MIAMI: Two US astronauts successfully embarked on Tuesday on what Nasa described as a “critical” spacewalk to repair a failed piece of equipment that helps power the International Space Station.

“We have declared victory,” Nasa commentator Rob Navias said about two hours into the emergency spacewalk by space station commander Peggy Whitson, 57, and flight engineer Jack Fischer, 43.

The reason for the outing was the sudden breakdown on Saturday of a computer relay box known as multiplexer-demultiplexer (MDM) unit.

The MDM — which is about the size of a small microwave oven and would weigh 50 pounds (23 kilograms) on Earth — helps operate solar arrays, electrical power generation, and robotic equipment at the ISS. It also regulates the operation of radiators and cooling loops.

Since there are two MDMs at the orbiting outpost, the loss of one did not jeopardize the lives of the crew or bring a halt to station operations.

Still, a space agency spokesman described Tuesday’s mission as a “critical contingency spacewalk” and called it a “high priority” to replace the failed box as soon as possible.

During the shorter than normal spacewalk which lasted just two hours and 46 minutes — much less than the typical 6.5 hours — Whitson took the lead and replaced the MDM. “We now have two healthy MDMs,” Navias said.

Meanwhile, Fischer, making the second spacewalk of his career, installed a pair of antennas on the US Destiny Laboratory module to enhance wireless communication capability for future spacewalks. It was unclear what caused the MDM to fail.

Published in Dawn, May 24th, 2017