China Chang′e 4 Probe

Introduction The Moon, while one of the closest celestial body to Earth, in many ways has been mostly forgotten since the largely publicized Apollo missions of the 1960s and 1970s. With the success of a few missions in its space newly claimed state space agency to the Moon, China has plans to continue its study of the lunar surface. This time they plan to study the southern polar region on the dark side of the moon, a place that until recently had been restricted as an lunar landing sites due to technological limitations at the time they could only able to visit the midlatitudes of the moon. (Li et al., 2019) The mission is called Chang'e-4 probe it provided humanity’s first-ever soft landing on the far side of the moon to study a few different aspects of the lunar surface from within the largest, oldest, and the deepest crater on the moon known as Aitken Basin. Body The mission which is being operated by the CNSA (China National Space Administration) is the current mission in a long line of Chang’e probes that have been going to the moon to land or survey from afar for a few years. While technically Chang'e-4 was the backup of Chang’e -3 it did possess different scientific equipment, allowing for different examination. The mission launched on a Long March 3B from Xichang, China, on 7 December 2018.  The landing site was in the 186 km diameter Von Karman crater in the northwestern South Pole-Aitken Basin (45.5 S latitude, 177.6 E longitude). Since the lander is on the far side, the Moon is blocking direct radio contact with the Earth, so a relay satellite is used for communications. The Chang'e four landers was a backup to the Chang'e three mission with the same basic structure, a landing platform, and a rover, but a different science payload. The lander has a dry mass of 1200 kg, carrying its experiments and the rover. The experiments include a low-frequency (0.1 - 40 MHz) radio spectrometer (LFS), a Landing Camera (LCAM), Terrain Camera (TCAM), a Lunar Lander Neutrons and Dosimetry Experiment (LND), and a biological experiment. It includes a rover, Yutu 2, based on the Chang'e 3 Yutu ("Jade Rabbit") rover. The rover, with a total mass of 140 kg, has a rectangular body 1.1 meters high, 1.5 m long, and 1 m wide, but unlike the Chang'e-3 rover will not have a robotic arm. It has six wheels, two solar panels, and a dish antenna. Its scientific payload comprises cameras, including a Panoramic Camera (PCAM), a Visible/Near-Infrared Imaging Spectrometer (VNIS), Lunar Penetrating Radar (LPR), and the Advanced Small Analyzer for Neutrals (ASAN). Chang'e 4 entered lunar orbit on 12 December. After three weeks of lunar orbital maneuvers, Chang'e-4 landed in Von Karman crater in the South Pole-Aitkin Basin on 3 January 2019 at 02:26 UT becoming the first spacecraft to make a controlled landing on the far side of the Moon. The far-side landing location meant that during the final phases of the approach, Chang’e-4 was on its own, and could not be operated remotely. Starting from an altitude of 15 kilometers, the probe used a rocket booster to brake and briefly hover. Meanwhile, an on-board camera and a laser ranging system scanned the terrain to avoid boulders. Landing coordinates were calculated within 20 meters from LRO images as 45.457 S latitude, 177.589 E longitude. The Yutu-2 rover was driven down ramps onto the surface about 12 hours later, at 14:22 UT. The rover moved forwards towards a small crater and turned on its instruments. On 6 January the rover went into a planned hibernation to protect itself from the heat of lunar noon and reawakened on 10 January and continued traveling and making measurements. The rover shut down over the local lunar night, beginning about January 13-14. Both the lander and rover used a radioisotopic heat source to maintain survival temperatures. Yutu-2 resumed daytime operations on 29 January, and the lander a day later. It has been hibernating during the lunar night and operational during the day, as planned. It started its fifth lunar day on 29 April. Chang'e-4 uses a communication relay satellite, in a halo orbit around the Earth-Moon L2 point to maintain communication between the lander and Earth ground control. The satellite, Queqiao, “has been circling around a gravitationally stable point about 60,000 kilometers beyond the Moon since it launched in May” (Castelvecchi, 2019) 2018. It’s based on the Chang'e two design, launched on 20 May 2018 to enable communication with the far side. Two scientific microsatellites, Longjiang-1 and Longjiang-2, were launched with Queqiao. With such an historic accomplishment its very surprising that China would keep so many things about the mission a secret. Apparently, the Chinese space program has kept many details about the mission secret — including the planned timing of the landing — even from scientists who collaborated with it. Before the touch-down, Robert Wimmer-Schweingruber, a physicist at the University of Kiel in Germany who has a radiation-detection experiment on the lander, said that he expected to find out about the landing from Chinese news sites. Conclusion In conclusion, this mission, while one of many in the chain of its mission designs the Chang’e-4 like those before it, is a stepping stone. Never before has humanity landed on the dark side of the moon on one of the poles no less. It has proven that with the advancements in laser imaging that can map an area before touching down, giving the spacecraft a spot for a soft touch down is possible and doable and needs no outside help for operators on the ground. It’s a major step forward for the China National Space Administration and China as a country, in becoming of the a few countries to land objects on other celestial bodies. References Li, B., Yue, Z., Zhang, J., Fu, X., Ling, Z., Chen, S., … Yao, P. (2019). High-Resolution Terrain Analysis for Lander Safety Landing and Rover Path Planning Based on Lunar Reconnaissance Orbiter Narrow Angle Camera Images: A Case Study of China’s Chang’e-4 Probe. Earth and Space Scien technological ce. https://doi.org/10.1029/2018EA000507 Castelvecchi, D. (2019). China becomes first nation to land on the Moon’s far side. Nature. https://doi.org/10.1038/d41586-018-07796-x Sellers, J. J., Astore, W. J., Giffen, R. B., & Larson, W. J. 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