A precise visual localisation method for the Chinese Chang’e‐4 Yutu‐2 rover

Abstract

Precise localisation of the Yutu-2 moon rover plays an important role in path planning, obstacle avoidance and navigating to target features. To provide highprecision localisation information, a stereo bundle adjustment method using the theory of the unit quaternions is presented for the first time. To improve the precision and robustness of the proposed method, the rover's pose, from a visual odometry technique assisted by an inertial measurement unit and the rotation angles of the mast mechanism, is viewed as a pseudo-observation. A reasonable weighting strategy and a rational geometric constraint condition of the stereo cameras is also invoked. Experimental results demonstrate that the proposed method provides more accurate localisation results than either a bundle adjustment alone or a weighted total least-squares method. The proposed method has been successfully used in Chang'e-4 mission operations. (a) Chang'e-4 lander (b) Yutu-2 rover FIG. 1. The Chang'e-4 probe. (a) An image taken by the Yutu-2 rover's Pancam camera of the lander. (b) An image taken by the lander's topographic camera of the rover.The Photogrammetric Record

Lunar Surface Fault-Tolerant Soft-Landing Performance and Experiment for a Six-Legged Movable Repetitive Lander

“…The leg distribution design needs to meet landing and roving functions simultaneously. On the one hand, to withstand the impact force uniformly during buffer landing, all legs are arranged as an equilateral polygon like a regular triangle in Surveyor-1 [ 2 ] or Square in Apollo program [ 3 ] and Chang’e series [ 4 , 6 , 28 ]. As for the six-legged lander, the angular interval between adjacent legs should be 60°.…”

“…Nowadays, the separated design of an immovable lander and rover is still the core method of zero-distance exploration on the moon. Many countries have made world-renowned achievements such as the Soviet/Russian Luna-9 [ 1 ], the first lander to achieve lunar soft-landing, which absorbs impact energy using four airbags; American Surveyor-1 [ 2 ], the first legged lander to reach the lunar surface, which uses three three-branch buffered legs filled with aluminum honeycomb material, providing technical support for Apollo program [ 3 ]; Chinese Chang’e 4 [ 4 ] reaches the far side of the moon first, which utilizes four similar buffer legs. Notably, all these landers are immovable and are designed to help the rover finish landing, so their exploration capacity is restricted to around the fixed landing site.…”

“…Notably, all these landers are immovable and are designed to help the rover finish landing, so their exploration capacity is restricted to around the fixed landing site. Two kinds of rover are applied to expand the exploration range, one is a manned lunar rover, like LRV [ 5 ], which can carry up to two astronauts, another is the unmanned wheeled rover, like Yutu 1 & 2 [ 4 , 6 ], which can maneuver quickly with scientific instruments. However, the separated design of the lander and rover creates a heavy and complex prober system.…”

“…For a three-legged lander like Surveyor-1, the remaining two legs cannot support the lander. As for four-legged landers like Apollo 11 [ 3 ] or Chang’e 3, 4, & 5 [ 4 , 6 , 28 ], the center of mass of the lander will move to the side of the supporting triangle constructed by the remaining three legs, leading to a failed buffer landing on the uneven lunar surface. Therefore, hard strict standards are required for the manufacture and control of such landers and would be abandoned if any failures occur.…”

Lunar surface soft-landing analysis of a novel six-legged mobile lander with repetitive landing capacity

“…Luna16 8 that uses four inverted triangle legged is the first probe to achieve soft-landing and sampling return task on the backside of the Moon. The cantilevered soft-lander with a four-legged structure is applied in Appollo-11, 9 EuroMoon2000, 10 SELENE-B, 11 Chang’e-3 & 4 Program, 12,13 etc. Generally, all four legs are evenly distributed on the bottom of the lander at a 90° interval.…”