I was wondering if plans exist for machines, that are
physically possible, but cannot constructed because technology hasn’t advanced far enough.
I refer you to a statement by the late Dr. Richard Feinmann (sp?), a theoretical physicist who worked under Einstein and Oppenheimer on the bomb, and such. As written towards the end of his humorous, auto-biographical book “Surely, You’re Joking, Mr. Feinmann”:
Wanting to maintain an edge esp. during the early days of the nuclear age the start of the Cold War, the Federal Government had asked such great scientists (of that time -circa 1950-60ish?) to give serious thoughts to what inventions may yet come to be. The military was HIGHLY interested in patenting their ideas. One such idea included the concept of a nuclear-powered submarine.
I didn’t know you could just patent an idea without a model, especially back then but (A) today, you don’t need a working model - unless it’s a perpetual motion machine and (B) even if a model was needed bakc then, the military ould pull strings, anyhow.
This is what I know for sure. Also, having worked in the Patent office, I can assure you I’ve seen issued patents on devices which MAY work in the future, but for now it’s highly questionable.
- Jinx
A reusable rocket. In the past it was impossible to make them light enough. Currently it should be just about possible, but still too expensive to be practical. (At least, nobody who has the money thinks it’s worth it) A more extreme example would be space elevators - the technology is trivial, just an electric elevator, but we have no material strong enough for a tower that reaches geosynchronous orbit and beyond.
Actually you’ll find such designs in any field, I’m sure.
The first one that comes to mind is a ‘beanstalk’, which is a giant tether that stretches from the ground into space. Centripetal acceleration keeps it taut. Then you can hang elevators on it and take a ride into orbit using plain old electricity to get you there. Put a nuclear power plant on the ground, and it not only provides power to the space station at the end of the tether (or maybe even lots of stations at different points along the way), but powers the cars. In fact, you can use regenerative braking on the cars on the way down to power the ones going up, and all you have to replace are friction losses. And those might even be made up by having the tether cutting through the earth’s magnetic field. So you essentially can have a self-powered perpetual elevator into space.
We know exactly how to build these things today. The only thing stopping us is a material with a high enough tensile strength. The best materials we have today would require such a thick taper to maintain strength that the amount of material required is too expensive. But if we find a material with a tensile strength even 10x better than what we have now, you could build one of these.
Then you can build one on the moon as well (this one is MUCH easier due to the 1/6 gravity), and now you have a free way to get out of the Earth’s gravity well and into the moon’s. and down to the surface and back. Now travel from the surface of the moon to the surface of the Earth is almost free (just the energy required to traverse the distance between them, which is a small fraction of what the entire trip would take. And now we can get the fuel for that into orbit for free).
You can do the same thing in orbit. Put a big tether in the sky and spin it at exactly the velocity required to get you to mars. Now you dock at the hub, and travel out to the rim, where you pick up the velocity required to get to mars. Let go, and you’re on your way! Of course, the wheel will slow down a bit as you move out due to conservation of angular momentum, and it will stay slower after you release (the energy from your trip has to come from somewhere). But here’s the cool thing - when people come back from the other way they latch on to the rim, return all the energy back to the system. As they descend to the hub, the tether speeds up again. Voila! Free travel between Earth and Mars. If the mass of the whole tether assembly is a large multiple of the mass of the ships, the rotational velocity won’t change very much at all. Also, you can put space stations at each end to service the ships, and those stations will have an artificial gravity so we avoid all the zero-G physical problems.
Now put a tether on Mars…
Anyway, this will all be possible when we find the right material. Buckeyballs, maybe? Perhaps some nano-engineered micro structure. Maybe some new material that gets stronger when you put an electric charge on it. Who knows?
The “Beanstalk” device was referred to in a book called Friday by Robert Heinlein… but he didn’t go into nearly so much detail as Sam did, and I never actually managed to understand what he was talking about. I mean, the implication that it was an elevator up to GEO was obvious, but the mechanics were kind of left out.
The construction confuses me, though… do you build a really really really high tower and just stick a space station on the end, or do you put a space station in orbit and then let down a rope?
Anyway, I know this has nothing to do with the OP, so please pardon the hj, but I’ve really wondered about that for a long time.
To build one, you put a big satellite full of raw materials in geostationary orbit. Then you start extruding your cable towards the Earth, while extruding a cable in the opposite direction to maintain equilibrium (or a smaller cable with a weight on the end of it). Eventually, the cable will touch the Earth, and then you attach it to a gigantic anchor point, and run more weight up the other cable in order to put tension on the whole thing and keep it rigid.
Another way to do it is to build the cable horizontally in space, then rotate it so that it drops down through the atmosphere. Then you can either grab it and anchor it, or let it keep rotating and let it grab payloads at the bottom and haul them into space. But the mechanics of that are very tricky, so I suspect the extrusion method would be the method of choice.
One interesting thing about this is if you are on the elevator but not yet at the geostationary point, you aren’t really in orbit - you’re just above the atmosphere. So if you fell off the thing 500 miles up (3 times the height of a shuttle orbit), you’d still FALL. Straight down (well, not quite straight - coriolis effect would make your fall be an arc). Yee-haw!
Point of information: Einstein did not work on the A-Bomb project other than call the possibility to Roosevelt’s attention in a letter. He later regretted doing even this.
Can I assume you are being silly, or was that a semi-serious proposal? If the former, well, ha ha… 
If the latter, how do you propose to maintain the line when Mars and Earth are on opposite sides of the Sun? I imagine it would have to be amazingly elastic, equally amazingly resistant to meteors, and very scissor-proof.
(It is a hell of a take on the Mars Direct plan, though.)
Uh no… Not a tether between Mars and the Earth, but a tether on Mars to Martian orbit (I also didn’t mean a tether between the Earth and the Moon, in case that’s what you thought).
Basically, a tether gives you a very cheap way out of a planet’s gravity well, and also gives you a way to convert rotational energy into linear energy once in space. If we ever get to the point where we can build these, access to space will be so cheap as to be essentially free. It still doesn’t solve the problem of getting around quickly once you are IN space, but it gets you to orbit.
And as Robert Heinlein once said, once you are in orbit, you are halfway to anywhere. In terms of energy, that’s about right.
Well, according to Arthur C. Clarke, in his book The Fountains of Paradise, monofilament diamond wire is the needed material. We should be making some of that soon enough.
So, on this little tangent, would it really be easier to link up with a tether instead of just landing? Landing is hazardous and rather expensive (at least when you want to leave again), but it isn’t like you can miss Mars (and any tether hookup would be smaller than Mars), and the basic technique has been worked on since the Wrights’ day. On the other hand, using spacecraft just to fly between tethers would simplfy their design (no landing system, no aerodynamic concerns, just an engine, cargo space, human space, and a tether link (in that order of size, no doubt)) and make the trips cheaper (no need to carry reactant mass to get out of a gravity well). Well?
I think you lost me somewhere along the way. The whole point to having a tether on Mars would be to save the fuel required to land (if using rockets), and the fuel required to take off again. Also, you can use a spinning tether in Mars orbit to grab the ships coming in and convert their momentum into rotational velocity, which can be used to launch it back home again. In this way, the trip between the two planets can be made with nothing but manoevering fuel.
And sure, I think it would be WAY easier to rendevous with a satellite in Mars Geostationary orbit than to land on the surface. Don’t you?
But you don’t really need the spinning tethers anyway, because once you have tethers from the surface into orbit, you can bring reaction mass for rockets up to orbit very cheaply, so you can let the vehicles accelerate under their own power and decelerate at the other end.
I wouldn’t know. That’s why I asked.
Okay, there’s a few definite advantages. But wouldn’t there be a problem with finding the tether and then making your speed close enough to its speed to dock with it?
Why? We’ve been doing orbital docking manoevers for thirty five years. We’re pretty good at it. The shuttle docks with the ISS on every trip to it. The Apollo missions required a lunar rendezvous and docking. What makes you think a tether would be any tougher to dock with? Remember, at the end of the tether you’ll find a space station of some sort, with docking ports, navigational beacons, or anything else we need to put on it to make the task easier.
The problem of landing on Mars and then taking off again is at least an order of magnitude greater than the problem of just docking with a satellite in orbit. Remember, unlike the Apollo landers, the Mars lander has to have enough fuel to accelerate through the Martian atmosphere, and Mars’ gravity is much stronger. And, hauling all that fuel to Mars is extremely expensive and difficult.
I would have to agree. If you are in an orbit that doesn’t allow you to rendezvous, you just have to change your orbit a little and wait. Landing involves huge expenditures of fuel, and the uncertainty of what terrain you are landing on (unless there is an airport or spaceport or something at a known location.)
If you miss a rendezvous, and you are in a closed orbit, you can try again later. It is unlikely that you would be able to abort a landing and try again later, due to fuel usage.
well, i had a great idea. it was incredibly expensive, but it would make interstellar travel fairly cheap (in the extremely long term).
but it died so fast, so fast…
oh well. maybe you all can ressurect it!
Okay, good. All my objections have been rationally discounted. It’s good to know that the system can withstand at least my attacks. 
We actually do have the requisite technology for a Space Elevator. The material required is carbon nanotubes, which are sort of like elongated buckyballs. Current estimated cost is forty billion bucks. Incidentally, a space elevator does even better than getting you into orbit for free. It can also get you anywhere else for the same cost. As Sam Stone pointed out, if you stepped off below the geosynch point, you’d fall down… But if, on the other hand, you stepped off above the geosynch point, you’d “fall” up, being tossed out by the centrifugal force. Let go at the right time, and at the right height, and you can arrange to end up pretty much anywhere. The extra energy would actually come from the Earth’s rotation, but that’s such a huge store of energy that it really isn’t worth worrying about.
Are you saying that if Congress approved a $40 billion budget now, we could have a space elevator in a few years (or 10, or whatever)? Do you have a source for this? You could recover the cost with just a couple hundred trips.
Well, sort of. So far, nanotubes have only been manufactured in miniscule quantities, far short of the 25,000 miles we’d need (per strand). Plus we have to design the rest of the system and figure out how to put it up there.