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You can build something like this, but much bigger, and with no external casing, on the Moon or anywhere with little or no atmosphere. Professor James Longuski
by troymc 5y ago
You can build something like this, but much bigger, and with no external casing, on the Moon or anywhere with little or no atmosphere.
Professor James Longuski and his students at Purdue University have done quite a bit of research on this idea over the years. They call it a tether sling. To keep the tip acceleration (v^2)/r low, you want a large r. Some papers:
https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=longuski+tether+sling&btnG= https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=long...
Note 1: Professor Longuski was my PhD advisor, but I never did any research on tether slings myself.
Note 2: Others have also researched tether slings. The papers linked above give many citations to related research.
- soheil 5y agoSomething like the large hadron collider?
- troymc 5y agoThe LHC uses electric and magnetic fields to accelerate charged particles to near the speed of light inside a circular vacuum tube. To picture a tether sling, imagine a lighthouse on the Moon with a giant arm sticking out of its side, and the arm can revolve around the lighthouse like a merry-go-round. The thing to be launched goes at the end of the arm. Just spin up the arm and let go!
- soheil 5y agoSorry I meant for a solution that would work on earth. Couldn't we use magnets to accelerate the ship like a maglev train inside a version of LHC with wider tubes?
- melenaos 5y agoI am no scientist, I just used to play in playground as a kid and watched allot of figure skating. When something is rotating as you said, their mass is away from the rotation point, you can increase the rotation speed by moving the mass closer to the rotation point. When the skater spins with their hands open they gain rotation speed by just gather their hand around the body. When the kids spin on the round game, they get closer to the center to gain speed and away to slow down. Is this a thing? Does this actually translates to increased centripetal force? Why they didnt get more speed by using this method?
- bagels 5y ago"speed" or rate of rotation?
- gizmo686 5y agoIn principle this would work. If they had a spinning mass, then moved the mass closer to the center of rotation, its speed would increase. The reason they do not do this is that it is just not that useful in this context. One of the major limitatinos of the SpinLaunch approach is the g-forces. As it is, objects launched by SpinLaunch experience a g-force on the order of 10,000G. For a constant velocity, this force goes up as the inverse of the radius. As a result, you want the mass to be as far away from the center as possible so that the g-force experienced is minimal. The other problem is that this approach is not actually an efficient way of gaining speed. Conservation of energy is still a thing. The rotating mass experiences an apparent centrifugal force pushing it away from the center of rotation (the 10,000Gs that I mentioned above). In order to move move the mass closer to the center, you must counteract this apparent force. At that point, you are likely better off taking the energy you would spend pulling the mass towards the center and simply apply it directly towards increasing the rotational speed.
- redprince 5y ago> In principle this would work. If they had a spinning mass, then moved the mass closer to the center of rotation, its speed would increase. Actually it wouldn't speed up. The speed of the mass traveling on it's circular path around the center remains the same. The orbit just becomes smaller and thus the path becomes shorter. The mass now makes more rounds in the same time. It is thus spinning faster around the center but traveling at the same speed on its path around it.
- iamthemonster 5y agoIf you were on the moon you would only need to match spinlaunch's launch velocity of 8000 km/h and you wouldn't even need rocket fuel. You would only need a $200 battery and a $200 solar panel to fling 1 kg into space every hour of the day, assuming 100% efficiency. I was quite surprised to discover how cheap it is to fling chunks of the moon into space. I mean... I'm not sure why you'd bother, but still, it interested me. (My working: 2380 m/s escape velocity, 0.5 * 2380^2 energy in Joules required, convert to kWh, googled battery and solar panel costs, totally didn't consider efficiency anywhere)
- jareklupinski 5y agonow you have me imagining some strange field of lunar rock flingers, ejecting mass into space ceaselessly until the sun stops, all for a very motivated PhD student's thesis
- TMWNN 5y ago>I was quite surprised to discover how cheap it is to fling chunks of the moon into space. It is easier to send something to low Earth orbit from the Moon than from Earth.
- Turing_Machine 5y ago> I'm not sure why you'd bother Raw material for space station construction.
- flog 5y agoCould we throw enough moon rocks into an orbit which would block some % of sunlight hitting the earth (to cool it)?
- amurthy1 5y agoAmong other drawbacks, that would interfere with satelites
- londons_explore 5y ago
- abledon 5y agoso Starship could theoretically bring the supplieis to the moon to build a sling... whoa
- fy20 5y agoWouldn't something like a rail gun be simpler? Its basically just a maglev train than carriers a spacecraft. Admittedly a large spinning wheel may be simpler to aim than a few hundred meters of track though.
- remus 5y agoThe tricky thing about using a rail gun is that you need to deliver all the power very quickly which is hard and expensive. With this launch system you can spin it up slowly by feeding in energy and then release the projectile once you're up to speed.
- rklaehn 5y agoYes, the spinning system is also an energy storage device that can release its stored energy instantly.