HopDavid

As I just said upthread, getting off a body isn't the only thing an elevator would be used for.

This is a good observation. Many wrongly believe an elevator's only purpose is getting off the ground. But the elevator can also impart velocity. Speed of a payload on an elevator is ωr where ω is angular velocity in radians and r is distance from body center. The farther you are from center, the bigger r is. So an elevator from Ceres, Vesta or Phobos can provide delta V for insertion to a transfer orbit to another destination in the solar system. However in an elevator between Charon and Pluto, synchronous orbits would be at Pluto, Pluto Charon L1 and Charon. Releasing from points other than these will drop you towards either Pluto or Charon. To luanch into a heliocentric transfer orbit you'd need an elevator from Charon's far point through Pluto Charon L2. Or an elevator from Pluto's far point through Pluto Charon L3.

Incorrect. Eccentricity of Charon's orbit about Pluto is very, very close to zero. I believe the obliquity is also very close to zero. Quite high. That describes Pluto and Charon. The zero eccentricity is an outcome of eons of tidal evolution. See The Orbit of Charon is Circuler by Buie et al.

Towers and elevators are different animals. A tower needs compressive strength, an elevator tensile strength. A hair thin Zylon tether can support a lot of newtons. Again, here's a description of the model I'm using to determine tether mass. Which is less massive? Tens or hundreds km of railroad tracks or thousands km of fish line? Much of a zylon tether might be even thinner than fish line. Nope. A lunar elevator or orbital tether doesn't presume a lunar construction industry. Zylon tethers don't come from metallurgical plants either lunar or on earth. Trusses aren't relevant.

1.6 km/s is kinetic energy of 1.28e10 joules per kilogram. Let's say you wanted to launch a 10 tonne payload each week. That would be 604800 seconds to charge up the maglev's capacitors. Looks like you'd need a 21 kilowatt power source. If your PV panels crank out 250 watts per kilogram, the panels need only mass 85 kg if you're on a plateau of eternal light, 170 kg for lower latitudes. That's more doable than I expected! However the track is a problem. For easy arithmetic I'm approximating a g as 10 m/s^2. 5 g's would take 32 seconds to reach 1.6 km/s and the track would need to be about 26 kilometers long. Clearing a straight 26 kilometer runway on the moon is not an easy exercise. And what is the mass of the 26 km long rails? And as already mentioned, these rails are no help for a soft landing. A lunar soft landing takes about 3 km/s if coming from LEO. For Ceres a soft landing is not doable with ion craft. Yup -- a sportscar can leave a small body. (Yawn). It's tedious repeating myself. The object of such an elevator is not getting off the surface. It's flinging or dropping payloads. Phobos, for example. It is extremely easy to leave Phobos, no sports car needed. A Ford Focus or maybe even a bicycle could do it. But it's not so easy to drop payloads into Mars atmosphere at .6 km/s. Or fling payloads From Mars orbit to earth transfer orbits or even Ceres transfer orbits. A 14,000 km Phobos elevator could do all these things.

Did you read my post on a lunar elevators through L1? I don't like the idea. Much of what you say is incorrect. When climbing an elevator, horizontal velocity is imparted to the climber from the elevator. So no, energy requirements are not exactly the same as a surface maglev. If you don't know anything about Ceres, why do you mention it? Venus? I posted to the wrong thread recently. Did you do the same? And who's talking about SSTOs? Although they are possible from the Lunar surface. I know the rocket equation but I'm not sure you do.

One of the biggest launch constraints is volume and mass. Especially true in the early stages when everything comes from the bottom of earth's gravity well. So an important metric is ratio of launch infra structure mass to payload mass. You can see that's what I'm looking at with the tether spreadsheets. A mag lev needs a lot of juice, it goes up with the square of the velocity needed. To send stuff into orbit requires massive rails as well as a stud hoss power source. Mag lev launches on airless worlds are another technology that would be much more doable with a better alpha. And as you mention, rail guns are little help for a soft landing. One of the things that excite me most about a Ceres elevator is it would enable coming and going from Ceres with ion engines. As you probably know, ion has fantastic ISP but weak thrust. Ceres has a shallow gravity well but still deep enough that thrust to weight ratio prevents soft landing on Ceres with ion engines. The solar acceleration at 3 A.U. is around .7 mm/sec (if I did my arithmetic right). So an ion craft with 1 mm/sec^2 acceleration could do impulsive burns for injection to elliptical transfers between Main Belt asteroids (unlike deep in earth's gravity well where an ion path would be long, slow spiral). A ion craft could dock with a Ceres or Vesta elevator. A Ceres or Vesta elevator might also lend a hand sending an ion ship on it's way with a .5 to 1 km/s toss. Not much of a propellent saver with ion's great ISP, but it would save some time. Ion craft and elevators would make travel about the Main Belt much less difficult.

Sorry for the thread necromancy but I've added elevator stuff to my blogs. I came across a spread sheet that gives an estimate of tether mass needed for a given payload mass. Here's an explanation of the spreadsheet as well as links to various tether scenarios. I assume Zylon tethers throughout. I am not that enthusiastic about a lunar elevator. I am more excited about a Phobos elevator, both extending towards Mars as well as extending away from Mars.

d'oh! I am a dufus. I'd participated in several threads but opened the wrong one. Sorry. Here's the thread I meant to post to. Is there a way to delete my off topic posts in this thread?

Sorry for the thread necromancy but I've added elevator stuff to my blogs. I came across a spread sheet that gives an estimate of tether mass needed for a given payload mass. Here's an explanation of the spreadsheet as well as links to various tether scenarios. I assume Zylon tethers throughout. I am not that enthusiastic about a lunar elevator. I am more excited about a Phobos elevator, both extending towards Mars as well as extending away from Mars.

Haven't watched the vid. Do they point out Mars near vacuum wouldn't have winds that could blow over an MAV? Not in the movie, but Tyson's trailer was pretty clueless in several ways.

Getting off a body's surface isn't the only elevator use. If the elevator is long enough and angular velocity (ω) is high, the tether can sling payloads at high velocity. Speed is ωr, where ω is angular velocity in radians over time and r is distance from center of rotation. Thus a Ceres elevator could not only get stuff off Ceres' surface, it could provide some of the delta V needed for a heliocentric transfer orbit to another destination in the solar system. Another benefit of a Ceres elevator: it could dock with ion driven spacecraft. Ion engines have fantastic ISP but very poor thrust. Even with Ceres' very low gravity, thrust to weight ratio would be less than 1. So an ion engine couldn't take off from Ceres, nor could it soft land. A Phobos tether of relatively modest length could sling stuff earthward, Ceresward as well as lower stuff almost to Mars' surface. See Phobos, Panama Canal of The Inner Solar System.

"legendary"? Well, maybe I'm a legend in my own mind. Thanks for the warm welcome.

Robots vs humans is a false dichotomy. Robots will make plausible a sustained human presence on another body. If robots can establish infrastructure to extract water, Tsiolkovsky's rocket equation becomes much less of an obstacle. Life support becomes more doable. Humans nearby eliminates light lag latency. On-site humans can also maintain robots. A combo of robots and humans is more able than either alone.

To find most retrievable asteroids go to JPL's NEO Close Approaches page, sort by Vinfinity and choose nominal distance <=0.05AU. I wrote about Catching An Asteroid. If an asteroid is already coming close to the earth, it doesn't take much to nudge it so it passes through earth's sphere of influence. If timed just right, the moon's gravity can remove enough of the hyperbolic excess velocity to trap in the asteroid in an elliptical capture orbit. Then a good place for it would be a Distant Retrograde Orbit (DRO) about the moon. That's one of the option the Keck folks proposed anyway. They want to use Hall ion thrusters which a 30 km/s exhaust velocity.