Chinese Chief Lunar Designer Describes Chang’e II Mission

A photo of a lunar crater from China's Chang'e II orbiter. (Credit: China National Space Administration)

The China National Space Administration published an interesting Q&A last month with lunar exploration chief designer Wu Weiren. He discusses the Chang’e II spacecraft now orbiting the moon, the nation’s future plans, and the reason it is exploring Earth’s closest neighbor. Below is an English-language version.

Q: Mr. Wu, you tell us the “Chang’e II” The overall objective of lunar satellites and technical characteristics?

A: The “Chang’e II” China’s lunar exploration satellite is detecting the leading stars of stage II, the main part of a soft landing validate key technologies to reduce risk of future projects, in order to gain experience behind the project, in fact, lunar exploration phase pioneer.

“Chang’e II” is characterized by “fast, close, refined, and more.” “Fast” is the time to fast, the original “Chang’e I” need 12 days to reach the moon, this is 5 days 112 hours. “Near” is the entire lunar orbit has changed, “Chang’e II” is 100 kilometers, “Chang’e One” near 100 km, 15 km down the track but also, more recent, more detailed observation of the moon. “Fine” is a high precision, because the CCD camera imaging of 100 km on the time better than 10 meters in 15 km time of 1.5 meters, than the “Chang’e One” in the 200-kilometer time greatly increased. “More” is the pilot project and more, test more content.

Q: Why should speed directly into the earth-moon transfer orbit?

A: Because the ultimate goal of flying to the moon still hope manned lunar landing. The experience from abroad, manned landing on the moon in orbit time is as short as possible. China’s “Chang’e One” in the PM orbit by more than 10 days, this test directly flying to the moon, which require more stringent emission window, the rocket thrust is even greater, precision and control precision orbit is also more demanding.

Q: From 200 km down to 100 km lunar orbit, the difficulty is what?

A: The mountains and valleys on the moon and Earth are broadly similar. For example, the equivalent of 10 km of Mount Everest on Earth, the deepest valley 10 km. Plane calculated monthly, then 10 km mountain, valley below is about 10 kilometers. So, when the 100 km lunar satellite to control the monitoring and control technologies and our technical requirements to a higher, and fix may hit the moon. At the same time, the Moon mass distribution is uneven, some parts of gravity is small, some big local attraction, which control technology requirements are relatively high.

An image from China's Chang'e II lunar orbiter. (Credit: China National Space Administration)

Q: “Chang’e II” imaging goals?

A: The “Chang’e II” mainly as a 2013 launch of the “Chang’e III” soft landing, the pilot star. “Chang’e III” currently selected in the Bay Area to implement a soft landing lunar rainbow, which is about 43 degrees north latitude, 31 degrees west longitude. We want to go to some reconnaissance to see how the terrain like land area, there are no mountains, no rocks, landforms good, it is not easy to land. Therefore, the “Chang’e II” is one of the goals of the landing area to high resolution imaging, the resolution to 10 meters, 15 kilometers in the time, and then increased to 1.5 meters, which more accurate than before , so called “sophisticated investigation.”

Q: There is also a key technology is the X-band monitoring and control?

A: We have satellite now, most of the Earth around the turn. In orbit around the Earth low orbit and high orbit, the maximum orbit is 36,000 km, which is the Earth’s orbit. If you enter deep space, including the future exploration of Mars, Venus probe, it is necessary to use X-band. X-band this is the first time, is 8000 trillion, its transmission rate higher, the precision of determination of higher, farther distance communication.

Q: “Chang’e II” Why only scheduled to run half a year?

A: It is now tentatively scheduled for the six months, but may be extended. Why be half? Because the lunar surface to do a lot of experiments, including the orbit, track down all kinds of power equipment, and the “Chang’e I” not the same, mainly pilot projects and more, the relative increase in fuel consumption. Although scheduled to run six months, but the available data than the “Chang’e I” more. The key is the “Chang’e II” large amount of data, data accuracy, we should transfer the data back, and the “Chang’e One” is not the same. “Chang’e I” with the code rate of 3 trillion, this set is 6 trillion yards, with 12 trillion is actually code for, so the transfer rate will be greatly enhanced.

Q: “Chang’e II” which links greater risk?

A: The big risk is there are three stages. The first rocket launched into Earth orbit of 200 km, 38 million kilometers away track, this link can not be precise orbit is the most critical. The second is near the time of reaching the moon, the moon can not be captured. Because the lunar orbit of 100 km and 200 km is not the same. When the degree of freedom in the 200 km is also larger, at 100 km, if not reach the control precision, then mess it might impact the moon, or lunar grip, it is possible to run. Third, lower track. Because we have chosen landing area in front of the moon, according to track down the time to be measured in the back of the moon. The back of the ground control out of reach, in this case, relies entirely on satellite autonomous control, which are difficult.

Q: The lunar exploration project coordination in the system have any difficulties?

A: In the “Chang’e II” development, we introduced two command lines, one is the administrative command line, a technical command line, and this is a successful experience in aerospace engineering. Administrative command line is leading the project, the human, financial, and material aspects of the overall coordination. The total technical command line as a division system, the main responsible for the technical program, technical line, technical research, to ensure the technical feasibility. The whole project is divided into the following five systems, including launch vehicle systems, satellite systems, control system, the ground application system, and launch systems, these five units in the system about the participation of thousands, tens of thousands of people involved, according to these five systems, The whole project is carried out methodically, and my personal work has been supported in all aspects.

Did not encounter much difficulty at present is the key risks, chief engineer must fully consider the project risks. For example, nearly more than 30,000 rocket system components, cables and wires nearly 100,000, more than 4,800 welds. Satellite system has more than 50,000 components. Rockets and satellites add up in the air, the Fire will be the ignition initiation 200 kinds of bottles, these bottles can not accurately Fire Attack initiation, there is no leakage of the weld, more than 80,000 components, any one problem will affect the success or failure so the risk is relatively large. We need to question the risk to full and ready to go by the worst for the best results. I think the biggest challenge here.

A lunar crater as viewed by China's Chang'e II orbiter. (Credit: China National Space Administration)

Q: Comparison with foreign countries about China’s lunar exploration at what level?

A: and the United States, compared to the former Soviet Union, China 50 years later, some people say 50 years behind China, I do not agree. China only started 50 years too late. Now the second round of lunar exploration upsurge, with Japan, India comparison, the Japanese started early last century, 90 years on the launch of the “Feathered number” detector, and finally failed, did not enter the lunar orbit. 15 years later, in September 2007 launched a second probe was successful. India is also the 90s of last century lunar exploration, the last to leave behind in China. India launched a major international cooperation, the United States, Europe, Russia, have helped it. China is characterized by a late start, began in 2001, but the starting point is relatively high, the overall plan to gradually implement more stringent programs, inputs are relatively small. And Japan, India compared to its advantages.

Q: Follow-up of lunar exploration plan for that?

A: The second phase of exploration is in full swing. Phase II includes “Chang’e II”, “Chang III”, “Chang’e IV”, a total of three tasks. “Chang’e II” ready to go; “Chang III” and “Chang IV” in the prototype development phase, is advancing. “Chang’e III” and “Chang IV” The development is very difficult, of which 80% is new technology, new products. We used to maximize the use of aerospace engineering is a mature technology, generally 70% -80%, the newly developed no more than 20%. The reversed, 20% are mature, 80% of newly developed. The newly developed technology research difficult. Estimates, “Chang III” after 2013 to achieve a soft landing in the lunar surface, but also the release of the rover.

This will be realized after the “back” of the task, that is, three exploration projects. Phase III is mainly no sample return, and now have demonstrated the implementation of the program, the state has approved the program, is organized and implemented, roughly 2020 to complete the project. Walk according to manned lunar landing, the current development of China “around the fall back” is the lunar phase. If you are around, and down to go, and safe sample return, then we have the basic conditions for a manned lunar landing, it is estimated that in 2020 after the.

Q: Why did China’s deep space exploration to exploration as a starting point?

A: The deep space exploration of the deep is purely a certain definition, generally considered to be 1.5 million kilometers away is deep space exploration. The moon is 400,000 km, 400,000 km to 1,500,000 km in space between the planets is no more detectable, so our country is defined as the exploration of the moon starting point for deep space exploration. We first do a good job exploration, access to the rocket technology, transportation technology, detection technology, control technology, can be used in future exploration of Mars, on Venus probe. In the near future, China’s exploration of Mars, Venus is entirely possible, because the two planets closest to the earth.

Q: “Chang’e II” which carried out international cooperation?

A: The lunar exploration project is a cause of peaceful use of space, we hope relevant countries and the premise of equality and mutual benefit for more international cooperation. At present, the “Chang’e One” and “Chang’e II” has also undertaken a number of international cooperation. For example, in monitoring and control, the European Space Agency has given us a lot of support. The scientific data we have available to them free of charge, so that sharing of resources, study together. However, the high-tech is not be bought. China’s basic national policy and social system determines the need to rely on self-reliance and independence.

Q: China’s lunar exploration project progress more smoothly, what is the reason?

A: The first is the superiority of the socialist system. Our country as long as the argument is clear, technically feasible, the party and the country attached great importance to concentrate on doing big things. Like some European countries, engage in an activity, engage in a project, more than 10 countries consent to it. The second reason is that we indeed have a good technology, has some basis, but also dare to independent research team. This is what we can smoothly carry out the most fundamental reason.