결함안전기능이 고려된 위성용 흑체시스템에 관한 연구

Abstract

The infrared (IR) Sensor has been applied to the observation satellite for military purpose, surveillance, and environmental sciences. IR Sensor has non-uniformity caused by the time elapses and repetitive on/off operation in-orbit in a wide range of reference temperature and it causes degradation of the IR image quality. In order to acquire a high quality IR image, the non-uniformity characteristic of the IR sensor should be calibrated using blackbody system to provide radiance temperature at various temperature ranges. For example, Olschewski et al. [1-2] proposed blackbody system mounted on Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). This blackbody system is composed multiple number of blackbody to provide various temperature. Each blackbody is controlled by thermoelectric cooling element, thereby increasing the volume and the weight of the overall system. To overcome the drawbacks of the conventional systems, Oh et al. [3-4] proposed a blackbody system, which can provide the reference temperature ranging from low to high temperature using a single blackbody and can calibrate the non-uniformity characteristics of the IR sensor. In this blackbody system, however, a temperature sensor for estimating the surface temperature of the blackbody is embedded inside of the blackbody, thereby it increases the thickness of blackbody, and difficult to insert the sensor. A heat pipe for transporting the residual heat to the outside after heat up the blackbody is mounted perpendicular to the blackbody to minimize temperature gradient on blackbody surface. However, thermal conductance value of the heat pipe could be seriously declined due to the deflection of the heat pipe under serious launch vibration and on-orbit thermal environments. This leads to the performance degradation of the blackbody system due to the loss of heat rejection performance from the blackbody to the radiator. In this study, we proposed an on-board blackbody system to provide representative surface temperature for radiometric non-uniformity calibration of spaceborne IR sensor at various temperatures. The thermal design for blackbody includes a heater to heat-up the blackbody and a radiator with heat-pipe to reject residual heat of the blackbody after calibration. The main advantage of the proposed blackbody is the application of dual heat pipes for implementing a fail-safe function when one heat pipe is failed in on-orbit. In addition, the thermal interface design for heat pipes installation does not affect the temperature uniformity of the blackbody, which is important factor to precisely estimate representative surface temperature. The effectiveness of the proposed design was investigated by on-orbit thermal analysis. The representative surface temperature of blackbody was also estimated based on the analysis results. In addition, blackbody heat-up test was performed under ambient condition to investigate the surface temperature uniformity of the blackbody.