OT - A long way to go for a short distance

[Ragnarok]

Perhaps this explains it:

The spacecraft cannot fly straight to Mercury; it does not carry nearly enough fuel. So it will fly once past Earth, twice past Venus and three times past Mercury for gravity assists — and make 15 loops around the sun — before slowing enough to slip into orbit around the small, hot planet.

I don't know how going around planets that many times will solve the fuel issue unless they use the gravity somehow to slingshot the whole way.