Washington, Feb 20 (IANS): The US space agency is all set to perform three spacewalks -- the first one scheduled for Saturday -- to reassemble parts of the International Space Station (ISS) to create parking spots for Boeing and Space Exploration Technologies (SpaceX-- two commercial space taxis.

The Expedition 42 astronauts Barry Wilmore and Terry Virts are preparing the ISS for a pair of international docking adapters (IDAs) that will allow future commercial crew vehicles to dock, NASA said in a statement.

The reconfiguration is the first major overhaul of the ISS which was completed in 2011.

Amid the spacewalk preparations, the Expedition 42 crew members continued ongoing advanced microgravity science benefiting life on the Earth and current and future crew members.

The crew looked at stem growth for the Aniso Tubule botany experiment, cell cultures grown on orbit and a crew member's cardiac activity during long-duration missions.

"The biggest change will be the relocation of the Leonardo multipurpose module from the Unity to the Tranquility connection nodes -- an operation that will be tackled robotically via ground control," space station programme manager Mike Suffredini was quoting as saying.

The first spacewalk is set to begin Saturday at 7.10 a.m. (EST).

NASA has awarded contracts to Boeing and SpaceX to develop, test and fly capsules that can taxi astronauts to and from the station.

According to SpaceX, the upgraded Dragon V2 passenger spacecraft should be ready for an unmanned debut test flight to the station in late 2016 and a crewed test flight in early 2017.

Boeing plans is to dock an unmanned CST-100 test flight to the station in April 2017.