Simulation of an on-the-fly measuring system of a descent module under uncertainty of the lunar-surface composition

The measurement method for determining the motion parameters of the module de-orbiting upon the lunar surface has been suggested. The surface-scattered gammas emitted by a radioactive source are detected using four receptors under uncertainty of the lunar soil's elemental composition. The radar-tracking system in the module allows adapting the gamma-ray altimeter to the lunar-soil composition. A mathematical model of the measuring system has been put forward, and dependences of the gamma flux level on the module altitude and the angle of the slanted surface were obtained. The model makes it possible to analyze the relative position of the radioactive source and the receptors and the composition effect of the substrate. The measurement algorithm uses a recursive neural network, which is proposed to be trained in advance and adapted during the module landing.