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Updated: Oct 29, 2015 01:28 IST

Two Nasa astronauts stepped out on a spacewalk on Wednesday for upgrades and maintenance at the orbiting International Space Station, the US space agency said.

Spaceflight veteran Scott Kelly, who is in the midst of a year-long stint at the ISS, began the first spacewalk of his career at 8:03am (1203 GMT), according to a live broadcast on Nasa television.

His colleague, flight engineer Kjell Lindgren, is also embarking on his first spacewalk, the US space agency said.

Lindgren accidentally turned on his spacesuit’s water switch too early in the process of preparing to float outside the airlock, and Nasa experts at mission control in Houston were closely monitoring the cooling system on his spacesuit “just to be sure,” a Nasa commentator said.

Their tasks during the six and a half hour spacewalk include installing a thermal cover on a state-of-the-art particle physics detector, known as the Alpha Magnetic Spectrometer, which has been attached to the space station since 2011.

They also plan to “apply grease to components on the space station’s robotic Canadarm2, and route cables to prepare for new docking ports for US commercial crew spacecraft,” Nasa said.

While it is a pioneering spacewalk for both Kelly and Lindgren, it is the 189th in support of space station assembly and maintenance.