After axing its research on nuclear-powered rockets in the 1970s, NASA spent $18.8 million last year on a deal with BWXT Nuclear Energy Inc. to develop fuel and a reactor to power a nuclear-thermal propulsion engine. The decades-old technology is NASA’s most viable option for landing humans on Mars. Its revival has also renewed a Cold War-era competition among the United States, Russia, and China to reach the next landmark in space—this time, the red planet.

The engine works by heating fuel, which expands and gets channeled through a nozzle to create thrust. Compared to standard rockets, which create thrust by burning fuel, the nuclear-powered system has huge payoffs.

That doubles the efficiency at which the rocket uses fuel, allowing for a “drastically smaller” craft and shorter transit time, said Stephen Heister, a professor at Purdue University’s School of Aeronautics and Astronautics. “This factor is absolutely huge, especially for very difficult missions that necessitate a lot of propellant such as a Mars flight.”

In fact, this factor would nearly halve the travel time compared to recent Mars missions.

Other countries have already begun working on the same technology. Russia has the lead, having already deployed dozens of nuclear-powered rockets in space, and China has announced plans to use atomic power to fuel its space exploration. In this reincarnation of the space race, NASA also faces domestic competition from private companies like Elon Musk’s SpaceX and Jeff Bezos’ Blue Origin , which are developing their own fission engines.

Despite the technology’s promise, the cost of development and testing—the reason the original effort was canceled in the 1970s—continues to be a challenge. Yet building on prior research may give NASA an advantage.

If it succeeds, the same technology could even be the basis of energy production for future colonies on the red planet.