power generating satellite flown out of shuttle bay

[slidelock]

Anybody remember the mission described above. If I remember correctly, it was a satellite tethered to a reel in the shuttle bay. First time flown the motor froze, the second time the tether "broke", looked fused to me indicating way more power than anticipated. I have thought since, hooking that technology to an ion engine could prevent ever having to deorbit anything again. Anybody know if thats still being looked at? What was the experimental satellite called?

 

[nacnud]

It was STS-75. Google 'electrodynamic tethers' to find out more about the idea.

 

[mikejz]

Really is a shame no other work has been done on the concept.

 

[comga]

Remember that energy is not free. One can only trade it, and usually the trade is lossy. In the case of electrodynamic teathers, one has to have electic power. ONe could try to use nuclear power, but that is unpopular in Earth orbit. Most every sattelite uses solar power. Below some altitude, probably higher than the ISS, the drag of solar panels exceeds the thrust one can get from the teather. The satellite woudl fall faster with the system than without.<br /><br />My recollection was that the cable was cut by something much more prosaic than high current. Wasn't it something like snagging on a bolt? (I realize that this could be researched at the supplied link.)<br />

 

[j05h]

Several tethers have been flown, some broke from stresses, others from electric charge. <br /><br />i have a question for any physics-types. If you had several electrodynamic tethers on a spacecraft, could you draw power from several of them and thrust with one? Is this possible?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[nacnud]

A lot of studies have been done into the idea, NasaSpaceFlight.com has some articles on them.<br /><br />Tether solution for ISS - study<br /><br />As well as momentum exchange tethers<br /><br />Sling me to the Moon

 

[mikejz]

I actually remember a vague idea that I saw on a Nasa PowerPoint presentation about using an electrodynamic tether for capture into Jovian orbit.

 

[willpittenger]

How is that going to work? Is the tether going to power an ion engine or something else powered by electricity? <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[comga]

Remember that energy is conserved. If you use one tether to generate power and another to generate thrust, you gain nothing, and lose lots in converting one to the other. An electrodynamic tether is good for converting power into thrust or vice versa if you have an excess of one.<br /><br />For instance, if you had lots of Shuttle and Soyuz visits to the ISS, and each one used its excess fuel and boosted the stations orbit so that it was higher than optimum, you could convert the excess momentum into power with a device that was much smaller than another large solar panel. In this case you would be converting easy-to-launch rocket fuel into hard to generate regulated power. However, this is not the case and probably will never be. Right now, they are having trouble getting enough boost to keep the station at its design altitude and out of the thicker upper atmosphere. (See the ISS altitude plot at www.heavens-above.com) On the other hand, there is a severe lack of power. They can neither affort to lose altitude or consume large amounts of power. <br />

 

[j05h]

Comga- what I was asking was if you could use, say 6 tethers for power generation to power 2 "pusher" electrodynamic tethers? I know something of conservation, but am wondering if this is possible? I'm thinking more microsatellite, not ISS. <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[mikejz]

I have no clue...<br /><br />I just remember seeing it on a Nasa Powerpoint. <br /><br />I'm guessing the delta-v would be provided by power generated, all they would need would be a way to expend all that power.

 

[nacnud]

Like a big fat resistor, and a radiator.

 

[pathfinder_01]

“Several tethers have been flown, some broke from stresses, others from electric charge. <br /><br />i have a question for any physics-types. If you had several electrodynamic tethers on a spacecraft, could you draw power from several of them and thrust with one? Is this possible? “<br /><br />Not a physics-type, but if I remember correctly the power generated came from the spacecraft’s velocity. I don’t think you could use the power to run a thruster to raise the orbit, but it could be a nice way to lower a spacecraft’s orbit without propellant. <br /><br /><br />

 

[nacnud]

Or increase it if you pump power through the tether, you'd have to get the power from another source though sutch as solar cells.

 

[mikejz]

I wonder who much power such a tether would generate at Jupiter? Maybe enough to make JIMO look like a toy....

 

[pathfinder_01]

Now that would be cool. Having a bunch of electrical tugs pushing objects into lower and higher orbit, no propellant needed. Just dock to the tug and slowly ride up as high as the earth’s magnetic field will take you. Or dock to the tug and save propellant on the way down. <br /><br /><br />I wonder what would be the consequences of running power in the tether. Will it create some sort of large magnetic effect that wrecks the spacecraft's electronics? Considering the advantages, what are the engineering problems (which I assume are probably pretty major).<br />

 

[j05h]

> Not a physics-type, but if I remember correctly the power generated came from the spacecraft’s velocity. I don’t think you could use the power to run a thruster to raise the orbit, but it could be a nice way to lower a spacecraft’s orbit without propellant.<br /><br />Check out www.tethers.com they offer a whole slew of different Tether applications, both structural and electrodynamic: deorbit, propulsion, sensor deployment, rotovators, etc. TUI offers "propellantless" systems that pump power from photovoltaics into a tether to push against the magnetic field, providing thrust. They also mention dragging a tether in certain configurations to generate power. <br /><br />So, it makes sense that with the right equipment you could generate power along one or several tethers, then use another tether to provide thrust from that electricity.<br /><br />Could it work?<br /><br />josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[nacnud]

No tethers produce power by convering momentum into electricity, same as a dynamo, OR you can pump eletrcity through them to produce momentum as in an electric motor.<br /><br />Having one tether produce electricty to power another tether to produce momentum is like coupling a dynamo to an electric motor and expecting perpetual motion.

 

[j05h]

I am basing my understanding on this page.<br /><br />http://www.tethers.com/EDTethers.html<br /><br />In which are described methods for using tethers to generate electrcity, as propulsion and for ISS reboost. What I'm wondering is if you could use one tether to generate power, and several other tethers to power it. The only trouble I see is if the drag is to great over thrust. Not perpetual motion, just feeding/pushing a bunch off the magnetic field. <br /><br />What your saying is this can't work, even with a photovoltaic assist?<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[henryhallam]

What you are talking about is effectively the same thing as most "perpetual motion" concepts, like using a water wheel to drive a pump bringing all the water back up to the top again.<br /><br />When you "generate" electricity using a tether, the energy is really coming from your orbital kinetic energy. So using that to power any means of propulsion, tether, ion engine or otherwise, is counterproductive.<br /><br />You can drive a propulsion tether with electricity from a solar panel and gain velocity. But adding more "generative" tethers to provide "more" power will at best accomplish nothing at all, and in reality will slow you down because of inefficiencies in the transfer from "generative" to "propulsive" tether.<br /><br />My question: do these tethers require a return path for the current through ions in the (very thin) upper atmosphere?

 

[pathfinder_01]

“In which are described methods for using tethers to generate electricity, as propulsion and for ISS reboost. What I'm wondering is if you could use one tether to generate power, and several other tethers to power it. The only trouble I see is if the drag is to great over thrust. Not perpetual motion, just feeding/pushing a bunch off the magnetic field. <br /><br />What your saying is this can't work, even with a photovoltaic assist?”<br /><br />No, what they are saying that you would REQUIRE additional power to raise orbit. The photovoltaic part would not be assisting it. It would be the only thing powering it. <br /><br />Here is how it works, a spacecraft traveling along lets out a tether and drags the tether through the earth’s magnetic field generating electrical power.<br /><br /><br />Generators on earth do the same thing. They move a magnet through a coil of wires and generate power. <br /><br />In both cases the generator or the tether take one form of energy and turns it into another. <br /><br /><br />In the case of the generator the generator takes the kinetic energy of the moving magnet and turns it into electrical power. If whatever is causing the magnet to move stops, then the magnet will slow to a stop even without friction. <br /><br /><br />An example of this is the regenerative braking on hybrid cars. The brakes takes the energy present in the turning wheels and turns it into electricity. Slowing the car and generating power. <br /><br />In the case of the tether, the tether takes the kinetic energy of the spacecraft and turns it into electrical power. As a consequence the spacecraft will slow down and the orbit will lower.<br /><br /><br />Adding tethers will only cause the spacecraft to slow down faster. You will generate more electical power in less time but you can not generate more electrical energy than what was present in the kinetic energy of the craft to start with. <br /><br />If you want to use a tether to raise orbit you will need to add some outside power

 

[j05h]

Path, Nac, Henry - Thanks for the repeated explanations. I'll be honest- I never took high school physics and have some holes in my knowledge about How Things Work. I typically learn things via repetitive "brute force" learning. The only thing that is intuitive is geometry and 3D space.<br /><br />On topic, I misunderstood what creates tether electricity. I had thought incorrectly that the energy came from "mining" the magnetic field, not as a feature of momentum. I now get what part was mistaken, thanks. The assertion comes from studying OTEC and tidal generators, I was not understanding which part of a tether was the "tide".<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[barrykirk]

It's a common misunderstanding. IIRC<br />Dr. Robert Forward one of the leading researches in the<br />field of tethers made that same mistake in a scifi book <br />he wrote many years ago. I believe it was called <br />Dragon's Egg.<br /><br />He used a tether on a spacecraft orbiting a neutron star<br />to generate electricity. He completely forgot about the<br />drag force generated by such a system.

 

[nacnud]

Well if the magnestic feild is rotating faster that your orbit you can boost your orbit and generate power as the energy comes from the plantes rotation rather that the orbital velocity, IIRC.<br /><br />This might be useful around fast spinning planets like jupiter.