Chang'e 4

• 1. The First Touchdown On The Far Side

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  At 02:26 UTC on the 3rd of January 2019, a robotic lander touched down inside Von Kármán crater. This moment marked the first time any spacecraft had ever landed on the far side of the Moon. Direct radio communication with Earth is impossible from that location because the Moon itself blocks all signals. Engineers had to solve this problem years before the landing attempt began. They launched a relay satellite named Queqiao in May 2018 to orbit behind the Moon at the L2 point. This satellite acts as a bridge between the distant rover and mission control on Earth. The Chang'e 4 mission was originally built as a backup for the earlier Chang'e 3 mission. It became available after Chang'e 3 successfully landed in 2013. Chinese engineers modified the design to handle the rough terrain found on the lunar far side.

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• 2. Relay Satellites And Microsatellites

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  Queqiao carries a large antenna designed to receive X band signals from the lander. It relays those messages back to Earth using S band frequencies. The satellite took twenty-four days to reach its final halo orbit around the Earth-Moon L2 point. Two smaller microsatellites named Longjiang-1 and Longjiang-2 traveled alongside it during launch. Both were developed by Harbin Institute of Technology in China. Longjiang-1 failed to enter lunar orbit but Longjiang-2 succeeded. Longjiang-2 operated until the 31st of July 2019 when it crashed into Van Gent crater. That impact created a small four by five meter crater on the surface. These tiny satellites observed the sky at very low frequencies ranging from one to thirty megahertz. No observations in this frequency range have been done from Earth orbit due to interference from the ionosphere. This data offers potential breakthroughs in understanding energetic phenomena from celestial sources.

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• 3. Scientific Payloads And Biological Experiments

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  The lander carried several instruments including a Landing Camera and a Terrain Camera. A Low Frequency Spectrometer researched solar radio bursts between 0.1 and 40 megahertz. A neutron dosimeter developed by Kiel University in Germany measured radiation levels for future human exploration. The rover held a Panoramic Camera capable of rotating three hundred sixty degrees. It also carried a Lunar Penetrating Radar with a probing depth of approximately thirty meters. A sealed biosphere cylinder contained seeds and insect eggs to test life support systems. Cottonseed, potato, rapeseed, Arabidopsis thaliana, yeast, and fruit fly eggs were placed inside. Environmental systems kept the container hospitable except for low gravity and high radiation. Within hours after landing the temperature was adjusted to twenty-four degrees Celsius. On the 15th of January 2019 reports confirmed that cottonseed, rapeseed, and potato seeds had sprouted. The experiment ended on the 16th of January 2019 when external temperatures dropped too low to maintain warmth.

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• 4. Operational Longevity And Scientific Discoveries

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  Yutu-2 traveled about one thousand five hundred meters during its first full lunar day. The rover went into hibernation for its first lunar night and resumed activities on the 29th of January 2019. It powered down again on the 11th of February 2019 for its second lunar night. In May 2019 scientists reported identifying what appear to be mantle rocks on the surface. This discovery addressed one of the mission's primary objectives regarding the Moon's internal structure. By the 21st of November 2019 Yutu-2 broke the lunar longevity record previously held by Lunokhod 1. That Soviet rover operated from the 17th of November 1970 to the 4th of October 1971. Chang'e 4 continued functioning well beyond its nominal three-month operating time. Engineers hoped it would operate for a few years thanks to design improvements. In January 2020 China released high-resolution images showing a lunar ejecta sequence. These images provided direct analysis of the far side's internal architecture using data from the Lunar Penetrating Radar.

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• 5. Global Partnerships And International Recognition

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  The Netherlands-China Low-Frequency Explorer instrument was developed by Radboud University in the Netherlands. Scientists from Sweden, Germany, and Saudi Arabia also contributed payloads to the lander and rover. NASA Administrator Jim Bridenstine congratulated China on the success of the mission. He called it an impressive accomplishment despite political tensions between the two nations. Martin Wieser of the Swedish Institute of Space Physics noted that the far side remains uncharted territory from the surface. The mission team received a Gold Medal from the Royal Aeronautical Society in November 2019. They were awarded the World Space Award by the International Astronautical Federation in October 2020. Both awards marked the first time a Chinese mission had won their respective rewards. This international collaboration represents the first major United States-China partnership in space exploration since the 2011 Congressional ban. China has agreed to allow future American Moon missions to use the Chang'e 4 probe and Queqiao relay satellite.

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