The Chang'e 4 robotic probe, the first artifact to touch down on the moon's far side, was lifted atop a Long March 3B carrier rocket at 2:23 am Beijing time at the Xichang Satellite Launch Center in Southwest China's Sichuan province, Dec 8, 2018. (LIANG KEYAN / CHINA DAILY)
Mankind will soon be able to discover the far side of the moon as a Chinese lunar embarks on its journey toward the silver sphere early Saturday.
The Chang’e 4 robotic probe, the first artifact to touch down on the moon’s far side, was lifted atop a Long March 3B carrier rocket at 2:23 am Beijing time at the Xichang Satellite Launch Center in southwestern China’s Sichuan province, according to a statement from the China National Space Administration.
During its multi-week flight toward the moon, the probe will enter a lunar transfer trajectory and then orbit the moon before making an autonomous soft-landing on the Aitken Basin of the south lunar pole
During its multi-week flight toward the moon, the probe will enter a lunar transfer trajectory and then orbit the moon before making an autonomous soft-landing on the Aitken Basin of the south lunar pole, the statement said.
Tidal forces on Earth slow the moon’s rotation to the point where the same side always faces Earth. The other side, most of which is never visible from Earth, is the far side of the moon. However, it is not a “dark side” of the moon because the far side is as illuminated by the sun as the “near side” facing us.
Though the far side has been extensively photographed by spacecraft, starting with a Soviet probe in 1959, no probe had ever made a soft-landing on it so scientists around the world have yet to be able to conduct close observations and surveys of it.
The program’s scientific tasks are to perform low-frequency astronomical observations, to investigate landscapes, mineral compositions and geological structures of the landing site, and to conduct lunar environmental research on elements such as neutron radiation and neutral atoms, the administration explained.
"The soft landing and exploration of the far side, which has never been done before, will gain first-hand information about the terrain and lunar soil components and other scientific data, which will help enrich our understanding of the moon and the universe," said Zhang He, executive director of the Chang'e-4 probe project.
The Chang’e 4 mission will enable scientists to discover what they haven’t known about the moon. They also can take advantage of the far side’s shield against Earth’s interference to make clearer observations into deep space, scientists involved in the program noted.
Chang’e 4’s rover has six wheels, two solar panels, a radar dish as well as multiple cameras, show pictures published by the China National Space Administration.
China launches Chang'e-4 lunar probe in the Xichang Satellite Launch Center in Southwest China's Sichuan province, Dec 8, 2018. (JIANG HONGJING / XINHUA)
Liu Jizhong, director of China National Space Administration’s Lunar Exploration and Space Engineering Center, said that Chang’e 4 has been engineered to fit the complex landscape and sophisticated communication conditions on the far side of the moon.
In addition to Chinese scientific equipment, the Chang’e 4 mission also involves scientific apparatus developed by the Netherlands, Sweden, Germany and Saudi Arabia.
China started sending robotic probes to the moon in 2007 and has carried out several lunar missions since then. It landed the Chang’e 3 probe, which carried the first Chinese lunar rover, on the moon in December 2013. The Chang’e 3 mission marked first soft-landing by a spacecraft on the moon in nearly four decades.
The next step in China’s lunar exploration agenda, the Chang’e 5 mission, is scheduled for 2019 and will put a rover on the lunar surface to take samples and then bring them back to Earth.
Nobody had ever seen the far side of the moon before the Soviet Union launched the Luna 3 probe in 1959, which was the first-ever mission to photograph the far side.
The United States Apollo 8 mission sent three astronauts to fly around the moon in 1968, the first time that people saw the moon's far side with their own eyes.
Remote-sensing images show the far side is thickly dotted with impact craters and has much fewer lunar mares than the near side. Scientists infer that the lunar crust on the far side is much thicker than the near side. But why so is still a mystery.
"As no astronauts or rovers have ever landed on the far side, we know little about it except for speculation based on remote-sensing images," Zhang said.
Scientists hope to land the probe in an area with many geological features such as the transition zone between highlands and basins to get more scientific information.
The region (Aitken Basin) is believed to have great research potential, and is at a similar latitude to the landing site of Chang'e-3. The sunlight there can ensure the probe's energy supply
But engineers worry about the safety of the landing and the rover, and are searching for relatively flat areas.
After careful analysis, the experts chose the Von Karman Crater, named after a Hungarian-American mathematician, aerospace engineer and physicist, in the Aitken Basin, as the landing site.
The region is believed to have great research potential, and is at a similar latitude to the landing site of Chang'e-3. The sunlight there can ensure the probe's energy supply.
However, the chosen landing area for Chang'e-4, which is a smaller crater within a larger crater, is much narrower than the landing site of Chang'e-3, and the terrain is more rugged, posing great challenges for the landing, said Wu Xueying, deputy chief designer of the probe.
"So the landing accuracy of Chang'e-4 must be higher than Chang'e-3," Wu said.
In addition, landing and roving on the far side of the moon requires a relay satellite to transmit signals.
China launched the relay satellite "Queqiao", meaning Magpie Bridge, on May 21 to set up the communication link between the earth and the moon's far side.
The satellite has successfully entered a halo orbit around the second Lagrangian (L2) point of the earth-moon system, about 455,000 km from the earth. It is the world's first communication satellite operating in that orbit, said Zhang Lihua, chief designer of the satellite from the China Academy of Space Technology.
In orbit, the relay satellite can "see" both the earth and the far side of the moon. The earth's and moon's gravity balances the orbital motion of the satellite and makes it very fuel-efficient.
VISITORS FROM CHINA
Named after Chinese moon goddess "Chang'e", China's lunar exploration program, which began in 2004, includes orbiting and landing on the moon, and bringing samples back to earth.
The country's first lunar probe, Chang'e-1, was launched in 2007, making China the fifth country to develop and launch a lunar probe on its own.
Chang'e-2, launched in 2010, created a full lunar map with a resolution of 7 meters, as well as images of the Sinus Iridum, or the Bay of Rainbows, with a resolution of 1.5 meters, showing the details of the proposed landing site of Chang'e-3.
After accomplishing its tasks, Chang'e-2 flew to the L2 point of the sun-earth system about 1.5 million km from earth to conduct scientific experiments. It was then tasked to fly by and observe the Toutatis asteroid, about 7 million km from the earth, and continued its journey into deep space.
Chang'e-3, launched in 2013, was the first Chinese spacecraft to soft-land on and explore an extraterrestrial object. The scientific instruments on its lander are still operating, making Chang'e-3 the longest working man-made probe on the moon.
China launched an experimental spacecraft in 2014 to test technologies to be used on Chang'e-5, which is expected to bring moon samples back to earth. The spacecraft re-entered the earth's atmosphere at a speed of about 11.2 km per second.
The lunar program ushered in a new era for China to explore the universe and peaceful utilization of space.
(With Xinhua input)
HONG KONG NEWS