Reliability improvement of low-cost camera for microsatellite

Abstract

Remote sensing is one of the most defective means for environment monitor, resource management, national security and so on, but existing conventional satellites are too expensive for common users to afford. Microsatellites can reduce their cost and optimize their image products for specific applications. Space camera is one of their important payloads. The trade-off faced in a cost driven camera design is how to reduce cost while still have the required reliability. This paper introduces our path to develop reliable and low-cost space camera. The space camera has two main parts: optical system and camera circuits. Commercial off-the-shelf (COTS) lenses are difficult to maintain their imaging performance under space environment. Our designed optical system adopts catadioptric layout, so that its temperature sensitivity is low. The material and structure of camera lens can bear the vibration and shock during its launch. Its mechanical reliability is approved through mechanical test. A window made of synthetic fused silica is used to protect the lens and CCD sensor from space radiation. Optical system is completed with compact structure, wide temperature range, large relative aperture, high imaging quality and pass through the mechanical test, thermal cycling and vacuum thermal test. Modular concept is developed within the space camera circuit, which is composed of seven modules which are power supply unit, microcontroller unit, waveform generator unit, CCD unit, CCD signal processor unit, LVDS unit, and current surge restrain unit. Module concept and the use of plastic-encapsulated microcircuits (PEMs) components can simplify the design and the maintainability and can minimize size, mass, and power consumption. Through the destructive physical analysis (DPA), screening, and board level burn-in select the PEMs than can replace the hermetically sealed microcircuits(HSMs). Derating, redundancy, thermal dissipation, software error detection and so on are adopted in the camera design phase. The degree of reliability of the circuits can achieve 0.98/0.5Year. Environmental tests, including vacuum thermal test, thermal cycle test and radiation test, verify the component reliability in the space environment.