Riding nuclear rockets to Mars will get us there incredibly fast, but is it the craziest, most irresponsible idea ever?

Getting to Mars is not easy, particularly when the interplanetary journey is measured in months instead of days. For robotic missions, the transit time poses no great challenge; as long as the batteries keep the mechanics from freezing, a robot doesn't mind the wait. But a manned mission is another story.The fastest transit to Mars is currently in the neighborhood of 180 days or six months. That's a long time for humans to sit and wait patiently. It's not an easy job to keep men alive and in good health outside the cocoon of the Earth's magnetic field for that long. There is one alternative, however. A faster rocket.

A rocket with greater thrust could propel a hypothetical crew to Mars faster, greatly lessening the transit time to the red planet. Traditional chemical rockets like the liquid fueled Apollo era vehicles and the solid rocket boosters of the Shuttle era are pretty much at their limit in terms of thrust generated. So without much room for advancement in our current means, we need to move to other types of rockets. In the case of Mars, and indeed for any mission to other planets and their moons, nuclear rockets are our best bet.

The first thing that jumps to my mind at the thought of a nuclear rocket—and I don't think I'm alone in this—is how can NASA launch a nuclear missile over Russian or Chinese airspace without starting a world wide crisis? The same holds if the situation were reversed: if China launched a nuclear rocket to put a satellite in orbit or send one towards the moon and it travelled over U.S. airspace, there would likely be an uproar citing endangerment of the American people. Perhaps this is an understandable reaction. No one wants to think about a Hiroshima-style bomb floating over their homes.

But like it or not, nuclear material has been an integral part of spaceflight for decades. It's just never been overly publicized.

NASA began pursuing propulsion of nuclear rockets in the early 1950s after idle discussion of applications for nuclear power eventually turned to flight; a nuclear reactor was thought to generate sufficient energy to propel aircraft or rockets higher and faster than any chemical rocket. The final push from talk to action came from Robert Bussard. Bussard fused his research into the unconstrained power of nuclear reactions with available hard data of chemical rocket launches to determine definitively that nuclear rockets were far superior in thrust, range, and payload capacity.

In light of his finding, Bussard was given lab space at Los Alamos test range to develop his nuclear rockets in 1955. Officially known as Project Rover, the quest for a nuclear powered rocket was jointly funded by NASA, the Atomic Energy Commission (AEC), and the U.S. Air Force.

The program progressed in phases, building progressively larger and more powerful nuclear reactors that could provide enough propulsion for a rocket launch. The first tests to fire a nuclear powered rocket engine—NERVA for Nuclear Engine for Rocket Vehicle Applications—took place in 1959 and were successful; moderate thrust through a controlled reaction proved nuclear propulsion was viable. Throughout the 1960s, Project Rover delivered more powerful nuclear rocket engines that produced more thrust for longer durations.

Like all programs within NASA, however, budget cuts at the end of the 1960s took a heavy toll on the nuclear rocket program. The nuclear Mars program fizzled and was cancelled. Although program managers in 1968 projected the first nuclear rockets to be ready for a Mars launch by 1975, this would never be. The rockets that took Vikings 1 and 2 to Mars in the 1970s used traditional chemical rockets.

Nuclear material, however, was still a key component in spaceflight. It just wasn't part of the rocket. At the heart of most planetary spacecraft set for long voyages through the solar system is a radioisotope thermoelectric generator (RTG), which is an energy source that gets its power from the decay of radioactive material. The subsequent heat released is converted to electricity that can power the spacecraft's instruments. With a slow enough decay, a spacecraft could live for decades as the Voyager spacecraft have done. Voyagers 1 and 2 (which have recently reached the heliopause, where our solar system formally ends) are powered with a nuclear source.

The same RTGs were used on Apollo missions 12 through 17 as an auxiliary power source for the instruments and experiments left on the Moon. But not all RTGs were left out of harms way. When Apollo 13 was aborted, the astronauts were forced to bring their nuclear payload home with them; the Lunar Module and its contents splashed down into the Pacific ocean just before the crew reentered the Earth's atmosphere. The nuclear core of an RTG is somewhere at the bottom of the ocean.

So should we be a little freaked out? Not if you trust NASA engineers. All nuclear material sent into space is properly packaged. It goes in a sort of black box on steroids; the casing is so strong that if it were next to a rocket that exploded it wouldn't rupture nor would the material inside be disturbed. The cases don't leak, don't react to decay, and are guaranteed for at least 100 years.

There's an obvious difference between a nuclear energy source and a nuclear rocket: the RTG may be safe if the rocket explodes, but if a nuclear rocket explodes, there's no containing that radioactive material violently expelled from the rocket's core.

Potential failure, however, has not deterred proponents of nuclear propulsion from pursuing nuclear rockets. The idea of a nuclear rocket to Mars has never really disappeared. In the 1970s, Robert Ragsdale proposed a nuclear-assisted mission that could get humans to Mars in 30 days. In the late 1980s, various NASA research sites including the Jet Propulsion Laboratory, the Marshall Spaceflight Centre, and the Los Alamos Laboratory presented nuclear propulsion to NASA as a necessary technology for the future of Mars missions. More recently, proposals have emerged suggesting a series of nuclear bombs detonated behind a spacecraft be used to propel it to Mars or another planetary destination.

For the moment, there are no definite plans for a nuclear powered rocket to launch a mission to Mars. But who knows—spaceflight may take on a whole new level of danger in the future.

Mars on Earth: The People Who Are Already Living On the Red Planet, No Spaceship Required
Mars Enthusiast Robert Zubrin Explains Why We Must Go to the Red Planet