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Using Sling Shot Power to Hurl Into Orbit
the_2nd_coming writes "space.com has an article
about a new application of a very old technology.
NASA is putting money into Momentum-eXchange/Electrodynamic Reboost tether technology -- MXER for short -- an innovative concept that if implemented would station miles and miles of cart-wheeling cable in orbit around the Earth. Then, rotating like a giant sling, the cable would swoop down and pick up spacecraft in low orbits, then hurl them to higher orbits or even lob them onward to other planets."
- The Fountains of Paradise by Atrhur C. Clarke
- Mars Trilogy by Kim Stanley Robinson
I'm sure there are more.A sling shot is not the same as a sling.
A sling shot uses a rubber band to propel its payload.
A sling uses the sudden stop of centripedal force.
Sling shot = Dennis the Menace.
Sling = David killing Goliath
Slings are good for hunting small animals, apparently.
Wasn't this the subject of an Aurthur C. Clarke SCI-FI novel? Apparently they found methods to create a super strong material that allowed them to make an elevator to space? It was a very interesting read, especially to us nerds. The book dabbled in some interesting physics, the methods required to create such an elevator (given that a strong enough material exists), etc. Anyone remember the title of this book? I vaguely remember 'paradise' as one of the words. Alex
By Gregory Benford. In either "Great Sky River" or "Tides of Light" Benford (physicist and astronomer at UC, Irvine), can't recall which, there is an organism that does this...only its ends actually come much farther down into the atmosphere than NASA's proposal. This organism was even used by the main character in the story to hitch a ride into space.
In Bushworld, they struggle to keep church and state separate in Iraq as they increasingly merge the two in America.
IIRC, a similar-sounding device (known as the Pinwheel) appeared in "Beyond the Fall of Night", by Gregory Benford. This book was a sequel to the Arthur C. Clarke short story "Against the Fall of Night", which Clarke later re-wrote as the full-blown novel "The City and the Stars". All three tales are well worth a read!
Tubal-Cain smokes the white owl.
I'm sorry, you must be confused. King George II lived in Germany and died on 25 Oct 1760 from a burst blood vessel. You should get current...I can understand being a few days behind the times, but 243 years?
--Jubedgy
Si hoc legere scis nimium eruditionis hebes
_The Fountains of Paradise_
/. is making me wait 20 seconds, I can go get the book and find other useful info, such as ISBN and date of publication...
I guess since
ah, good thing, too, as I'd forgotten the "The" in the title.
copyright 1978, ISBN 0-345-25356-6
-calyxa
Decay! Decay! Decay! -Helium
The people making the tethers, TUI (www.tethers.com) are making it out of Spectra fibres. You can check out their website for the full gist, but they have fabrication down pat.
So, yes, this is the real deal, not something 'down the road 5 years'.
--foolish
In the works you site they build an elevator all the way from surface to space; in other words it is extremely long.
In this case, the craft is much shorter and already in space. Rather than lifting something all the way along a cable, you accelerate it by swinging a shorter cable and throw it off.
From an energy perspective, you exchange rockets working inefficiently for a short time for solar-powered engines working efficiently but slowly for a long time. In the space elevators you mention, you rather use more conventional engines like in an electric train.
Tor
Tm
Support TBI Research: http://www.raisinhope.org
Well, looking at this image, it looks like once the tether's orbit has begun to deteriorate, it will just keep falling until it burns up/hits Australia. Rather an odd form for a disposable propulsion system, though...
Karma: Oldschool
Robert Forward was one of the principals at TUI [www.tethers.com] and was a contemporary of RAH, Clarke and Sheffield.
So he actually figured out how to make the damn things work, and spent about a decade trying to pitch it to NASA... but the failure of a single stranded Tether experiment made them really 'gun shy' of the technology, even though the Hoyt/Forward tether is multi-stranded.
If you're trying to use a tether system to transfer from a low orbit to a high orbit, a tether will only get you halfway there. The transfer from a low orbit to high involves one thrust event to change your orbit from circular to elliptical, with the perigee (closest point) staying the same, but the apogee (farthest point) higher up. The second thrust event happens when the satellite hits apogee, accelerating it so that the orbit becomes circular again.
You can hurl rocks up high all you want, but you'll need another force to make sure they stay there.
Note that this doesn't apply to the moon shots or interplanetary boosts. I'm only talking about parabolic and circular orbits, not hyperbolic or complex orbits. I'm sure this would be cool for those cases.
Kevin Fox
That is true, but every time the teather enters the atmosphere, it will be hitting alot of resistance.
Mo00o
There are two ways to get energy to restore orbital momentum to the sling system. One is mentioned in the MXER tether discussion at tethers.com. You can use solar power and the earth's magnetic field to move the system like an electric motor in space.
Another that doesn't seem to be mentioned is slinging things back to earth. You could toss the payload up and the expended payload vehicle down in separate tosses.
Oh, man, I read your post and thought "Robert Forward is dead? I hope he's mistaken about that." Unfortunately, he died last year, and I for one will miss him for his unique style of hard science-fiction and his innovations in physics and space travel. He did a lot of work on tether propulsion systems. Unlike Arthur Clarke, he patented a lot of his inventions. I wonder if the company he set up will see any money from their use, or if he was just a little too far ahead of his time?
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
That's the electrodynamic bit. The conducting tether cuts magnetic field lines. This induces a voltage and causes a current to flow along it. (You emit ions at both ends to complete the circuit). Normally, that causes electromagnetic damping (like a dynamo). But, if you use solar cells to drive the current the opposite way, you can get a propulsion force... See here for more.
the question is still where do you get that force from. The point here is storing and transferring power in and from these 'rubber bands' to use to slingshot stuff. Fine, your answer tells me that I can get a strand moving with very little difficulty in space. This is not really true, since we are talking about centrifugal force, the force is similar to what we would have to apply at sea level. Yes it will stay longer, but you still have to apply the force.
Where does that force come from?
hmmmm?
Making the tether out of a mesh is a pretty cool idea, but all you've done is extend the lifetime by some factor. What you really want to do is find a way to repair the damage relatively easily.
Picture two mesh tethers between the endpoints. Each tether is made of a series of lines. The lines come out of the tether and are _unwoven_ from the mesh weave. They are then looped back around and _reweaved_ into the tether going back in the other direction. Each line within a tether is actually participating in a complete loop, there are back again. Each line is an unbroken circle.
The tether is then _moved_ through the continuous loop, unweaving and weaving at each end. In this way the tether acts like a belt.
If a break occurs, then movement of the belt/tether will eventually bring the break to one of the terminals, where it can be repaired. The weave localizes the damage and ensures that the line will not simply fly off into space. The repaired line is then rewoven into the loop.
A belt-like tether like this can last indefinitely.
This thing is definitely cool. The other posters were right in pointing out that it regains the energy via converting solar energy into momentum by applying a current to the Earth's Magnetic field. I just wanted to point out the purpose of the devices name:
Momentum-eXchange: this refers to how the tether adds momentum to the spacecraft
Electrodynamic Reboost: this refers to the mechanism that recharges the orbit
The one poster is right about the momentum-exchange working both ways in that spacecraft coming back could tether down and reboost the device. However, in most cases the craft will be leaving a payload up there (such as a satillite, or even just burned fuel/oxygen) so it would never regain as much momentum as it lost. The electrodynamic reboost ensure it keeps flying.
-no broken link
At least part of the cable has to be conductive. That's the Electrodynamic Reboost mentioned in insufficient detail in the article. They run a current through the cable, and the Earth's magnetic field then exerts a force on the cable that pushes it up into a higher orbit. Each cable will have multiple layers.
"I'm so moist I'm sticking to the leather." -Kermit the Frog on The Late Late Show
"The other would lock one face of the earth towards the sun."
Tidal forces will eventually do that anyway, in the same way that they locked the moon to always face earth.
Except that tidal forces from the moon are greater than from the sun, one side of the earth will end up facing the moon, not the sun.