Stereo topographic mapping concept for the upcoming Luna-Resurs-1 orbiter mission

Abstract

We report on the Lunar Stereo Topographic Camera (LSTC), currently being developed for the upcoming Luna-Resurs-1 Orbiter mission, which will perform observations from an orbit with the altitude to be optimized in the range from 50 to 100 km. The LSTC is composed of two identical optical heads and a common data processing unit. Each optical head has a similar optical system and an area array detector of 5120 × 3840 pixels, covering an area of 14 × 10 km (cross-track x along-track) from a 50-km spacecraft orbit. One of the optical heads looks forward within the orbit plane and the other looks backwards. The mission will focus on mapping mid- and polar latitudes up to 80° north and south to derive cartographic/topographic data products needed to support navigating future Luna-Resurs lander missions in polar regions. Extensive image simulations were produced to study the effects of illumination conditions and shadows on surface coverage and the precision of digital image matching for stereo photogrammetric processing. Also we studied a variety of possible off-nadir angles of the two camera systems and how these might affect the point measurement accuracy. We found that off-nadir angles of ±12.5° is a reasonable compromise to maximize topographic accuracy in varying observation conditions over both flat and rugged lunar terrains. Also, we investigate data compression algorithms at different compression ratios to minimize the impact of compression artifacts upon the photogrammetric image processing. The LSTC will take up to 400 images per orbit, i.e., 4800 images per day. During one month, we expect to cover 20% of the lunar surface on average, including the northern or southern polar areas. Imaging schemes and operation schedules will be optimized to maximum stereo coverage while producing the best DTM quality. We propose to increase the orbit altitude from the minimum altitude of 50 km to 70 km to enhance both along and cross track image overlap, yielding more geometrically stable image blocks.