What Does It Take To Reach Lightspeed In Kerbal Space Program?

After travelling relativisticly in A Slower Speed Of Light a few people asked about building lightspeed capable rockets in Kerbal Space Program. Here I do a few calculations to examine just what’s needed to do this, starting out with stock rockets, modded rockets and of course the infinite fuel cheat from the debug menu. Or you can always get lucky with glitches - like this entertaining one from Danny2462