When we do go back to the Moon or Mars 3D printers will be most valuable tools.  We can replace parts, build unforeseen needed objects - and perhaps create a new ride back 

Here is my personal factory fabricating S hooks, which I use to hang pots and pans in my kitchen.  It is printing 3-up.  May seem quaint but I have never liked how commercial metal hooks work.  The hooks come off with the pan handle in the flow cooking and interrupt the zen.  I designed the geometry of the hook to stay affixed while still being able to easily slide. Here is what the finished product looks like in use. http://pinterest.com/pin/242209286179707277/