Electric propulsion for small satellites

Abstract

The University of Malta Astronics research group has been developing a family of low-cost compact PocketQube (PQ) picosatellites, with the smallest having a total mass of under 250 g and dimensions of a 5 cm cube. PQ picosatellites with different complementary subsystems onboard can be attached together to form larger satellites. These PQs are set to navigate in the Low Earth Orbit (LEO) envelope in large constellations, where they will experience very little atmospheric drag, resulting in a slow orbital decay. In the event of system failure, the PQ, which will be travelling at a velocity greater than 7400 m/s will be re-classified as space debris, threatening future missions and orbital spacecraft with possible collisions. A failsafe methodology is to launch the PQs into a lower meta-stable orbit where they will naturally de-orbit in a relatively short time when malfunctions occur. In this case, Electric Propulsion (EP) systems are utilised to actively maintain the satellite’s orbit while the mission is underway. This thesis describes the development of an entire propulsion system contained within a 1P PQ module and provides a detailed analysis of the elements that affect the PQ while navigating the LEO envelope. An investigation in the latest EP technology resulted in the Pulsed Plasma Thruster (PPT) being the most promising technology for developing miniaturised propulsion systems. However, scaling down this technology to the tight volumetric, weight and power constraints of the PQ standard presents new challenges. A low-cost, compact Power Processing Unit (PPU) with effective Electromagnetic Interference (EMI) mitigation measures and potential system level radiation hardening has been developed for this project. Multiple coaxial and electrothermal PPTs with possible carbonisation mitigation measures having a discharge energy of around 310 mJ have been investigated as part of this study. The results include the orbital decay simulation of the PQ, the PPU behavioural and functional tests, electric field strength simulations of two coaxial and electrothermal PPTs, the operation analysis of the developed PPTs, and the discharge voltage waveform of the coaxial PPT.