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Tethers Will Be Tested To Boost, Deorbit Payloads
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?
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?:)
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
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...)
Bill - aka taniwha
--
Leave others their otherness. -- Aratak
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.
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For more information about the endmass (the other end of the tether from the satellite) check out this page. 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.
---- Dave
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
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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?
I'm a leaf on the wind. Watch how I soar.
Sounds like you need an unbreakable (or nearly so) tether. Dr Robert L. Forward has designed such a tether, 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.)
You cannot apply a technological solution to a sociological problem. (Edwards' Law)
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!!!
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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 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).
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Klactovedestene!
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 (where I worked last summer). Or for the less intelligently inclined Tethers Unlimited.
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.
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www.mp3.com/Undocumented
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
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www.mp3.com/Undocumented
--
Time is Nature's way of keeping everything from happening at once... the bitch.
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, 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.
Seastead this.
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?
--------========+++Dont Feed The Lab Techs+++========--------
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.
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.
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.
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 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.
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
--Fesh
Kill -9 'em all, let root@localhost sort 'em out.
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. Their site has a lot of information about how tethers work and what can be done with them.
I stole this sig from a more creative user.
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.
Eh...
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.
The Mongrel Dogs Who Teach
All those days spent playing tether ball will serve me well in my quest to become an astronaut!
-- You see, there would be these conclusions that you could jump to
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.
science is a religion
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.
--
Time is Nature's way of keeping everything from happening at once... the bitch.
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.
The Mongrel Dogs Who Teach
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.
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!
science is a religion
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
AIAA-2000-3615 Design and Simulation of Tether Facilities for the HASTOL 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)
AIAA-2000-3870 Future Application of Electrodynamic Space Tethers For Propulsion (Santangelo, Michigan Technic and Johnson, Nasa Marshall )
.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.
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
Rev. Neh
propulsion geek
... and there is no doubt, that one day he will be
where the eye of his telescope has already been
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
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.