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Shanghai scientists have shoulders to the wheel of far side lunar rover
01.07.2019

    Shanghai scientists have shoulders to the wheel of far side lunar rover

    Photo provided by the China National Space Administration shows a wheel of the lunar rover Yutu-2. The rail system of China’s Chang’e-4 probe and the wheels of Yutu-2 were researched and manufactured in Shanghai.
     
    Shanghais technological expertise is helping China’s space scientists explore the far side of the moon.
     
    Launched on December 8, China’s Chang’e-4 lunar probe, comprising a lander and a rover, landed on the far side of the moon on Thursday morning.
     
    The Shanghai Academy of Spaceflight Technology, a member of the China Aerospace Science and Technology Corp, researched and manufactured a number of subsystems on the lander and rover. 
     
    They include 28 mobility, structure, data transmission, power and electronic units.
     
    The lunar rover, Yutu-2, or Jade Rabbit-2, left the first “footprint” on the far side of the moon late on Thursday, after it separated from the lander via two rails developed by scientists from the academy.
     
    “Thanks to accurate designs, the rails ensured the rover got off the lander smoothly, in spite of the rugged terrain,” said Zhang Yuhua, deputy chief commander and deputy chief designer of the Chang’e-4 probe.
     
    Zhang, who has been working on China’s space exploration mission for 17 years, said it was challenging work.
     
    The South Pole-Aitken Basin, where the spacecraft landed, is full of hills and valleys. If the rover had slipped off the rail, the whole mission would have failed, she said.
     
    The No. 805 institute of the academy was in charge of the mobility subsystem. It developed pawls on the six wheels of the rover to catch with pawls on the rails.
     
    Scientists with the institute also managed to decrease the weight of the rover’s mobility system to prevent it slipping, sinking or rolling, said Liu Dianfu, the directing designer for the mobility subsystem of Chang’e-4.
     
    The mobility system is only 20.5 kilograms to support the 135-kilogram rover, the lightest-ever lunar rover. Though each wheel is only 735 grams, lighter than the wheel of a common baby pram, the rover can climb over 20-centimeter-tall rocks and run at 200 meters per hour.
     
    Further, each of the six wheels is individually driven, and four are steering wheels to make the Yutu-2 move freely. Even if one of the wheels was trapped, the other wheels can pull the rover out, Zhang said.
     
    Power supply was another major challenge, with long lunar nights.
     
    The moon rotates on its axis once every 28 days, so every night/day of moon lasts 14 Earth days. 
     
    Temperatures on the moon also vary between extremes of some 200 Celsius degrees and minus 200 degrees.
     
    Local scientists designed “sleeping” and “awakening” modes for the lander and rover.
     
    Before sunset, the rover will find an appropriate place, pack up the masts and solar panels, and power down.
     
    When the sun comes around it will power up and resume working again.
     
    Napping conditions were also designed for the extremely high temperature in the lunar day. 
     
    The Yutu-2 has entered the “napping” mode and is expected to resume moving on Thursday.
     
    “We managed to increase the conversion efficiency of solar cells to 30.84 percent, 3 percentage points higher than the predecessors,” said Xu Zefeng, who is in charge of the power subsystem for the Chang’e-4 mission.
     
    “The more powerful solar array can ensure the lander and rover be awakened every time,” he added.
     
    The design lifetime of Yutu-2 is three months, the same as its predecessor that actually worked for more than two and half years.
     
    Compared with Chang’e-3, Chang’e-4 has to communicate with the Earth through the relay satellite Queqiao, or Magpie Bridge, from the far side of the moon.
     
    The communication system of Chang’e-4 has to be more sensitive since the transmitting power of the satellite becomes weaker, said Huang Bo, a researcher with the academy in charge of the data transmission subsystem for Chang’e-4.
     
    “It is like the voice becoming lower so the ear has to be more sensitive,” Huang said. His team managed to double the sensitivity of Chang’e-4’s communication system.