A Magic Moment in Space Rendezvous and Docking

I graduated from college in the 1980s, and was soon after sent to France for a postgraduate course in electronics and communication at the government’s expense. After obtaining my doctorate in 1992, I returned to China, and in 2000 I joined an institute under China Aerospace Science & Industry Corp. (CASIC). The institute was mainly engaged in the development and production of precision navigation and guidance equipment for spacefaring.

In 1999 China’s first experimental unmanned spaceship Shenzhou-1 had been launched in Jiuquan, and successfully returned to the landing site in Inner Mongolia of China 21 hours later. The victorious flight marked a technological breakthrough and gave a green light to China’s manned space flight project. Of course, our institute was eager to be part of this great project and started work as early as 1999 on a scheme for the space rendezvous radar system. After I joined the team, I immediately immersed myself in the task and hoped to contribute my expertise to it.

The original scheme proposed to adopt a millimeter wave radar system, because it was a mature technology both at home and abroad. However, it had several obvious defects. First, some components of the system had to be imported due to substandard domestic technology. Second, it needed a servo system, which is, to put it simply, a kind of equipment for turning the antenna. With this servo system, the overall bulk, weight and power consumption of the radar would be increased. In addition, under the microgravity environment of space, the necessary lubricant would not stay where it was needed to perform its function, so turning the antenna would be difficult. All these defects are hard to overcome in space. Therefore, a better system was needed.

Sun Wu checks test data with his team.

We also considered the option of using a satellite navigation and positioning system, such as the GPS (Global positioning system) and GLONASS (Global Navigation Satellite System) that the U.S. and Russia had used respectively for their space rendezvous and docking programs. China has a similar system – Beidou Navigation, but it only covers the Asian and Pacific regions and is unable to carry out global positioning. However, there would have been uncontrollable risks if we had adopted either of the two available choices, because it would put us in others’ hands.

Hence, in 2002, I proposed the pseudo random coded continuous waveform modulated radar technology for the performance of space rendezvous. This technology is based on a completely new instrumentation system and is an innovation in the field.

The subsequent microwave radar developed demonstrated evident merits. First, it is small in size, light in weight and low in power consumption – features that have decisive impacts on the quality and performance of a space vessel. The radar also has a large search range and operating distance and a high degree of accuracy. It can search targets within an angle of ±60° and a range of 20 m to more than 100 km. It is also highly interference-resistant, flexible with light conditions, and capable of all-weather operation. Finally the radar can carry out measurements autonomously without any reliance on external information, and it does not involve mechanical movement, which gives it a high degree of reliability.

When I first put forth this scheme I was not sure of its feasibility so my institute didn’t submit it as a tender. However, my leaders and colleagues were extremely impressed, so the institute decided to develop the system through self-financing. Trust can be a source of motivation. In the following years, I devoted all my energy and time to the development of the system. But few of my team members and supporting partners were familiar with its basic theories and concepts, so I wrote “The Study of Pseudo Random Coded Continuous Waveform Modulated Interferomitric Rendezvous Radar” as a guide for its development and production.

Finally in 2007, the assessment group of China’s Manned Space Flight Project approved the system theoretically, but a great amount of experimental data was still needed to verify its application.

In the following two years, I and my young teammates carried out a spate of experiments in our laboratory and darkroom, on high towers and slide rails, and in cars, helicopters and other flying vessels. To find suitable testing sites, we went to many places across the country. We spent the two years making trips to carry out experiments. At the beginning of 2010, our project passed inspection and was adopted officially. Then we began to carry out experiments concerning the practical prototype, rather than just the engineering prototype.

At that time, we faced great pressure due to the fact that the tricky task had a tight deadline. Most elements related to the rendezvous and docking project were officially adopted in 2002, several years earlier than our project. And it had to be a success, because it was for the rendezvous and docking of Shenzhou-8 and Tiangong-1. It would be simply unthinkable if anything went wrong. Since we were working on a new technology, with no precedents to refer to except for a vast amount of experimental data to rely on, I set extremely strict requirements for our team members, allowing them not even the slightest mistake. They were all familiar with my quick temper, but knew I was doing the right thing. Finally, in November 2010, the responder was installed in Tiangong-1.

On November 1, 2011, Shenzhou-8 spaceship equipped with the microwave radar was launched. Although it was its maiden application, I was quite confident of our product. However, during the three days and two nights from the launch of Shenzhou-8 to its successful rendezvous and docking with Tiangong-1, sleep abandoned me.

The microwave radar started working and unexpectedly captured its target, still 217 km away, in less than half a minute. At 1:36 on November 3, when Shenzhou-8 docked with Tiangong-1 perfectly, my whole team, including me, were overwhelmed with emotion. That day, we drank ourselves silly, celebrating our great triumph. Ten years of effort had finally paid off.

The microwave radar was again used in Shenzhou-9’s rendezvous and docking with Tiangong-1 last June, and its performance was even better. It captured and started to track its target when they were 224 km apart, and its tracking and ability to take measurements at a distance were precise.

Today, we’re still improving the technology. In the future, it will be used in the successive space missions like Shenzhou-10, Tiangong-2 and freight spacecraft, or even in the lunar exploration project. In the improved version of the microwave radar system, the weight of the responder has been reduced by three quarters and the weight of the radar has been reduced by two thirds. We have confidence in our independently developed technology and our ability to propel the country’s technological advancement.