Sprachenheitz

I'm not sure if someone asked this question before,but what is the RCS for so far I have no clue on what it does and I' not sure what it is for P.S thank you for the answers LIVE WELL AND PROSPER FELLOW KERBONAUTS!!!

Hello everyone. I am new to KSP ,I had fun playing it for the past 88 hours I haven't made it to any planet so far but it's really fun to try over and over again! LIVE WELL AND PROSPER GUYS!!!