ABSTRACT
The spacecraft surface repels ambient electrons and attracts ambient positive ions. For the repelled charged species, the distribution shifts to the left on the plot. This is because every particle loses an energy qϕ when it arrives at the surface. Retarding potential analyser has been used for many years for measuring the energy distribution of incoming charged particles. Another popular type of instrument for measuring charged particle distributions is the plasma analyzer. The principle is essentially that of a mass spectrometer, although the charged particles have the same mass with an energy distribution. Particles of different energies can be received by different receptor electrodes. Instead of measuring particle energies, experiments have been done to measure the potential difference Δϕ between the tip of a long boom and the satellite body.
