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Space Science

Tethers Will Be Tested To Boost, Deorbit Payloads 111

Posted by timothy from the flying-wallenda dept.
Constellation writes: "The IEEE is posting an article on how a tether (a long thin piece of wire) can be used to increase to orbit of, or deorbit, a spacecraft. The article also details NASA's plans to test this technology in December. A further article describes how a similar technology will be applied to Mir later this year, or early next year." Sure -- while you're up there, why not drag a 5km wire around for a while?
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Tethers Will Be Tested To Boost, Deorbit Payloads More

Tethers Will Be Tested To Boost, Deorbit Payloads

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  • Being an open minded individual I decided to test several setups for Firewalls. One option was Linux. It installed smoothly and the firewall setup went Ok. I put all of the ipchains rules into a file called rc.firewall and integrated into my startup. The ipchains syntax is a bit strange, but nevertheless it's usable.

    Next I tried FreeBSD. It seemed fine, in fact, easier to install than Linux, but ... once I tried to tighten up the security on the box, I found FreeBSD 's biggest flaw: security. I've heard that Free/Open/NetBSD are similar. Therefore, they're all insecure. I tried the ipf technology, sepcified the rule file I created, ipf -f [file]. But it told me the device wasn't configured. Since I had been online with the box, that was an absurd statement. My network card interface, ed1, was up and running perfectly. I ran the debugging mode, but the only advice it could offer me was: "ioctl(SOIADDR): Bad file descriptor".

    BSD actually doesn't seem like such a bad system, but if you consider that their firewall code seems to be not be ready for the prime time, I'd say you're better off with Linux for now. Perhaps when the ipf is ready for the mainstream, it'll be better. For now, Linux is definitely the way to go. Despite the easier syntax of ipf, the system really, unfortuantely, is clearly not ready.

  • Simple.. they got sued (or were threatened) and changed the name to Trinity.

    White Wolf [white-wolf.com]

    Trinity [white-wolf.com]

  • Hmm, I was thinking more of Arthur C. Clark's "The Fountains of Paradise" (1979). There the fibre from the satelite is lowered to earth to carry up a thicker wire (and so on) in order to eventually construct a tethered space elevator. Why launch to orbit when you can just lift?

    Regards, Ralph.
  • Although I don't have a link to this, they were using the tether in this case to boost a satelite into orbit not via electricity, but just by letting the tether out. It was not meant for power generation, just for getting the (in this case just a test satelite) object into orbit.
  • Styopa? Stepan maybe, Stephan?
    I can't claim I've got all of the above, but none the less -

    No-one will die on MIR. Not unless they nail themselves into forehead with a space age nail-gun. Mir has an escape capsule docked at all times. Russia has excellent relaunch capability in case they need to send up a rescue crew. MIR can be upgraded to prolong its life indefinetly.

    Besides, space exploration imlies a certain amount of risk and adventure, that's why regular Joes dont get to be cosmonauts. The guys who crashed the resuply ship into MIR may have had their pants full, but at least they've got an experience of a lifetime that they'll be telling their grand kids about and that movies will be made from. And the station is still up there, alive.

    I don't mind ISS, but as a multinational project it is bound to have it's problems. Russia can avoid these problems because it has a station of its own. If the national priorities on the ISS will collide, at least Russia will have something to fall back to.

  • Change your login name from Anonymous Coward to Arrogant Cynical Coward, it suits you. In any case, offering your wonder bread to me will do you no good, talk to MirCorp. By the way, if you think Russia is so poor, tell that to the G8, because they seem to think otherwise and have declined to write of the debts of the Soviet Union.
  • Ok, threatenning to shoot down Russian property from orbit - real funny. Try it.

    I am Russian, and I am sick of hearing American yahoos talking about MIR space station as if it was US property. It's not, so stop telling us what to do with it. We like it the way it is - an independent space station vs. an international space station under the committee rule. We like Freedom too, and you simply cannot be as free as you might want with a project like ISS, because it is owned by several nations, not by one, which implies that decisions are not made by one but by many, and those decisions do not always agree.

    Having MIR in orbit gives us more options and keeps Russians, especially the engineers who built it, happy and proud. What many Americans are proposing is to take that away from us. Sorry, but we must disagree.
  • I recall about three attempts on the Shuttle to
    use them, none great successes. They've had
    mechanical problems deploying. Once, the electrostatic
    gradient fried the equipement.

    Doesn't mean they should be used. Just there are issues left to work out.

  • "Physics is the Math as Sex is to Masturbation"
    -- Richard Feynmann

    Math, for it's own sake, is pretty useless. Sure, we get to see some pretty symmetries and learn some interesting relationships, but without applying what we learn, math is gratuitous self-appeasement. Physics, and then Engineering, is mathematics with a purpose. It relates to the real world in the former, and serves others in the latter.

    "Science is like sex; sometimes something useful comes out of it, but that's not why we do it"
    -- Richard Feynmenn

    But on the other hand, doing things for pure enjoyment is where the passion for the pursuit lies. The word 'amateur' is today seen as an insult as compared to 'professional', but the root of the word implies that something is done for the love of doing.

    The satisfaction derived from pure math is very internal to the individual doing the math. The satisfaction of seeing math done is greatly diminished for the observer. There is significantly more satisfaction to be had by an observer of physics - such as all of us reading the tether article than by the observer of the underlying math. An article on the 'same principles' would not be anywhere as accessible as one on the application of the math. The true benefit of the math and the physics comes from the beneficiaties of the engineering - those who actually get power from the tether as it cuts through the Earth's magnetic field. Those people, living on the station in the future, will have a tangible appreciation of the math and physics in the form of lights and air.

    So, if by "glorified" you mean "more useful" and "better", I whole-heartedly agree. If instead you mean that in some derogatory sense, re-evaluate.

    A computer is, after all, nothing more than a "glorified" Turing Machine, yet I would not trade my little beige box for a pencil and a bunch of paper.
  • Sorry, screwed up the link. Try this [umich.edu].
  • So, is this an example of applied superstring theory? :)
  • Wasn't that tether used to keep the astronaut attached to the spacecraft rather than an electromagnetic experiment?
  • This was exactly what I thought of when I saw the article posting. For the curious, "Tank Farm Dynamo" can be found in Brin's short story collection entitled "The River of Time".

    MJP
  • "Without propellant" is a little misleading. The ship still needs propellant to get INTO orbit in the first place and it still needs an energy source to reel the wire in/out (and a 5 km wire must weigh quite a bit) Could this latter be provided by the inducted electro?
    --
    Give us our karma back! Punish Karma Whores through meta-mod!
  • Talk about slicing up your palms :) - grabbing a sharp aluminum wire moving at a 15,000 km/h... And I thought tug-of-war tore up my hands!
  • David Brin (Uplift War, Startide Rising) wrote a short story based on exactly this principle called "Tank Farm Dynamo"...

    Using the tether to *generate* electricity would de-orbit a space station (tether as dynamo), requiring thrust from {rockets,small mice in spacesuits} to keep it in orbit. Pumping electricity *through* the tether would cause the station to acclerate and could be used as thrust instead of rockets or mice (tether as motor).
  • Ah, but there has been a SF story based on this concept! I don't remember who wrote it, but the basic plot was there was guy who bought the spent fuel tanks of shuttle lauches (the big red things), and used them construct a space habitat. People scoffed at the idea initially, but eventually it became economically viable, and corporate/government interests wanted it for their own. The habitat was a closed system and was mostly self-sufficient, but needed propellant to keep the orbit stable. That was the angle that the bad guys used to coerce the owner of the habitat into selling, but in a moment of serindipity (due to an accident I think) the protagonist realized that if he applied or drew a current from the superstructure he could change orbit using the earth's magnetic field. Ah, yes, the title was "Dynamo", no wait, "Tank Farm Dynamo", and it was written by David Brin. (Thanks Internet Speculative Fiction Database [sfsite.com]!)
  • RTFA == ???
    Read The Farmer's Almanac?
    I didn't know they covered stuff on space travel!
  • Comment removed based on user account deletion
  • So would the space craft have to travel directly above the position on the earth where the wire is anchored? Wouldn't the wire break (or Imagine the shuttle in orbit over China, connected to a wire in Florida). So how does this work?

  • What ever happened to MIR's 5 year lifespan? The thing is 14 years old, and MIRcorp wants to start sending people up in 2003. I understand that it is an engineering masterpiece, and that it is a piece of space history but why can't it be donated to some country in the same way that SkyLab was donated to Australia, ie as flamming space junk falling from the sky.

    Every time I start to get SOME semblence of hope that it will burn up and fall to earth something like this pops up. It has done a great job for the many years that we have used it but it became a death trap a couple years ago. How long till someone dies up there? Perhaps we should conduct a slashdot pole, or take bets, on when we will have the first death on spacestation MIR. We should not be risking the lives of the scientists with aluminum wires, or duct tape, or whatever they happen to use. I am all for science for the sake of science, but if we lose someone up there because of arogance that will bring huge negative press and the space program will lose money. I don't want that to happen.

    Perhaps it is time I dropped studying particle physics and go into optics. Then maybe I can construct a high powered ground based laser cannon like the one in Arizona and give it a final farewell. It has served us well but it is time for us to let it rest in peace.
  • I have been unable to get koi8 to work properly, and it has been a while sence my last class so bear with me, if possible.
    Eezvenitya pozhalusta. No, kogda ya slishal ob MIR, ya slisha shta eto ne-robotat oochen hrasho. Ya ne buil ne ckazal y americantsui yest MIR, no kogda ruskiye kosmonotui ili americantsui avstronutui eedyot v Mirye, ya dumal shta MIR ochen stari, chyetirnadtsyet lyet, ee kogda budit chelovyeki ymet (to die?)?
    Russki engeneri eto ochen hrasho ee MIR buil hrasho. Rossiya, net, mir nuzhnal MIR. MIR ochen stari, kogda budit chelovyeki ymet?

    I don't know if that is readable. I attempted to make it some what phonetic. Sorry if it is unreadble, and I know my grammer and use of declentions are both poor.
  • At the risk of stating the obvious...
    Maddogsparky, YHBT!
  • When they say "5 km" do they really want to say "km" or do they want to say "miles"?

    Who Knows!
  • If your interested in this see http://www.tethers.com/ . Also as you can see this company is run by Dr Robert L Forward.

    Who has written a number of SF stories based on these tethers and other technology currently at the edges of the feasible.

    The stories are good and the technology reasonable. Therefore Great hard SF.
  • Is there any limit to how many of these could be used per object, or on our atmosphere at one time? The article mentions powering deep space probes to Jupiter with this, could the ISS drag 4 or 5 of these around at once to provide extra power? Or have them rolled up waiting to be used incase of solar array failure? Oooh a BeoTether cluster to power ISS :) And if this becomes feasible/popular is there any limit to how many can be used at once on the atmosphere?
  • I was going to mention this. In Homer H. Hickam's "Return to the Moon," they used a line like this for the express purpose of generating electricity.
  • I haven't read the article yet (yes, yes, I really should develop that habit), but any craft with an orbit around the earth can dangle a wire of significant length (100's of yards to miles) out behind or to the side of them and get a lot of induced current from the earth's magnetic field.
  • Just when there wasn't enough space junk in orbit.
    Tethers will do a lot to help get rid of space junk, actually. The problem with space junk is that there's no easy way to get it down. With a conductive tether, unwanted objects - say, spent boosters or old satellites - can deploy a "generator" which turns energy from their orbital motion into electric power (which can be used, or dumped). This causes drag against the satellite's motion, which causes it to fall towards Earth. This allows you to de-orbit a satellite in weeks or days, without using any rocket fuel, without having to wait for air drag, and without having to have any control over the satellite's attitude as you do for a rocket. Had the Compton Gamma Ray Observatory been carrying one of these, it could have been left up until the gyros completely died instead of bringing it down as a precaution.

    In practice, this means that boosters and satellites won't be in orbit much longer than their useful life. Without spent rocket stages blowing up, shedding paint and leaving other junk in orbit, orbit will be cleaner for the things we do want to leave up there.

    There's another couple tricks that make tethers useful for space stations. The first is orbital reboost; by hooking a tether to a visiting spacecraft, e.g. a Shuttle, and lowering it toward Earth on its departure before finally unhooking, some of the energy and momentum from the visitor is transferred to the space station. This is a "free" reboost for the station and also a "free" retrofire for the visitor. If the station is in too high an orbit after this maneuver, it can then use a conductive tether in "generator" mode to turn some of its orbital motion into electric power. This might be useful for running high-powered experiments that don't need microgravity, like perhaps large-scale high-vaccum sputtering. And if the station gets too low, you divert power from the solar panels and run the tether in "motor" mode to push the station back up. The extra solar panels to do that are probably cheaper than shipping up low-energy propellants.

    Unfortunately, NASA isn't likely to do this anytime soon. That's one of the problems with NASA; contrary to people's claims that they are off on the bleeding edge of things, they are actually not running far enough ahead to really get anywhere. A pity.
    --

  • Hmm, I was thinking more of Arthur C. Clark's "The Fountains of Paradise" (1979).
    That's a geosynchronous anchored tether, aka a "skyhook". It's a somewhat different beast.
    Why launch to orbit when you can just lift?
    If you know integral calculus, you can figure how much material you would need for different values of the tensile strength and density. I did the numbers for a steel skyhook once; it would have out-weighed the Earth. To make the material quantities (let alone the capital costs!) within reason, we need materials which are quite a bit stronger than what we've got readily available today.
    --
  • Talk about slicing up your palms :) - grabbing a sharp aluminum wire moving at a 15,000 km/h...
    People have already thought about that, and the trick is to spin the tether end over end like spokes on a wheel so that when it comes down it's almost not moving. Bring it down to 50 miles and a mile or so a second, and it wouldn't take much of a craft to go up and meet it. Latch on, and it carries you up into orbit. You ride it back down the same way, leaving your borrowed energy and angular momentum with the tether.
    --
  • Not to mention that Seti@Home is essentially 'over' unless they can get time and data from the southern hemisphere. The project goals have been reached, they're wrapping it up, they're analyzing data and doing followups, running out of storage and perhaps money, and so forth.

    (Unless there's some news that's come out in the last 3 months to the contrary.) This info is from a talk by Dr. Anderson that I attended in the spring. If anyone has info to the contrary I'm listening.
  • June 7, 1965
    Duration: 4 Days, 1 hour, 56 min, 12 seconds
    Objective: Evaluate effects of prolonged space flight, demonstrate and evaluate performance of spacecraft
    and systems in 4-day flight, evaluate procedures for crew rest and work cycles, eating schedules, and realtime flight planning. Secondary
    objectives included: Demonstrate and evaluate EVA and control by use of HHMU and tether. Stationkeep and rendezvous with second stage of
    GLV. Evaluate spacecraft systems. Make in-and-out-of plane maneuvers. Further test OAMS retro backup capability.

    "If you believe they put a man on the moon" REM
  • Guess it was Gemini XI where they actually got around to tethering two spacecraft together and practiced changing orbits. I was thinking that the logical way to know if the tether had broken would be to pass a current through the tether securing the two spacecraft. Of course they must have used a nonconducting tether or else they would have detected the induced current.
  • So would this work for geostationary orbits that spend 12 hours in the Earths shadow? If so this would be the obvious solution for power generation when a satellite is in the umbra and can't use the solar panels. During the day the orbit could be restored from excess energy from the solar panels. If you search the web there is a link to the 60's Mercury project and tethers I beleive.
  • The power can be provided only if the space station resultantly loses altitude. The normal procedure for maintaining the orbit altitude requires the space station to actually generate power and use it to drive a current on the tether.
  • And if I had read the article before posting, I'd have realized that the current tether concept is totally different. Oh well...


    --Fesh

  • Yep, I'm quite familiar with Trinity... One of my friends snapped up all the new stuff for it when it came out. Unfortunately, we haven't played it in a goodly while... It was a pretty good system.


    --Fesh

  • That's nothing. Dr. Forester took this to another level by suspending a giant tube from the SoL. It was big enough for Crow to escape back to earth! NASA is obviously way behind the times.
  • The tethers work on collection electrons or ions from plasma. You don't get ionized plasmas in dense gases (normal pressure air) without pumping in a lot of power. The stuff the tether taps is way above what we think of as air - say 100 to 200 km up - no birds, airplanes, and so on.

    For a look at some of the natural stuff that goes on in the lower reaches of the area of interest try :
    http://www.sciam.com/explorations/012097sprites/01 2097explorations.html

  • Yeah! Or `thrust`, or whatever any of the clones are called...
  • yeah, sounds about right. Its on MAME :) Think you had a choice of 2 player tethered or untethered.

    What i was talking about was more like Gravitor, which was probably released around the same time, by the same people. Thats definately on MAME!

  • David Brin wrote a book set in around 2030... it was called "Earth" and was rather interesting. Some of the story takes place in orbit, and they are using these tethers...
    not to sound like an advertisement or anything, but it was a good read and it's nice to read a fiction novel written by someone with a PhD in Astrophysics...
  • I know this might be a silly question, but I never understood how they plan to protect the space tethers from things closer to earth, like airplanes and birds. Although tethers would be infinitesimal targets, I don't suppose NASA would take any chances.

    And if these things ever come outta the vapor stage, I'm climbin that sumbitch to the moon! I was the fastest rope climber in gym class...

  • Just when there wasn't enough space junk in orbit. Now we can drag around a 5km wire. This should make it even harder for Seti to pick up anything.
  • The description fails to mention that the article also discusses how the tether is "current carrying" and can be used to provide power to the craft as well.
  • I enjoy good conversation, I like to apply help when people ask for it. If someone wants to mod this down, please, go for it. I really could care less.


    We're all different.
  • 4. stabilization. Even quite a short (100m) tether will be stabilized by Earth's tidal forces and can be used to keep a satellite pointed in a certain way
    Yep, tethers are cool. The stabilization aspect was pointed out to me by a buddy when we were talking about control systems (I think he was in Controls [calpoly.edu] at the time).

    Most satellites must be kept in a certain attitude to perform correctly, and lots of effort is put into maintaining this attitude. The real expenses start to build as you try to create an ever-more precise system. But if you hang a mass from a line, gravity gradients will pull the line straight down, orienting the satellite.

    Gravity gradient: gravity depends on distance [F=G*m1*m2/(r^2) with 'm1' & 'm2' being the Earth and the orbiting stuff in this case, and 'r' being the distance between the centers of mass of the two objects], so the closer you are to the Earth, the more gravity you feel. Not a whole lot more, but there aren't a whole lot of other forces acting on your satellite. So a few kilograms on the end of a line (100m -> 1000m) should straighten your satellite out. This is great for communications satellites: they must face the center of the Earth for best performance, and that is exactly what a tether does for you.

    The author of the NASA tether article alludes to that in this section [ieee.org], saying, in part,

    Once the rocket's stage and the tether's end mass are far enough apart, the difference in the gravitational force at the two locations will in effect pull the objects apart. Eventually, the tether will be vertical with respect to Earth.
    Physics is cool.

    Louis Wu

    "Where do you want to go ...

  • You said: Orbital momentum is worth about $1/(kgm/s).

    That is linear momentum. In a straight line. Orbits are circular, so we are concerned with angular momentum. Angular momentum is a function of the radius of the circular motion, the orbit. That would make the units kg*m*m/s, with the equation being: H=m*r*v.

    Louis Wu

    "Where do you want to go ...

  • It was called TSS for Tethered Satellite System. I worked on it several years ago when I was still at Kennedy Space Center. What happened was that someone installed a screw on the reel late in the testing and didn't consult the drawings or go through th proper design reviews. Once in space the tether was unrolled and at a certain point the keeper on the reel jammed against the screw. It couldn't be unrolled any further nor could it be reeled back in so they cut the tether. Before they cut it they managed to get some useful data though that confirmed the predictions. I think I heard that they tried it again on a later launch with much more success.
  • "Hey, dude, what did you catch today?"
    "Let's see... i got astra and copernic, what did you get?"
    "Oh, just this thing that says 'Eschelon Space Project' on it..."

    (knocking on MIR's door)
    "NSA, open up or we're coming in!"
  • Now I understand the true meaning of the term "Fly by wire" :-)
    How to make a sig
    without having an idea
  • Yes, its a nice long wire... the wire is wrapped around the space ship and it is thrown into space by a giant slingshot like device... once it gets in orbit it is at the end of its string is is allowed to just spin there (NASA calls this "walking the ship" which additionaly provides gravity to the ships crew) when it is time to bring the ship in one just needs to tug the wire and it returns to the sling-shot... nice eh?
  • Actually, only the efficiency (and current direction) of the tether is affected by being above or below geosync altitude. Drawing power from it will always lower the orbit and pumping power into it will always up the orbit.
  • I YELL CAUSE I'M BLIND.

    What grandpa [parent/parent] is alluding to
    is the research being done to power crafts
    by tapping the electrical & magnetic
    differences in space, solar flares, ion storms etc, utilizing a drag wire.
    The [Voyager [?]] space craft has been utilizing a drag wire to distribute the
    the charge differences associated with its
    ion drive.They have been monitoring the
    voltages on the line with favorable data
    for a 'power cord' type of power system.

    |X|

    A MICROWAVE LASER can put
    a lump in a politically
    active chest. The heating effect
    can cause a localized turgor
    remarkably similar to a carcinoma.
    Reinforced aluminum foil
    can stop these rays.
  • Thanks for the kind word, it gets
    wearisome being snubed by the grits crowd,
    & everybody else, the 'silent cowards' are
    afraid of getting their comment headers
    associated with my stuff.
    We've got these interrupted developement
    types sitting on urine soaked bails,
    of the S F Times, in their dimly lit bedrooms
    taking pot shots at their betters.
    You ever talk to one of these twits who
    gets off on: " I turned down this guy,
    he was a doctor, but he didn't even
    have Guido Sarduchio jeans on. a real geek".
    You ever see the glow on some twits face
    when she beats you out on a checkout line...
    with a month of groceries.
    So one of this guy's many many accounts
    pans out & he's got 5 spittle soaked
    moderation points to make the world
    notice him, little realizing that important people
    *are* noticing him, w/ sorrow.
    Then there are the pros, who are
    selling out tommorrow for cash today.

    They' ain nothin' kin do for them
    achordatae.

    P E A C E
    One of the more remarkable aspects
    of dental caries is that the
    trauma to the cheek tissue is
    signifigantly greater than
    the turgor elaborated about the
    damaged roots in many patients.
    Sounds like radiation damage
    caused by a MICROWAVE LASER.

  • There's another problem: V=Blv (unless the tether's are non conducting, but then, if they are, they can be used as a motor). The voltage difference between the two ends of a 5k wire going at 25000k/h whould be pretty extreme (anybody got a flux capacitor handy?:)
  • Just like a sailboat on the water today, only moreso. That would only make interplanetary navigation more interesting, not impossible.

    Hmmm, combine this with solar sails and you could be in for an interesting ride (and make the sails solar panels while you're at it...)

  • This is my option 1. You can force a current along the wire, using up electrical power, and push the satellite up to a higher orbit. Alternatively, you can tap the electrical current induced in the wire and accept that the forces resulting will drop the satellite into a lower orbit.

    There are two possible connections with "particles". One is the electrons in the tether which will be pushed up or down it. The other is the tenuous upper fringes of the atmosphere which form the return part of the current carrying loop. Electrons are sprayed out of one end of the tether and gathered in at the other by specially designed electrodes.
  • If you buy a computer that has a five-year warranty, do you expect it to fail after five years? The five-year design lifetime was how long the engineers could guarantee that the thing would work well, from before it was sent up. It wasn't designed to only last five years. As far as risk goes, what's so bad about it? Ok, so they had a crash and a fire. Accidents happen. Nobody dies. The place isn't any less safe now than it was before those things happened, it's just your perceptions that have changed. Let me tell you, if I were given the choice to either stay six months on the international station or six months on Mir, well, I'd pick Mir without question. The ISS has been up just a short while, has been blessed with human occupants for only a few days total, and has really never been tested. Mir is known to work, and hasn't killed anybody yet. We're not risking the lives of scientists, they're risking they're own lives. Nobody tells them that they have to go up there. It's their choice. Besides all that, people need to get used to the idea that people can die even in space. It's not 100% safe up there, even though you're probably as safe sitting atop the shuttle as you are driving down the interstate. The sooner people get used to the idea that people can die even there, the better off we'll be.
  • As I understoiod the article from reading it in my issue of IEEE, they were refering to using the magnetic fields to move electrons.
    Electrodynamic tethers work by virtue of the force a magnetic field exerts on a current-carrying wire.
    I believe that they would drop the line down towards earth and then as the earth spun it would create the necessary megnetic field to act like a generator in space. I think this is what they were planning. Then they mentioned something about moving particles with this field to move the object (satelite).

    send flames > /dev/null

  • For more information about the endmass (the other end of the tether from the satellite) check out this page [slashdot.org]. The endmass will be running a radiation-hardened 386 which will be collecting information from an on-board GPS receiver and a magnetometer as well as a few other things. This information will be relayed down to Earth and compared with the data from the ProSEDS satellite to determine how the tether is oriented, etc.
  • See Kim Stanley Robinson's Mars triology for an interesting take on how this might be constructed.

    Ugh! Am I the only one who hated those books? They had to be some of the crappiest sci-fi stories I've ever read. Red Mars was OK, but after that...ugh!

    If you want to read a good story about a space elevator, check out Arthur C. Clarke's Fountains of Paradise. Quite a good read

  • From the article:
    The force acts on any charged particle moving through a magnetic field (including electrons moving in a wire), in a direction perpendicular to both the direction of current flow and the magnetic field vector.
    This doesn't sound right. If the tether is hanging up or down (and thus the current flow is up-down), the magnetic field is north-south (assuming we're above the equator), then according to this, the force would be in an east or west direction, right?

    It's been a while since I've had a physics class, but the force is perpendicular to the magnetic field and the velocity, right? If the magnetic field is north-south, and the velocity is east-west (assuming orbit above the equator), then the force (and electron flow) would be up-down.

    But also, this means I have to be moving in relation to the magnetic field. So at what speed is the magnetic field "rotating"? Same as the Earth's rotation? If so, then this technology would not work for satellites in geosynchronous orbit, right?

  • In motor mode, the force is the cross product of field direction and current flow, in other words east/west along the orbital path...
    If the object attached to the tether has significantly more mass than the tether itself, wouldn't this force simply cause the tether to be moved from an up-down position into an east-west position? Unless it is rigid or much more massive than the spacecraft, how could it ever be used to provide acceleration to a spacecraft?
  • Sounds like you need an unbreakable (or nearly so) tether. Dr Robert L. Forward has designed such a tether [tethers.com], and the uses discussed on the website include exactly this usage.
  • Yeah, don't you get it, and get it, and get it, and get it.

    It only gets mentioned 20 times a NASA article is posted, after a while it get's old.

    George
  • Larry Niven published "Rainbow Mars" a year or so ago. It's the first full-length Svetz novel (a kind of humour sci-fi based on the idea that time travel is fantasy; there are lots of literary jokes).

    Anyhow, the idea of an orbital tether plays a significant role in the book. There's several pages of explanation, and since the main character is not at all a scientist, it's written at a very non-technical level. (And it's funny.)
  • Okie this one's from a SciFi RPG.

    There's an RPG out there called Aeon. I THINK it's made by the same guys who make those vampire RPGs. It takes place in 2120. Earth was invaded in the 21st century by aliens called "Abberants", and just barely won with China nuking the Abberants' bases down to bedrock from orbit. Man then established colonies throughout the solar system, a few interstellar ones via big ships that amplify the human mind to make it possible to psionically teleport. China runs most of the show, via their space superority, and human telepaths (plus telekinetics, teleporters, and a few others) are forced to be part of the "Ministry" a la Babylon 5's PsiCorps.

    The point? Oops, lemme get back to it.

    Anyway, in 2120, the second wave of Abberants arrives to invade Earth again. One of the settings in this RPG is a battlestation in orbit around Jupiter. Now, Jupiter, as you know, has a magnetic field that makes Earth's look like a kitchen magnet. These battlestations around Jupiter use their movement through Jupiter's magnetic field to power huge laser cannons that put out power in the terawatt (!) range to defend against this second wave of attacks.

    I looked through this "Aeon" book in the bookstore a few times when it first came out. I haven't seen it in a LONG time tho. I don't think it sold very well, compared to the vampire RPGs and I think it got cancelled.

    It was a pretty nifty looking thing tho, if you can find a copy in a used bookstore somewhere.

    john
    Resistance is NOT futile!!!

    Haiku:
    I am not a drone.
    Remove the collective if

  • OK, like this in that it involved a big string. It seems like NASA tried a shuttle experiment a while back that involved dragging a satelite or probe from a big long wire off of the back of the shuttle. The tether broke, and the experiment was abandoned. It seems as if the object at the end of the tether was going to be used to generate power, to reduce fuel costs. Anyone remember the details on this one? It was a few years back, IIRC.

    "Sweet creeping zombie Jesus!"

  • Russia may in fact be diverting ISS resources to Mir (as the IEEE article suggests to the point of virtually stating it as fact) but putting a tether on Mir before putting one on ISS makes lots of sense. Russia was ready to let Mir turn into a crispy critter in the atmosphere, so if the tether doesn't work so well, c'est la vie.

    But if the tether does work, then NASA [nasa.gov] for once gets something back from industry - a cheap way to keep the muy expensive ISS from becoming muy caliente. The theory behind government-funded research (like NASA) is that eventually, the research becomes disseminated to industry. The taxes that payed for the research in the first place end up benefitting the entire economy (TCP/IP and the Internet would be a sterling example of that). It's much more unusual for industry to provide something new and useful to government without a big fat government contract (i.e., not just overpriced versions of widely available products).

  • We're not talking kilonewtons of thrust here: probably closer to decinewtons. True, the cable will pull a little in the east/west direction, but gravitational tidal forces will tend to correct this. The thing to remember is that a little force over a long time is better than a lot of force over a little time.
  • You overlooked something:
    • The earth's magnetic field extends north and south, and rotates at 2pi radians/day (same as the earth).
    • The tether is vertical.
    • The motion is east/west

    So far, you were quite correct. Now, the system operates in one of 2 modes: generator or motor.
    • In Generator mode, the current is the cross product of velocity and field direction, in other words up and down along the wire.
    • In motor mode, the force is the cross product of field direction and current flow, in other words east/west along the orbital path.

    Now, below geosync orbit, generating power will bring the satelite down earth, but above geosync the sat will actually be pushed higher. Much the same sort of thing is happening with the Moon: Earth's tidal forces are dragging the Moon around and pushing it away. Different cause (gravity vs. electromagnetism), but the same effect.

    Also, at geosync, you want the sat to say put. If it drifts away from geosync, then you are moving, and can use the earth's field to get back.
  • The plan is for every satellite to eventually have a tether. This is mainly to deorbit all inactive satellites, so they don't clutter space, but also as a means of movement. If you want to check out some good websites, go to Airseds [airseds.com] (where I worked last summer). Or for the less intelligently inclined Tethers Unlimited [tethers.com].
  • When the Shuttle is up, the Space Control Center at Cheyenne mountain watches the shuttle and places a 1km box around it. If anything comes within 36 hours of hitting that box based on trajectory and speed, A special NASA hotline is notified so course adjustmens can be made. In all of the shuttle missions, this had to be done 7 times.

    I believe that if they started tethering things, they would increase the size of the box and the lead time to any possible impact for notification of NASA.


    www.mp3.com/Undocumented [mp3.com]
  • However, I can see MANY complications, IE you are moving some satellite and the tether breaks, leaving the device with a completely different orbit and speed.

    I know docking or catching a sattelit with the Shuttle is inherently dangerous, so while this may seem safer, you are putting the sattelites at more risk.

    SUPPORT SATTELITE PROTECTION LEGISLATION :)


    www.mp3.com/Undocumented [mp3.com]
  • I dont know if this would work as well for general solar system travel, the suns magnetosphere is less dense out here than earths is, so youd need more power or a longer tether.
    The real problem is that the magnetic field we see from the Sun is carried in the solar wind, and has neither a consistent strength nor a consistent direction. Since you can only push at right angles to the field, this means you're at the mercy of the immediate conditions.
    --
  • There is a real potential here for a "momentum exchange market".

    Orbital momentum is worth about $1/(kgm/s).

    This is because that's about how much it costs to generate that much orbital momentum -- which can be conserved.

    Combined with a momentum conserving technology like momentum exchange tethers [tethers.com], this creates a very important potential market in orbital momentum.

    The primary demand for this momentum would be transfer from low earth orbit to geosynchronous orbit and the primary supply for this momentum would be derelict low earth orbit satellites. A big issue here is who owns the momentum of derelict satellites? By the law of the sea, it should be those who can first demonstrate control the derelict satellite's momentum.

    This market is particularly important.

    • The bottleneck to technological civilization is commercially viable access to the unlimited environment of space.
    • The bottleneck to space commerce is transport.
    • The bottleneck to space transport is lofting propellant.
    • The bottleneck to lofting propellant is reaction mass due to the fact that momentum is linear in velocity but energy is square in velocity. In other words every bit of reaction mass at orbital velocity buys you a lot of effective propellant and rocket at the ground.

  • Would Dragging a 5km Wire around be "Safe" i mean there is alot of space debris up there floating about. ANd If the wire were to hit one or even get tangled on one (like fishing line on tree branches) wouldn't that cause a problem?
  • So would this work for geostationary orbits that spend 12 hours in the Earths shadow?

    Geostationary orbit's do not spend 12 hrs in shadow, GEO is about 32000 km up ( I think), the earths radius is about 6000 km. If it takes 24 hours to orbit, then a GEO satellite is in shadow for about 1.4 hrs, and thats only if you orbit right through the whole shadow, you can orbit so that you pass around the shadow, just like the moon doesnt get eclipsed by the earth every month. Everyone also forgets that when you generate power, your orbit decays, and eventually you burn up, tethers are not viable for long term power generation, only soalr and nuclear are, but tethers work very well for changing altitude once in orbit.

  • Is there any limit to how many of these could be used per object, or on our atmosphere at one time?

    No, there is no limit to how many tethers can be used at once, except of course by the square footage that can be pointed towards or away from the earth. There is a trade off however, the more power you generate, the faster you fall towards the earth, eventually burning up in the atmosphere, The more massive the object the slower the rate of decay, if you could get a good sized asteroid into LEO you might be able to generate quite a bit of power for awhile before it crashed into the earth (which would pretty much negate the whole purpose of generating power). If you want to go up, you need to use power, and generate it some other way, usually through solatr panels although nuclear would work. I dont know if this would work as well for general solar system travel, the suns magnetosphere is less dense out here than earths is, so youd need more power or a longer tether.

  • So would the space craft have to travel directly above the position on the earth where the wire is anchored? Wouldn't the wire break

    You misunderstand the concept, the wire isnt connected to anything except the satellite, space station, shuttle etc. It isnt connected to the ground at all. Power is generated on board the orbiting object and used to create a magnetic field that reacts against earths and raises or lowers the craft.

  • ? If I remember correctly Mars (and possibly the moon as well) have no magnetic fields to speak of.

    youre right, neither the moon nor mars have any discernable magnetic field ( except for the Tycho Magnetic Anomoly, or TMA-1 ;-) so using this for orbiting those bodies is out of the question, but once your in LEO youre halfway to anywhere, and this system will be very handy for shuttling things around LEO and MEO

  • The ship still needs propellant to get INTO orbit in the first place and it still needs an energy source to reel the wire in/out (and a 5 km wire must weigh quite a bit) Could this latter be provided by the inducted electro?

    The first part of this staptement is true, you do still have to launch the thing, but there is no longer a need for stationkeeping propellant. The energy needed to raise the orbit is produced the same way energy is produced on orbit now, by solar panels. And 5km of wire doesnt "weigh" anything in space, it does mass quite a bit, but after you get it moving, power requirements for reeling/unreeling/ are negligable considering that you need several kW to raise the orbit of a craft, which can easily be provided by panels, but in the long run winding power isnt too important.

  • However, I can see MANY complications, IE you are moving some satellite and the tether breaks, leaving the device with a completely different orbit and speed

    In a conventional satellite your engine could explode, your fuel could leak out, your gyros can fail, you can get hit with micrometeoroids, you can run out of fuel etc etc. The point is, sending a satellite into space is a risky venture, therefore you shoudl do all you can to ruduce your risk, and your cost exposure. Tethers are cheaper, tethers are simpler, and tethers can be made redundant so that they are more reliable. Space is risky, deal with it

  • This was actually a major plot point in a book by Larry Niven and Stephen Barnes entitled The Descent of Anansi. Basically, there was this spool of monofilament wire (several million kilometers worth) that had been produced in orbit and needed to be brought back to Earth. However, a Brazilian company that lost the bid for the wire sabotaged the space shuttle that was to recover the spool so they could claim salvage rights.

    I had a point somewhere... Where is it... Ah.

    Anyway, the act of sabotage damaged the shuttle so it couldn't deorbit. The crew came up with the idea of attaching the free end of the wire to the shuttle and letting the wire spool out, thus deorbiting the shuttle and putting the spool itself in a higher orbit. Anyway, it's neat to see that a concept that I first saw in an admittedly pulpy piece of science-fiction writing is finally getting scientific attention.


    --Fesh

  • Tethers have long been a theoretical tool utilized in Science Fiction by authors like Larry Niven. They have recently been made real though by companies like Tethers Unlimited [tethers.com]. Their site has a lot of information about how tethers work and what can be done with them.
  • It's a good idea, to use the forces surrounding the aircraft rather than brute forcing them about with rockets. This is real ingenuity at work, rather than just sticking a bigger cherry bomb under the garbage can.


    We're all different.
  • Asketh the poster:
    So would the space craft have to travel directly above the position on the earth where the wire is anchored?
    The beauty is, the wire isn't anchored. Simply passing it through the Earth's magnetic field (as it orbits) generates emf and thus power. I believe the original experiment envisioned spraying ions off the Shuttle to (a) create a return path for the current and (b) avoid highly ionizing the Shuttle, which would mess with navigation, etc.

    On the other hand, a "space tether" might be cool, too, but is currently well within the realm of sci fi. See Kim Stanley Robinson's Mars triology for an interesting take on how this might be constructed.

  • All those days spent playing tether ball will serve me well in my quest to become an astronaut!

  • Uh... The atmosphere doesn't extend to the altitudes where this would be used. We're taling over 100K, while the atmosphere is significantly less than that. Electric fields at that altitude generated by man would be insignificant anyway. Right now the sun is kicking up orders of magnitude higher electrical disturbances through solar flares reacting with the Earth's magetic field (read Northern Lights or Aurora Borealis). A number of studies have been done showing that this interaction doesn't affect weather. As far as polluting space, the total volume of a sphere increases as a cube of its radius, meaning that there is a LOT of space in space.
  • You can avoid large objects, but there are lots of things down to the size of paint flecks which can't be tracked, let alone avoided.

    The problem with dragging a wire is that the wire is smaller than the size of the hole many pieces of micro-debris would make. This means 1 impact = broken tether. To avoid this, at least one company is working on a "mesh" tether which has multiple redundant load paths and is interconnected at relatively close spacings. If one strand of the mesh is broken, other strands take up the load. This greatly extends the lifespan of the tether even in a hazard-rich environment.
    --

  • Re:Great News for Seti@Home (Score:3)

    by gilroy ( 155262 ) on Monday July 24, 2000 @05:21AM (#910277) Homepage Journal
    I was going to be mercilessly sarcastic, but I'll be kind and assume you're just uninformed.

    Although space junk is a real and growing problem, this will not contribute to it unless the tether breaks. While you can't rule out that probability, conventional satellite boosters contribute to space junk by their nature, as they spew out flakes of, say, aluminum. So I think we win here.

    The SETI comment simply makes no sense. The wire might be long, but it's thin -- according to the article, 1.2 millimeter (=0.12 cm) in diameter. According to SETI@home, the search uses 1.64 GHz, or a wavelength around 20 cm. As elementary wave physics tells you, the wire is much too small to be "seen".

    I suppose it might be possible that this could act as an antenna. In that case, it is small and high, and the signal almost certainly will be negligible ... even if it happens to radiate around 20 cm, which requires a cosmic conspiracy to happen.

  • Dual Purpose Wire (Score:4)

    by arberya ( 176464 ) on Monday July 24, 2000 @04:25AM (#910278)
    NASA has been experimenting for sometime using long strands of wire and the earth's magnetic field to generate large amounts of electricity to power space stations and the like. Now they seem to be using it for a different purpose. Still relies on all the same principles. I suppose physics is just glorified math anyway.

  • A good thing (Score:4)

    by maddogsparky ( 202296 ) on Monday July 24, 2000 @04:27AM (#910279)
    This will actually reduce space junk, not make more of it. Rather than having to send up new satelites when the fuel runs out or sending extra resupply flights with fuel for the space stations, solar panels can collect electricty and provide thrust via these wires. All this and its environmentally friendly, since it doesn't waste millions of pounds of fuel just trying to get fuel into orbit!

  • Tethers (Score:5)

    by stevelinton ( 4044 ) <sal@dcs.st-and.ac.uk> on Monday July 24, 2000 @06:00AM (#910280) Homepage
    Just to clarify a bit. There are a few different things you can do with tethers once you've mastered the art of winding and unwinding them, building tethers resistant to single-point breakage, and so on.

    1. Trade off electrical power for orbital altitude. You can do this either way, running as either a motor or a dynamo.

    2. Dangle an object in the upper fringes of the atmosphere. This is an area which is normally hard to study, as you can't stay in orbit long, but it's too high to fly a plane or balloon. A big orbitting spacecraft dangling a small instrument package on a tether can be a useful combination.

    3. Rotating tethers can be used to tranfer orbital momentum between different satellites in various possibly useful ways. The most extreme case has one end of the tether actually touching the ground (with no horizontal velocity) every rotation. You just grab hold and get lifted up into orbit, or even launched out of Earth orbit -- of course you have to land enough matter to keep the tether spinning.

    4. stabilization. Even quite a short (100m) tether will be stabilized by Earth's tidal forces and can be used to keep a satellite pointed in a certain way

  • Space Tether information (Score:5)

    by Nehemiah S. ( 69069 ) on Monday July 24, 2000 @05:47AM (#910281)
    Dr. Hoyt, from Tethers Unlimited [tethers.com], presented several papers and chaired a general session on this at this years AIAA [aiaa.org] Joint Propulsion Conference in Huntsville last week. If you are really interested in this stuff you can order them from AIAA ($11.95 each!) or get them from a tech library near you:

    AIAA-2000-3615 Design and Simulation of Tether Facilities for the HASTOL [nasa.gov] Architecture (Hoyt)

    AIAA-2000-3866 Design and Sim of a Tether Boost Facility for GEO, Lunar, and Mars Transport (Hoyt, Grant, and Bangham)

    AIAA-2000-3865 Computation of Current to a Moving Bare Tether, (Onishi & Martinez, MIT, and Cooke, AFRL [afrl.mil])

    AIAA-2000-3870 Future Application of Electrodynamic Space Tethers For Propulsion (Santangelo, Michigan Technic [airseds.com] and Johnson, Nasa Marshall [nasa.gov] )

    I apologize for not being able to link to the specific papers or give much additional information, since this panel ran at the same time as one I was more interested in and the papers are copyrighted by AIAA. The fact that technical publications are generally not available upon demand except in bulk or by federal express is increasingly irritating to me, since 1) they are available in .pdf format on CD-ROM at the conference anyway, and 2) many distribution systems exist which would allow the organizations to distribute them electronically and still get paid. Please complain (nicely) to Webmaster@aiaa.org about this, since my lonely voice is probably not loud enough to cause action.

    Rev. Neh
    propulsion geek

  • ha ha (Score:5)

    by cybercuzco ( 100904 ) on Monday July 24, 2000 @04:21AM (#910282) Homepage Journal
    Sure -- while you're up there, why not drag a 5km wire around for a while?

    you may make light of this development, but it really is quite significant. The earth has a magnetic field, and as we all know from our basic physics class we had to slog through in college, that a conductor passing through a magnetic field generates a current, and from the current a force. If you play the wire down from your position, and let it generate electricity ( IE dont provide a stopping voltage) your speed decreases and your orbit drops, if you play the tether up from yoru position and apply a voltage to the wire, say from some solar panels, you increase your speed and your altitude increases (actually your speed goes down when you go up and up when you go down, just one of the kinks of orbital mechanics) All of this can be done WITHOUT PROPELLANT, which really kicks some major ass, because a huge amount of money is spent on propellant and complicated ion and regular rocket engines, and wire is really really cheap. THis is a major development for the space and satellite industries

  • Leashes? (Score:5)

    by beau455 ( 197679 ) on Monday July 24, 2000 @04:15AM (#910283)
    So thats whats with all those kids i've seen running around the mall with leashes attached to them... that was just NASA testing the feasability of tethers on high speed objects.

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