I'll third this, the cannons in Expunge are much more "hostile" than in other locations (Mercury comes to mind). And they are inconsistent; one will act sort of normal, another won't launch you at all unless you stand in front of it and jump just right, another will kill you if you touch its exterior at some wrong location. It's either a problem, or just another chickens*** death-by-environment thing brought to you by Bungie.