Rotating/Spinning

Hi unity folks I've been working on a game set in space and have been able to use mouse orbit script for a lot of what I want, making very slight adjustments to suit what I need, still very new to scripting so only know the basics. My astronaut can rotate around a planet on the x, using left and right and up and down on the y, with up and down arrows,but I also want to be able to spin around planets y using 2 other keys. Heres an illustration of what I mean, figure 2. is what I am having problems with, I want astronaut to be able to spin all the way around going upside down, and there returning right side up. Advice and pointing me in the right direction would be great. Thanks for your help guys