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Comment by avmich | Hacker News Reader

I don't understand why so many seemingly educated people keep discussing Earth space elevator. For a long time there is a conclusion that the elevator is incompatible with Earth satellites, which mostly fly below GEO, and elevator will collide with satellites, with all negative consequences. The inherent elevator problem has nothing to do with the material of the cable.

Am I missing something?

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To me, a long-time sci-fi reader but hardly a hardcore space nut, your argument reads a little like "I don't understand why people are discussing horseless carriages, I mean what would the street sweepers do without all the manure to clean up?".

In other words, a functioning space elevator would be grand, epic and useful in ways that make the potential loss of some satellite orbits look like a very minor detail. At least that's my take. Too bad about the materials science not doing its part, huh. :)

No, a better comparison would be "why people discuss antigravity sleds". Space elevator could have uses, if it wouldn't conflict with reality about as much as antigravity sleds, levitating a meter above the road, are.

Horseless carriages in this comparison are rockets.

Space is big. 1) The cable's vibration resonance can be adjusted to avoid the bulk of larger objects, 2) new satellites can be mandated to have emergency maneuver systems (with larger objects not yet de-orbited cleared out by an elevator consortium), and 3) the cable will necessarily have close range defense systems probably at intervals for smaller objects that might be harder to detect at long range. The cable, also, is enormous, which is the largest barrier to its implementation - it would dwarf every other artifact in human history, put together - and can not be made with any material we can currently create at scale. Compared with that, orbital TCAS of some sort is fairly trivial. In the long term, a space elevator is inevitable, but it's inevitable in the same way that . . I dunno, human-crocodile hybrids are, or fusion drive, or the way a lot of other medium-term future stuff is.

EDIT Also, this thing stops at the Karman line. That's not a viable space elevator. Pretty widget, though.

> In the long term, a space elevator is inevitable

There are plenty of zero-fuel launch possibilities and a few very high-ISP ones. On the long term one of them is inevitable, but it's pushing it a bit to claim that it will be the space elevator.

Space elevator is by far the most efficient though . . right? Stuff that's on the end of the cable has enough angular velocity to get flung all across the inner system. Lunar orbit could be reached with release at 50,960 km. At the end of a 144,000 km cable you could get to Jupiter. I dunno what sort of other zero fuel launch techniques are getting considered though - there's no doubt a space elevator is just out of our capabilities today and for a while yet. Probably until our automation is good enough for self-directed asteroid factories to be a Thing.

The zero fuel options all sit around the same efficiency possibilities. A launch-loop won't get you as far as a GEO space elevator, but it can get farther than a non-stationary one. A sky hook can in theory get you a larger delta-v than a GEO elevator. A space fountain can do GEO, but no further...

And the very high ISP options are all on the same category in that they can save you more fuel than the zero fuel ones, but only if you want enough delta-v.

None of those are viable today, but most are in a "we can make all parts, but it's a fucking big machine that we can't assemble", while the elevator is still missing parts.

I think the space-elevator concept is sort of silly, but this doesn't seem like the most pertinent criticism to me. Presumably in a hypothetical future in which a space elevator is under serious consideration, vastly greater resources are being devoted to space technology, launch costs are much less than now, and are about to get cheaper still due to the elevator in question. It seems like if we were on the cusp of being able to 100x the number of satellites or whatever, sacrificing the existing fleet for new ones in different orbits that avoided the elevator wouldn't be too big a sacrifice.

1) It's the only static non-rocket launch system. As such it doesn't require people to buy into the "active support structure" concept which is a prerequisite for orbital rings (<3), launch loops, or space fountains. (Rotovators, though arguably static, require exotic setups for terrestrial use.)

2) It's been around long enough to have made it into mainstream culture, especially via big-budget Hollywood movies.

3) The name is straightforward and approachable to laypeople. An elevator to space nicely obscures issues like its mind-boggling size, duration of transit, and even "reach space" vs "achieve orbit."

4) Picturing the structure fixed over a point on Earth seemingly sidesteps sovereign territory issues and international cooperation, further simplifying the conversation.

The Space Elevator is a gateway to megastructures more than a gateway to space.

It's an idea that straddles science fiction and reality, but is simple enough for normal people to understand and have an opinion about.

Cause they are fucking rad! Its grandiose and big but plausible, its like some one heard of archimedes lever and took it as a challenge. Basically it sparks the imagination :)

Is that sort of collision inevitable or can you have parallel orbits that don't collide? I'm ignorant and this is the first I'm hearing of this issue. Last I heard the material science part was the heartbreaker.

Maybe because it's an old idea, from a time when non-GEO satellites were rare?

(when I was a kid in the 60s/70s, the cool thing was geostationary satellites)

GEO is harder to achieve than LEO. There was never time when non-GEO satellites didn't outnumber GEO ones.

As satellite density increases every satellite will need a collision avoidance system anyway. And getting from geo to leo is way less difficult than launching to leo from the ground.

It's not clear. Maybe satellites will be assigned flypaths, like in aviation? Or you can have either a short-lived satellite, a GEO sat, a well-maintained constellation for communications or observations, singular exceptions like Hubble - or go fly away from Earth? Or something else? Not sure it's good idea for space elevator engineers to trust as much that all satellites will always behave as they, space elevator engineers, absolutely require. The error cost is pretty high.

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