LIVE: Astronauts spacewalk to fix space station
NASA astronauts are undertaking a spacewalk lasting more than six hours today to repair the International Space Station.
Drew Feustel and Ricky Arnold are going to replace a failed cooling component and install a camera system and communications receiver on the outside of the craft.
The pair previously completed another six-hour walk on 29 March to install wireless communications antennas and fix a buggy cooling system.
It will be the 210th spacewalk at the ISS since 1998, and the fourth so far this calendar year.
Specifically, the pair will be swapping out thermal control gear that circulates ammonia to keep the station's systems cool.
Any time an astronaut gets out of a vehicle while in space it's called a spacewalk.
The first ever spacewalk was conducted by Russian cosmonaut Alexei Leonov on 18 March 1965 and lasted for 10 minutes.
American astronaut Ed White followed on 3 June 1965 and lasted 23 minutes.
The typical spacewalk today takes place outside of the ISS and lasts between five and eight hours, depending on the job.
The astronauts wear spacesuits which provide them with the oxygen they need to breathe and the water they need to drink, and put these on several hours before the walk.
While in their suits they breathe pure oxygen for a few hours, getting rid of all the nitrogen in their body to avoid getting the bends – also common among divers.
When on a spacewalk, the astronauts are tethered to their spacecraft to stop them floating off into space and their tools are tethered to their suits to stop them from floating off as well.
The real safety mechanism for astronauts is their SAFER backpack, which stands for Simplified Aid for Extra-vehicular activity Resure".
SAFER uses small jet thrusters to let the astronauts move around in space and is controlled with a small joystick.
Before going into space, the astronauts train for spacewalks by swimming.
Astronauts practice spacewalks underwater in a large swimming pool called the Neutral Buoyancy Laboratory, or NBL near NASA's Johnson Space Center in Houston, Texas.
The pool holds 6.2 million gallons of water and astronauts spend seven hours training in the pool for every single hour they will spend on a spacewalk.
More from International Space Station
They also train by using virtual reality, wearing a helmet with a video screen inside and special gloves.
A video of what they will see during a spacewalk is shown on the screen inside the helmet and when the astronaut moves, the special gloves allow the movements to be shown with the video.