China's Shenzhou-15 crew, currently onboard the country's space station, recently completed its first spacewalk.

Like many spacewalk missions, extended pump sets and foot limiters featured in their first spacewalk. They may sound familiar. But what are they and how do they function?

Extended pump sets: 'Heart' of thermal control system 

China's space station has a thermal control system, which is like a central air conditioner. 

It can adjust the temperature so as to provide a suitable environment for astronauts and equipment.  

The extended pump is needed to circulate the liquid in the system. 

All three modules of the space station are equipped with extended pump sets, which function like the heart of the human body, Su Nan, chief designer of overall machinery for the space station spacewalk mission with the China Aerospace Science and Technology Corporation, told China Media Group. 

The heat of equipment in the space station is absorbed by a large metal plate that is leaned against the equipment. By circulating the liquid through the extended pump sets, the temperature can be decreased, Su explained.

The extended pump sets are installed outside a capsule. They can be plug-and-play and replaced if they malfunction in the future, he added.

Foot limiters: Fixing astronauts at working position 

Astronauts are in a weightless state after leaving the cabin, and if they want to work at a designated location, their position needs to be fixed. The solution is foot limiters, which are commonly used auxiliary devices when astronauts conduct extravehicular activities.  

"The foot limiter has a fixed position on the cabin body, when astronauts need to work at a certain point on the bulkhead, there must be a foot limiter," Su said.  

The space station has four foot limiters, which are stored in the hatches of the airlock compartment and the node compartment, Su said. 

When astronauts leave the cabin, they will determine the installation position of the foot limiter according to their mission needs, he added.  

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Space Log: How is the 1st spacewalk of China's Shenzhou-15 crew?