BEIJING, Jan. 22 (Xinhua) -- Space-tracking ship Yuanwang 3 and Yuanwang 7 returned to the port of the China Satellite Maritime Tracking and Controlling Department after completing three monitoring missions, the Science and Technology Daily reported Wednesday.

So far, all four space-tracking ships in service, including Yuanwang 5 and Yuanwang 6, have made it back to China.

Since November 2019, Yuanwang 5, Yuanwang 7 and Yuanwang 3 had sailed out in succession to carry out maritime monitoring in relays for the Long March-5 Y3 rocket launch in the Pacific Ocean.

Afterward, Yuanwang 5 returned and Yuanwang 3 went to the next mission area. Yuanwang 7 subsequently spent five days performing monitoring and control tasks for China's heaviest satellite Shijian-20.

Over the past year, vessels of the Yuanwang fleet have completed 17 monitoring missions and one rocket transporting task.

They operated more than 550 days at sea, sailing over 130,000 nautical miles in 2019, said the newspaper, citing sources from the China satellite maritime tracking and controlling authorities.