CHANG E 3-6: FROM ROVERS TO SAMPLE RETURN

China now sketched out a sequence for its subsequent lunar missions, the main spokesperson being program director Ye Peijian. Although the dates appeared to move around, the fundamental sequence did not, namely two rovers (Chang e 3 in 2013, Chang e 4 later) and then 2-m core sample return missions (Chang e 5 in 2017, Chang e 6 later). Chang e 3 was expected to double the size of the previous missions and weigh up to 3,750 kg, requiring a CZ-3B launcher. The objectives of the mission were listed as to survey the topography and geological structure of the Moon, to analyze the content and the distribution of its mineral and chemical elements, to explore the Earth’s plasma layer from the Moon, and to carry out optical astronomy observations from the Moon. The mission profile was for it to first enter a 100-km circular orbit, adjusted to 100-15 km for the descent maneuver. At the 15-km point, retrorockets would bring the craft down from a velocity of 1.7 km/sec to dead stop at an altitude of 2 km. Smaller throttleable engines would then bring the craft down to 100 m as its radar searched for a debris-clear crater-free landing area, the engine being commanded off at 4 m for a final free fall, with crushable material in its landing legs.

Chang e 3 was expected to deploy a small rover with a plutonium 238 nuclear power source to keep it warm for the lunar nights. The six-wheel rover would investigate the material and geological composition of the surface for a minimum of 90 days. Considerable effort was devoted to hazard avoidance during landing: the landing radar would be loaded with terrain features identified by Chang e 2’s reference data, which the incoming spacecraft would match against its own radar and steer the lander to the right, flat point. At an early stage, landing, radar, and hazard-avoidance tests were carried out in the eastern Xinjiang desert, selected as the best Earthly analogue to the Moon for testing out lunar rovers and other equipment to function on the Moon.

Models of the mother craft and rover were exhibited at the Zhuhai air show in 2009. The lander had a descent camera to image the surface during the landing, a

topographic camera to photograph the landscape and the rover moving across it, an extreme ultraviolet camera, and an astronomical telescope to focus on a number of astrophysical objects to magnitude +15. The rover had a panoramic camera, x-ray spectrometer, infrared spectrometer, and radar [14].

Chang e 4 was expected to be a follow-up rover mission, much as Chang e 2 had followed Chang e 1, but at the south pole. In the meantime, work began on the sample return mission, Chang e 5. Studies began of the best return route for samples, even sketching out a return path on a given date (1st July 2016) and the navigation systems for take-off from the lunar surface while work started on the drill that would bring a core sample back to the Earth, much as Luna 24 had done as far back as 1976 [15]. The schedule projected was:

Chemical map of the landing area for the Chang e 3 rover. Courtesy: Chen Shengbo.

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1000

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Magnetic map, identifying anomalies to be explored using the Chang e 3 rover. Courtesy: Chen Shengbo.