I was stuck in a lift with 5 other people today, thankfully not too long. Was rescued by some construction workers who happened to be working on the basement floor we ended up going slightly below.

Probably unlikely to break but I wonder who fixes the lift that breaks down in space?

I read a text book on tethers about a year ago. The proof of concept tests that have performed to date had problems with micrometeorite damage, they would snap after a relative short time in space. You need a much chunkier cable than 0.2mm so that the load bearing material is protected. It doesn't sound like 0.2mm is much of a target, but as every peice is critical, over the 55,000km length it adds to a target area of 11km^2 that can't be hit. There are just too many micrometeorites up there so this kind of area would get hit rapidly. Check out SPENVIS for micrometeorite fluxes.
I was really sad when I realised this problem because I think space elevators are so cool!

GrahamK wrote: There are just too many micrometeorites up there so this kind of area would get hit rapidly.

So you build it thick enough that it can take damage for say 50 years and so be safe to use. Puts the cost up, but so what.

The tether test done so far have all been in low Earth orbit, where the density of man-made space debris is very high.
Out in cislunar space, the density of space debris is essentially zero. There will be a background of natural micrometeorids, which will cause on average one or two impacts per year. A damage tolerant multi-strand tether can easily handle a single broken strand, and this can be repaired quickly before a second or third impact.

Michael B wrote:

GrahamK wrote: There are just too many micrometeorites up there so this kind of area would get hit rapidly.

So you build it thick enough that it can take damage for say 50 years and so be safe to use. Puts the cost up, but so what.

Yeah that is the solution. Cost goes up a lot though as you've increased the amount of material so much (increasing diameter squares the mass). But then adding that extra mass per unit length of the elevator means you have to add more strength to the cable at the high tension sections making them even larger still. The cost just skyrockets with all that mass you have to get into the right orbit.

charlesfradley wrote: The tether test done so far have all been in low Earth orbit, where the density of man-made space debris is very high.
Out in cislunar space, the density of space debris is essentially zero. There will be a background of natural micrometeorids, which will cause on average one or two impacts per year. A damage tolerant multi-strand tether can easily handle a single broken strand, and this can be repaired quickly before a second or third impact.

True point about the man-made debris increasing the risk of impact. But I think you are underestimating the amount of natural micrometeoroids that pass through a 11km^2 area per year in cis-luna space and the ability of your cable to resist even the tinyest impactor (My guess is that its higher than 1-2 a year, but it does depend very strongly on the impactor size required to break the tether so I can't run the numbers in SPENVIS accurately).

I do think its possible for space elevators to exist, just not something we should focus on for now. Its the length required for space elevators that makes them hard to put into practice. Struggling to imagine 55,000km is the problem for me at least, it's basically impossible as it larger than the circumference of the earth!

The multi-strand design is a must (Seperated so that one large impactor doesn't damage them all.) just a shame Chief Space Elevator Repair Engineer would be a lonely job (although I know some people who wouldn't mind that) because it sounds really cool!