Axial Field Pulsed Thruster for CubeSat Propulsion earthweb.ess.washington.edu/space-propulsion ---------------------------------------------------------- --------------------------------------------------------- Advanced propulsion Laboratory Department of Earth & Space Sciences ------------------------------------------ ----------------------------------------- Chayse Aubuchon, Ian Johnson, 2015 Undergraduate Research Robert Winglee Symposium Contact: [email protected] ---------------------------- --------------------------- Abstract Pulsed Plasma Thrusters (PPT) represent a simple, lightweight, cost effective solution for in-space propulsion onboard small, power-limited spacecraft. PPTs operate by electromagnetic and electrothermal acceleration of a solid propellant, creating a high velocity, low mass exhaust plume. A thruster’s impulse bit is the product of the ablated mass and its velocity. To increase the impulse bit, and therefore the thrust efficiency (exhaust power / input power) of the PPT, an axial magnetic field was added around the discharge chamber region. The addition of a 0.1-1kG field to the thruster will increase the gyromotion of the electrons in the discharge region, which in turn will increase the mass ablation and ionization rate of the thruster, both of which will increase the impulse bit. The field should better confine the expanding gas to prevent perpendicular thermal expansion. Initial perpendicular gyromotion will be converted to parallel axial velocity as the particles travel downstream and into a weaker magnetic field. Current testing with Langmuir probes and a high speed camera will compare varying magnetic field configurations and determine if the applied field adds to the thrusters total thrust efficiency. An electromagnet was chosen over a permanent magnet for laboratory testing to allow for variations to the fields strength and shape. The Concept Pulsed Plasma Thruster (PPT) is hybrid electromagnetic (J r xB θ ) and electrothermal (pressure gradient) in-space propulsion thruster. • Historical operation: main discharge across propellant surface between anode/cathode creates moderate J r &B θ and large ΔP • Previous research has added external B θ with little success • We are adding external B z to increase ΔP -- analogous to magnetic nozzle -- B z will impart a θ gyromotion increase thrust -- Increase e - in source increase ablation & ionization -- Axial fields decreased radial plasma movement -- V perp to V parallel as field weakens increased axial velocity Previous Experiments Current Experiment Peak field strength of 780G Dipole magnetic field configuration Experiment built from apparatus of Solid Fuel High Power Helicon in collaboration with Eagle Harbor Technologies, Inc. - 1” diameter coaxial PPT with Teflon propellant - 60uF main discharge capacitor rated to 2kV (120J) - 780G base field from six electromagnets - PPT in the center of a dipole magnetic field This testing of a high energy (100J+) laboratory thruster designed for interplanetary travel called the High Power Helicon. - New experiment to determine if results scale to CubeSAT size and power Shown on the far left is the PPT (within plasma) placed the within dipole magnetic field (6 concentric brown magnets) and (left) the downstream plasma plume. Construction and Results to Date: - Results show increased light emissions increased ablation - Typical PPT ablates ~2μg/J of Teflon - 32J PPT discharge (66μF capacitor charged to 980V) - Solenoid: 60 wraps, 1.2” diameter, 1” length, 133μH - 33μF capacitor charged to 570V - Results in 260A discharge creating ~5kG peak field Acknowledgments Future Improvements: - Machine wound solenoid (uniform field) - Move PPT electrical connections, allowing solenoid to be closer to surface - Removable solenoid - Isolate RLC circuit to avoid magnetic interference with instruments - Optimize timing of field with respect to thruster discharge I would like to thank the graduate students in the Advanced Propulsion lab for all there help. This would not have been possible without their guidance and advice. Special thanks also to the people at the Mechanical Engineering Machine Shop for their help in creating all the parts needed for this experiment. Traditional coaxial PPT Circuit (top), Telfon PPT (left & center), Sulfur PPT mounted within a CubeSAT (right). Solenoid Magnetic Field = 0 Inductor Equation = − Field as function of V = 0 4 Plume with external B-field Plume without external B-field