NASA astronauts Robert Behnken and Chris Cassidy are going to perform an important task that requires them to step outside the International Space Station (ISS). The pair will conduct the final spacewalk in an effort to complete a 3.5-year mission of upgrading the station's power system.

According to NASA's blog, the duo will perform several tasks during the spacewalk apart from replacing the last remaining nickel-hydrogen batteries with new lithium-ion batteries. The operation could last up to seven hours and will be streamed live.

The operation of changing batteries began in the year 2017. So far, 11 spacewalks have taken place in the endeavour. Now, the 12thand the final one will take place on Tuesday as conducted by Behnken and Cassidy. Meanwhile, this will be the 300th spacewalk carried out by astronauts from the U.S., since the first one in 1965 by Ed White. Furthermore, it is the 231st spacewalk in the history of space station assembly, maintenance, and upgrades and ninth for both Cassidy and Behnken.

During the walk, Behnken will perform as extravehicular crew member 1 and Cassidy will be extravehicular crew member 2. Watch out for the two astronauts during the live stream by recognising them from their varying spacesuits. While Behnken will be dressed in a spacesuit with red stripes, Cassidy will wear one with no stripes.

As per the release, once the systems are upgraded, astronauts will perform some other maintenance tasks outside of ISS, a modular space station in low earth orbit which has been visited by astronauts, cosmonauts, and space tourists for more than 20 years.

"When the power upgrades are complete, the astronauts will shift gears and remove two lifting fixtures used for ground processing of the station's solar arrays prior to their launch," reads the press release explaining astronauts' tasks during a spacewalk.

"They'll also begin preparing the Tranquility module for the installation of a commercial airlock provided by NanoRacks and scheduled to arrive on a SpaceX cargo flight later this year. The airlock will be used to deploy commercial and government-sponsored experiments into space."

Cassidy landed at ISS in April for Expedition 63. Meanwhile, Behnken, the flight engineer for the expedition, arrived at the station in May along with Commercial Crew astronaut Douglas Hurley on SpaceX's Crew Dragon Demo-2 test flight.

NASA astronauts Douglas Hurley and Robert Behnken
NASA astronauts Douglas Hurley, left, and Robert Behnken, right. Photo: NASA / Bill INGALLS

The spacewalk will take place Tuesday and will be live-streamed on NASA's official YouTube channel, NASA television, and its website. The live stream will begin at 12:35 pm BST.