesting reading on this subject. I’ll cast a “me too” vote. I’m no expert, but it doesn’t set off my obvious-crackpot-detector, at least.
That’s it. Burnign up during reenmtry is all because of friction with the atmopshere. Space junk hits the atmosphere doing mach 20+ and gets incinerated by heat generated by hitting the air molecules that fast. The space elevator is stationary with respect to the atmosphere.
Can you imagine having to work on this thing? At anywhere other than geostationary orbit, you’d be hanging off the thing, look straight DOWN.
Having to repair damage at 1000km up would be interesting.
That is why we might want to wait until repairs can be carried out by reliable robots for most of the time,
although a competent steeplejack would perhaps be proud to be able to fearlessly hang 20km above the earth.
Of course, the thinnest part of this thing is just above the freestanding platform… the space-elevator types are talking about the tether being a couple of centimetres wide at that point.
It hangs from the orbiting COG, and only has to support its own weight, and that of any elevator cars.
In fact you could attach the earth end to a balloon…
Thanks for all of the great responses. It seems to me that the greatest obstacle to overcome is the problem of objects in low earth orbit. Since the elevator will be stationary at a point on the equator, everything in orbits at a lower altitude then geosynchronous will eventually run into it. Vehicles under active control could just alter their orbits at a critical point and steer around it, but space junk is another matter.
I just can’t stop thinking about the ride up. Will the observation deck have a little sign that says “Please do not throw objects from the elevator.”?
In the proposals I’ve seen, the elevator isn’t stationary at a point on the equator. One of the reasons to put the base on a floating platform is that it makes it easier to move. Anything big enough to cause a potential problem is already tracked by NORAD, and you’d have plenty of advance warning to move the cable out of the way. Note that even a cluttered region of space such as low Earth orbit above the equator is still best described as “empty”, so you wouldn’t need to move it very far or very often.
The cable will have to be protected against micrometeoroids in any event, so low-mass space debris won’t be much of an additional problem. Heck, one additional benefit of the cable is that it’s shielding will sweep LEO of unwanted debris. As for active vehicles and satellites, they can be put into orbits timed to always miss the cable when their path crosses the equator.
Also, bear in mind that the cable would replace a lot of the free-orbiting hardware we currently have up there. Once built, the cable would make it cheaper to send satellites to geosynch orbit or beyond than to place them in low earth orbit. And you could string communications relays and weather cameras up the whole length of the cable, not just at the geosynch point. From 8000 kilometers and up, the line of sight covers all but the highest latitudes.
It’s probably the responsibility of the tether to move out of the way, not the vehicles in orbit (because they wouldn’t want to use their very limited, precious fuel to change orbital paths). The tether not only has a movable base, but it also has oscillation modes that can probably be used to bounce it out of the way.
Probably not needed, since the elevator will have to be sealed air-tight. I mean, you’re going up into the vacuum of space on a trip that will take ~5 days.
There’s no magical shield they can use against space debris. The only protection it will have is that a) the nanotubes are tough, but more importantly b) their cross-sectional area and layout (in a curved ribbon) are such that only a couple of the strings could be broken at any one time, and there are “joiners” every few meters to attach the strings to each other (in other words, limiting the damage done by a break in a string to the area between joiners). Statistical studies of orbital debris etc. impacts at HighLift Systems have suggested that the lifetime of the elevator (assuming no upgrades, re-building, etc.) should be ~50-100 years.
Since it’s not going to have special shielding, it won’t be able to clear away debris. But even if it did have shielding, that would not get rid of debris – it would, in fact, cause more! Every time a piece of something impacts another object in space, the relative velocities are usually so large that impact causes more breakage, producing a larger number of smaller pieces of debris. When you consider the potential damage of even tiny bits (for example, once a fleck of paint buried itself a quarter or half inch into one of the quartz windows on the shuttle) and the increased difficulty in tracking pieces the smaller they become, breaking up orbital debris sounds more and more like a bad idea. De-orbiting debris, e.g. via an expanded atmosphere or gas injected into orbit, is a much better, though difficult, plan.
I can’t visualize this - how does it work?
By friction. In other words, back in the '70s when Spacelab was up, part of the reason it de-orbited was that solar activity warmed up the Earth’s atmosphere enough to expand it, thereby increasing the drag on Spacelab and decreasing its lifetime. It turns out that the combination of its decreased orbital lifetime and the delays in launching the shuttle meant that the shuttle couldn’t go up to Spacelab to re-boost it, and I guess we didn’t have any other reasonable capability for doing so. So Spacelab eventually (I think a year or two before originally expected) plummeted to the ground.
Similarly, there have been some proposals put out to ‘dump’ some amount of gas into low earth orbit. You’d have to heat it up enough that it would disperse very far before cooling enough to condense into solid droplets (otherwise you’d have the problem of the debris hitting a solid instead of a gas). The problem with this is that it would also put drag on satellites that want to stay up in addition to debris you want down. And it’s not clear how effective or long-lasting any amount we could haul up to space would be.
A related proposal is to ‘blast’ a localized part of the atmosphere to heat it up and cause a plume or jet to expand up into space, rather than expanding the entire atmosphere. This would have the benefits of being short-lived and localized, so you could avoid regular satellites. Besides the obvious power requirements and legal/environmental issues, though, I’m not sure how feasible it is – I’m not familiar with the atmospheric dynamics (and, for example, how high you could get a jet to reach).
Nitpick: Spacelab was a Shuttle payload, which stayed in the cargo bay at all times. Skylab was the free-floating space station launched by a Saturn V.
:smack: Yes, you’re right – sorry about that. I was thinking it didn’t sound right, but I thought “the thing that goes in the Shuttle is SpaceHab.” But maybe that’s just the name of the company?