Magnetohydrodynamic(?) Propulsion

[b0ss]

I remember there being a SciShow video on a method of propulsion where a magnetic liquid's surface is changed by a magnetic field so that it has little "spikes" and then subsequently charged so that little droplets can break surface tension and float away, providing a tiny amount of thrust. I can't find the video anywhere though, or anything about the topic whatsoever, anyone know what I'm talking about or what this propulsion is actually called?

[Scotius]

There you go:

https://en.wikipedia.org/wiki/Colloid_thruster

[Cheif Operations Director]

3 hours ago, b0ss said:

I remember there being a SciShow video on a method of propulsion where a magnetic liquid's surface is changed by a magnetic field so that it has little "spikes" and then subsequently charged so that little droplets can break surface tension and float away, providing a tiny amount of thrust. I can't find the video anywhere though, or anything about the topic whatsoever, anyone know what I'm talking about or what this propulsion is actually called?

Hunt for Red October Comrade!

[p1t1o]

The magnetic fluid with the little spikes is called a "ferrofluid", its not the fluid that is magnetic here but microscopic particles of iron.

I dont think it is related to Magnetohydrodynamics though, which deals more with the manipulation of fluids which themselves have electric or magnetic properties, like plasmas and other conductive fluids.

[b0ss]

No it's a little different from colloid thrusters (SciShow just did an episode recently on those), and i distinctly remember there being spikes not unlike ferrofluid but definitely not actual ferrofluid.

[p1t1o]

13 minutes ago, b0ss said:

No it's a little different from colloid thrusters (SciShow just did an episode recently on those), and i distinctly remember there being spikes not unlike ferrofluid but definitely not actual ferrofluid.

Are you sure it wasnt a ferrofluid?

https://phys.org/news/2017-07-spiky-ferrofluid-thrusters-satellites.html

 

[b0ss]

Yup. It was something else covered by SciShow a long time ago, it was something about propelling tiny postage-stamp sized craft to explore extrasolar star systems or something, but I can't find anything about it

[p1t1o]

So the only thing we have to go on, are:

It is a low thrust/high efficiency thruster.

That somehow involves a fluid that can create "spiky" structures in a magnetic field.

The fluid is not a ferrofluid.

That works by using an electric charge to repel droplets/particles/ions of itself away at high speed.

But isnt a colloid/electrospray thruster...

 

 

Well unless someone at SciShow has made a mistake, Im stumped.

 

[SuperFastJellyfish]

4 hours ago, b0ss said:

Yup. It was something else covered by SciShow a long time ago, it was something about propelling tiny postage-stamp sized craft to explore extrasolar star systems or something, but I can't find anything about it

The only place I've heard the term 'postage-stamp sized craft' was the Breakthrough Starshot concept, but that uses a ground-based, phased array of lasers, afaik.  I'm at work otherwise I would look it up.

[b0ss]

20 hours ago, Cheif Operations Director said:

Hunt for Red October Comrade!

what?

1 hour ago, SuperFastJellyfish said:

The only place I've heard the term 'postage-stamp sized craft' was the Breakthrough Starshot concept, but that uses a ground-based, phased array of lasers, afaik.  I'm at work otherwise I would look it up.

Well if it helps at all I distinctly remember the specification that the craft would be small enough to fit in your pocket

[StrandedonEarth]

"Magnetohydrodynamic" reminded me of a Clive Cussler novel (featuring his favorite protagonist Dirk Pitt) called Valhalla Rising. Magnetohydrodynamic thrusters became a favorite ocean-going ship drive in the Dirk Pitt universe. From that Wiki:

Quote

 Pitt also unravels the work of a brilliant, reclusive scientist who had made great advances in oil technology, traced the history and found the remains of a Viking settlement on the Hudson River, and discovered the remains of Captain Nemo's Nautilus and unriddled and improved its power system (a magnetohydrodynamic engine).

Following the MHD link leads to another wiki page, which had this to say about drives:

Quote

MHD is related to engineering problems such as plasma confinement, liquid-metal cooling of nuclear reactors, and electromagnetic casting (among others).

A magnetohydrodynamic drive or MHD propulsor is a method for propelling seagoing vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics. The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical.

The first prototype of this kind of propulsion was built and tested in 1965 by Steward Way, a professor of mechanical engineering at the University of California, Santa Barbara. Way, on leave from his job at Westinghouse Electric, assigned his senior-year undergraduate students to develop a submarine with this new propulsion system.^[17] In the early 1990s, a foundation in Japan (Ship & Ocean Foundation (Minato-ku, Tokyo)) built an experimental boat, the 'Yamato-1,' which used a magnetohydrodynamic drive incorporating a superconductor cooled by liquid helium, and could travel at 15 km/h.^[18]

But there was no mention of any spacecraft drive...

[YNM]

To be honest, the heating of solar corona have been proposed to do with magnetohydrodynamics, so perhaps it's not too far-fetched to use MHD to fling particles (generating thrust).

[Cheif Operations Director]

On ‎3‎/‎27‎/‎2018 at 1:20 PM, b0ss said:

what?

Well if i

t helps at all I distinctly remember the specification that the craft would be small enough to fit in your pocket

Its a movie

[Scotius]

Book was much better than the movie, but that opening scene kicked all kinds of behinds

[Zeiss Ikon]

But in the book, Jack Ryan and the crew of Dallas concluded that Red October's "caterpillar" drive wasn't MHD (though you could build an MHD pump/drive using sea water as the working fluid -- in the book they decided the superconducting magnets needed were impractical for a submarine), but rather sound-baffled mechanical pumps (like a jet boat's drive, only REALLY BIG and with slower flow).  In the movie, they kept it as MHD because it was easier to hand-wave a new technology than to explain how the economically strapped Soviet navy could have deployed something Americans knew about, but considered impractically expensive).  The movie also completely deleted everything about Cardinal, the spy inside the Soviet apparat who had already given information about Red October -- including photographs during construction -- to the CIA.

The reason MHD won't work for a sea drive is that it's impractical to make a magnetic field large enough and dense enough, at the same time, so you wind up needing to pass enough electric current through the water to virtually boil it in order to get enough pumping action to use the thing as propulsion.  When pumping liquid metal, as with reactor cooling, it's a lot easier, because the metal is a good conductor, and you can pump in the throat of a venturi and keep the magnetic field compact, so less current is needed.  Look on YouTube for "NaK fountain" to see an example using the eutectic alloy of sodium and potassium, which is liquid at room temperature but far lighter than mercury -- it's used for certain cooling applications, because it stays liquid over a very wide temperature range, can be pumped without contact except the conduction plates, and has very high conductivity compared to water-based coolants.