Long cables to power plasma rockets to orbit.

[exoscientist]

Magnetoplasmadynamic thrusters have the advantage that they can be<br />scaled up to produce large amounts of thrust, while still maintaining<br />the high ISP of ion drives:<br /><br />Magnetoplasmadynamic Thrusters.<br />"Testing for these thrusters has demonstrated exhaust velocities of<br />100,000 meters per second (over 200,000 mph) and thrust levels of 100<br />Newtons (22.5 pounds) at power levels of 1 megawatt. For perspective,<br />this exhaust velocity will allow a spacecraft to travel roughly 11<br />times the top speed of the space shuttle (18,000 mph)."<br />http://www.nasa.gov/centers/glenn/about/fs22grc.html<br /><br />MY ELECTRIC ROCKET ENGINE.<br />http://www.waynesthisandthat.com/mpd.htm<br /><br /> The problem is the high amount of power required. However high<br />electrical power has been delivered up to hundreds of kilometers on<br />Earth over power lines. Then this could be used to deliver the<br />required electrical power to the thrusters from the ground.<br /><br /> Bob Clark<br /><br />c.f.,<br />Newsgroups: sci.astro, sci.space.policy, sci.physics<br />From: "Robert Clark" <rgregorycl...@yahoo.com /><br />Date: 20 Mar 2006 20:23:18 -0800<br />Local: Mon, Mar 20 2006 11:23 pm<br />Subject: Long cables to power arcjet rockets to orbit?<br />http://groups.google.com/group/sci.physics/msg/0cd3fba4a33a6d13<br /> <div class="Discussion_UserSignature"> </div>

 

[kelvinzero]

How heavy is the plasma rocket that produces 25 pounds of thrust?<br /><br />Hey, here is an idea: maybe you could conduct the power up it's plasma-hot exhaust trail! Dunno if it would work, but it would sure look cool...

 

[j05h]

<i>> Hey, here is an idea: maybe you could conduct the power up it's plasma-hot exhaust trail! Dunno if it would work, but it would sure look cool...</i><br /><br />Truly "Ride the Lightning".<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[vogon13]

VLEC technology has been discussed at Spacedotcom before . . . . <br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[crix]

Hah, I had to load up some Metallica as I was reading this thread. <br /><br />Realistically though the plasma "circuit" would be broken after the craft reached a certain height, not to mention the weather conditions (winds, gusts) that would disrupt the plasma.<br /><br />Wires hanging from the craft is something I had never thought of... mostly because it sounds like a bad idea. But I guess if you only need really high thrust for launch and lower thrust for getting places in space then it might make sense.

 

[richalex]

Atmospheric research rockets used in New Mexico have copper wires trailing from them to ground, in an effort to attract lightning strikes. I have seen photos in which they were successful. <br /><br />The military has used wire-guided rockets, but the practical limit is about 3 miles horizontally, due to the weight of the wire. I don't know how far vertically they could go, or how thick a cable one would need to carry enough current. Maybe something superconducting?

 

[vogon13]

VLEC technology was origianlly proposed for aircraft to supplement on board electrical consumption. While 'signals' are conducted on the 'TOW' missles, the wire is thin enough that it could not carry appreciable wattage to power the missle.<br /><br />Additionally, VLEC technology requires 2 conductors to complete the electrical circuit.<br /><br />Insulation for a superconducting VLEC would most likely be prohibitively heavy. Keep in mind the cooling requirements would be scaled to the length of the conductors.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[exoscientist]

Instead of making the full length of wire be trailing from the rocket, you could have the horizontal distance required by a cable lying on the ground and only the vertical distance be covered by a cable reaching from the rocket to the ground.<br /> Or you could have the long cable be extending from the ground to high altitude, using balloons for example to keep it aloft and only a short length extending from the rocket to the long cable.<br /><br /><br /> Bob Clark <div class="Discussion_UserSignature"> </div>

 

[richalex]

Yeah, we could put a multi-megawatt power generator on a balloon platform up about 4 miles, with the cable descending down to the rocket. That way, the rocket could reach about 8 miles altitude with just a 4 mile long cable. <br /><br />Or, we could figure out ways to engineer multi-megawatt power generators that could fly or orbit. <br /><br />As for launches, I've always liked the idea of a magnetic launcher, though that would be severally limited with human passengers.

 

[vogon13]

{responding to the entire thread}<br /><br />Note that the space shuttle main engines produce power roughly comparable to the TOTAL INSTALLED ELECTRICAL GENERATING CAPACITY OF THE UNITED STATES !!!!!!!<br /><br /><br /><br /><br /><br />How big of an extension cord is it going to take to transmit this much power, and can the craft possibily lift it ???<br /><br /><br /><br />Please, do some math!!!<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[richalex]

<blockquote><font class="small">In reply to:</font><hr /><p>Please, do some math!!!<p><hr /></p></p></blockquote><br />2 + 2 = 4<br /><br />My work here is done. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Note that the space shuttle main engines produce power roughly comparable to the TOTAL INSTALLED ELECTRICAL GENERATING CAPACITY OF THE UNITED STATES !!!!!!! <br /><br />How big of an extension cord is it going to take to transmit this much power, and can the craft possibily lift it ??? <p><hr /></p></p></blockquote><br />I'm thinking that the rockets using a few megawatts of electrical power might be less massive than the Space Shuttle.

 

[vogon13]

Shuttle weighs approximately 100 tons. How small is this craft ? 1 ton?<br /><br />Then it is still ~1% of the TOTAL US ELECTRICAL GENERATING CAPACITY !!!!!<br /><br />The extension cord is still massively huge. Instead of weighing 100,000 tons, (quick calculation I just did, might have slipped a decimal) now it weighs a thousand tons!!<br /><br />It's still too heavy !!!<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[exoscientist]

Vogon, you can reduce the weight of the cable that needed to be carried along by the craft by having most of the cable simply being static, either lying on the ground or extending up some distance to altitude, held up by helium balloons or small thrusters all along its length that do not need to create a high velocity but only support the weight of that portion of the cable. A shorter cable, call it the tether, would then extend from the rocket to this longer fixed cable, and perhaps only 10 or 100 meters long, just enough so the inaccuracy in the trajectory doesn't cause the craft to hit the fixed cable. <br /> Note that for the case of the fixed cable lying on the ground, if the craft's tether was such a short distance, this would mean the craft would get its full, high Mach velocity close to the ground, at full atmospheric pressure. Theoretical studies have shown this is feasible for small bullet shaped craft, that might be say only 10 kg total weight. However, for larger craft carrying large satellites you would want the fixed cable to extended 10's of kilometers into the atmosphere so at the final velocity of the craft, the atmospheric pressure is very low.<br /> To get the an idea of the length of the long, fixed cable, the velocity v attained at a constant acceleration a over a distance d is: v^2 = 2ad. So for v = 8,000 m/s and a = 10 g's = 100 m/s^2, d is 320 km. The craft would have to undergo this for t =v/a = 80 s. If you made the acceleration be 10 times larger, then the distance would only have to be 32 km. But this would reduce the total craft weight by the same proportion for the same power engine.<br /> For a large size craft this long cable would have to be supported in the air. Let's say it was aluminum 1 cm = .01 m wide. For the the 320 km length this would have a volume of about .01m x .01m x 320,000m = 32 cubic meters. At 2700 kg/m^3 density of aluminum, this would be 86,400 kg weight. This might be supported by say 10 to 20 large sized high alt <div class="Discussion_UserSignature"> </div>

 

[vogon13]

You're trying to transmit an appreciable fraction of the total US electrical generating capacity.<br /><br />Your extension cord will be an appreciable fraction of the total US electrical transmission cable total!<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[billslugg]

I roughed it out at 16% of US generating capacity. <br />US capacity is 1TW. Allow a generous 1500 Amps per square inch at 1,000,000 V.<br /><br />The cross sectional area of each of the two wires would be 666 inches^2. <br /><br />Each wire would be about 3 feet in diameter.<br /> <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[scottb50]

Home Depot has some pretty hefty extension cords. <div class="Discussion_UserSignature"> </div>

 

[richalex]

Out of curiosity, how light could you make a cable that could carry 1 MW for, say, 1 minute? No one said this cable has to be re-usable, so we could pump so much power through it that it vaporizes, as long as nothing important gets hurt in the process. It could be like a lightning bolt hitting our rocket in a controlled way. Maybe something like PBFA could supply the current? <br /><br />If the thrust of this type of rocket engine is 22.5 lbs per megawatt, as the OP indicates, then we want to ensure that our delivery system is a small fraction of 22.5 lbs per MW delivered. Can that be done with reasonable, current designs? <br /><br />Incidentally, 22.5 lbs per MW implies that a 1 ton launch vehicle would need to have about 100 MW delivered to it. What would that cable likely weigh (particularly if we could power it until it destroys itself)?

 

[scottb50]

I think the lighting bolt analogy is appropriate, the problem is you would need a sustained flow not and instantaneous jolt.<br /><br />When I read about this what comes to mind is the old Flash Gordon rockets, spewing sparks and sounding like electric motors. <div class="Discussion_UserSignature"> </div>

 

[billslugg]

It totally depends on what voltage you assume. To transport 1 MW at 1MV you only need to carry 1 Amp. The problem with a mega Volt is handling it at the rocket end. The voltage wants to jump to the other cable and leave the "load" out of the loop. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[vogon13]

I note the cables on the Golden Gate Bridge (steel, BTW, not copper) are roughly 3 feet in diameter, and IIRC, each is ~ 10,000 feet long, and each weighs over 10,000 tons.<br /><br /><br />Glad I don't have to drag them around.<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[richalex]

Well, let's go modern. High-temperature Superconducting Cable is about to begin operation in its first real-world system (actually, I thought this happened back around 2001 or 2003, but the press release says it is to go live this year). This cable can carry 574 MW at 138 kV, which implies 4 kA of current. The only thing I don't know is how much it weighs. <br /><br />American Superconductor: Long Island Power Authority (LIPA) HTS power transmission cable project

 

[vogon13]

Well, we are looking at extension cords weighing thousands of tons (for 2 miles worth), if superconductivity gets you a hundred fold increase in power transfer, for a vehicle weighing 1 ton, does a 100 ton extension cord help that much ??<br /><br />And what happens to the cord when the vehicle speed passes the speed of sound in your cable ?? <br /><br />{mechanical tensile stress exceeds any known materials strength around that speed, IIRC}<br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[richalex]

I found a Website that gives a power/weight ratio. I don't know how generalized this would be, but it doesn't bode well for the concept: <br /><br />properties of a single 3 kA, 12 kV Triax cable <br /><br />Physical properties<br />Size Ø143 mm<br />Weight 12 kg/m<br />Pulling force 2 tons<br /><br />Ultera: Successful testing of a 3 x 3.0 kA Triax HTS cable<br /><br />As I read it, this tells me that this cable could deliver 36 megawatts. The OP implies this could provide <br /><br />22.5 lbs/MW * 36 MW = 810 lbs thrust = 370 kg thrust. <br /><br />If the rocket did not weigh anything, and all the weight is cable, that lets us have a cable that is <br /><br />370 kg / 12 kg/m = 30 meters<br /><br />So, even with superconducting cables, this does not look like a feasible concept, unless you ensure that the rocket never supports more than 30 meters of cable. We could still have the cable dropped from an overhead balloon, but the cable would have to be reeled in fast enough to keep up with the rising rocket and it could not power the rocket very far past the balloon. The balloon, itself, would have to support the cable plus enough electrical power for a few minutes of rocket flight, probably not more than 1 minute or so, given the other constraints, so 36 MW*minutes of power. <br /><br />Maybe this concept would work better in space? We could have a giant power station with this cable powering a rocket out of Earth (or any other) orbit.

 

[nexium]

If we have a laser array powered by solar panels, balloon supported at 30 kilometers altitude, solar panels on the craft may provide enough power for lift off, rapid accelleration as the craft passes the balloon, and at least slight acceleration against decreasing gravity out to about 100,000 kilometers, beyond which most of the laser energy will miss the solar panels. I'll guess the craft can coast to Mars, perhaps anywhere in the inner solar system. Some on board delta v is needed for mid course correction, and manuvering at the destination, so there would be only a little payload. Neil

 

[exoscientist]

<blockquote><font class="small">In reply to:</font><hr /><p>Well, we are looking at extension cords weighing thousands of tons (for 2 miles worth), if superconductivity gets you a hundred fold increase in power transfer, for a vehicle weighing 1 ton, does a 100 ton extension cord help that much ??<br />And what happens to the cord when the vehicle speed passes the speed of sound in your cable ??<br />{mechanical tensile stress exceeds any known materials strength around that speed, IIRC} <p><hr /></p></p></blockquote><br /><br /> You wouldn't need a 3 ft. cable that is used to support a million ton bridge. High tension power lines that may run for distances of hundreds of kilometers are typically only 3 mm to 3 cm wide, made of bare (uninsulated) aluminum.<br /> These power lines typically run at voltages of 110 kV and above to save on power losses over long distances, though there is at least one that runs at over 1 megavolt.<br /> See here for instance:<br /><br />Electric power transmission.<br />http://en.wikipedia.org/wiki/Electric_power_transmission#AC_power_transmission<br /><br /> Also, this web page shows there are several high strength materials already in common industrial use that have sound speeds greater than the orbital velocity of 7,000-8,000 m/s :<br /><br />STRUCTURAL MATERIALS.<br />http://www.islandone.org/LEOBiblio/SPBI1MA.HTM<br /><br /> At least one of these, carbon fiber, could be used for the short tether conductor that reaches from the rocket to the long, fixed cable. Carbon is not as good a conductor as aluminum, but since this is for a short tether the power losses wouldn't be too great.<br /><br /><br /> Bob Clark <div class="Discussion_UserSignature"> </div>