Chang'e 4

Chang’e-4 is a Chinese lunar mission that became the first spacecraft to successfully land on the far side of the moon. The mission was launched in December 2018 and touched down in early January 2019. Landing on the moon’s far side is a challenge because it is constantly facing away from Earth, making any direct communication with a spacecraft impossible. The Chang’e-4 mission solved that problem by using a relay satellite in lunar orbit to send data back to Earth. The mission also included a lunar rover named the Yutu-2. The mission’s goals included a radar study of the moon’s geology, radio astronomy observations, and even an attempt to grow plants on the lunar surface. In 2024, Chang’e-4 and Yutu-2 were still operational. China subsequently launched Chang’e-5 and Chang’e-6.

Background

As Earth’s only natural satellite, the moon has been one of the primary targets of exploration since humans became capable of launching vehicles into space in the mid-twentieth century. Both the Soviet Union and the United States sent probes to the moon in the early 1960s. The United States was the first, and as of 2024, the only nation to send manned missions to the moon, initially accomplishing the feat in July 1969.

As the Soviets and the Americans were starting their respective programs in the late 1950s, the Chinese began developing their own space technology. For decades, Chinese progress was slowed by political instability and the government’s focus on military control of the program. In 1993, China reorganized and modernized its space program, creating the China National Space Administration (CNSA). Under the guidance of CNSA, China’s space program grew quickly, and by 2003, the Chinese became only the third nation to successfully send an astronaut into space.

That same year, CNSA began its Chinese Lunar Exploration Program, better known as the Chang’e program. In Chinese mythology, Chang’e was a goddess who fled to the moon after drinking an elixir of immortality. The first Chang’e mission launched in 2007 and was the first Chinese spacecraft to orbit the moon. Chang’e-2 was launched in 2010 and designed to map the lunar surface and scout sites for future landing attempts. Chang’e-3 landed on the moon in December 2013, deploying a lunar rover named Yutu. Yutu, meaning “jade rabbit,” was a celestial rabbit whose outline can supposedly be seen from Earth in the patterns on the moon’s surface.

Overview

CNSA’s next lunar mission was Chang’e-4, which was planned for a December 2018 launch. Chang’e-4 would attempt to land on the far side of the moon, a feat that had never been accomplished before by any nation. Because of Earth’s gravity, the moon’s twenty-eight-day rotation matches the time it takes to make one revolution around Earth. This means the same side of the moon is always facing Earth. As a result, any spacecraft that landed on or orbited the far side of the moon would lose contact with Earth. American astronauts encountered this problem during lunar missions in the late 1960s and early 1970s.

In May 2018, China launched the Queqiao communications satellite into a special orbit to act as a relay device. The satellite was stationed at a point where the combined gravities of both Earth and the moon would hold it in place. The spot gave the satellite direct sightlines to Earth and the moon’s far side. The Chang’e-4 spacecraft was launched from the Xichang Satellite Launch Center in south-central China on December 8, 2018.

The Chang’e-4 landing vehicle was about 14.4-feet (4.4-meters) wide and weighed about 2,646 pounds (1,200 kilograms). It carried several cameras that monitored the craft during descent and photographed the terrain around the lander. It also contained an experiment to study radiation in space and a radio telescope to observe the thin lunar atmosphere, the sun, and other space objects. The lander even included an experiment to study how silkworms and several types of plant seeds would grow in lunar gravity.

The lander also carried the Yutu-2 rover, a six-wheeled vehicle about 3.8-feet (1-meter) tall and 5-feet (1.5 meters) long. The rover weighed about 309 pounds (140 kilograms) and had two foldable solar panels to draw power from the sun. In addition to a number of cameras, the Yutu-2 carried a ground-penetrating radar system to measure the thickness of the moon’s crust and an infrared spectrometer to analyze minerals in the lunar soil. The rover also included a device that measured charged particles emitted by the sun.

Chang’e-4 arrived in lunar orbit on December 12, 2018, and successfully landed on the moon’s far side on January 3, 2019. The spacecraft touched down in the Von Kármán crater near the lunar south pole. The site was chosen because it was the site of an ancient impact that may have left part of the moon’s inner mantle exposed. Scientists hoped to use the rover’s equipment to study this region to learn more about how cosmic impacts influenced the formation of the moon and the early solar system.

Ten hours after landing, the Chang’e-4 deployed its lander on the lunar surface. Both lander and rover took photos of their surroundings—the first photos of the lunar far side ever taken from the surface. In another first, Chinese scientists reported that cotton seeds sent with the lander started to sprout just a few days after the landing. It was the first time humans had ever grown plants on another world. However, the plants died a few days later when the Chang’e-4 was forced to power down.

Though the far side of the moon is often called the “dark” side of the moon, it gets an equal amount of sunlight as the side facing Earth. When one side is bathed in sunlight, the other is covered in darkness. After a period of two weeks, the two sides switch night and day. Both the lander and the Yutu-2 are designed to temporarily shut down during the two-week lunar nights to save power and preserve their equipment in the frigid temperatures.

The planned year-long mission was still providing scientists with data as of 2024. The CNSA launched additional missions to the lunar surface, including the Chang’e-5 in 2020 and Chang’e-6 in 2024. Chang’e-5 collected and brought back lunar soil samples. It was the first of the missions to return to Earth. Chang’e-6 brought back soil samples from the far side of the moon. China planned to launch Chang’e-7 in 2025 and Chang’e-8 in 2028.

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