Voltage Power Spectroscopy on a CubeSat in Earth's Ionosphere

Abstract

The practicality of detecting thermal Langmuir waves, charged particle impacts (i.e. ``shot noise”) and impacts from dust particles on a CubeSat in the Earth’s ionosphere are investigated in this thesis. The voltage power spectra predicted for thermal Langmuir waves (QTN) and particle shot noise are modelled for a dipole antenna, and shown to provide two good, independent, passive, in situ methods of measuring the plasma density and temperature in the ionosphere. If implemented, these data would be more frequent and cover a much greater domain than current ground-based methods, improving empirical ionospheric models. Antenna lengths 20 – 40 cm are found to be ideal for ionospheric conditions with QTN peaks and shot noise at the microvolt level, nicely matching CubeSat sizes. A monopole antenna response function is derived and QTN spectra are enhanced by an order of magnitude over the dipole. However, the function breaks down predicting shot noise and remains an area for future work. Using a NASA dust environment model, predictions for dust detection using the power spectrum show it useful only for large (approx. 4 microns or larger) single-particle impact events, which are rare. Assuming a CubeSat in a polar orbit at 300, 800, and 1,500 km altitude, the average dust spectrum is 3 times larger than the shot noise spectrum only once every 2,150, 110, and 225 min, respectively. Lastly, an amplifier circuit was built to detect the plasma wave signals inside a plasma chamber with conditions modelled on the lower ionosphere. An electron gun was used to produce the plasma and 3 exposed wires to simulate antennas. The amplifier was found to linearly amplify the weak signals inside the chamber across 0.1 – 1.5 MHz. Multiple peaks were measured and those at approx. 1.6 and 4 MHz were concluded to be the electron cyclotron frequency and Langmuir waves, respectively, albeit from the electron gun. Future work will require a less impactful plasma generator such as extreme UV light.