European Space Agency astronaut Alexander Gerst prepares his suit for a planned six-and-a-half-hour spacewalk Tuesday outside the International Space Station. Gerst and astronaut Reid Wiseman plan to move a faulty cooling pump to a secure location and to carry out a variety of maintenance tasks. NASA

Space station astronauts will venture outside the complex Tuesday and again next week to move a failed ammonia pump to a more secure storage location, to replace an electrical component that will restore one of the lab's solar power channels to normal operation and to carry out a variety of "get-ahead" maintenance tasks.

The two U.S. spacewalks will set the stage for a complex series of eight to 10 NASA spacewalks and module relocations next year that are needed to prepare the station for dockings by Boeing and SpaceX commercial crew ferry craft.

Two commercial crew docking adapters will be installed, one on the front end of the forward Harmony module where shuttles once docked and the other on the module's upper space-facing port. Harmony's Earth-facing port will remain available for use by visiting cargo ships.

A pressurized storage module now attached to the Earth-facing port of the central Unity module will be moved to the forward side of the Tranquility compartment where the multi-window cupola is located, making way for equipment that will enable visiting cargo ships berth at Unity.

The relocations will be carried out remotely using the station's robot arm, but multiple spacewalks will be needed to route and re-route power and data cables and to install a universal communications and navigation system that will be used by Boeing and SpaceX crew craft during station approaches and departures.

When the work is complete, the U.S. segment of the station will be able to accommodate two commercial crew vehicles and two cargo ships at the same time, providing fully independent access to the lab complex for the first time since the space shuttle's retirement in 2011.

"When you look out a little further as to how the EVAs stack up after the first of the year and out into the spring, we're really going to start this transformation of the space station," said Kenny Todd, space station integration and operations manager. "We're going to be doing the things we need to do on these EVAs to prep for moving some modules around.

"All that is in preparation for being able to support future commercial crewed vehicles coming to station. We're trying to get out in front of that. We'll be prepping for moving modules, we'll be installing a new docking adapter system. All of that will be happening throughout the next several months."

But first, NASA is staging a pair of spacewalks to complete unfinished business, to restore an electrical power channel to normal operation and to move camera lights and equipment needed for the upcoming commercial crew reconfiguration.

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Space station crew gears up for two spacewalks