Abstract: A pressure relief valve having two rigid sealing surfaces lapped to a smoothness Ra of 8 micro-inches or less, and flatness within 80 micro-inches, forms a reliable seal by direct contact therebetween without an elastomer. The sealing surfaces and surrounding structures can be made of one or more metals, such as alloys of stainless steel, and can be CTE-matched, so that the valve is not impeded by environmental temperature changes. In a disclosed embodiment, a “poppet” is axially pressed against a seal plate by a spring. The poppet can be axially stabilized by sliding within a surrounding cylinder or spacer, and can contact the surrounding surface with a plurality of “arms” that reduce friction and enable gas flow therebetween. The poppet can be made from anti-galling Nitronic 60 alloy, and the surrounding structures can be stainless steel. Embodiments are suitable for low-pressure gas applications in extreme environments.

Abstract: A pressure relief valve having two rigid sealing surfaces lapped to a smoothness Ra of 8 micro-inches or less, and flatness within 80 micro-inches, forms a reliable seal by direct contact therebetween without an elastomer. The sealing surfaces and surrounding structures can be made of one or more metals, such as alloys of stainless steel, and can be CTE-matched, so that the valve is not impeded by environmental temperature changes. In a disclosed embodiment, a “poppet” is axially pressed against a seal plate by a spring. The poppet can be axially stabilized by sliding within a surrounding cylinder or spacer, and can contact the surrounding surface with a plurality of “arms” that reduce friction and enable gas flow therebetween. The poppet can be made from anti-galling Nitronic 60 alloy, and the surrounding structures can be stainless steel. Embodiments are suitable for low-pressure gas applications in extreme environments.

Abstract: Either of two scenes of interest may be detected by use of a scanning sensor having a rotatable polygonal scanning mirror coupled to receive incident radiation from such scenes of interest. Apparatus is included for directing such incident radiation onto a detection device. A movable shutter is coupled to block receipt by the mirror of radiation from the first scene of interest when the second scene of interest is viewed, and vice versa.