NASA engineers are building the largest rocket ever constructed — one that will eventually take us beyond the moon — using 3D-printed materials.

Creating this rocket, called the Space Launch System (SLS), is a top priority at the agency because it has a big date: Obama wants to get humans to an asteroid and then on to Mars by the mid 2030s. To speed up the construction process, NASA is relying on a form of 3D printing to fabricate some of its engine parts virtually out of thin air.

The machine, called selective laser melting, uses a laser to build a component. Unlike traditional rocket building, which relies on welding together disparate parts, 3D printing starts with an empty table. That space fills up with a completed component, built one layer at a time, out of NASA's 3D-printing material of choice.

What used to take weeks to build now only takes hours.

"We were looking at a way to save costs, be more efficient and reduce weight. That's how we got here," says NASA Administrator Charles F. Bolden, Jr.

"The big thing about 3D printing is that there are no welds with seams, no places for stuff to leak in a component," he tells Mashable. "It starts from nothing and grows into what you want in one fell swoop."

NASA engineers fabricate a nanolaunch injector and calorimeter as an engineering test piece for the Space Launch System.

NASA has been using 3D printing technologies for years. However, selective laser melting is a new process, and using it to develop rocket engine parts is something the agency has never done before.

The SLS rocket is significant because it can do something our now-retired Space Shuttle fleet never could: take us into deep space.

As a first-stage rocket, the SLS's main booster blasts off from the launch pad and gives the initial thrust to the vehicle in order to get it out of the atmosphere. For any rocket launch, speed (and power) is everything; the SLS will have 8-to-9 million pounds of thrust.

Right now, SLS can lift 70 metric tons into space, but it will eventually be able to lift 130 metric tons. That is significant for a long-term mission that could take months. "When we go to the moon, we don't need a heavy-lift rocket," Bolden says. "But we do need significantly more weight [when traveling to an asteroid or Mars]."

SEE ALSO: Are Humans Meant to Live on Mars?

Why does 3D printing help the SLS? It turns out that these light-weight plastic components actually handle the stress of a high-speed launch better than some heavier, welded materials.

While Mars is in SLS's future, an asteroid will more than likely come first. One of the advantages of this vehicle is the ability to get to an Earth-threatening asteroid before it's too late. That task is even more pressing after last week's surprise meteor in Russia, followed by an unrelated asteroid flyby that came, by recorded standards, a little too close to Earth.

"The farther out you intercept an asteroid, the less you have to do to throw it off its orbit," Bolden points out. "If we can detect and characterize an asteroid, we can get to it quicker. It will be less work to steer it off its path."

How would NASA stop an asteroid from slamming into Earth? While there have been proposals to nuke space rocks, Bolden disagrees with that strategy, saying this would just create more asteroids. Instead, he suggests nudging an incoming asteroid off course.

"Everything we know about has magnetic properties. So if we can find a way to get a vicinity of an asteroid, then you may be able to tractor it or repel it," he says.

Perhaps 3D printing will one day save planet Earth, but for now the process satisfies a more pressing need: domestic manufacturing.

"When the president highlighted advancement in manufacturing in his State of the Union Address, our ears were bubbling," Bolden says. "We've been doing this for several years."

Frank Ledbetter (right) of chief of nonmetallic materials and manufacturing division at NASA’s Marshall Space Flight Center, discusses the pogo z baffle assembly with materials engineer Nancy Tolliver. The baffle is part of the RS-25 engine that will power the core stage of the Space Launch System engine.

Images courtesy of MSFC/Emmett Given