Russian astronaut Alexei Leonov made history on March 18, 1965 when he stepped outside the ISS for a spacewalk.
The incident paved the way for many more to follow suit to not only look after the station but to study space more than ever before.
But, in the conspiracy community, spacewalks also offer another glimpse into a new world – alien craft.
Sensationally, theorists often claim to have seen UFOs lurking in the distance on NASA’s live feeds.
So, on Alexei’s iconic anniversary, Daily Star Online has brought together a list of some of the best – or most bizarre – sightings.
Mysterious ‘disc-shaped’ UFO
In a strange video recorded on the ISS in 2017, a white object was seen zooming into view in the lower left side of the shot when an astronaut carried out works.
The clip – at the top of this page – showed the object seeming to slow down as if being controlled.
Bruce Fenton, a researcher at Anomalous Phenomena told Daily Star Online: “Objects do not decelerate in space unless they are under some kind of control.
“Hard to tell the size but it seems far off in the distance so it is probably very large.”
NASA cuts ISS feed as UFO ‘appears’
An astronaut clip last year was mysteriously cut off after a circular object came into view while approaching the Earth’s atmosphere.
The live feed, which was transmitting with good quality and showed no sign of interference or disruption, became glitchy and eventually switched to a blank blue screen.
Conspiracist Tyler Glockner, who owns the YouTube channel Secureteam10, said: “They can’t leave the feed down for too long because then people will know they’re trying to hide things, you’ll notice an obvious change in what the astronaut is doing and how he is now panning the camera away from the object and back towards the ISS where you can no longer see it.
“Every time one of these UFOs appears, we would normally see this blue screen.
“They’re [NASA] watching the feed, we know that they cut it.”
‘Space Force craft’ watches astronauts
Conspiracists were convinced they had spotted the US Air Force’s Space Force in action when a mysterious object was spotted floating in space behind an astronaut in November.
The white object glided along and appeared to be watching and following the spacewalker.
A conspiracist reviewed the footage in slow motion and claimed the craft had “windows and obscure contours”.
MrMBB333 commented on his YouTube channel: “You’re going to see the object come into view multiple times from multiple different angles.
“I’ve put it in slow motion, look at it right there, unbelievable.”
And the comments section was filled with viewers’ claims they were witnessing the Space Force in action.
By firstname.lastname@example.org (Tiffany Lo)