Along with the letter, Chen Dong also recorded a video in the space station to share the student's letter and his reply. Teachers and students from the school gathered to watch the video together.

In encouraging the student, Chen Dong recalled how he fumbled along the way to becoming an astronaut. He shared how he had conquered drowsiness when he had to start over to learn astronomy, physics, aerospace technology and everything necessary to become an astronaut. He told her how he was tested to the limit during hypergravity training, a technique that largely involves wearing weights for several hours a day.

"During the training, every inch of my skin, my cells was put under unbearable pressure. It felt like my internal organs were being 'displaced'," he said.

His intense training went on for six years. He almost cut himself off from the outside world during that time and was finally able to qualify for the mission in space.

It was his dream that kept him going when he was feeling lost and fatigued, he wrote.

On Oct 17, 2016, during his first space mission, Chen Dong was amazed when he saw the universe unfold in front of his eyes for the first time.

"To level with you, life is like the sky, which comes with different weather. It is not all sunny days. There will be rainy, snowy and stormy days, making the sky a riot of color. Don't worry about stumbling blocks in life, or you will not have been at your best. Every day you encounter is a valuable sight to behold, making you one of a kind. Please cherish those days, which will reward you with great surprise," he said.

"Before I went to bed in the space station, I would always like to search for our country through the windows of the spacecraft. In the gleams of the lights of every household, it is a thriving country. That is what I have been fighting for," he added.

The letter from space was also a fitting tribute to mark the 25th anniversary of Hong Kong's return to the motherland. Recalling the joy of celebrating the return of Hong Kong 25 years ago, the astronaut also encouraged young people in Hong Kong to follow their dreams and contribute to the development of the city and the country.

The letter stuck in Chen Man-lin's mind.

"I'll do what he said in the letter－study harder and work out to keep healthy and stay curious about the universe and make contributions to the nation's aerospace development in the future," she told China Daily.

Sun, Hong Kong's secretary for innovation, technology and industry, encouraged the students in the city to contribute to the nation's legacy of aerospace development by challenging themselves, getting to know the nation's development, and getting more involved in the field of technological innovations.

Jack Ng Wun-kit, the principal of Pui Kiu Middle School, was also among those feeling the encouragement from space.

Ng told China Daily that Hong Kong students need not become astronauts themselves to contribute to the legacy. They could also contribute via Hong Kong based satellite and communication companies in order to help aerospace development.

The connections can be small but meaningful. In October 2003, China's first man in space, Yang Liwei, visited the school and planted a tree on the school grounds. That tree now stands tall and strong on the campus.

Last year, a delegation of leading aerospace experts and scientists visited the city. During the visit, they met with students, gave lectures on the nation's aerospace development and brought along samples collected from the moon during the country's fifth lunar exploration mission in late 2020 for exhibitions in the city.

Professor Quentin Parker, who teaches physics and directs the Laboratory of Space Research at the University of Hong Kong, said the letter campaign is crucial in promoting subjects in the natural sciences to Hong Kong students.

As for Chen Man-lin, she had already made up her mind to become a researcher and hopes she can contribute to China's aerospace development.

Curtis Lo contributed to this story.