Well I've tried to come close :
I used reaper, Izotope Trash 2 for saturation and Izotope Ozone 5 for multiband compression.
1. pitch shift - 3 semitones
2. Cut some low freqs with EQ
3. Izotope Trash with these settings : http://i.imgur.com/Sd5k2lq.jpg
4. Izotope Ozone with these settings : http://imgur.com/a/6RC4G
I have just seen the following article where this sound effect is mentioned (http://www.latimes.com/entertainment/envelope/la-en-craft-star-wars-sound-20160204-story.html). It is interesting to note that the dialogue was recorded with two mics: one in the helmet itself and the other on the chest. Clearly the timbre of the two recordings will be different, ...