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Science

Using Sling Shot Power to Hurl Into Orbit 310

Posted by CmdrTaco from the still-wating-for-my-space-trebuchet dept.
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."
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Using Sling Shot Power to Hurl Into Orbit More

Using Sling Shot Power to Hurl Into Orbit

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  • The key scientists behind this project are Dr. Bartholemew J. Simpson [snpp.com] and Dr. Dennis "The Menace" Mitchell. [kingfeatures.com]

    Mike

  • Hmmmm (Score:5, Funny)

    by jeffkjo1 ( 663413 ) on Thursday June 19, 2003 @04:08PM (#6247670) Homepage
    Dennis the Mennis apparently grew up and got a job at NASA!

  • Or perhaps (Score:5, Funny)

    by 1984 ( 56406 ) on Thursday June 19, 2003 @04:08PM (#6247671)
    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.

  • hm... interesting possibilities... (Score:5, Funny)

    by Wakko Warner ( 324 ) * on Thursday June 19, 2003 @04:08PM (#6247673) Homepage Journal
    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.

  • Been there, done that (Score:3, Informative)

    by NetDanzr ( 619387 ) on Thursday June 19, 2003 @04:08PM (#6247678)
    From the top of my head, I can remember two identical proposals in sci-fi works:
    • The Fountains of Paradise by Atrhur C. Clarke
    • Mars Trilogy by Kim Stanley Robinson
    I'm sure there are more.

    • Re:Been there, done that (Score:5, Informative)

      by podperson ( 592944 ) on Thursday June 19, 2003 @04:11PM (#6247709) Homepage
      Those both were space elevators -- a different technology NASA is also exploring.
      • The elevators AND this "slingshot" have the same problem. Tension ripping the cable. This has the added fun of the acceleration mashing you into the rear wall...i hope they don't sling the craft TOO hard!

    • Important differences (Score:5, Informative)

      by f97tosc ( 578893 ) on Thursday June 19, 2003 @04:27PM (#6247895)
      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

    • Re:Been there, done that (Score:5, Informative)

      by crmartin ( 98227 ) on Thursday June 19, 2003 @04:27PM (#6247900)
      And, in fact, Tethers Unlimited [tethers.com], the company proposing this beast, was founded by scientist, engineer and science fiction writer Dr Robert L Forward. Sadly, Dr Forward died [sfwa.org] last September.

      • Re:Been there, done that (Score:2, Funny)

        by Anonymous Coward
        >>And, in fact, Tethers Unlimited, the company proposing this beast,

        Damn. I read that at Titties Unlimited, the company proposing the breast,

        I really, really need to get some lovin. Soon.
      • He has lots of other cool ideas, such as using magnetic propulsion to levitate satelites by having them capture slugs fired from the ground, reverse their course, and fire them downwards again (== upwards momentum on both halves of the equation). I'd draw ascii-art, but your loving slashdot team have deemed that "lame" so you get none.

        Satelites that levitate above the poles by tacking with solar sails against gravity (higher the "orbit", smaller the sail needed).

        His book "indistinguishable from magic" is
    • For some reason this idea kind of reminds me of the thing they've got running in Bubblegum Crisis (2040 version) that picks up cargo and passengers and takes it into orbit. Probably not what I would call an identical proposal but the mental picture is close.
    • gregory benford tides of light has these as genetically modified trees. Neat series of books. Starts off about now, and continues following the same caharactes for like 50-100,000 years, theyre still around due to time dilation.
    • Charles Sheffield's Web Between the Worlds [sff.net] deals with not only Elevators, but Slings as well.

  • SciFi does it again (Score:5, Insightful)

    by PaulK ( 85154 ) on Thursday June 19, 2003 @04:09PM (#6247686)
    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.
    • You forgot generals - just wait until an international conflict results in a satellite getting disabled. That could get real ugly.

    • Re:SciFi does it again (Score:4, Informative)

      by foolish ( 46697 ) on Thursday June 19, 2003 @04:43PM (#6248049)
      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.

    • Re:SciFi does it again (Score:3, Interesting)

      by Daetrin ( 576516 )
      Given that one of Heinlein's books is titled "The Man Who Sold the Moon," i think he saw both sides of the issue. However i'm not sure if sales people as motivators of technology was more of a "vision," or just a concession to reality.

  • Great, just great... (Score:4, Funny)

    by loucura! ( 247834 ) on Thursday June 19, 2003 @04:09PM (#6247692)
    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]

  • Are they serious? (Score:2, Interesting)

    by curtlewis ( 662976 )
    A bunch of whirling cables in space? I wonder how many satellites will happen to stray close enough to those cables to get the crap beat out of them.

    The Japanese have failed recently with using the slingshot for space purposes, although in a different application. They tried to use the Earth's gravity to slingshot a probe to Mars but screwed it up the first time causing a 5 year delay. It's coming around for it's last try now, but it's damaged and not very maneuverable and will likely wind up being a to
    • Not only that, but cables in space tend to gain an electrical charge. Get to close to a satelite, and that's some serious static shock.

      The other issue with cables lighting up electrically is that they heat up and snap.
      • errr, only if they're conductive. Spectra fibre is one of the candidates, as is Kevlar.

        • Re:Are they serious? (Score:5, Informative)

          by barakn ( 641218 ) on Thursday June 19, 2003 @07:29PM (#6249263)
          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 wonder how many satellites will happen to stray close enough to those cables to get the crap beat out of them."

      The chances of that happening are vanishingly small. I'd be more worried about orbital debris damaging the cable - but it seems they've already thought of that (multistranded). If the cable did get damaged, the worst that would happen is the satellite (if already "picked up") would get shot off in an unstable orbit.

      A plus with this would be you could use the power generated by a conducti

  • DOS? (Score:5, Funny)

    by stoolpigeon ( 454276 ) <bittercode@gmail> on Thursday June 19, 2003 @04:10PM (#6247703) Homepage Journal
    "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.

  • Fishnets!!! (Score:5, Funny)

    by petronivs ( 633683 ) on Thursday June 19, 2003 @04:10PM (#6247706) Journal

    "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!

  • Not while I'm aboard... (Score:5, Funny)

    by freeze128 ( 544774 ) on Thursday June 19, 2003 @04:11PM (#6247713)
    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?
    • I wonder if they could attach closer to the center where the tangential velocity is lower and then slide their way out to the end via centrifugal force?

      That would be a hell of a carnival ride. :-)
      • A retractable lanyard might work, just hook the sling thing onto the lanyard type device which would reel out quickly at first and then slowly apply braking to the reel to accelerate the spacecraft. Then when you are ready to slingshot out, cut the lanyard.

  • Also (Score:5, Funny)

    by Anonymous Coward on Thursday June 19, 2003 @04:12PM (#6247723)
    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!

    • Re:Also (Score:2, Funny)

      by Tablizer ( 95088 )
      In the 1950's they thought that we would have nuclear and ionic space ship engines by now. Imagine their expression when someone from the 50's wakes up from a cryogenic sleep to instead see a giant slingshot aimed into space.

      "Damn! I told that egghead to set it to 2005, not 1905."

  • With support of ACME Inc.? (Score:5, Funny)

    by OrangeGoo ( 678478 ) on Thursday June 19, 2003 @04:12PM (#6247728)
    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!

  • not a sling shot (Score:5, Informative)

    by proj_2501 ( 78149 ) <mkb@ele.uri.edu> on Thursday June 19, 2003 @04:13PM (#6247747) Journal
    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.
    • A sling shot is not the same as a sling....A sling uses the sudden stop of centripedal force.

      Shut up! You are ruining our jokes, Bastard!

  • Degrading Orbit (Score:5, Insightful)

    by sublimusasterisk ( 539187 ) on Thursday June 19, 2003 @04:14PM (#6247752)

    I noticed on one of the diagrams [space.com] 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?

    • Re:Degrading Orbit (Score:5, Interesting)

      by foolish ( 46697 ) on Thursday June 19, 2003 @04:24PM (#6247867)
      The tether system (more at www.tethers.com) decreases its potential energy after propelling the payload. Which is why they suggest a mix of tether technologies, one for the payload transport, and another electro-dyanamic propulsion. Brin wrote a story about the latter.

      What is kind of sad is that Dr. Robert Forward was one of the originators of the technology but he never got to see his work in space.

      Again, tethers.com explains it all much better than I can.

      --foolish
      • I guess that's what the big solar panels are for?

        To convert solar energy into some kind of propulsion to boost the orbit when not in slingshot mode.

      • Re:Degrading Orbit (Score:3, Informative)

        by spun ( 1352 )
        What is kind of sad is that Dr. Robert Forward was one of the originators of the technology but he never got to see his work in space.

        Oh, man, I read your post and thought "Robert Forward is dead? I hope he's mistaken about that." Unfortunately, he died last year, [planetary.org] 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 [space.com]. Unlike Arthur Clarke, he patented a lot of his inventions. I wond

    • Re:Degrading Orbit (Score:3, Interesting)

      by overshoot ( 39700 )
      The orbit degrades (loss of angular momentum) on each "toss up" and recovers on each "snatch." One of the cheap sources of angular momentum would be a mass driver on the Moon (think "The Moon is a Harsh Mistress") tossing rock or whatever down the chain. The stations on the chain snatch the falling rocks and recover both energy and angular momentum.

      Rockets would also work, but would be much more wasteful. Solar sails might work too, but I suspect you'd need some honkers to get adequate results.

    • Easy. Launch another sling above it...
    • They have to use some way to increase the momentum. For example, some fuel can be transferred to the tether to raise its orbit (perigee) between catches.

      This could be done with an ion drive (which needs hardly any fuel) or conventional rocketry.

      However, ion drives have very low thrust and hence can take many weeks to recover the altitude.

      Alternatively, with conventional rocketry not having to launch the tethers rocket engine with each launch is a win- and the rocket engine on the tether can be much sma

    • This page [tethers.com] describes it in more detail.
      • Electrodynamic Reboost In order for the tether facility to boost multiple payloads, it must have the capability to restore its orbital energy and momentum after each payload transfer operation. If the tether facility has a power supply, and a portion of the tether contains conducting wire, then the power supply can drive current along the tether so as to generate thrust through electro-dynamic interactions with the Earth's magnetic field. By properly controlling th

    • Re:Degrading Orbit (Score:5, Informative)

      by Fjord ( 99230 ) on Thursday June 19, 2003 @06:12PM (#6248731) Homepage Journal
      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.

  • Cable Strength (Score:2, Interesting)

    by crispy1083 ( 636320 )
    Is this something that can be done with conventional materials, or is this another carbon nanotube based idea that might never come to pass?

    • Re:Cable Strength (Score:5, Informative)

      by foolish ( 46697 ) on Thursday June 19, 2003 @04:27PM (#6247893)
      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

  • Brings a whole new meaning to the phrase (Score:3, Funny)

    by drgroove ( 631550 ) on Thursday June 19, 2003 @04:16PM (#6247775)
    "you've got your ass in a sling now!"

  • Borrowed from good sci-fi... (Score:5, Informative)

    by praedor ( 218403 ) on Thursday June 19, 2003 @04:17PM (#6247801) Homepage

    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.

  • A pinwheel? (Score:2, Informative)

    by Aardpig ( 622459 )

    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!

  • Tether Snatch! (Score:3, Insightful)

    by overshoot ( 39700 ) on Thursday June 19, 2003 @04:18PM (#6247811)
    The proposal has been around in science fiction circles for decades. The engineering is nontrivial, but carbon filiament cable makes it possible. You also need an energy source at the waystations to make up for the transfer (think nuke here, solar ain't enough).

    In some ways the neatest thing about it is that it does away with the need for reaction mass, which is is nothing else an environmental improvement.

  • Isn't this how Commander John Crichton got sucked into that wormhole? He didn't use cables, but he did use the earth's gravitational field to slingshot him through space.

  • What I don't get... (Score:4, Insightful)

    by TamMan2000 ( 578899 ) on Thursday June 19, 2003 @04:19PM (#6247824) Journal
    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...

    • unlike on earth, there is no atmosphere in space. Once you give something a little momentum, it keeps spinning until a counter force. Now all you need is very short/small burst of power to get it started. And using the centrifugal force, the outside spins faster than the center.
      • That is true, but every time the teather enters the atmosphere, it will be hitting alot of resistance.

      • what? (Score:3, Informative)

        by perrin5 ( 38802 )
        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?
    • it is about the amount of power needed not he amount of energy needed.

      power is damn expensive, so the less power you need to get that smae work done the cheaper it will be...to maintain the orbit of this thing and keep it spining will cost a hell of a lot less than it would be to keep launching chemical rockets which get the same work done but in a shorter time/distance. plus you have to carry all the energy with you withthe rocket but with a spining sling you have all that energy saved in the sling so you
    • Well, looking at this image [space.com], 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...
    • Agreed, and I'm not sure the other replies understood your point.

      As I see it, the other end of the cable is hooked to a bigass weight - at least, that's what the massive, spacecraft-size block looks like in the schematics. Where does that block come from, and how do you boost it even to LEO? Do you mine a passing comet for all that metal?

      Spinning the cable I don't think would be the problem - get a weight (spacecraft) attached to the other end and the whole mess will rotate, with the cable ballast droppin
    • 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 [tethers.com] for more.

  • This might not be as easy as it seems (Score:5, Interesting)

    by jj_johny ( 626460 ) on Thursday June 19, 2003 @04:19PM (#6247826)
    From an earlier experiment [nasa.gov] 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.

  • Hurl into orbit? (Score:5, Funny)

    by Columbo ( 111563 ) on Thursday June 19, 2003 @04:22PM (#6247842)
    Gives new meaning to "Projectile Vomiting".

    Heh. Alright, I'll go away now.

  • Re: (Score:2, Funny)

    by account_deleted ( 4530225 )
    Comment removed based on user account deletion

  • Pedantic note ... (Score:3, Funny)

    by Daniel Dvorkin ( 106857 ) on Thursday June 19, 2003 @04:29PM (#6247916) Homepage Journal
    ... "sling" != "slingshot". They're two completely different things. Conflating the two is kind of like calling a canvas-sided trailer with some rusty tanks and piping a "weapon of mass destruction."

  • Obligatory... (Score:5, Funny)

    by Lane.exe ( 672783 ) on Thursday June 19, 2003 @04:29PM (#6247924) Homepage
    Meep meep.

  • The Jules Verne Gun (Score:5, Interesting)

    by Equuleus42 ( 723 ) on Thursday June 19, 2003 @04:30PM (#6247935) Homepage
    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 [literature.org]. Popular Mechanics had a write-up [popularmechanics.com] about it a few years back (check out the pictures on page 2 [popularmechanics.com]!) -- apparently some guy at Lawrence Livermore National Labs is trying to build one that actually works. :^)
  • if I'm not too much mistaken they did something like that in the Bubblegum Crisis: Tokyo 2040 series.

    Even if it never pans out, it's nice to see them trying to make fiction into fact...if only in well grounded theories

  • Another fine product... (Score:4, Funny)

    by Rorschach1 ( 174480 ) on Thursday June 19, 2003 @04:33PM (#6247963) Homepage
    This thing doesn't happen to say 'ACME' on the side, does it?
  • Maybe they can rig one big enough to throw out the International Space Station.
  • Aldrin has been talking about this for years [space.com] for a Mars transit system.

    No mention of him at all?

  • Seems kinda silly to me... (Score:3, Interesting)

    by fudgefactor7 ( 581449 ) on Thursday June 19, 2003 @04:41PM (#6248031)
    A sling that "falls" each time you use it is kinda wacky to me. Why not just build gigantic railgun instead and magnetically accellerate the spaceship (once in low orbit) instead?
    • Railguns can't reach orbital velocity (about 4.5km/s is the best that has been achieved) and have enormous problems with atmospheric drag of the projectile. Additionally railguns suffer from rail erosion with each launch.

      Further, guns of all kinds can't directly go into stable orbit around the earth- orbits necessarily go through the last point where a force was applied to the vehicle. This means that the vehicle intersects the ground unless a circularisation rocket engine or similar is employed.

  • Heat things with a giant magnifying lens until the object smokes or pops. Nope

    Shoot bb guns at stop signs (not lights). Nope

    Slingshots...that's taken.

    Blow darts with straws and paper...hmmm, yes, giant air pressure pipe to launch space capsules into orbit.

    Anyone know a good modernized implementation of pouring salt on snails?

  • It only gets you halfway. (Score:2, Informative)

    by KFury ( 19522 ) *
    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 ne

  • DON'T DO IT! (Score:5, Funny)

    by Xzzy ( 111297 ) <sether@tr u 7 h . o rg> on Thursday June 19, 2003 @04:51PM (#6248128) Homepage
    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.

    • Re:DON'T DO IT! (Score:3, Interesting)

      by FrankSchwab ( 675585 )
      Ahh, but the question is, are they stealing momentum from the earth as it orbits the sun, or from the earth's rotation? One would spiral us into the sun. The other would lock one face of the earth towards the sun. (Wasn't there a SciFi novel with that theme? The beings lived in the twilight ring between the scorching desert hemisphere and the frozen dark hemisphere). Not sure either is a good deal. /frank

  • Can it be used with Sub-orbital delivery vehicles? (Score:3, Insightful)

    by Ugmo ( 36922 ) on Thursday June 19, 2003 @05:05PM (#6248242)

    Do you think this could boost payloads delivered from small non-NASA suborbitals like Rutan's:

    SpaceShipOne [scaled.com]?

    It would be great if you could just fly up to the edge of space, chuck your payload up, have a tether catch it and then land. Very cheap compared to rockets.

    Also I wonder if the tether guys are working with: Carbon Fiber 60% stonger than steel [news24.com]

  • Swing Low... (Score:4, Funny)

    by Mu*puppy ( 464254 ) on Thursday June 19, 2003 @05:23PM (#6248358)

    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.

  • Continuous repair of the tether (Score:3, Informative)

    by rossjudson ( 97786 ) on Thursday June 19, 2003 @06:11PM (#6248721) Homepage
    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.

  • Two great tastes that don't go great together (Score:3, Funny)

    by Daetrin ( 576516 ) on Thursday June 19, 2003 @08:10PM (#6249534)
    ...when orbital mechanics go awry...

    "You plastered your Teather System across my Space Elevator!"

    "You got your Space Elevator caught in my Teather System!"

  • Expert on subject in the house (Score:4, Insightful)

    by DanielRavenNest ( 107550 ) on Thursday June 19, 2003 @09:26PM (#6250030)
    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

  • Tempur-Pedic (Score:3, Funny)

    by mabu ( 178417 ) on Thursday June 19, 2003 @10:49PM (#6250599)
    Nasa is back to working on space stuff? I thought they gave it up to focus their energy on mattresses [tempurpedic.com]?

  • cosmic trebuchet (Score:3, Funny)

    by technoCon ( 18339 ) on Thursday June 19, 2003 @10:56PM (#6250643) Homepage Journal
    Has Ron Toms at Trebuchet.com been awarded a NASA contract?

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