As we know it, 3D printing is usually confined to small-scale projects like headphones. NASA is ever so slightly more ambitious. It's using a closely related technique from Concept Laser, selective laser melting, to build elements of its Space Launch System on a pace that wouldn't be feasible with traditional methods. By firing brief, exact laser pulses at metal powder, Concept Laser's CAD system creates solid metal parts that are geometrically complex but don't need to be welded together.
Engadget , NASA building Space Launch System with laser melting, adapts 3D printing for the skies (video), NASA building Space Launch System with laser melting, adapts 3D printing for the skies (video)