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S: Hi everyone. Welcome to CBN Friday Special, I’m Stephanie LI.

R: And I’m ZHANG Ran. 

S: Ran, do you cry often?

R: Hmm, sometimes. More often when I was a little girl. Why do you ask?

S: Well, do you know that technically, astronauts can not cry? 

R: Why not? 

S: In micro-gravity, your eyes make tears but they stick as a liquid ball. In other words, astronauts technically can’t cry, China’s first female Taikonaut Wang Yaping told students on the second live class from China’s space station held on Wednesday.

R: Ah, yes! I must have missed that part of the lecture. Shenzhou-13 crew members Wang Yaping, Zhai Zhigang, and Ye Guangfu conducted several scientific experiments during the hour-long class, such as the crystallisation of supersaturated solution, a liquid bridge demonstration, water-oil separation and throwing objects under the zero-gravity condition, amazing numerous students on Earth. How about you, Stephanie, which experiment impressed you the most?

S: I would say it's the first micro-gravity experiment. In this demonstration, Wang used a bag of supersaturated sodium acetate solution to demonstrate its crystallisation in micro-gravity. After Wang squeezed the solution from the bag, it became a transparent fluid ball floating in front of the camera. She then used a small stick covered with crystal nuclei to touch the fluid ball and it quickly became crystallised. It looks like an ice ball, but Wang told the class that it's actually warm.

R: Yes, that was really impressive. The space teacher explained that the solubility of sodium acetate in water of higher relative temperature is very high, and it very easily forms a supersaturated solution. Just a small trace of crystal nuclei causes the sodium acetate to crystallize, releasing a lot of heat. 

Another micro-gravity experiment showed how to separate oil from water in space. Wang and the students followed the same procedure to mix oil and water into a fluid mixture. But the students found their mixture gradually separated into oil and water again, while the fluid in space remained as a mixture. Do you know why that happened, Stephanie?

S: Yes, I do. In the weightless environment of space, Taikonauts have to separate oil and water by spinning the mix, using the influence of centrifugal force. Wang also told us that the space station is equipped with a centrifuge, which the crew can use to separate and prepare medical samples such as blood and urine.

R: Yes, you’re right. Wang and Ye then jointly introduced two laboratory cabinets aboard the Tiangong space station. They first showed how they used the high-quality microgravity experiment cabinet, which can conduct more precise experiments to enhance the measurement accuracy. They then showed students the “container-less” experiment cabinet, in which samples can float in the middle to avoid possible contamination and shape changes caused by the contact with the container surface.

S: In fact, China plans to conduct more frontier scientific experiments on Tiangong space station with “Wentian” and “Mengtian”, the two laboratory modules, scheduled to be launched this year. The experiments include raising fish, growing vegetables, setting up the most precise clocks in space, developing new materials, studying physical laws and exploring how humans can survive in space for long periods. Both Chinese and foreign scientists will then have the opportunity to carry out research aboard China's space station, which will serve as a space experiment platform for the world.

R: The session lasted less than an hour, but students were fired up with questions about the cosmos even after waving goodbye to the crew. At the end of the class, Wang said, “we hope you will continue to gain scientific knowledge and explore the mysteries of science. The future space station is waiting for you guys.”

S: It’s true. For ordinary people, like you and me, a space tour is no longer a fantasy. In September 2021, US private spaceflight firm SpaceX sent four tourists, not astronauts, into the space. Other private aerospace manufacturers, such as Blue Origin and Virgin Galactic, have succeeded in sending passengers on their spacecrafts and made it back. 

With the development of space tours during the 14th Five-Year Plan period, the general public in China may have a chance to visit the country's space station in the next decade, China's first astronaut Yang Liwei said earlier in March.

R: We are witnessing the history of China’s manned aerospace. With the Shenzhou-13 trio set to conclude their six-month mission in orbit and prepare next week for their return to Earth, the Shenzhou-14 and -15 manned missions will be rolled out this year. According to the plan, China will complete construction of its Tiangong space station by the end of this year, drawing a satisfactory conclusion to the 30th anniversary of China's manned aerospace history.