You're looking to, or you've already downloaded @Nertea's shiny, shiny things so the air filters on your Laythe base keep filtering, or so the cryogenic fuel in your Eeloo probe doesn't escape.   But how do you use these exactly? How do you balance the reactors, engines, radiators and overall dry mass to get decent TWR, consistent burns and keep the reactors in their prime too? Here is all the introductory info you need to get you going. Topics will be added over time so don't worry t