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Sensor Substitution

A final option for pointing control after target acquisition is to substitute tracking information from the AST to the IPS control loop instead of the data from the OSP. This mode was designed for Astro-1 in case the IPS were to malfunction (as it did). Unfortunately, various problems, including poor knowledge of the alignment, errors in the coordinate systems used, and timing errors in the control loop also prevented sensor substitution from working. All these problems have been resolved, and this mode should provide another viable pointing control method for Astro-2.