2
$\begingroup$

A South African company is developing a solid metal fuel thruster that was initially researched by NASA but was not further developed,

an electric reaction could be used to vaporise solid metal fuel, a process which then created a jet of fast-moving plasma that could propel a satellite

They hope to develop a system that can,

move stuff around in space with cheap and abandoned iron ore or other metals.

For such a system to work, would the metal fuel need to be powdered, granular or in a slab, ribbon or metal strip form?

$\endgroup$
2
  • 1
    $\begingroup$ That is a rather terrible article. It claims 3200 nanosatellites in orbit, possibly by lumping in Starlink satellites. It specifically calls a Starlink launch a "batch of nanosatellites", despite Starlinks being 20+ times as large as the largest nanosatellites, and it implies they tumble with no propulsion, when they have full control of their attitude and orbit. Aside from that...what kind of answer are you looking for? It could be a lot of things, but a ribbon or wire seems convenient and easy to handle. $\endgroup$ Oct 26, 2021 at 18:01
  • $\begingroup$ "cheap and abandoned"? Surely "cheap and abundant". $\endgroup$ Oct 27, 2021 at 1:42

1 Answer 1

2
$\begingroup$

Checking Google scholar for Jonathan Lun at Hypernova I found the title Development of a vacuum arc thruster for nanosatellite propulsion and then I found Lun's thesis Development of a vacuum arc thruster for nanosatellite propulsion

I'm not going to read the whole thing, I think another answer author can do that. Instead, here I'll address materials issues and physics related to making metal ions.


See also

From Hypernova Space Technologies (click for larger):

enter image description here enter image description here

If it's a metal gas

Generally ion sources operate in gas phase so that you can sustain a plasma so that neutral atoms can be hit by energetic electrons many times until one gets lucky and ionizes it. Then an electric field pulls it out, through a hole or grid, and accelerates it. Pressures are usually roughly around the point where breakdown is not too difficult. Fluorescent light tubes are a few Torr for example.

So heating a high vapor pressure metal could be one way, but now you've got basically a super-inefficient incandescent light bulb.

Instead of making a plasma, you can also use surface ionization. You use a high vapor pressure group 1 alkali metal (e.g cesium) and evaporate it in the presence of a catalyst like (probably hot) platinum, which will kindly remove its "superfluous" group I electron.

At least you're making a toaster rather than an incandescent light bulb.

It's not some kind of liquid metal field ionization device, but if it were...

A better way would be to use field ionization and/or a liquid metal ion source. I made both a gallium and a gold LIMS. Gold melted and flowed to a tungsten needle's tip where the high electric field ionized it. Gallium was inside a glass capillary tube and a tiny back pressure pushed it into the field where electrostatic forces (high electric field) pulled the liquid meniscus out into a liquid sharp tip.

In both cases the radius of curvature of the liquid tips were of order of one micron, so that the electric field was of order 10 volts per angstroms. At this point field ionization happens and metal ions are ripped from any atoms at the surface.

A thruster can be made from thousands or millions of nanofabricated needles and some liquid metal that flows out on to them at low temperature. There are plenty of low temperature eutectics but gallium is a great starting material; you can melt it in your hand. (29.76 °C)

See this answer to Troubleshooting a DIY Ion Thruster for a detailed discussion of field ionization. While it's in the context of an ambient gas rather than a liquid, the basic principle is the same.

It also links to Miniature Ion Electrospray Thrusters and Performance Tests on Cubesats; SSC12-VI-5 which describes the use of low vapor pressure ionic liquids (here you do not want them to evaporate!) but ionic liquids are just a more convenient substitute for a metal, as discussed in this answer to Why can't we build a huge stationary optical telescope inside a depression similar to the FAST? which describes the use of a spinning tub of ionic liquid instead of mercury to make a huge reflecting telescope mirror on the Moon.

Miniature ion electrospray thrusters under development at MIT are opening a new range of possibilities for applica- tions requiring precision thrusting, or for nano-satellite mission design. With a specific impulse (Isp) in excess of 2500 seconds, no moving parts and unpressurized tanks containing zero-vapor pressure liquid propellant, they can be integrated into cubesat compatible multi-thruster assemblies. The technology and the thruster performances are described in this paper in addition to the current development of cubesat compatible prototype assemblies for per- formance tests in space. The assembly under development in this research effort fits within 1/3 of one 1U cubesat and is designed to provide fine three-axis attitude control and precision thrusting, to deliver a total Delta-V in excess of 200 m/sec to 3U cubesats (3 kg). The overarching goal is to assess in flight the performances of the thrusters as precision actuators. Potential nanosat applications include attitude control and precision pointing, orbital adjust- ments, constellation control and maintenance, formation flight, re-entry, debris removal and other maneuvers.

Fig 1. iEPS modules fabricated in silicon (SPL) Fig. 2 Electron microscope images of ion emitting structures micro-fabricated in porous metals (6)

left: Fig 1. iEPS modules fabricated in silicon (SPL). right: Fig. 2 Electron microscope images of ion emitting structures micro-fabricated in porous metals6 (click for larger)

6D. Courtney and P. Lozano, Electrochemical micromachining on porous nickel for arrays of electrospray ion emitters, Journal of Mi- croelectromechanical Systems (submitted) (2012)

From that DIY thruster answer:

below: Slide 52 from Ion sources Ionization and desorption methods explains that the extremely strong field of order 1E+10 V/m needed to ionize atoms is obtained by a needle at 10 kV potential when the radius of curvature of the tip is decreased to 10 microns. As long as the distance to ground is large, it matters very little if it's 1cm or 10cm. From the point of view of the field at the sharp tip, that's nearly infinity. Almost all of the potential drop happens in the first millimeter or so, and the field is only high enough to ionize atoms or molecules at the very tip.

enter image description here


breakdown of gasses source

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.