Two Expedition 55 NASA astronauts ventured outside the International Space Station May 16, 2018, for a 6.5-hour-long spacewalk. They were tasked with rearranging coolant pumps and replacing external cameras and antennas.

The primary task of the spacewalk was to move two pump flow control subassembly, or PFCS, units. These devices are designed to drive and control the flow of ammonia coolant on the exterior of the ISS to regulate the temperature of the station’s power-generating equipment, according to NASA.