The space helmet does appear on the D-Pad (Inventory), I just print-screened right before it.
Space Helmet On (Notice how there aren't any Frag Grenades or Gersch Device's):
The picture above is when he has it on, but not when he can move while he has the space helmet on.
Space Helmet in Inventory (Now the Space Helmet, Frag Grenades, and Gersch Device Appear):
http://callofduty.wikia.com/wiki/P.E.S
Yeah, you are right. I just noticed that.
According to COD Wiki, P.E.S. stands for Pressurized External Suit, which makes sense.
P.E.S.:
This is for people that didn't see the P.E.S., when the person was putting on the space helmet.
Yes and the biggest thing is that there are different animations. When he puts that on, the gas mask blocks different areas than when the character has the space helmet on, leading me to think they are completely different.
Like I said before, maybe they were lazy and didn't want to make a new animation for the space helmet.
Hudson with Gas Mask On (Same Outline as Space Helmet):
Skip to 9:30