So I am trying to find this anime I watched as a child - recently I re-watched all of robotech 1 2 and 3 and it was awesome.
So what I remember from this anime was: the good guy's space ship: was like a long tube which elongated or contracted based on necessity and was green color. The crew left earth and wound up on some other planet where they saw many people being enslaved.
Some substance was at the heart of everything.
Also I saw it in europe in the late 80s or early 90s.
EDIT: Oh and to get to this planet they hit its surface and it was all water, and they kept going deeper, while the ship could barely withstand the pressure, then they suddenly emerged from the bottom in to a paradise like scene.