At the end of the week, American astronauts will perform two spacewalks to replace the broken cooling pump

The pump, which is responsible for cooling half of the station's avionics and electrical systems, broke down on Saturday due to a short circuit. It will be replaced by a spare pump stored at the station

NASA decided to wait until Friday to perform a spacewalk to replace a faulty ammonia pump on the International Space Station.
Mission managers, flight controllers, engineers, astronauts and spacewalk experts made the decision Monday evening after analyzing and refining the engineering requirements and reviewing the results of training conducted underwater and transmitted to the station.

The two American space station astronauts Doug Wilcock and Caldwell Dyson are currently scheduled to perform the first of two spacewalks on Friday. Their colleagues Cady Caldwell and Sunny Williams spent Monday afternoon in the Underwater Training Laboratory at the Johnson Space Center to examine the tasks required to restore the cooling system during two spacewalks.

Meanwhile, robotics experts continue to plan the procedures that astronaut Shannon Walker will use to guide the robotic arm as she moves Wilcock into position to replace the damaged unit with a spare unit stored on Storage Platform 2. The spare part will be attached to the Quest airlock that Wilcock and Caldwell-Dyson will use for exit and return. to the station

The situation at the station today was stable. The crew continued their normal sleep shifts and supported normal work hours, but most of their scheduled activities for the current week were postponed or changed in order to support preparations for the spacewalk.

According to the plans, the carrier located on the outside of the station will be placed on Thursday in component s1. By positioning the carrier at the start of the mission, the team will be able to collect additional data to check if the power resources are sufficient for the robotic arm to be used during the spacewalk or if additional power is required.

Each such pump weighs 350 kg, is 90 cm high, 1.57 meters long, and 1.25 meters wide. The spacewalkers will require disconnecting and reconnecting five electrical connectors, four fluid tubes, one connecting rod and four belts. The spare pump that will be used to replace the damaged unit was brought to the station on mission STS-121 in July 2006.

The pump broke down on Saturday night after an electrical spark caused a short in the electrical circuit. When the pump stopped working it shut down half of the station's cooling system. Attempts to restart the pump, which delivers refrigerated ammonia gas to the cooling loops to maintain the low temperature of the station's electrical and avionics systems, were unsuccessful. Station crew members worked together with control center personnel to restore the station to a stable configuration.