What technology would exist in this vast subsurface ocean?
Perhaps they might harness the hydrothermal vents to melt holes in the ice to get to the surface.
Fortunately, this is an Apollo level project, the ice is estimated to be 10 to 15 miles thick. By the time they get close to the top, they should be aware of the dangers at the surface. Especially the explosive geyser they would create when they breached!