There's a funny thing about space exploration: If something goes wrong aboard ship the consequences could easily be terminal. Outer space is one of the most inhospitable environments imaginable, and meat bodies are remarkably resilient as long as you don't remove them from their native environment (which is to say dry land, about one atmosphere of pressure, and a remarkably fiddly chemical composition). Space travel inherently removes meat bodies from their usual environment and puts them into a complex, fragile replica made of alloys, plastics, and engineering; as we all know, the more complex something is, the more things can go wrong and Murphy was, contrary to popular belief, an optimist. Case in point, the Apollo 13 mission, which was saved by by one of the most epic hacks of all time. It's worth noting, however, that the Apollo 13 CO2 scrubber hack was just that - a hack. NASA really worked a miracle to make that square peg fit into a round hole but it could easily have gone the other way, and the mission might never have returned to Earth. Sometimes you can make the parts you have work for you with some modification, but sometimes you can't. Even MacGyver failed once in a while.*
So, you're probably wondering where this is going. On the last resupply trip to the International Space Station one of the pieces of cargo taken up was... you know me, so I'll dispense with the ellipsis - a 3D printer that uses ABS plastic filament as its feedstock. It was loaded on board the ISS as part of an experiment to test how feasible it would be to microfacture replacement parts during a space mission rather than carry as many spare components as possible. It is hoped that this run of experiments will provide insight into better ways of manufacturing replacement parts in a microgravity environment during later space missions. The 3D printer was installed on 17 November 2014 inside a glovebox, connected to a laptop computer (knowing NASA, it was probably an IBM Thinkpad), and a test print was executed. Telemetry from the test print was analyzed groundside and some recalibration instructions were drafted and transmitted to the ISS. Following realignment of the 3D printer a second, successful test print was executed three days later. On 24 November 2014 the 'printer was used to fab a replacement component for itself, namely, a faceplate for the feedstock extruder head. Right off the bat they noticed that ABS feedstock adheres to the print bed a little differently in microgravity, which can cause problems at the end of the fabrication cycle when the user tries to extract the printer's output. An iterative print, analyze, and recalibrate cycle was used to get the 'printer set up just right to microfacture that faceplate. 3D printers are pretty fiddly to begin with and the ISS crew is trying to operate one in a whole new environment, namely, in orbit. The experimental schedule for 2015 involves printing the same objects skyside and groundside and comparing them to see what differences there are (if any), figuring out how to fix any problems and incorporating lessons learned and technical advancements into the state of the art.
NASA's official experimental page for the 3D printer effort can be found here. It's definitely worth keeping a sensor net trained on. * Technically, it was just the one time - if memory serves, it was a kidney dialysis machine that he wasn't able to fix, and the focus of the episode changed to getting a brand-new one to a hospital in the middle of nowhere or something.