During the Acquisition and Safe Hold (ASH) mode, attitude of FORMOAT-5 (FS5) satellite is not fully controlled. Direct sun exposure on Remote Sensing Instrument (RSI) sensor of the satellite telescope may occur. Effect of the sun exposure on the RSI sensor performance is investigated to evaluate the instrument’s survivability on orbit. Both satellite spin speed and sun exposure duration are considered as the key parameters in this study. A simple radiometry technique is used to calculate the total sun radiance exposure in order to examine the integrity of the RSI sensor. Total sun irradiance on the sensor is computed by considering the effect of spectral variations through RSI’s five-band filter. Experiment of directly exposing the sensor to sun on the ground was also performed and no obvious performance degradation was found. Based on both analysis and experiment results, it is concluded that FS5 RSI sensor can survive from the direct sun exposure during the ASH mode.