New Mission to the Moon

By Wang Hairong

Though a septuagenarian， Ye Peijian—a lead aerospace scientist with the China Academy of Space Technology（CAST）—was particularly busy recently. He was preoccupied with the launch of the Change-4 lunar probe， which blasted into space on December 8.

Ye has been involved in Chinas lunar exploration program since 2001 and is currently a consultant for the program. He is also chief designer and lead scientist for all four Change lunar probes launched by China since 2007. Change-4， consisting of a lander and a rover， is expected to make the fi rst soft landing on the far side of the Moon in human history.

Because its revolution and rotation cycles are nearly identical， the Moon always has the same side facing Earth. The far side is also called the dark side because it cannot be directly observed from Earth.

Previous information about the far side has been gained through photographs taken by the Luna 3 probe launched by the Soviet Union in 1959， images caught by the U.S. Apollo 8 spacecraft that cruised around the Moon in 1968， as well as remote-sensing images.

Scientific tasks

Originally built as a backup to the Change-3 probe launched in 2013， Change-4 was tasked with the new mission of probing the far side of the Moon at the insistence of Ye and other scientists.

The probe is expected to land on the Moon about 26 days after its launch， according to CAST. It will first fly along an Earth orbit； then gradually shift onto a lunar orbit. The trajectory was chosen because it is fuel-effi cient， allowing the probe to be smaller. As the Moon rotates once on its axis over approximately 27 days， Change-4 will continue its orbit and conduct some experiments， biding its landing time. The touchdown is scheduled for early morning on the Moon so that the rover can be powered by sunlight while working.

Change-4 will land in the Von Karman crater， named after Hungarian-born U.S. aerospace engineer and physicist Theodore von Karman.Since the landscape on the far side of the Moon is more complex， with more craters and steeper terrain， the probe will make a nearly vertical landing to dodge cliffs.

Change-4 will carry out a number of scientifi c tasks， including surveying the Moons terrain and landforms， detecting the mineral composition and shallow lunar surface structure， making low-frequency radio astronomical observation and measuring the neutron radiation and neutral atoms in efforts to study the environment on the far side of the Moon， according to the China National Space Administration.

The probe also carries four scientific payloads developed by scientists from Germany， the Netherlands， Saudi Arabia and Sweden.

Since the Moon can shield its far side from radio interference from Earth， it offers a quiet electromagnetic environment for capturing weak signals exuded from remote celestial bodies in deep space and studying the origins and evolution of stars， galaxies and the universe.

Several scientifi c and technological experiments designed by Chinese universities will be carried out on Change-4. One experiment is a miniature lunar ecosphere designed by a coalition led by Chongqing University.

A prototype displayed at the university shows the ecosphere in a cylindrical jar made of special aluminum alloy. It is 18 cm high and 16 cm in diameter， with a total weight of 3 kg. The vessel houses potato and Arabidopsis seeds， silkworm eggs， soil， water， nutrients and air， as well as micro cameras and information transmission systems. A small catheter directs natural light into the jar to help seeds grow.

Why were potato and Arabidopsis seeds chosen？ “Because the growth period of Arabidopsis is short， so it is convenient to observe， while the potato may become a major source of food for future space travelers，”Liu Hanlong， Vice President of Chongqing University， said. Arabidopsis is a small fl owering plant related to cabbage and mustard.

“Our experiment may help accumulate knowledge for building a lunar base and a longterm residence on the Moon，” Liu added.

The entire process， including seed germination， seedling growth and flowering， the hatching of silkworm eggs， larval growth， cocoon opening and silkworms metamorphosis into butterfl ies will be observed from Earth via cameras.

“This will be the fi rst time humans carry out biological experiments on the Moon. Our goal is to produce the fi rst blossoming fl ower on the Moon，” said Xie Gengxin， head of the Institute of Advanced Technology at Chongqing University.

Previously， astronauts have grown plants on space stations. For instance， Chinese astronauts cultivated rice and Arabidopsis on the Tiangong-2 space laboratory launched in 2016. But those experiments were carried out in nearEarth orbit about 400 km above the ground. The environment on the Moon， 380，000 km from Earth， is much more complex. Lunar gravity is only one sixth of the Earths， and the temperature difference between day and night is more than 200 degrees Celsius， explained Zhang Yunxun， Director of the Center of Space Exploration of the Ministry of Education.

Bridge of communication

A big technical challenge for landing a probe on the far side of the Moon is the fact that communication signals from Earth cannot penetrate the Moon. Chinese scientists have solved the problem by launching a satellite to relay data transmission. The relay satellite， named Queqiao， or Magpie Bridge， was launched on May 21 into an orbit around the second Lagrangian （L2） point of the earth-moon system， about 455，000 km from Earth. Its position can be observed both on the far side of the Moon and on Earth.

Queqiao is the worlds fi rst communication satellite operating in that orbit， Zhang Lihua， chief designer of the satellite， told Xinhua News Agency.

“The name Queqiao is not only easy to understand， but also has a romantic hue to it since it is derived from an ancient Chinese folk love story，” Ye said. The tale is about cattle herder Niulang and his wife， Zhinu， a weaving fairy from heaven. The couple is separated by the Milky Way as punishment for the wifes violation of heavenly rules and they are only allowed to meet once a year on a bridge built by magpies.

Three-step plan

China has a three-step plan for its lunar exploration program： fl y a spacecraft around the Moon in 2007， land a probe on the Moon in 2015 and return a probe with lunar samples in 2020.

It launched three Change lunar probes in 2007， 2010 and 2013. Ye said after completing the three-step plan， China intends to establish a scientifi c station on the Moon.

As Chinas lunar exploration program progresses， Yes desire for the Change probes to collect lunar soil samples gets stronger.

His first contact with a lunar soil sample was in the early 1980s， when he saw the Piece of the Moon displayed at the headquarters of the World Intellectual Property Organization in Geneva， Switzerland. He was very impressed at the time， yet he did not foresee that he would play a significant role in Chinas lunar-probing missions.

Ye told the media that one of the missions of Change-5， which is scheduled to be launched in 2019， is to collect 2 kg of lunar soil for Chinese scientists to study.