Andrew Aurigema explains how to build a DIY replication of the patented Exodus Propulsion Technologies propellantless propulsion system using a low-tech, DIY ion thruster design. Aurigema is co-founder of Exodus Propulsion Technologies, a space startup developing next-generation propulsion systems based on the Asymmetrical Electrostatic Pressure concept. To date, his propulsion team has created, tested and documented more than 1500 separate “thruster” test articles in air, oil, and vacuum, and is involved with ongoing research into meta materials, electrostatic field interactions, RF based thrust generation and more.

In this interview, Andrew Aurigema and Falcon Space co-founder Mark Sokol discusses the construction of a Styrofoam-sealed, epoxy-coated unit with copper foil electrodes and generated ~0.1 millinewtons of thrust at 40kV. While achieving ~1 millinewton is possible at higher voltages, this force is insufficient to lift the device itself. Testing revealed that a vacuum environment improves thrust, but requires robust, printed structures (e.g., PVA or plastic) to withstand the pressure changes. High vacuum (10⁻⁵ to 10⁻⁶ torr) is optimal, but challenging to achieve and dangerous due to high voltages.

Paschen’s Law is relevant, showing the relationship between voltage, pressure, and electrical breakdown. Andrew Aurigema strongly discourages using high voltages (above 40kV) due to safety concerns. While alternative gases like sulfur hexafluoride could extend operational range, they are environmentally unfriendly and impractical. Atmospheric pressure operation with a sealed box is recommended. The speaker has built approximately 1500 iterations of the thruster and encourages safe replication, emphasizing the importance of proper sealing and wiring.

The Humble Beginnings: A Styrofoam-Based Design

The journey began with a surprisingly rudimentary design: a 1x1x1 unit cube constructed from Styrofoam, sealed with UV-cured epoxy.  The core of the thruster consists of a copper foil tape arranged in a U-shape, connected using wire and carbon paper. This acts as an electrode, connected to a metal grid acting as a heat sink, embedded within the Styrofoam. (00:00:15) The asymmetrical design of the copper foil creates an uneven pressure surface, crucial for generating thrust. The key is the precise separation distance between the grid and a grounded plate, maintained by the Styrofoam to prevent shorting. This simple setup, sealed with silicone sealant and Kapton tape to withstand high voltages (10⁶-10⁷ V/m), generates thrust through the electrostatic field between the grid and the ground.

Understanding the Force: Micronewtons and Milligrams

The thrust generated by this initial design was surprisingly small: around 100 micronewtons (0.1 millinewtons) at 40kV. To put this in perspective, that’s roughly equivalent to the weight of 10 milligrams – about the weight of a small piece of paper or a butterfly wing. While insufficient to lift the thruster itself, early tests using a long string showed slow rotation over time, demonstrating the presence of thrust. These initial tests were conducted in open air.

Vacuum and Voltage: Pushing the Boundaries

The discussion then shifted to the potential for improvement using a vacuum. While higher voltage in a vacuum promised increased thrust, the Styrofoam proved unsuitable due to expansion and structural degradation under vacuum conditions. This led to the adoption of 3D-printed PVA or plastic structures, allowing for much smaller gaps between the electrodes (e.g., ⅛ inch polycarbonate or glass). This refinement yielded approximately 0.5 millinewtons of thrust.

However, achieving optimal performance required a high vacuum (10^-5 to 10^-6 torr), a significant challenge requiring specialized equipment and expertise. The podcast strongly cautions against attempting this without proper knowledge and safety precautions. (00:03:30) The discussion delved into Paschen’s Law, highlighting the complex relationship between voltage, pressure, and electrical breakdown. Dry air, less conductive than humid air, allows for triboelectric charge buildup, influencing the thruster’s performance. (00:04:00)

Atmospheric Pressure vs. Vacuum: A Balancing Act

The podcast emphasizes that optimal operation occurs either at atmospheric pressure or at ultra-high vacuum (10^-6 torr). Low vacuum, while visually interesting due to plasma effects, is inefficient and prone to arcing. The use of gases like sulfur hexafluoride or Freon 156A was mentioned as a possibility to extend the operational range, but their environmental impact, cost, and handling difficulties make them less desirable. The podcast strongly recommends sticking to atmospheric pressure with a properly sealed enclosure.

Beyond Atmospheric Pressure: High-Pressure Hydrogen

Interestingly, the discussion also touched upon the possibility of operating at pressures higher than atmospheric. High-voltage switches operating at 20 atmospheres of 100% hydrogen gas were cited as an example, capable of switching 100,000 volts without arcing. This technology, while older, has been used in applications such as linear accelerators and even by SpaceX.

Safety First: A Word of Caution

The podcast repeatedly stresses the importance of safety. The voltages involved are lethal, and improper wiring or inadequate sealing can lead to serious injury. The creators strongly discourage operating at voltages above 35,000-40,000 volts. They encourage safe replication, video recording of experiments, and a thorough understanding of the underlying physics. The design is open-source, but the potential dangers cannot be overstated.

Conclusion: A Stepping Stone to Greater Things

This miniature ion thruster, while producing only a minuscule amount of thrust, represents a fascinating foray into the world of high-voltage physics and spacecraft propulsion. Its simplicity makes it an excellent learning tool, but always remember to prioritize safety and proceed with caution. The iterative development process, involving over 1500 iterations, highlights the importance of experimentation and refinement in achieving even modest advancements in this field.