Abstract: A "bang-bang", i.e. digital tracking system for a remote laser designated target having position, rate and acceleration errors. The system is responsive to the sign of the error signal (up/down, right/left) in relation to boresight as opposed to the amplitude of the received signal output from an optical quadrature detector to determine the occurrence of two consecutive zero crossings of boresight following a system gain change where there is a change in sign for consecutive signal detections and as a result thereof reduces the size or amplitude of the digital control step which is utilized to determine the limit cycle of the oscillation of the tracker's optics. Additionally, an estimate of the velocity error is determined from the number of signal detections between successive zero crossings, i.e.

Abstract: Crystals formed of a solid-solution of NiSiF.sub.6 6H.sub.2 O provide very good materials for filtering ultraviolet light and will not deteriorate in temperatures as high as 115.degree. C. They are particularly useful in sensing devices which seek to identify the presence of ultraviolet light in the UV missile warning band.

Abstract: Crystals formed of a solid-solution of K.sub.2 Ni(SO.sub.4).sub.2 6H.sub.2 O provide very good materials for filtering ultraviolet light and will not deteriorate in temperatures as high as 110.degree. C. They are particularly useful in sensing devices which seek to identify the presence of ultraviolet light in the UV missile warning band.

Abstract: Crystals formed of a solid-solution of Ni(BF.sub.4).sub.2 6H.sub.2 O provide very good materials for filtering ultraviolet light and will not deteriorate in temperatures as high as 110.degree. C. They are particularly useful in sensing devices which seek to identify the presence of ultraviolet light in the UV missile warning band.