Significance   The technical characteristics and development process of four generations of EO (electro-optical) targeting pod are compared. The design focus and key points of each generation are summarized. Focusing on the overall design of the detection system of AN/AAQ-33 Sniper XR ATP pod and AN/ASQ-228 ATFLIR pod, as well as the newly emerging fourth generation products such as Litening 5 and Talios pods, this paper provides a reference for the development of the new generation EO targeting pod detection system.

  Progress  Firstly, the ratio of optical aperture to pod diameter (ROP) is defined as a standard for measuring the integration level of optical machinery and servo control system. The higher the ROP is, the higher the system integration degree is. 　　Secondly, the optical system of ATP and ATFLIR is analyzed, which are regarded as the typical 3rd generation targeting pod, both adopt the series common optical path architecture of front telescope system and servo frame platform are placed at the head of the pod. And the compressed parallel beams are introduced into the beam splitter and rear detection/laser emission system which are placed at the middle of the pod through the optical hinge and fast steering mirror (FSM). The two pods' small field of view (sFOV) is about 1.5°×1.5°, and the wavelength is 0.7-0.9 μm & 3.7-4.8 μm, and their modulation of transfer function (MTF) are close to diffraction limit. A refractive front telescope system like ATP with φ150 mm common optical path is forward designed, and the result verifies the optical system considering the servo frame platform can be installed into a pod of φ305 mm diameter, and the ROP is 0.492; A off-axis three mirror astigmatism (TMA) front telescope system like ATFLIR with φ150 mm common optical path is forward designed, and the result verifies the optical system can be installed into a pod of φ330 mm diameter, and the ROP is 0.455 (Fig.4, Fig.7). 　　Finally, as a comparison, the optical parameters of Litening 5 and Talios (Fig.9-10) are introduced, which are regarded as the fourth generation targeting pods. The detection systems adopt a parallel common cabin layout, with all the optical payload and servo frame platform installed inside a sphere with φ406 mm diameter, and their largest optical apertures are still φ150 mm. The ROP of Litening 5 and Talios is 0.37 and 0.38, much lower than ATP and ATFLIR, indicating low integration levels. Litening 5 pod addes a shortwave infrared imaging band, which has high fog penetration ability; Talios pod addes the step-and-stare scan imaging ability; Both of them add visible light color imaging function to improve detection and recognition probability. However, based on the optical design analysis, ATP and ATFLIR can easily modify their optical systems to achieve these functions, indicating the two pods have strong vitality due to their forward-looking overall architectures, and the improvement of ATFLIR optics is much easier than that of ATP.

  Conclusions and Prospects  In the future, the targeting pod needs to integrate functions such as air-to-air detection, laser communication, and directional infrared countermeasures (DIRCM), and must have high functional density. The series layout architecture using a pure reflection common path front telescope system, optical hinges, FSM, rear detection/laser emission system has strong scalability and expansibility.