One of the reasons why man hasn't visited other planets is because it's essentially a one way ticket to eventual suicide. A rocket can get you to Pluto, but how are you going to come back? If 3D printing takes off in space, we could be printing our spaceships to get back to Earth in the future.
A company called Made in Space is looking into using 3D printers to print parts for spacecraft and space stations in space. The benefit of printing parts in space is obvious — there's no need to shuttle it up from Earth. Imagine printing a lunar rover or an entire space deck to attach to the International Space Station. As an added bonus, if a space part is damaged, it can be recycled back to produce new replacements. How eco-friendly.
Testing to see how 3D printing will withstand zero gravity are scheduled with a trial on the ISS set if everything goes well. We're sure that the fine astronauts up in space wouldn't mind getting a printed iPhone 10 or whatever directly from Steve Jobs' top secret schematics.