Mugen no Ryvius, Sidonia no Kishi Recommendations
It's been about about 8to5 year since I watched ryvius but, from the first episode of sidonia it made me think of ryvius. They have semi-similar sub plots.
Ryvius is about somewhat of a militarily academy that teaches kids and teens do job such as pilot faint robots. Some thing happens to the ship to the point where all the kids are left alone and have to fend for the selves( similar to Lord of the flies). It's vary physiological. Overall it's a vary good anime that anyone should check out. Personally I'm probably going to re watch it again even though