Two NASA astronauts have installed a tools storage unit, dubbed robot hotel, to the outside of the International Space Station, freeing up living space inside the station.The "robot hotel", officially called the Robotic Tool Stowage (RiTS), was attached to the station's Mobile Base System (MBS) during a spacewalk conducted by NASA astronauts Robert Behnken and Chris Cassidy on Tuesday.The MBS is a moveable platform that provides power to the external robots, NASA said.This special location allows RiTS to traverse around the station alongside a robot that will use the tools it stores."RiTS provides thermal and physical protection for tools stored on the outside of station, not only freeing up room on board but also allowing the Canadian Space Agency's Dextre robot to access them more quickly," said RiTS Hardware Manager Mark Neuman.The first step in the RiTS installation process involved preparing the unit inside the space station.The astronauts unpacked RiTS' occupants from storage -- two units of a tool called the Robotic External Leak Locator (RELL) -- and affixed them inside RiTS' aluminum housing.The installation required the astronauts to mechanically attach RiTS to an available worksite socket then mate two electrical cables to unused power outlets on the MBS.The power connection was critical to enabling heaters within RiTS that keep the RELL tools from getting too cold.Apart from installing the robot hotel, the two NASA astronauts completed a number of other tasks designed to upgrade International Space Station systems.This was the 10th spacewalk for each astronaut.