# Electromagnetic Propulsion **URL:** \ **Category:** Factual Questions\ **Created:** [July 6, 2003, 10:32am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550 "2003-07-06T10:32:03Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 6, 2003, 10:32am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/1 "2003-07-06T10:32:03Z")
**Muad’Dib** ’s [anti-gravity](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=195643) thread reminded me of something I saw once in an [otherwise crappy and incomprehensible video](http://www.johnsonsmith.com/website/store/product_detail.asp?UID=2003070606262941&item_no=8990&keyword=jread&cat_keyword=jread&search_page_no=2). At the end of the video they showed film clips of research that some folks had done back in the late 1950s/early 1960s using Tesla coils to zap metal disks (they looked a lot like hubcaps, but obviously _weren’t_), the disks then hovered in the air while giving off an electrical discharge. This leads me to wonder what the deal with this was. Were the images faked? (Judging by the way they looked, it seems highly unlikely, but one certainly can’t rule out that possibility.) Or was it legitimate? If so, why hasn’t anyone, NASA or otherwise, followed up on this? It certainly _looked_ like one would be capable of using it to propell a spacecraft. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 6, 2003, 11:59am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/2 "2003-07-06T11:59:52Z")
Sounds similar to the [“Lifter”](http://www.americanantigravity.com/technology.html) and probably based on the same principle. It’s not a very efficient way of travelling in the atmosphere. But [ion propulsion](http://science.nasa.gov/newhome/headlines/prop06apr99_2.htm) is used on many satellites and interplanetary probes. They have small thrust and require a lot of electrical power, but they have much higher specific impulse (exhaust speed) than chemical rockets. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [July 6, 2003, 12:53pm UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/3 "2003-07-06T12:53:10Z")
Ion lifters mght be the best system for those little fly-sized robot flyers them since it’s tricky to make engines and propulsion systems for them. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [July 6, 2003, 1:07pm UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/4 "2003-07-06T13:07:14Z")
Upon further consideration, while ion propulsion doesn’t work well enough for full sized aircraft it might be useful for controlling the airflow around the craft perhaps even holding a stable skin of air around it to reduce drag and provide some inslation from heat during supersonic travel. Yanno, now that my brain is up and running with this, why doesn’t the space shuttle use a magnetic field to repel the supeheated air during re-entry? the air gets hot enough to ionize so why not ditch those pain-in-the-ass tiles and repel those ion with a nice magnetic field? hell why not make car windshields with hair thin wires woven into em to ionize and repel rain? ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 6, 2003, 10:07pm UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/5 "2003-07-06T22:07:29Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\*Sounds similar to the [“Lifter”](http://www.americanantigravity.com/technology.html) and probably based on the same principle. It’s not a very efficient way of travelling in the atmosphere. But [ion propulsion](http://science.nasa.gov/newhome/headlines/prop06apr99_2.htm) is used on many satellites and interplanetary probes. They have small thrust and require a lot of electrical power, but they have much higher specific impulse (exhaust speed) than chemical rockets. \*\* Yeah, I’d say it was a “lifter.” Still doesn’t explain why there’s not been a lot of research on them, though. ---
**Author:** ![Trigonal\_Planar](https://avatars.discourse-cdn.com/v4/letter/t/0ea827/32.png) [@Trigonal\_Planar](https://boards.straightdope.com/u/Trigonal_Planar)\ **Post date:** [July 7, 2003, 12:16am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/6 "2003-07-07T00:16:41Z")
I would presume the lack of research is due to the fact that to lift any significant weight would require huge huge amounts of power. The paper ones I’ve seen use around 25kV (?) of direct current. ---
**Author:** ![Zenster](https://avatars.discourse-cdn.com/v4/letter/z/cdc98d/32.png) [@Zenster](https://boards.straightdope.com/u/Zenster)\ **Post date:** [July 7, 2003, 1:02am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/7 "2003-07-07T01:02:50Z")
As an aside, the ion drive currently being considered for use in spacecraft, is identical in operating principal to the ion mills used in semiconductor fabrication. It is only advances in solar cell and battery technology that have held back their use in propulsion applications. The designs were first thought up back in the 1950s and 1960s. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [July 7, 2003, 1:39am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/8 "2003-07-07T01:39:28Z")
> [@](#): > > \*Originally posted by Trigonal Planar \* > \*\*I would presume the lack of research is due to the fact that to lift any significant weight would require huge huge amounts of power. The paper ones I’ve seen use around 25kV (?) of direct current. \*\* What were the amps? I think _that’s_ more important part of the equation. It’s easy, IIRC, to produce lots of voltage at very low amps, where it gets expensive is when you’re having to put out large amounts of volts _and_ amps. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 7, 2003, 3:15am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/9 "2003-07-07T03:15:29Z")
> [@](#): > > \*Originally posted by Sock Munkey \* > \*\*…why doesn’t the space shuttle use a magnetic field to repel the supeheated air during re-entry? the air gets hot enough to ionize so why not ditch those pain-in-the-ass tiles and repel those ion with a nice magnetic field? hell why not make car windshields with hair thin wires woven into em to ionize and repel rain? \*\* The air around the Shuttle isn’t 100% ionized, and even if it were, it difficult (if at all possible) to create a field configuration that redirects both positively and negatively charged particles away from the entire spacecraft. And even if you could do that, it would be heavier and less reliable than using insulators. As for windshields, you’ll need a very powerful electric field to repel drops of water. And I think you need a way to transfer charge onto the droplets before it actually comes in contact with the glass. I haven’t thought this through yet but it just doesn’t sound feasible. Besides, high voltage and water is usually a bad combination. ---
**Author:** ![Trigonal\_Planar](https://avatars.discourse-cdn.com/v4/letter/t/0ea827/32.png) [@Trigonal\_Planar](https://boards.straightdope.com/u/Trigonal_Planar)\ **Post date:** [July 7, 2003, 4:03am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/10 "2003-07-07T04:03:18Z")
The amperage on lifters would be very low. I’ve mounted ion motors on the top of my tesla coil (just a wire bent like the the letter “Z”) and they spin around pretty darn fast. The amperage from tesla coil output is in the miroamps. ---
**Author:** ![Sock\_Munkey](https://avatars.discourse-cdn.com/v4/letter/s/aeb1de/32.png) [@Sock\_Munkey](https://boards.straightdope.com/u/Sock_Munkey)\ **Post date:** [July 7, 2003, 7:31am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/11 "2003-07-07T07:31:02Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\*As for windshields, you’ll need a very powerful electric field to repel drops of water. And I think you need a way to transfer charge onto the droplets before it actually comes in contact with the glass. I haven’t thought this through yet but it just doesn’t sound feasible. Besides, high voltage and water is usually a bad combination. \*\* My initial idea was more along the idea of using something akin to the magnetohydrodynamic drive in The Hunt For Red October to repel rain from the windshield. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 7, 2003, 10:42am UTC](https://boards.straightdope.com/t/electromagnetic-propulsion/186550/12 "2003-07-07T10:42:22Z")
> [@](#): > > \*Originally posted by Sock Munkey \* > \*\*My initial idea was more along the idea of using something akin to the magnetohydrodynamic drive in The Hunt For Red October to repel rain from the windshield. \*\* The MHD drive works by passing current through the water and applying a powerful magnetic field on it. The water will push against the magnetic field just like the coil wires inside an electric motor. It might work on raindrops but only after the drops have come in contact with electrods, otherwise you can’t pass current through the droplets.