The Clear Sky (Чистое небо) faction is an independent scientific/military organization focusing on understanding the Zone.

We're researchers. We're trying to figure out the nature of the Zone, determine the reasons which caused it to appear, and formulate the rules that govern its existence. We are not consumed by a quest for money, we don't seek fields of artifacts, and we're not interested in turf wars with other factions. That is why we're hiding here in the Swamps and concentrating on our research. Our forte is not combat, but knowledge - knowledge of the Zone, accumulated over years of research. We know more about it than stalkers and the government combined, and our research was finally shaping up into a sound, coherent picture... until most of our members died trying to stop Strelok in the C.N.P.P. We might be getting great results again,but restoring and gathering further research seems complicated for now.