Slashdot Mirror
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 key scientists behind this project are Dr. Bartholemew J. Simpson and Dr. Dennis "The Menace" Mitchell.
Mike
Dennis the Mennis apparently grew up and got a job at NASA!
Swoop down and clobber spacecraft in lower orbits, smashing them into tiny pieces that could go one to clobber other spacecraft. Or perhaps larger pieces that re enter in fiery displays of wasted millions.
Or it might work. That'd be something.
I once used sling shot power to hurl little rocks at my neighbor's cat. Used the middle finger from a rubber kitchen glove, a cut-apart 2-liter soda bottle, and a pipe clamp.
If they built one of those in space, they'd be able to scare the shit out of my neighbor's cat.
- A.P.
"Remember when the U.S. had a drug problem, and then we declared a War On Drugs, and now you can't buy drugs anymore?"
- The Fountains of Paradise by Atrhur C. Clarke
- Mars Trilogy by Kim Stanley Robinson
I'm sure there are more.It seems that the greatest two motivators of technology are SciFi authors, and sales people.
This approach was used by Robert Heinlein in several books; it is a pleasure to see his vision honored.
As for sales people, I can't count the number of times that I have had to create what they have sold.
Alien species put up huge fences to keep us outside of their garden, and now we're going to be shooting stuff at them...
[Dennis the Menace]
Hey Mr. Freeeblgwaaxx!1
[/Dennis]
Black and grey are both shades of white.
"the ultimate dos-Ã-dos swing machine."
I know the caption says it uses old technology- but I'm not trusting my space flight to something that runs on DOS.
It's hard to believe that's how Micronians are made. Why don't we see it right now by having you both kiss one another?
"It's sort-of like a one-hundred kilometer long fish-net stocking in space, only it's incredibly strong, and it can withstand many years of bombardment by orbital debris," Hoyt said
Say, if they make these smaller, maybe I won't have to keep buying pantyhose for my girlfriend!
This is the real signature
(Beats those shadows on the cave wall, don't it?)
I don't think I would enjoy getting smacked upside the spacecraft by a cable going 25,000 MPH faster than me.
Can anyone say whiplash?
When probes from outer space attack the earth, we can use the slingshot to go back in time to retrieve the exact species of whale they're trying to contact!
Slingshots never worked out very well for the Coyote. Doesn't anyone pay attention to the great value of cartoons? Sheesh... how many boulders must fall on the heads of coyotes before someone gets it?
On the other hand, rockets never worked for the Coyote either... maybe NASA is on to something! Is it possible... could cartoons be... unrealistic? Noooooo!
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.
I noticed on one of the diagrams that the orbit of the slingshot itself degrades after each launch pick-up. Maybe the decrease in orbit isn't very significant, but would this system require self-adjustment? How would the system stay in service over the long term?
True believers seek redemption from the sin of death.
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.
This thing is going to transfer momentum to the space craft it is boosting, right? Where is it getting it from? Something has to get that cable spinning, and I don't see how to get the tether started/respun after it has be put in orbit/used to boost without using just as much energy as you have saved by using it.
I am sure I am missing something, but I don't know what, could someone fill me in?
P.S. I did RTFA, doesn't explain it...
"I'll have a Guinness, no wait, make that a Coors Light" -Grad student I work with, who shall remain anonymous...
From an earlier experiment it is clear that there are forces that will wreak havoc on most equipment. Travelling that fast through even the thinnest atmosphere or magnetic field will do some serious stress on things.
Gives new meaning to "Projectile Vomiting".
Heh. Alright, I'll go away now.
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
IAALS.
One similar device is the Jules Verne Gun -- essentially it is a huge cannon that fires things into space, at about 1000 g's. The idea originated from Jules Verne's book From The Earth To The Moon. Popular Mechanics had a write-up about it a few years back (check out the pictures on page 2!) -- apparently some guy at Lawrence Livermore National Labs is trying to build one that actually works. :^)
Slashdot's first reaction to VMware
This thing doesn't happen to say 'ACME' on the side, does it?
Don't these guys know anything about thermodynamics?!
By launching a ship in this fashion, they will be STEALING momentum from the earth's rotation, degrading the planet's equilibrium and ultimately destroying the orbit and sending us to a firey death in the sun!
This is obviously a "plan B" coming from those same wackos who want to send the moon crashing into earth by harnessing the energy in the tides.
Swing low, sweet NASA slingshot,
Comin' for to launch me to Mars;
Swing low, sweet NASA slingshot,
Comin' for to launch me to Mars.
I looked over low orbit,
And WHAT did I see,
Comin' for to launch me to Mars,
A band of "Hoytether" comin' after me,
Comin' for to launch me to Mars.
Swing low, sweet NASA slingshot,
Comin' for to launch me to Mars;
Swing low, sweet NASA slingshot,
Comin' for to launch me to Mars.
If you get there before I do,
Comin' for to launch me to Mars,
Tell all my friends I'm being slung too,
Comin' for to launch me to Mars.
There's no wrong way, to eat a Rhesus...
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
I am a rocket scientist. In fact I've worked both on space tethers and giant space guns
professionally.
Electromagnetic tethers work on the same principle as an electric motor - put a current
through a wire in a magnetic field and you get a force. In earth orbit, you can make electrical
contact with the ionosphere so that you have a
one-way current in your wire, and thus a net force. The wire will accelerate one way, and the
ionospheric plasma accelerates the other way, but there is plasma all around the earth, so you
don't run out.
The force you get is IL x B, where I is current
L is the length of the wire, and B is the magnetic field. Since the strength of the
Earth's magnetic field is a given, you can only
play with the current in the wire and the length of the wire to get more force.
The only consumable you have is a bit of gas
that is ionized and squirted out to make your electrical contact with the ionosphere. It turns out you only need about 2% as much gas as a normal rocket would use for the same push, and only 1/8 as much as an ion thruster, so it is very mass-efficient. It can be powered by solar panels.
The downside is it only works well up to about 600 miles. Above that the ionosphere gets too thin to be of much use. That's where the momentum exchange tether comes in.
Vertical cables, or tethers, can be built in a wide range of lengths and spin rates. Any long vertical object in orbit tends to want to remain vertical because the Earth's gravity changes with the inverse square of the distance from the center of the planet.
So the bottom of the object, being closer to the Earth's center is tugged by gravity more than the middle, and the top is tugged less. This is the same effect that causes tides.
Left to itself, then, a vertical cable will stay vertical. The entire thing takes the same amount of time to orbit the earth. So the bottom end, which is moving in a smaller orbit, is moving slower, and the top end is moving faster.
A free object in a lower orbit actually moves
faster, thus if you let go at the bottom of
the cable, you will find yourself at a suborbital speed and re-enter. Similarly, if you let go at the top end, you were moving faster than the local orbital speed, and are thus flung into a higher orbit.
So if you are heading to, say, the Moon, you could ride up in a suborbital rocket that gets you to a landing platform at the bottom of the tether, ride an elevator to the top, then let go and get flung outwards.
While you were riding up the elevator, the rest of the tether is moving down due to Newton's law. Thus the electrodynamic motor, which is typically 10 km long and attached to the much longer momentum tether, is used to make up the altitude lost.
If the momentum exchange tether is short, i.e.
hundreds of km long, the difference in gravity
between the top and bottom isn't too great and
you can build it out of ordinary strong materials. When it gets sizeable in relation
to the Earth's radius, then you need materials
somewhat stronger than what we have available
in quantity.
Because the Earth's orbit has both natural and
manmade objects flying around, you need to be
able to tolerate damage to the tether. At a
minimum you need something like 6 cables, spaced
far enough apart that no single object can
take out more than 2 at a time (you can always
get 2 if you are aimed just right), and you need a way to replace damaged sections and transfer the tension around the damaged area in the mean time. The Tethers Unlimited design uses a fine mesh of many strands.
In the limit of a very long tether, you can get the bottom end to be stationary relative to the ground, and you get the space elevator. But it turns out that one that large, even using insanely strong nanotubes, weighs so much it would never make sense economically. A practical one would be in the 100s to a few 1000 km long.
Daniel