The γ-off sensor is an important sensor product in the application of lunar probe navigation guidance and control system.It collimates γ photons to the lunar surface and receives y photons backscattered on the lunarsur-face.By counting y photons,it is used to measure the height of the probe from the lunar surface in real time during the landing of the lunar probe on the lunar surface.A series of actions such as closing the brake engine enable the lunar probe to land on the moon stably and reliably.Aiming at the differences between the calibration and applica-tion scenarios of the γ altimeter in the lunar environment and the earth environment,based on the physical model of γ photon altimeter,the static characteristics of the γ altimeter in atmospheric environment and vacuum environment were simulated and calculated.The influence of the vacuum environment on the measurement accuracy of the γ shutdown sensor was analyzed,and the lunar landing environment simulation system was constructed for verifica-tion.The comparison between the vacuum environment and atmospheric environment was obtained The effect of the count rate is less than 10%,and the height error of about 40cm will be generated near the expected shutdown height.The analysis results can be used for the calibration and conversion of the Cislunar height of the sensor prod-ucts,to carry out height correction,and to guide the engineering development of the products.
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