Talk:Split Chamber/@comment-23270394-20131023033458

Mods don't drop on specific missions more then others of the same kind. There is an equal chance of it getting it every five minutes in a corpus tier three defense mission (2.01%), and an equal chance on all tier three survival missions every five minutes after the first 15. (6.67%)

Defence missions are: Venus: Kiliken (becomes tier 3 at wave 15), Venera (same). Mars: Olympus (same). Europa: Eligor (starts at T3, as do the rest), Paimon. Neptune: Thallassa, Despina. Pluto: Narcissus, Outer Terminus.

Survival missions are a bit more complicated, read the tables on this page to see stats (you will never guess where that link takes you).