Two NASA astronauts are carrying out a daring spacewalk in order to make vital upgrades to the International Space Station.
Kayla Barron and Raja Chari are conducting the six-and-a-half-hour mission, named US EVA 79, aimed at replacing equipment, some of which is 20 years old.
It is the start of a busy period of operations, NASA said - with uncertainty over Russia's cooperation.
Before the start of today's spacewalk, NASA posted on Instagram : "ASA astronauts Kayla Barron and Raja Chari will set their U.S. spacesuits to battery power on Tuesday at 8.05am EDT signifying the start of a six-and-a-half-hour spacewalk.
"The duo will install modification kits on the Starboard-4 truss structure that will ready the space station for its third roll-out solar array."
The pair were pictured during training at the Neutral Buoyancy Laboratory in Houston, Texas.
The operation is being live-streamed by NASA on YouTube.
Explaining the purpose of the spacewalk, the agency said in a statement: "The planned 6.5-hour Extravehicular Activity (EVA, or spacewalk) – US EVA-79 – is being performed by astronauts Kayla Barron and Raja Chari and is the 247th EVA for construction, operation, and maintenance of the International Space Station (ISS).
"The spacewalk officially began at 12:12 UTC to install a so-called “mod kit” on power channel 3A’s Mast Canister Assembly (MCA) located on the Starboard-4 (S4) Truss.
"The mod kit is essentially a mounting frame that will allow future spacewalkers to install a new ISS Roll-Out Solar Array (IROSA) as part of the ongoing ISS Power Augmentation (IPA) program.
"The IROSAs are gradually being installed on top of six of the station’s eight Solar Array Wings (SAWs) to increase the ISS’s electrical power output from its current level of 160kW up to 215kW."
NASA said the work is essential to replace ageing equipment.
It said: "Adding six new, smaller arrays – built by Boeing – is necessary due to degradation in the power output level of the SAWs, some of which have now been on-orbit for over 20 years.
"While the IROSAs are around half the size of the SAWs, they are around twice as efficient, meaning they produce about the same amount of power."
