One of the most obscure and overlooked Stormtrooper variants from the original trilogy is the trooper type seen outside the Death Star docking bay as the Millennium Falcon is being pulled in via tractor beam (pictured above). Although some fans refer to this trooper as the "Spacetrooper", the official Star Wars databank already has that particular name reserved for another Expanded Universe character. As such, I'm calling this a Zero-G trooper to avoid confusion and to emphasize the spacewalking nature of these troops.
There are only a few photos known to exist that document this rare piece of trooper equipment, and none show a great degree of detail. We know that the basis of this costume is the Stormtrooper armor with some additions (much like the Sandtrooper is really a Stormtrooper variant). This trooper wears some kind of oxygen-supplying backpack with a hose leading to the front of the helmet, and also wears his gloves untucked and pulled up over the forearm armor (giving the appearance of really long wrists!)
An interesting thread on the RPF (which has been going since 2005) revealed an unproduced Marmit 1/6 scale Zero-G trooper:
Marmit is known for their attention to detail and realism, but what is interesting is that the backpack tanks on the figure appear to be based upon the tanker truck model parts that were kit-bashed as part of the Death Star trench seen here:
This was speculated by RPF members even before the awareness of the Marmit prototype and you can see the same tanks in this screen capture:
TK-8456 of the UK Garrison has made a fantastic effort in reproducing the space pack with little reference to rely upon. A groundbreaking first try:
Meanwhile, the hunt continues as, even 30 years later, new images continue to pop up from the Lucasfilm archives.
TRIVIA: The two Spacetroopers from Episode IV are believed to be Star Wars alumnus Joe Johnston filmed twice and superimposed. However, this production photo seems to suggest otherwise:
Special thanks to everyone on the RPF for helping to source this information.