Representative on behalf of cities across China and the United States gathered at a sister cities summit in San Francisco on Friday to share insights on key topics spanning green urban development, culture, tourism, education and youth.
The 8th China-U.S. Sister Cities Summit was initiated by the Chinese People's Association for Friendship with Foreign Countries in 2014, serving as a significant bilateral event following the meeting between the Chinese and U.S. heads of state in May while receiving positive responses from localities and friendly organizations in both countries.
More than 150 representatives from 15 provinces, autonomous regions and municipalities and 12 cities in China, and 160 representatives from 21 states and 36 cities in the United States, gathered to engage in in-depth exchanges and mutual learning on three main themes of green development and urban governance, culture and tourism, and education and youth.
Five cooperation agreements were signed between relevant cities in China and the United States, showcasing the results of 31 cooperative projects covering areas such as sister city partnerships, cultural and tourism exchanges, and youth exchanges.
The participants said these links boost bilateral friendship and contribute to stable China-U.S. relations.
"China [is one of the] largest economies, all the fantastic discoveries and things being done in China. The U.S. and China have a lot to learn from each other and working together, we can conquer the world's problems," said Carol Robertson Lopez, chair emeritus of Sister Cities International.
"The attendees all expressed their willingness to further strengthen cooperation with sister cities. They believe that there is a great potential, a bright future, and strong vitality in local exchanges and cooperation, and they are willing to contribute to and solidify the foundation of the constructive strategic relationship between China and the United States through close cooperation," said Yang Wanming, president of the Chinese People's Association for Friendship with Foreign Countries.
At present, China and the United States have established 50 pairs of sister provinces and states and 238 pairs of sister cities.
8th China-US Sister Cities Summit held in San Francisco
Major breakthroughs by Chinese scientists have laid the foundation for a future where space-based solar power stations are capable of wirelessly transmitting energy to Earth and spacecraft, though significant engineering problems remain.
A research team from Xidian University in northwest China's Shaanxi Province has made significant progress on the Sun Chasing project, or "Zhuri" in Chinese. The team has developed a ground-based test system for wireless power transmission that can charge multiple moving targets at the same time.
In recent tests, the system achieved a wireless power transmission efficiency of 20.8 percent from direct current to direct current over a distance of 100 meters. It delivered 1,180 watts of power. The team has also built a wireless charging system for drones. In a test, a drone flying at 30 kilometers per hour was able to receive 143 watts of stable power from 30 meters away.
A space solar power station works exactly as its name suggests: a huge array of solar panels placed in orbit. It would collect sunlight in space, where the sun always shines, and then convert that energy into microwaves or lasers to beam down to Earth or directly to satellites and spacecraft. This could address two significant issues: supplying uninterrupted power for space missions and alleviating energy shortages on the ground.
"The construction of space solar power stations could become a major undertaking in the future. One potential benefit is access to a virtually unlimited power supply. Because energy can be collected continuously in space 24 hours a day, electricity could be supplied on an uninterrupted basis," said Fan Guanheng, an associate professor at the School of Mechano-Electronic Engineering at Xidian University.
"Secondly, it could reduce our dependence on fossil fuels, thereby lowering carbon emissions and helping protect the environment. Thirdly, it could support the development of charging infrastructure in space and enable wireless microwave charging for spacecraft, changing the way power is supplied to space vehicles," the professor added.
In 2018, the research team launched the first phase of the Sun Chasing project to build a ground test system. By June 2022, they had completed the world's first full-link, full-system ground validation system for a space solar power station. Now, the team has moved to phase two. The goal now is to solve the challenges of generating high power in space and transmitting it efficiently over long distances.
According to Duan Baoyan, an expert at Xidian University and an academician of the Chinese Academy of Engineering, recent breakthroughs include improving the efficiency of solar energy collection and conversion, increasing the precision of microwave beam control to reduce energy loss, and making the transmitting and receiving antennas smaller and lighter, which is critical for space application.
The team has also solved the problem of how to power multiple moving targets at once using a single transmitter. This means that in the future, one space power station could potentially supply electricity to several satellites or ground vehicles at the same time, Duan said.
Despite the advances in ground-based validation, a series of technical challenges must still be overcome before the technology can be deployed in space.
"The first issue that needs to be addressed is the adaptability of components to the space environment, as conditions in space are completely different from those on Earth, including radiation exposure and extreme temperatures. Another challenge involves the deployment and retraction design of transmitting and receiving antennas. We also need to develop thermal management systems to cope with extreme temperatures and temperature fluctuations in space. These are all areas where further breakthroughs are needed," said Qian Sihao, an associate professor at the School of Mechano-Electronic Engineering at Xidian University.
"We have now completed the development and validation of a ground-based test system, and our next step is to carry out in-orbit wireless microwave power transmission," Fan said.
With ground validation complete, the team now turns its attention to overcoming the harsh realities of space, aiming to demonstrate in-orbit wireless power transmission and bring the vision of orbital solar energy closer to reality.
Space-to-earth solar power moves closer to reality although hurdles remain: scientists
