Chang'e 3 update: 6 instruments active, new fan-produced landing video
Posted by Emily Lakdawalla
2013/12/17 10:51 CST
Today there was a lengthy press briefing by several members of the Chang'e 3 science team. A complete transcript was posted in Chinese here. I have run it through two machine translators (Google and a Chinese one, fanyi.baidu.com) and found it to be quite informative, not just about the mission but also about attitudes about Chinese space exploration and foreign cooperation. It was useful background for my participation in an hour-long panel discussion on China Radio International's "Today" program.
But before I get to that, I want to share this new fan-produced animation of the landing, putting the site into context, with music.
In this blog post I'm doing my best to translate the content of the press briefing. You can try to follow along yourself with this document, in which I compare the original Mandarin text with the two machine translations. Times in brackets correspond to times listed in that document.
- The host, Zhang Tengyue;
- Wu Weiren, chief designer of the lunar exploration program;
- Liu Jianzhong, deputy chief designer of the launch vehicle;
- Zheng He, deputy chief designer of the lander; and
- Su Yan, deputy chief designer of the ground segment (who seemed to be speaking for the science team).
Wu Weiren remarked that everything went so much more smoothly than they had expected. [14:18]
Zhang Tengyue talked about the confusion felt by himself and Ouyang Ziyuan on the live broadcast, when they were expecting to see pictures of the lander from the rover, but they did not. I smiled when I read this because I had likewise been confused about there being no pictures of the lander on the CCTV live broadcast; I wound up locating a photo of the lander on a forum after it had been shared on the Chinese-language broadcast. It was funny to know that he and Ouyang had been as confused as I. Zhang talked about exchanging handwritten notes with Ouyang during the broadcast to decide whether they should ask about the photo of the lander? Ouyang advised him not to. [14:23]
Wu explained that the reason they showed photos of the rover but not the lander on the English-language broadcast was because they were considering the historical importance of the photos, and were particularly concerned about showing the images of the Chinese national flag on the Moon. Since the rover was to the north of the lander and both were in the northern hemisphere, the Sun was to the south, so the rover (and hence the flag) were well illuminated by the Sun as seen from the lander, but badly lit as seen from the rover. So they chose, during the live broadcast, to transmit photos of the rover with its flag, since they were better lit. They showed one photo that had been transmitted prior to the live broadcast, and then a second that had been transmitted during the broadcast. [14:25] I hadn't figured out until this morning that the English-language broadcast did, in fact, show two different photos of the rover from the lander, with a significant amount of shadow motion between them; since shadows move so slowly on the Moon, the first image must have been taken quite a while before the second one.
Zheng He reported on the current status of the lander. As best as I can do with the translation: "Change 3 is working very well on the Moon. All conditions very good, nominal. It has already begun to do extreme ultraviolet optical imaging work."
The host asked about the surprising proximity of a crater to the lander. Zheng responds (again, my best translation): "After we landed and saw the camera image [of the crater], we felt very lucky, but also very successful....This picture shows us right in front of a pit, with stone blocks right in front of the lander. But underneath the lander's feet the ground is very flat. This shows that the autonomous navigation and obstacle avoidance that we designed has succeeded, and we landed on a safe area. The crater is ten meters away from the lander; we can navigate around it, our plans are not affected by it." [14:39]
Zheng talked about wanting to impress on people that, as easy as they made it seem, the landing was very difficult, for two reasons. The first: "It's an irreversible process. In the past, we have launched spacecraft into orbit around Earth. Celestial laws govern its path; it won't crash if there is a small problem. Once it goes over a ground station, we can control and operate it." She says that, by contrast, Chang'e 3 had two "irreversible" moments, lunar orbit insertion and landing, where they had only one chance to get it right; this was a first for a Chinese mission. [14:42]
The second thing that made the Chang'e landing difficult, she said, was the fact that they could not be certain what they would find in the landing site. Past lunar orbiters could assume the Moon a sphere and navigate accordingly. (This isn't quite true; she's oversimplifying.) But for the landing, "the lunar surface is undulating, and this has a great impact on the control of our landing process. And the final landing site could be soft soil or it could be on hard rock; this has a great impact on our landing cushion. We also wonder what kind of dust the landing will produce." She talks about how they had to design the lander and its software to "overcome the uncontrollability of these uncertainties." [14:47] I can imagine the JPL engineers who designed Curiosity's landing system nodding in agreement with all of this! Predicting all the uncertain aspects of a landing, and making your lander smart enough to diagnose and deal with all the possible different situations it may encounter, is what makes it so difficult. She goes on to talk at length about the problem of lunar dust and the difficulties that Lunokhod 2 faced because of it.
Next Su Yan talked about the scientific work being undertaken by Chang'e 3. They mostly can't operate during lunar night because of the intensely cold temperatures, so they perform scientific observations during the lunar day. Right now, it's a full Moon, which means that from the point of view of the surface of the Moon, Earth is dark; this is the best time for Chang'e 3 to conduct astronomical observations. She talked about testing the Yutu ground-penetrating radar on glaciers in the Qilian mountains, and clearly seeing the glacier and rock layering there; she looks forward to lunar data. [14:55]
Su talked about receiving data on Earth from both lander and rover, about monitoring the state of the payload, and of converting the raw data received from the spacecraft to "data products released to the whole of China and even the whole world of scientists to use." [14:57]
Su said that six of the eight instruments are now operating. This list I'll actually copy from an English-language article about the briefing: "Except for the alpha particle X-ray spectrometer and the visible and near-infrared imaging spectrometer, the instruments have all been activated and are undergoing tests and adjustments."
There was some discussion of the value of the scientific experiments being conducted by Chang'e 3, and then the briefing was opened to questions from the media. The first question was of the inevitable "how will this benefit Earth" variety. I found it interesting that Wu Weiren's lengthy response talked about the return on investment achieved through the Apollo missions, stating that for each American dollar invested into the Apollo program, 7 to 15 dollars were returned, by different estimates. Wu also talked about how, as a fraction of its GDP, Chinese investment in space is very small; and also pointed out that, to date, China's planetary exploration efforts have seen 100% success. Then they discussed how technologies and materials developed for the Chang'e program will eventually find civilian applications. [15:09]
Then, a very interesting statement from the moderator. He brought up the whitehouse.gov petition initiated by a 6-year-old boy to "Increase NASA funding. So we can discover new worlds, protect us from danger and to make dreams come true." The petition has been all over science and technology news this week, but I was still surprised to hear it brought up in this Chinese forum. He talked about China suddenly realizing this month that the South China Sea was important to China after 70 years of ignoring it, and remarked that it would be short-sighted of China not to go to the Moon, to let others go there instead. [15:11]
A reporter asked about Mars exploration. Again, a very interesting response, from Wu Weiren. He talked about how India had sent an orbiter to the Moon, an orbiter that failed to achieve its design lifetime of two years in orbit. They have launched a spacecraft to Mars, he said, but if I understand the translations correctly he seemed to be expressing reservations that they would be able to survive the long trip, based upon their past performance: "the future is uncertain." By contrast, he said, China's approach is "comprehensive," systematic, methodical, "every step laying a solid foundation for the next step." India, in contrast, is "leaping, mainly wanting to show strength." Perhaps, he implies, they are overreaching. "We are not competing with them, although they may want to compete with us; the mentality is not the same." I must admit, if I were Indian, I'd be a little affronted by these words! But the points he makes are fair. Wu goes on to say that China already established the technological capability to explore Mars with the success of Chang'e 1 and 2; it would be "easy." It's simply not their goal at present. A strong statement. [15:17]
Another reporter asked about Chang'e 5 and the plans to launch it from a new launch facility. Liu Jianzhong spoke about how Chang'e 5 will require the new Long March V rocket and will need to be launched from a new site in Wenchang, Hainan. The advantage of the new site is that it is at a lower latitude, 19 degrees as opposed to 28.5 for Xichang, which launches a spacecraft with more energy; also, Wenchang will be a coastal launch facility with launches over the ocean, avoiding the problem of rocket parts falling on populated areas. Finally, Long March V will be a five-meter-diameter rocket, and China's inland railways can only accommodate payloads 3.5 meters wide. [15:22]
The same reporter inquired about foreign cooperation and data sharing. Su Yan said that there are cooperative agreements in place with ESA, and that the Chang'e 1 and 2 data have already been made available to them. "NASA cooperation with us is more difficult," NASA is not permitted to host information about Chinese missions on their websites, and it is not possible to cooperate officially. But, she said, she works for the National Astronomical Observatory, which has very large cooperation with foreign countries. [15:25]
Wu Weiren said the project had set up a special committee on applications of the data, with the goal of sharing the data. He spoke of sharing data "in accordance with the principles of classification: level one, level two, level three, level four" -- if I am not mistaken, this is talking about sharing data products in accordance with the schemes originally laid out by NASA's Planetary Data System and adopted by ESA's Planetary Science Archive. So I was very happy to read that. "In addition, we and Europe also have some cooperation," and I think he was discussing the support of the Chang'e 3 mission by Europe's deep-space communications network. [15:26]
Then Wu went on to talk about NASA's specific interests in Chang'e data sharing. It's clear that NASA expressed interest in information about the Chang'e 3 lander's fuel expenditure during landing, which has direct application to the LADEE mission, as I've discussed before. NASA also asked for Chang'e 3 tracking data, so that the LADEE mission would know where and when Chang'e 3 was disturbing the lunar atmosphere. "But we also asked [NASA] to provide data [in return], and [NASA] did not agree. The U.S. Congress passed a resolution that stated that NASA cannot cooperate with China for fear we will steal their technology." If I understand correctly, I think he went on to say that in a way the American refusal to share information with China has helped China's space program, forcing China to develop their own technology, their own strength. [15:28]
I will note here that Representative Frank Wolf, the author of the policy that prevents NASA from cooperating with the Chinese space agency, announced today that he will not be seeking reelection. Perhaps this policy will be reexamined soon, and the LADEE team will be able to exchange information with the Chang'e 3 team that will enable better scientific results from both missions.
A reporter asked: what about cooperation with other nations? Wu Weiren responded that the European Space Agency is "increasingly interested in cooperation with China," because of the rapid development of Chinese capability and the long planning horizon for European missions. He said that this shows that other space powers now recognize China as being at their level. [15:29]
A reporter mentioned China's recent launch failure, their first since 2011, and asked about the public's tolerance for failure in the space program. Wu said that "aerospace is a high-risk business; failure is inevitable." He said they do the best they can to plan for problems; on Chang'e 3 they had planned for 200 different fault scenarios, but wound up needing to use none of them. "If we do fail, we will feel a lot of pressure, but I believe that people across the country can understand." [15:35]
Zhang He talked about preventing failure through the application of new technologies unavailable to Soviet or Apollo lunar landers, including the laser ranging to determine a flat place to land, and the highly accurate, variable-thrust landing engine. [15:38] (Both translation services insist upon translating the Mandarin term for "newton," the unit of thrust, as "bovine" or "cattle," which makes discussion of the "7500 bovine variable thrust engine" amusing.)
Wu Weiren also talked about the rover having autonomous navigation capability. The Soviet Lunokhods required television monitors and continuous round-the-clock shifts of drivers to manually tele-operate them. Wu said that Yutu can be operated in this mode, but that there is also a "completely independent operation mode" in which it can be navigated to waypoints. It can avoid obstacles using both long- and near-distance stereo vision through navigational cameras on the mast and hazard avoidance cameras on the body, just like NASA's Mars rovers. "If a stone is too big, the rover will automatically turn, then go around it." [15:41]
A reporter asked about the video of the landing, in which the lander pauses, slides to the side, then descends. Zhang He responded that the lander was able to perform up to three assessments of landing site suitability with laser ranging, but that the computer wound up needing only one assessment to locate a safe spot to land. [15:42]
There was some more discussion of Chang'e 5 and Chang'e 4, and a question about when we'd see Chang'e 3 science results, and counsel of patience. I'm sure there's a lot more in this discussion that I missed, but it's getting late and my mind is beginning to blur in the attempt to read and understand the machine translations. I welcome you to download my comparison document and try interpreting some of it for yourself! All in all, a wide-ranging and surprisingly frank discussion.
All well and good, but I still want to see more pictures! I have seen no new ones yet. Yutu is sleeping right now, because it cannot operate during the heat of lunar noon; it's supposed to start working again on December 23. Lunar Reconnaissance Orbiter will attempt an image on December 24.