Dead Space: Extraction

You'll unlock the Atrium Challenge after completing Chapter 9 of the story mode. The top score is 259,010 so you need more than this to earn the trophy.

This is another straightforward challenge that can be done using either the tactic outlined in Overtime Sheet or the one in Herbal Remedies. There are not any new enemies, although the map is quite a large one so you might find it a bit harder using the Flame-thrower. I got a streak of 56 which gave me 408,586 points. As there are a whopping 220 enemies in this challenge, getting a high streak is really not important.