It's all to keep the environment out. The vast fore shield, a now-ragged slice of a sphere casting its broken shadow across the hull- it is the most obvious aspect of this, but it's not the only one. The standoff shields, arrayed along the ship's spine and built to take the brunt of the terror involved in the turnaround maneuver, are pitted and torn open now. The engine is quiescent, with no helpful particle-blocking exhaust to speak of. Behind the shields... layers and layers of shipstuff, keeping a long-gone ecosystem in a bubble of habitable space. All, now, is equalized with the void.
