5 ms·

Isn't the true "ideal" a space elevator so you can continously deliver between the moon and the earth without having to burn lots of resources every single time

Isn't the true "ideal" a space elevator so you can continously deliver between the moon and the earth without having to burn lots of resources every single time? Shouldn't that be what we optimize for in the long run? Its the only way I can think of that space cargo becomes economical. Then you can ship raw material up to the Moon and build from there, launch from there etc. and vice versa. Maybe we'll see what Helium-3 can do for humans at that point

matheusmoreira 4y ago
Yeah, a space elevator would be the most efficient way lift payloads to space where it's a lot easier to maneuver. Anyone knowledgeable about space elevators on HN? I wonder why it's never been attempted.
- throwawaymaths 4y ago
  There are currently insurmountable materials science limitations, and even the materials that come close are not currently possible to manufacture at scale, or even assemble (one carbon nanotubes does not necessarily have the same properties of many carbon nanotubes) at scale into structures which will withstand the structural stresses. I believe this is not necessarily true for other celestial objects besides the earth
  - Smaug123 4y ago
    For example, Pluto and Charon is a pair that sometimes comes up; a space elevator connecting Pluto to Charon would very possibly just about be within our current civilisation's capabilities, if for some reason we cared to build one enough to sink the Earth's economic output into it. They're tidally locked. (https://en.wikipedia.org/wiki/Space_elevator https://en.wikipedia.org/wiki/Space_elevator has its section on "Extraterrestrial elevators".)
    - actionfromafar 4y ago
      A space elevator for our own moon would be far more interesting to me. It could be built with known materials.
      - throwawaymaths 4y ago
        Is that true? I thought getting a 28 day period on the moon is beyond the orbit of the moon itself.
        actionfromafar 4y ago
        I meant for going from the Moon surface to an orbit around the Moon, not reaching Earth.
        throwawaymaths 4y ago
        Yeah I looked up the moon proposals and fundamentally they have to go to L1/L2 points and they are not stationary on the surface or have to pivot around the poles. A tether that was lunostationary is impossible since it would have to cut through the earth
        actionfromafar 4y ago
        The anchor point on the moon will be fixed. It's the counter weight at L1/L2 that will drift and will need some (small, according to Wikipedia) correction.
        throwawaymaths 4y ago
        No. Stop and think about it. The moon rotates every 28 days with respect to L1/L2.
        actionfromafar 4y ago
- skykooler 4y ago
  We do not have any known materials which are anywhere near strong enough on the macro scale for a space elevator on Earth. If we did, we would still need to launch it into space using conventional rockets in the first place, which would cost trillions of dollars at current launch prices and require solving a bunch of new issues (if it's launched in segments, how do you join them together at full strength in space? if it isn't, how do you coordinate ten thousand rockets to launch into orbit simultaneously - and where do you launch them all from?) Once it's in space, you have the issue that it necessarily will need to be above the equator, which every satellite in space crosses twice per orbit - and there's no good way to make a structure as large as a space elevator try to dodge things, so it also needs to be strong enough that it can handle impacts from space debris or derelict satellites at orbital velocities without weakening to the point that it breaks. And then of course you need to supply power to anything climbing it - which is an immense amount of energy required to climb 30,000+ miles vertically - and there's no practical way of sending that energy up the cable itself (you could do it with superconductors, but the power requirements for cooling thirty thousand miles of superconducting cable is more than many nations consume). One option is to use microwaves to beam power to the climber, but this is currently only theoretical, and raises further materials science issues with the microwaves heating up the cable along its length. Finally, having a space elevator is a massive hazard to the Earth in general. If most structures on Earth fail, the damage is limited to a small area where the structure stands. If a space elevator ever fails for any reason, it would wrap around the equator as it fell, releasing the equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat. It's not quite as bad as the asteroid that wiped out the dinosaurs, but it would still be enough to significantly alter the climate and wipe out at least half a billion people from the impact alone. It's not a project that should be undertaken lightly.
  - dmitrygr 4y ago
    I am not sure what assumptions you are making in your last paragraph, but I think you are off by enough orders of magnitude to assume you pulled those numbers out of thin air (at best) > equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat. Little boy was 15 kilotons of TNT (63 TJ). Kinetic energy is 1/2 mv^2. So you are claiming that the mass of a mile of the cable is such that mv^2 = 126e12 J At equator the planet rotates at 463.8 m/s so you are assuming that the bottom mile of the cable weighs 585.5e6 kg? Ok, you're completely off base here. Maybe let's look at a higher segment (at geosync orbit). Velocity there is 3.1e3 m/s. You are assuming a mile of that cable weighs 13e6kg. But on the way down it will both ablate (lowering mass) and slow down (lowering velocity), so you are assuming an even more insane higher number. For comparison, a mile of one inch thick steel cable is ONLY 4e3 kg. Sure, space elevator needs something stronger, but even more so, lighter. Yeah, you are just off by MANY orders of magnitude, and that claim was likely pulled out of nowhere
- avmich 4y ago
  Earth space elevator is supposed to be grounded somewhere on equator, the orbital point is on the geostationary orbit and further away there is a counterbalance. There are currently no plausible way to avoid collisions of such a structure with satellites which are below the geostationary orbit. Sooner or later each passive satellite will hit the elevator, and active satellites will have to actively avoid collisions for the whole time they are on the orbit. Any collision would likely disintegrate the satellite and bring serious damage to the elevator - easily enough to break the elevator; after all we're talking about colossal kinetic energy in collision. Even if nanotubes would be used and could work by themselves - I'm optimistic on that - the inherent conflict between space elevator and the rest of cosmonautics currently is enough to prevent this idea from working.
zizee 4y ago
> Its the only way I can think of that space cargo becomes economical Depends what you mean by economical, but a totally, rapidly reusable craft that takes mass to orbit would massively reduce the cost of getting mass to orbit. Not as inexpensive as a space elevator, but more achievable in the near term.
lost_tourist 4y ago
Sure but we aren't even close to a space elevator to get satellites in orbit, no known material could handle being the cable, it's probably a century or more off, if it ever happens, so for now we have rockets.

matheusmoreira 4y ago

Yeah, a space elevator would be the most efficient way lift payloads to space where it's a lot easier to maneuver. Anyone knowledgeable about space elevators on HN? I wonder why it's never been attempted.

throwawaymaths 4y ago
There are currently insurmountable materials science limitations, and even the materials that come close are not currently possible to manufacture at scale, or even assemble (one carbon nanotubes does not necessarily have the same properties of many carbon nanotubes) at scale into structures which will withstand the structural stresses. I believe this is not necessarily true for other celestial objects besides the earth
- Smaug123 4y ago
  For example, Pluto and Charon is a pair that sometimes comes up; a space elevator connecting Pluto to Charon would very possibly just about be within our current civilisation's capabilities, if for some reason we cared to build one enough to sink the Earth's economic output into it. They're tidally locked. (https://en.wikipedia.org/wiki/Space_elevator https://en.wikipedia.org/wiki/Space_elevator has its section on "Extraterrestrial elevators".)
  - actionfromafar 4y ago
    A space elevator for our own moon would be far more interesting to me. It could be built with known materials.
    - throwawaymaths 4y ago
      Is that true? I thought getting a 28 day period on the moon is beyond the orbit of the moon itself.
      - actionfromafar 4y ago
        I meant for going from the Moon surface to an orbit around the Moon, not reaching Earth.
        throwawaymaths 4y ago
        Yeah I looked up the moon proposals and fundamentally they have to go to L1/L2 points and they are not stationary on the surface or have to pivot around the poles. A tether that was lunostationary is impossible since it would have to cut through the earth
        actionfromafar 4y ago
        The anchor point on the moon will be fixed. It's the counter weight at L1/L2 that will drift and will need some (small, according to Wikipedia) correction.
        throwawaymaths 4y ago
        No. Stop and think about it. The moon rotates every 28 days with respect to L1/L2.
        actionfromafar 4y ago
skykooler 4y ago
We do not have any known materials which are anywhere near strong enough on the macro scale for a space elevator on Earth. If we did, we would still need to launch it into space using conventional rockets in the first place, which would cost trillions of dollars at current launch prices and require solving a bunch of new issues (if it's launched in segments, how do you join them together at full strength in space? if it isn't, how do you coordinate ten thousand rockets to launch into orbit simultaneously - and where do you launch them all from?) Once it's in space, you have the issue that it necessarily will need to be above the equator, which every satellite in space crosses twice per orbit - and there's no good way to make a structure as large as a space elevator try to dodge things, so it also needs to be strong enough that it can handle impacts from space debris or derelict satellites at orbital velocities without weakening to the point that it breaks. And then of course you need to supply power to anything climbing it - which is an immense amount of energy required to climb 30,000+ miles vertically - and there's no practical way of sending that energy up the cable itself (you could do it with superconductors, but the power requirements for cooling thirty thousand miles of superconducting cable is more than many nations consume). One option is to use microwaves to beam power to the climber, but this is currently only theoretical, and raises further materials science issues with the microwaves heating up the cable along its length. Finally, having a space elevator is a massive hazard to the Earth in general. If most structures on Earth fail, the damage is limited to a small area where the structure stands. If a space elevator ever fails for any reason, it would wrap around the equator as it fell, releasing the equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat. It's not quite as bad as the asteroid that wiped out the dinosaurs, but it would still be enough to significantly alter the climate and wipe out at least half a billion people from the impact alone. It's not a project that should be undertaken lightly.
- dmitrygr 4y ago
  I am not sure what assumptions you are making in your last paragraph, but I think you are off by enough orders of magnitude to assume you pulled those numbers out of thin air (at best) > equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat. Little boy was 15 kilotons of TNT (63 TJ). Kinetic energy is 1/2 mv^2. So you are claiming that the mass of a mile of the cable is such that mv^2 = 126e12 J At equator the planet rotates at 463.8 m/s so you are assuming that the bottom mile of the cable weighs 585.5e6 kg? Ok, you're completely off base here. Maybe let's look at a higher segment (at geosync orbit). Velocity there is 3.1e3 m/s. You are assuming a mile of that cable weighs 13e6kg. But on the way down it will both ablate (lowering mass) and slow down (lowering velocity), so you are assuming an even more insane higher number. For comparison, a mile of one inch thick steel cable is ONLY 4e3 kg. Sure, space elevator needs something stronger, but even more so, lighter. Yeah, you are just off by MANY orders of magnitude, and that claim was likely pulled out of nowhere
avmich 4y ago
Earth space elevator is supposed to be grounded somewhere on equator, the orbital point is on the geostationary orbit and further away there is a counterbalance. There are currently no plausible way to avoid collisions of such a structure with satellites which are below the geostationary orbit. Sooner or later each passive satellite will hit the elevator, and active satellites will have to actively avoid collisions for the whole time they are on the orbit. Any collision would likely disintegrate the satellite and bring serious damage to the elevator - easily enough to break the elevator; after all we're talking about colossal kinetic energy in collision. Even if nanotubes would be used and could work by themselves - I'm optimistic on that - the inherent conflict between space elevator and the rest of cosmonautics currently is enough to prevent this idea from working.

zizee 4y ago

> Its the only way I can think of that space cargo becomes economical Depends what you mean by economical, but a totally, rapidly reusable craft that takes mass to orbit would massively reduce the cost of getting mass to orbit. Not as inexpensive as a space elevator, but more achievable in the near term.

lost_tourist 4y ago

Sure but we aren't even close to a space elevator to get satellites in orbit, no known material could handle being the cable, it's probably a century or more off, if it ever happens, so for now we have rockets.