MOSCOW -- The two Chinese astronauts aboard the Shenzhou-11 spacecraft entered the space lab Tiangong-2 on Wednesday morning, bringing China closer to its dream of building a space station.

Veteran Russian cosmonaut Sergei Krikalyov, on behalf of all the cosmonauts at the Roscosmos State Corporation, sent a congratulatory letter to the Chinese astronauts.

"I believe Russian and Chinese astronauts will step into each other's spacecrafts and fly together in space in the future. Roscosmos will do its best to achieve this goal. I wish the Chinese astronauts a successful flight in this mission, hoping that we can meet later both in space and on the ground!" the letter said.

"Chinese astronauts will spend 30 days in near-Earth orbit, this is an important test. We believe the outstanding exercises and precise theoretical knowledge will help the Chinese astronauts to tackle all kinds of tests," Krikalyov said.

As a veteran cosmonaut of six space flights and once the world record holder of having spent a total of 803 days and 9 hours and 39 minutes in space, Krikalyov said in the letter that he wanted to share his space experience with his Chinese colleagues.

He said astronauts have a unique feeling in space. They need to manage the difficulties of adapting to space, such as learning to live in gravity-free conditions and an enclosed space. To adapt to this environment, they need to go on more flight missions. Every mission will increase the astronaut's confidence.

"At the same time, the discomfort will gradually decrease. Because every astronaut has prepared the mission very carefully and seriously, they will not encounter major problems."

Besides the special physical feeling of being in space, astronauts also feel a sense of responsibility. "That's because astronauts are in the very front of a huge manned space program, to which the whole space department of their motherland is dedicated to," he said.

In the space station, astronauts are required to complete various tasks at their working area every day. In addition, they must exercise on a regular basis to keep their bodies fit for work, Krikalyov suggested.

To the astronauts, switching between different tasks is a way of relaxing, he said.

"I will be very happy if my experience could help the Chinese astronauts in this mission," the retired Russian cosmonaut said in the letter.