Contour crafting is effectively a form of 3-D printing. Using this technique they propose sending robots to seed the surface of the moon with the basic infrastructure for a moon base. Once the construction is completed, human crew could lift off and move into their new home. A robot arm extrudes concrete while automated trowels smooth the material into place. On earth, the promise it gives is low-cost, individually customized house construction—the same promises that 3-D printers give to object creation, but on an architectural scale.