structures while using enclosed inflatable habitats for housing the human occupants inside the hard-shell lunar structures. Overall, these habitats would require only ten percent of the structure mass to be transported from Earth, while using local lunar materials for the other 90 percent of the structure mass. "Printed" lunar soil would provide both "radiation and temperature insulation. Inside, a lightweight pressurized inflatable with the same dome shape would be the living environment for the first human Moon settlers." The building technology would include mixing lunar material with magnesium oxide, which would turn the "moonstuff into a pulp that can be sprayed to form the block" when a binding salt is applied that "converts [this] material into a stone-like solid." Terrestrial versions of this 3D-printing building technology are already printing of building material per hour with the next-generation printers capable of per hour, sufficient to complete a building in a week. 3D-printed structures On January 31, 2013, the ESA working with Foster + Partners, tested a 3D-printed structure that could be constructed of lunar regolith for use as a Moon base. Transportation Earth to the Moon Conventional rockets have been used for most lunar explorations to date. The ESA's SMART-1 mission from 2003 to 2006 used conventional chemical rockets to reach orbit and Hall effect thrusters to arrive at the Moon in 13 months. NASA would have used chemical rockets on its Ares V booster and Altair lander, that were being developed for a planned return to the Moon around 2019, but this was cancelled. The construction workers, location finders, and other astronauts vital to building, would have been taken four at a time in NASA's Orion spacecraft. Space elevators are another proposed concept of Earth-Lunar transport. On the surface Lunar habitation would need the ability to transport cargo and people to and from modules and spacecraft, and to carry out scientific study of a larger area of the lunar surface for long periods of time. Proposed concepts include a variety of vehicle designs, from small open rovers to large pressurized modules with lab equipment, such as the Toyota rover concept. Rovers could be useful if the terrain is not too steep or hilly. The only rovers to have operated on the surface of the Moon () are the three Apollo Lunar Roving Vehicles (LRV), developed by Boeing, the two robotic Soviet Lunokhods and the Chinese Yutu rover in 2013. The