In one episode The Doctor has to do a space walk in order to get the better of The Master and thus dons this space suit.
It’s a nice green number with duel oxygen cylinders and a matching silver space helmet. The helmet is the same as the ones used in Pathfinders to Mars but with the plastic visor left in. There’s a big padded neck piece that seems to match the big padded wrist bands but in truth this helps to hide the fact that the helmet doesn’t quite come all the way down at the back. This is why the Pathfinder space suits appeared to have hoods; in order to disguise this same shortcoming in the helmet’s design.
Coincidentally this Doctor Who story is also written by Malcolm Hulke, one of the two Pathfinder writers.