Information Bandwidth Problems in Instrumentation of Missile Flight Tests

The operation of missile flight-test instrumentation systems at minimum bandwidth is an important economic consideration. Design of instrumentation systems may become difficult or impossible unless intelligently chosen bandwidth parameters are specified. Since nearly all missile flight-test instrumentation systems operate as sampled data devices, the bandwidth parameter shows up as a sampling rate requirement. It can be shown, under fairly general conditions involving no highly restrictive assumptions, that the rate of information acquisition of a sampled-data instrumentation system, when considered as a function of sampling interval, has a maximum. This can be readily appreciated intuitively. For a position-measurement system, for instance, if the sampling interval is made very short, the amount of information gained with each subsequent sample is very small because of the large amount of prior information about the position of the object being measured. No information would be gained if a sample were taken an infinitesimally small time after an initial measurement. Also, a very long time interval between samples would permit considerable growth of ignorance about the object´s position, but the logarithmic information-gain function would grow slowly compared with t^-1; so the information rate for long sampling intervals would also be a small number. Somewhere between these two cases lies at least one maximum in information rate. The selection of a sampling rate corresponding to the maximum information rate is recommended as a good choice for many types of missile test instrumentation systems.