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Abstract

An optical system utilized to provide guidance information in the form of a modulated beam for a beamrider missile during its rocket powered flight phase. Our system comprises first and second zoom type optical subsystems arranged to function cooperatively in object space, utilizing coincident lines of sight, with these optical subsystems serving to provide guidance information to the missile when the exhaust plume from its rocket engine is relatively difficult to penetrate. The first optical subsystem is utilized in a closed loop servo system for positioning a mirror gimballed about two axes, such that it continuously tracks the missile. The second optical subsystem, along the optical axis of which the modulated beam is directed, comprises a negative optical group and a positive optical group combined into a defocusable beam expander. These groups are initially defocussed, and during flight of the missile, the negative group is movable in a linear manner away from the positive group, toward the focussed position, so as to maintain by utilization of the gimballed mirror, a constant beam diameter at the missile. This beam contains guidance information for directing the missile to a selected target, and quite advantageously, these positive and negative groups are constructed to be individually free of spherical aberration and coma, such that the shape of the transmitted beam is not disturbed in any of the zoom positions.

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