28 December 1992 Rugged yet lightweight: how can we achieve both in optical instruments?
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Today’s optical instruments must be lightweight, rugged, and economical. In the past, these three requirements were usually considered to be mutually exclusive. These demanding requirements are now being satisfied in a new class of optomechanical instrument designs. Creating rugged, yet lightweight optical instruments requires the use of new design techniques. New optomechanical design techniques include new materials, structural optimization, insensitive optical configurations, isolation of systems from environmental effects, and active control.

Rugged design implies a severe service environment. Typical severe service environments include mechanical shock, high inertial loading, mechanical vibration, temperature extremes, nuclear radiation, environmental contamination, and user abuse. Effective design requires precise knowledge of both the actual service environment and the effects of the service environment on the system.

Lightweight is a controversial word, but is usually taken to mean systems that are lower in mass than conventional systems. For example, a lightweight telescope primary mirror is defined as being lighter than a solid mirror of the same diameter and stiffness. A key parameter in lightweight systems is the ratio of stiffness to weight. This parameter affects response to both inertial and dynamic loading.

New materials include both newly developed materials, such as the metal matrix composites, and non-traditional metallic materials, such as titanium. Structural optimization is applied to improve stiffness to weight. Telescope primary mirrors are optimized by contouring the back of the mirror; support structures are optimized so that parts of the structure serve more than one purpose. Insensitive design includes traditional structural practice and clever optical design. An Airy point supported beam is highly resistant to dynamic and inertial loading. Tube bending is compensated by passive optical design in relay systems. Isolation from environmental effects includes the use of enclosures and vibration isolation systems. Finally, active control is used to reduce weight and stiffness of systems, while still maintaining optical alignment through the use of position sensors and actuators.

Design examples of rugged and lightweight systems include cryogenic space optics, ultra-lightweight telescopes, and large astronomical astrographic lenses. A 0.5 m, 15 kg, fused silica mirror for the Space Infrared Astronomical Facility operated successfully at 9 K, demonstrating the use of materials selection, structural optimization, and isolation from temperature effects. A series of ultra-lightweight telescopes, up to 0.4 m aperture, employs new metal matrix composite materials, and structural optimization. Passive optical compensation for temperature effects, non-traditional metallic materials, and isolation are effectively employed in a 2 m focal length, f/10 astrometric objective.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Daniel Vukobratovich, Daniel Vukobratovich, "Rugged yet lightweight: how can we achieve both in optical instruments?", Proc. SPIE 10265, Optomechanical Design: A Critical Review, 1026503 (28 December 1992); doi: 10.1117/12.61100; https://doi.org/10.1117/12.61100

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