Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2018, Vol. 15, No. 6, pp. 169-179
Simulation of optical navigation measurements during vertical descent onto the lunar surface
B.S. Zhukov
1 , V.A. Grishin
1 , S.B. Zhukov
1 , T.V. Kondratieva
1 , A.G. Tuchin
2 , V.S. Yaroshevsky
2 1 Space Research Institute RAS, Moscow, Russia
2 Keldysh Institute of Applied Mathematics RAS, Moscow, Russia
Accepted: 02.11.2018
DOI: 10.21046/2070-7401-2018-15-6-169-179
Computer simulations were performed of optical navigation measurements during the final stage of landing on the lunar surface when, after approaching the landing area, the spacecraft descends nearly vertically from a height of ~2 km. For this purpose, navigation camera images of the lunar surface were simulated with the interval of 1 s and the resolution improving from 1 m to 2 cm along a typical descent trajectory. The principal tasks of optical navigation during vertical descent can be construction of a risk map and using it to select a safe landing site, as well as measuring the horizontal velocity of the spacecraft. The accuracy of height and vertical velocity optical measurements was found to be insufficient. The proposed approach to risk map generation is based on analyzing image photometric nonhomogeneity that is related to complexity of surface relief. Its advantages are simplicity, fast image processing, shadow detection and the absence of significant requirements to spacecraft attitude and velocity stabilization. This makes it feasible to back-up a laser scanner for risk map generation. The spacecraft horizontal velocity was estimated by measuring landmark displacement in consecutive images using additional radio altimeter height measurements. The velocity estimation error decreased from ~1 m/s at heights more than 1 km to ~10 cm/s at 100 m and to ~1 cm/s below 20 m. Thus, this method can complement Doppler horizontal velocity measurements at small heights.
Keywords: autonomous optical navigation, landing on the Moon, measuring spacecraft horizontal velocity, risk map, landing site selection
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