The operations of analyzers A and B can be programmed independently. Consider the measurement cycle time of the plasma instrument if onboard software were not available to improve the operational efficiency. Thus the spin modes are each designed to obtain a specific type of plasma measurement during one spacecraft rotation, e.g. , a three-dimensional velocity distribution, high angular and energy resolutions of an ion beam, and the mass composition of an ion beam. A spin mode is constructed of nested control loops. The angular sectors are referenced to a fixed position on the celestial sphere by means of information from the spacecraft attitude control system.
Instrument software is available for five basic types of spin modes.
Default values for the sequence tables are also included in read-only memory in the instrument processor in lieu of values from ground commands. We briefly illustrate below the capabilities of the various spin modes. Spin mode 1. Survey of positive ion and electron velocity distributions. The number of angular sectors, the energy range, and the number of energy passbands are selected by ground command.