Hong Kong CNN  — 

Chinese astronauts on Sunday successfully carried out the country’s first spacewalk outside their space station – a significant milestone in its rapidly expanding space program.

The spacewalk is only the second by Chinese astronauts since the Shenzhou 7 manned mission of 2008, which was conducted outside a spacecraft, according to the China Manned Space Agency (CMSA).

China launched three astronauts – Nie Haisheng, Liu Boming, and Tang Hongbo – into space in June. On Sunday morning, two of them left the core module of the space station, called Tiangong or Heavenly Palace, the CMSA said.

During the spacewalk, they tested new-generation spacesuits, installed equipment, elevated a panoramic camera and tested the station’s robotic arm.

China sent three astronauts -- Tang Hongbo, Nie Haisheng, Liu Boming -- into space in June for a three-month mission on its space station, Tiangong.

The agency added that there will be another spacewalk during the astronauts’ orbital flight, which, at three months, will be China’s longest crewed mission. The country’s scientists successfully landed exploratory rovers on the moon in December and on Mars in May.

As part of its plans to have a fully crewed space station by December 2022, China launched the first core module, known as Tianhe or Harmony of the Heavens, on April 29. The module is the largest spacecraft developed by China to date, with a total length of 16.6 meters (55 feet) and a living space of 50 cubic meters (1,765 cubic feet), according to China Aerospace Science and Technology Corporation (CASC).

China has previously operated two space labs in orbit, the Tiangong-1 and Tiangong-2, both of which were trials for the larger space station the country is now building.

Chinese astronauts have long been excluded from the international space station (ISS), due to US political objections and legislative restrictions. Russia, a longtime contributor on the ISS, has also left the project and is now considering launching its own space station by 2030.

Zhou Jianping, chief designer on the country’s manned space program said in June that while China is not currently considering foreign participation in the space station’s development, non-Chinese astronauts will “certainly” be welcomed in the years to come.

“There are a number of countries that have expressed a desire to do that and we will be open to that in future,” said Zhou.

Lily Lee reported from Hong Kong, Amy Woodyatt wrote from London. Ben Westcott and Yong Xiong contributed reporting.