Jump to content

Free fall chain - (speculative) alternative for space elevator


Recommended Posts

I just had this thought quite some time ago. I made a drawing that deliberately looks like it could be an "popular science" illustration from 17th century.

If someone makes a cannon, that can shoot repeatedly cannonballs into space and the cannonballs can be connected with
a chain (or not), Would it be possible someone to walk slowly along the chain into space - that way that the walker steals 
some of the linear momentum of the cannonballs - and end up into orbiting earth?

I named this hypothetical setup as " Free fall chain ".

In the place where the cannonballs fall back to earths surface, there could be some kind of device that can gather the kinetic energy of the cannonballs, that may be somehow recycled and reused in the cannon again.

The momentum stealing could be done via electromagnetic interaction such a way that the walker shoes does not even touch
the cannonballs.

What would be the benefit of this compared to that the man is just shot into space? 
-it is that the walker can rise slowly there without high inertial forces.

What would be the benefit compared to space elevator? It is that you don't need strong materials. 

Well it could be better that someone just shoots smaller stones into spacewalkers back. And this would be close to laser propulsion.

I decided not to develop this concept more here for now.


Edited by caracal
Link to comment
Share on other sites

Bear in mind the minimum orbital velocity has to be around 7 km/s.  So your cannon ball, first encountering many miles of drag - air resistance - before reaching an orbit, would need to be moving faster than that as it departs the muzzle.

Watch that first step!

Link to comment
Share on other sites


(edit: I tend to write too much so i was thinking this text through. It is still quite long answer.)

Escalator is standing on the ground, this is like a slingshot,'rail' or counterweight, that has been shot into air. 

This kind of setup reminds of skyhook or orbital ring. ( https://en.wikipedia.org/wiki/Skyhook_(structure) ) According to this article skyhooks has been suggested in 1960's.

This is also close to fulton skyhook or Fulton surface-to-air recovery system. (that kind is used for example in Bond film "Thunderball" ending scene)

To avoid rapid punch, in the illustration the walker should tap each cannonball such a way that it would increase his momentum just sligthly that he
would be able to rise up slowly in order to avoid sudden pull. The walker could for example crab the the cannonball very slightly with a suction cup just to gain a slight amount of momentum before the suction cup looses. (That would require quite skills for the spacewalker.)

Or he could have some kind of special device that you can steal its momentum slowly enough that the inertial forces arent dangerous to you. The interaction between the space walker's device and the chain could be Electromagnetic such that the walker could gain momentum like bullet train does without actually touching the rail. (What kind of device it would be in detail?)

I could think of also slightly different kind of lift off maneuver: Shooting some counterweight first into air with a cable attached to it, then crabbing to the cable such a way that with some device the cable does not wrench you up instantly but starts to pull you up slowly while the cable still is going in high velocity. At the end the counterweight and cable could have lost all of their momentum or even move backwards.

The gain of such maneuver would be just that the space walker does not need to experience high inertial forces in the lift off compared to if he was just shot into air, and his acceleration to high speed would be tolerated by the passenger.

Actually What would be new or different in this "free fall cable" from skyhook is just that the cable can have high velocity while the lifter can still use its momentum to slowly rise up. 

Shooting this kind of chain or system into air from the surface of earth does require energy and there is also air drag. Thought the air resistance would be highest only on the foremost part of the chain. The required velocity to circular orbit is quite high - 8km/s . I don't know would there be any benefit for this compared to rocket propulsion or for example laser propulsion.

(How to avoid that the chain gathers up at higher altitudes when its velocity slows down? It can either curl like old phone wire
or get squeezed. This event could be computer controlled such a way that the chain contains some kind of actuators that can
sligthtly bend or change the shape of the chain during the flight. )


* I could actually write here few words about free fall chain Loop installations just because i have some thoughts about them.
This is not an answer to your remarks anymore. 

Free fall chain installations:

Besides used as liftoff maneuver, The free fall chain could also be continuous installation or even a loop. 

Besides as a lift mechanism, this kind of loop could also just serve as architectural monument that does not lift anything. This kind of monument would have safety concerns and challenges thought.

Shooting continuously cannonballs to air would require lots of energy! Maybe the chain could be that kind that it just have just enough momentum and kinetic energy that one passenger can gain enough speed. Or Maybe the kinetic energy is taken back and reused somewhere in the place where the cannonballs fall back to the ground. It could also be possible that the whole chain is in elliptical orbit (that would be close to or same as orbital ring) and is completely in the space, when it may be able to keep its kinetic energy for long time.

Human kind could also have a need that lots of material like water or some other resource should be imported from ground to the space given a little time available. They could be for example building very large space station or terraforming Mars. They may end up shooting cargo directly into space. They might establish this kind of chain to do that. The space walker, just uses some of the chains momentum and energy that is already needed to send resources into space.

The air resistance can be minimized if the shape of the chain does not move - the top end of the chain would encounter the highest air resistance. When the chain loop that could be a parabolic curve (in inertial coordinate system), is filled with chain, there could be small air resistance.

The needed velocity to end up stable orbit around earth is that 8km/s that is very high. It could be that this kind of
setup would not be enough for gaining such high velocities. It may be that space vessel would need also rocket propulsion. 
If the chain is continuous loop or parabolic curve (in non-rotating coordinates), it could be possible that space vessel could stand still on the top of the curve as long as it continuosly gains momentum from the chain. But in principle the space vessel
could gain all the needed momentum from the chain to have 8km/s orbital velocity - It just uses the chain elements as counterweigths.

Link to comment
Share on other sites

Be along the same lines as a space fountain or more broadly an active structure.



Main issue are the power requirements and any energy losses in the system. Nothing physically impossible about the concept though. I think it probable honestly. Not dealing with the same risk and tensile strength requirements of a traditional space elevator.

Link to comment
Share on other sites

I see.

This is quite interesting. Space fountain and space tethers.
After some search I found one interesting Science fiction blog text about space tethers 

"ToughSF - Space Tethers: Stringing up the Solar System "- 

And two science fiction texts about space fountain: 

"R.L.Forward indistinguishable from magic - chapter 4 ": 
- https://www.baen.com/Chapters/0671876864/0671876864___4.htm
(this text is not reader friendly) ( is this copyrighted?)

and "Orions arm universe project - encyclopaedia galactica - Technologies used to support large scale structures using momentum" 
- https://www.orionsarm.com/eg-article/47e1bb1fc898c

(Which i have only read by glimpse this far.)

I Give here yet illustration of two different kind of installations of this "free fall cable".


Left one is a "Wünchenberg's chair" (this is not a real name). It is an installation of computer controlled chain loop, that either wobbles around or looks to stand still without moving while there is no any mechanical support in the system. It looks like a chair or table, that is why the name. Wünchenberg is just imaginary name of a mathematician. This kind of installation could well be a home decoration or a part of public statue or monument. 

Red-colored part of the chain is raising up, and the blue-colored part of the chain is falling down. Black line in the central
axis is trajectory of the mass-center. The "mass-center" of the looped chain would follow upward free fall trajectory (drawn in black dotted line) if there were no air resistance. The tangential velocity of the chain is constant everywhere. If properly installed, it may be ? possible to achieve condition where the shape of the chain appear to stay still and only close look of the chain reveal that it is actually moving all the time. While not in this state, the chain will wobble around but stay inside some closed conical surface all the time. The conic central diameter may in fact not grow linearly upward.

In principle the chain could consist of two chains that are moving into opposite directions.

The system manages not to mess up only with constant computer control. The chain element joints contain actuators that can bend the angle between the elements on the fly and there is computer program that control the movement of these actuators.

Right one is another kind of illustration where the chain mass center follows parabolic curve. It curls into helical shape like a old phone wire
on the top of the curve to avoid gathering up when the free fall velocity slows down - this is also computer controlled mechanism.



Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.