Another pair of bugs from the beta-testers (us players)

[Psitticine]

Mothballing a ship (or base) relieves you of its maintenence cost but it needs to be unmothballed before it can be used again. All experience will be zeroed by being mothballed and both mothballing and unmothballing require a ship yard in the same sector.

To do it, just go into the same screen where you also refit and scrap ships and the option will be there if you have a ship yard present.