How should we set up a satellite network of space weather stations around the Earth? What type of instrument is optimal for this task?
Modern society relies heavily on electronic equipment. In space, this equipment can easily be disturbed or even damaged by intense bursts of particles or radiation emitted by the Sun. Most of these bursts are shielded by the atmosphere, which becomes ionized in its outermost layer – the ionosphere. However, the random bursts drive random fluctuations in the ionosphere. These fluctuations are referred to as space weather and have a severe impact on radio transmissions down on Earth as well as up into space.
In order to predict the space weather, we need to set up a large network of sensor stations. Economic, small satellites of the CubeSat type would be ideal for this, but they require a lightweight instrument such as an electric probe – a small metallic cylinder that collects and analyzes the charged particles. The physics of this collection is complicated and today’s space probe instruments rely on simplified models, which assume that the ionosphere is in equilibrium. This is not clearly the case since the random bursts constantly knock the ionosphere out of its resting state.
SPACEPROBE will develop a method for using electrical probes to measure the complete, non-equilibrium properties of the ionosphere. Capturing these rapid events requires advanced electronics, which will be prototyped and validated in a laboratory plasma chamber. The measurement will also be protected against errors caused by the emission bursts’ impact on the spacecraft itself. Another common error is that of aging and contamination of the probe surfaces. This will be investigated in detail, using experimental methods for advanced materials characterization. The knowledge will be used to outline the design, operation and performance of a space-grade instrument, fit for implementation aboard CubeSats.
The measurement scheme utilizes an underlying physical theory, which was originally developed for measurement probes that are standing still in the plasma. Therefore, we have started investigating the limits of the applicability and performance of this theory in the case when the probe is aboard a satellite flying at 7 km/s (around 25 000 km/h) in orbit around the Earth. For this purpose, we use supercomputers for running plasma simulations of millions of particles and track how they are collected by the probe. Our initial results indicate that the theory holds well also in this case of orbiting satellites.
SPACEPROBE will develop new plasma measurement methodology for use on small satellites. The large-scale aim is to enable integration aboard many satellites orbiting the Earth in a space weather monitoring network. The project will result in an electrical probe measurement technique for the electron energy distribution (EEDF), which provides information about the non-equilibrium processes in the ionosphere and facilitates extraction of the electron density and temperature without relying on equilibrium probe theories. To achieve good spatial resolution of small-scale plasma fluctuations while preserving accuracy, the voltage sweep speed limits will be determined. A laboratory prototype system will be developed and tested in a plasma chamber. Special emphasis will be put on making the measurement robust against spacecraft charging under conditions such as in the particle-bombarding auroral regions, so that useful measurements can be achieved also in these strong non-equilibrium conditions. SPACEPROBE will also perform a laboratory investigation of the impact of the probe surface properties on the measurement. Finally, the project will define system requirements and produce a System Design Description for the implementation of the methodology onboard CubeSats. This last step will consider the possible tradeoff between measurement performance and system footprint in terms of electrical power, size, weight, thermal management and data processing and transmission bandwidth.