Comments in another question led me to this image from A New Hope:
Why are stormtroopers walking around outside near the turbolaser batteries? What is there to guard or patrol in the cold vacuum of space? Are they doing an exterior patrol?
These appear to be regular stormtroopers. Maybe there is an extra pack suggestive of an EVA (Extravehicular Activity) shown.
They were retconned identified as such at Celebration Anaheim 2015, and got a collectible toy release from Hot Toys; quoting from their description:
The Spacetroopers are assigned to operate in Zero-G environments, and true Star Wars fans will see these troopers making their appearance when the Millennium Falcon was first captured by the Death Star.
[...]
This specialized trooper features a beautifully crafted armor and helmet, a highly detailed Spacetrooper rebreather pack with detachable parts, two types of blasters, and a specially designed figure stand.
Unfortunately, there's no mention of what they expect to find while patrolling the outside of a space station. For all we know, they're painting the hull.
true Star Wars fan". Marketing guy: "You are a genius, Mr Lucas. Have you ever considered a job in marketing?" Mr Lucas "I would not know what to do at marketing at all..."
As mentioned elsewhere, these are spacetroopers. There are all sorts of threats that could be spotted outside a space station, “in the cold vacuum of space,” and potentially effectively combated by stormtroopers:
Space-faring droids used as weapons. Buzz droids would be a particular threat, with the potential to destroy important installations, as demonstrated in the Rebel attack on the Star Destroyer Perilous.
Two vultures headed directly for the shield generator. He destroyed one and then another, but the buzz droids they carried floated out of the fire of the vultures’ destruction, glommed on to the shield generator, and there exploded into flame.
Lords of the Sith
The enemies of the Empire could even be employing leftover rocket battle droids, perhaps.
Even humans in space suits might be able to move along the outside of the ship, and potentially damage weapons or infiltrate the battle station.
This scene is taken wholesale from the Ralph McQuarrie concept art seen below:
In the concept art, troopers in black armor, presumably pressurized space suits similar to those of Darth Vader and TIE Pilots, stand in for the Stormtroopers / Spacetroopers seen in the final film.
Perhaps Stormtrooper extras were easier to source when filming.
In-(concept)-universe, these black-suited units are easier to imagine as Turbolaser Engineers and Death Star Trench Maintenance Staff than the military Stormtroopers seen in the final film. Perhaps they're even independent contractors.
"Do you think the average Stormtrooper knows how to [repair a Turbolaser]? All they know is killing and white uniforms."
They’re there to provide scale in the film, otherwise there wouldd be no way to tell if the “ceiling” in that shot was 20cm or 20m above their heads.
