As it was just a science experiment, infinite fuel has been used...
But in the end I achieved this tight orbit!
I tried to land on the sun as well for the fun of it. The surface at 0 m is not solid. Currently debating if I wanna wait the 30 minutes it takes to get to the centre of the sun.
That's great, this is what I like about ksp just coming up with whatever and being able to do it.