Quasi‐thermal noise and shot noise spectroscopy on a CubeSat in Earth's ionosphere

Abstract

AbstractWe investigate the practicality of using quasi‐thermal noise (QTN) and shot noise spectroscopy on a CubeSat in the Earth's ionosphere and constrain the satellite antenna length for optimal detection of these signals. The voltage spectra predicted for thermal Langmuir waves (QTN) and particle “shot noise” are modeled, and it is shown that the signals detected can provide two very good, independent, passive, in situ methods of measuring the plasma density and temperature in the ionosphere. The impact of the antenna potential ϕ is also discussed, and we show that the negative potential calculated for the ionosphere due to natural current flows has a significant impact on the voltage power level of the shot noise spectrum. The antenna configuration is also shown to play an important role in the shot noise, with a monopole configuration enhancing the spectrum significantly compared with a dipole. Antenna lengths on the order of 20–40 cm are found to be ideal for ionospheric plasma conditions, nicely matching CubeSat sizes and producing detectable thermal Langmuir waves and shot noise at the microvolt level. Further, with a continuous stream of data points at different latitudes and longitudes an orbiting CubeSat can produce a global picture for the ionospheric plasma density and temperature using QTN and shot noise signals. If implemented, especially in a constellation, these data would be more frequent and cover a much greater domain than current ground‐based or single‐satellite methods. This could lead to improved ionospheric models, such as the empirically based International Reference Ionosphere.