One of the many technologies being considered for future space flight programs are ion thrusters, which come from a subset of propulsion known as electric propulsion.
They’re particularly popular for their high efficiency and long accelerating times. Unlike chemical propulsion systems, which only have enough fuel to launch the rocket out of orbit, ion thrusters have fuel that can last many years. By inertia, constantly excreting this fuel allows them to accelerate bodies to extremely high speeds over time.
In short, they operate by ionizing propellant (usually xenon) and producing plasma, which can be manipulated by electric and magnetic fields to form thrust. If you’d like an in-depth explanation of ion thruster operation, you can read “2.1 Basic Ion Thruster Operation” from my review paper on Hall thrusters.
Building An Ion Thruster
I decided that I wanted to build an ion thruster — or at least a demonstration of the concept. It’s definitely not rocketship-worthy, but it uses similar mechanisms to show how ionic thrust/wind can be produced.
For my supplies I used:
- Battery container from a flashlight (mine held 3 AAA batteries)
- Boost step-up power module (DC6–12V to 1000kV)
- 3 metal screws (~6 cm in length is ideal)
- 3 aluminum cans (mine were Brisk Tea cans)
- Copper wire
- Crocodile clip
- Electrical tape (or heat shrinks)
- Binder clip
- Receipt (or another type of thin paper)
- 3D Printer (I used the Ender 3 V2)+ filament
- Hot glue
- Double-sided tape
3D Printing The Parts
I first started off by designing the components that would hold the thruster in TinkerCAD, an easy-to-use software for designing 3D prints.
- Platform A holds the stand and the can holder.
- Platform B holds the screw holder and has a lid. This platform is hot glued to platform A when it’s printed.
- The stand is made to have a receipt attached to it via binder clip.
- The screw holder fits into a flat component that can be moved on platform B. This allows me to adjust the distance between the screws and the cans.
- The platform lid goes onto the right platform after the screw holder is placed in.
- The can holder holds 3 cans.
Pro tip: When designing components made to fit into each other, make sure that the part that goes inside the hole is slightly smaller than the hole. I made the mistake of making them the same size and had to reprint some components a few times.
I printed these components over the course of a few days (they generally took between 5–13 hours to print) using white PLA filament. I used Ultimaker Cura as the slicer, with regular settings at 10% infill. If you want to print the components faster, I printed the lid and can holder at 150 mm/s instead of 50 mm/s, and they still turned out fine.
The battery container served as the power source and was (manually) connected to the power module through the green and red wires to achieve greater voltage (Approxiamately 4.5 volts to 1000 kV). I secured the power module and battery container on platform B using double-sided tape.
This is the same power module that’s used in tasers, so you have to be careful while using it. I made sure that whenever I was moving components that the battery container was far from the green and red wires that connected it to the power module. I also made sure to not touch conductive components (wiring, nails, metal, etc.) while it was operating.
One wire on the opposite end of the power module was connected to a copper wire using electrical tape. That copper wire was then wrapped around the three screws in the screw holder. Wrapping the copper wire around the three screws allowed all of them to receive voltage.
Pro tip: I would recommend copper-plating the screws to make them more conductive. You can do this by putting a lemon’s worth of lemon juice + 2 pinches of salt + 20 pennies in a bowl with your screws. After waiting a few hours, your screws will be darker/copper-colored. (I ran out of lemons, so I couldn’t copper-plate my screws)
The cans were placed on the can holder in a stacked position using no adhesives (they balanced on each other). Then I connected the other wire from the power module to one of the cans using a crocodile clip and some electrical tape.
The last part is putting in the stand. Then I attached a receipt paper to it using a binder clip. The movement of this paper will signify the production of ionic wind.
Fully assembled, the ion thruster should look something like this:
How Does It Work?
This model demonstrates how ionic wind can be produced using the basic mechanisms used in ion thrusters.
Providing voltage to the screws causes them to act as positively charged anodes, while providing voltage to the cans causes them to act as negatively charged cathodes. This generates an electric field.
The screws make good anodes because they’re sharp, and the cans make good cathodes because they’re round. The point of the anode allows the charges to become packed together, making the electric field stronger around that location. In fact, it becomes strong enough to rip negatively charged electrons from the surrounding air, turning them into positively charged ions.
These positively charged ions are now repelled from the positively charged anodes (screws) and attracted to the negatively charged cathodes (cans). As they’re moving towards the cathodes, they also bump into and knock electrons out from other air molecules, creating more ions that move towards the cathodes. These ions move through the cathodes as ionic wind, which you can see pushing the receipt when the ion thruster is operating.
Here are some videos of the ion thruster in operation. You can see that I manually connect the power module wires to the battery container, although you could design a switch if you wanted to. In the third video you can see the plasma at the tips of the screws as air molecules are being ionized.
This model is not perfect, and I definitely think that there are a few things that could be improved, such as:
- The screws could have been copper-plated and centered better. Centering the screws better would require some alterations to the original design of the screw holder.
- Certain parts of the 3D printed components could have been made smaller to save printing time and filament.
- A switch could have been added to the power part of this model so that the wires from the power module did not need to be manually attached to the battery container. It would have also made using this model safer.
Overall, however, I’m happy with the product, since it successfully produced ionic wind and even visible plasma.