We have developed a new IR optical system that consists of three mirrors and four lenses, and that operates in the temperature range 8°C-32°C. This temperature range can induce thermoelastic deformation in the lenses and their mounting subassembly, leading to a large defocus error associated with the displacement of the lenses inside the barrel. We suggest using a new three-shell-based athermalization structure composed of two materials with different coefficients of thermal expansion (Invar and aluminum). A finite element analysis and the experiment data were used to confirm that this new athermalization barrel had a defocus error sensitivity of 11.6 nm/°C; this is an improvement on the widely used conventional single-shell titanium barrel model, which has a defocus error sensitivity of 29.8 nm/°C. This paper provides the technical details of the new athermalization design, and its computational and experimental performance results.

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The fundamental role of stabilization loop in seeker application is to precisely follow the angular rate command which is proportional to the antenna bore-sight error during the target tracking. In order to achieve this requirement, it is prerequisite to highly isolate the gimbaled antenna from the missile body motion due to the maneuvering or low frequency vibration during flight. However, the isolation ratio and stability margin of stabilization loop adopting the gimbaled platform with both low stiffness and heavy inertia are limited by mechanical characteristic such as low resonance frequency and its high magnitude. Therefore, a multi -mass model, which can accurately presents the frequency behavior of the gimbaled platform, is indispensable to design of an optimal stabilization controller. In this paper, a pragmatic three-mass model for the direct-drive gimbaled platform from the motor to the antenna is introduced, and also the PI 2L controller that produces both the high gain at low frequency and high stability margins by combining a PI 2 controller with lead compensator is presented. In the end, the performance and the stability of designed stabilization loop are demonstrated using simulation and experiment results in both frequency and time domain.