The Martian Chronicles
Issue 8, Winter 2001

"Nuclear" Is Not a Four-Letter Word
by Richard Reifsnyder

Mars Craft in Mars Orbit

Mars Craft in Mars Orbit
Art: Yul Tolbert
(click for larger image)

There have been numerous Mars mission development teams over the past few decades, and there is one thing on which they agree: a human mission to Mars - or to anywhere else - would be far easier using nuclear power.

Yet for many environmental groups, "nuclear" is a four-letter word. When they hear that word they think of Hiroshima, Chernobyl, and Three Mile Island. They often forget that nuclear power supplies a significant fraction of America’s electricity, is the only source of power for many cities, and that there is a tradeoff between the risk of radiation from disposed nuclear fuel and the millions of tons of carbon dioxide and smog produced by fossil fuel plants.

In space there is a similar tradeoff between enormous power reserves provided by nuclear energy and the relative safety of chemical and solar technologies.

It is understood that nuclear propulsion, either thermal rockets that heat hydrogen propellant, or nuclear-powered ion drives, would both significantly increase the amount of payload that can be sent to Mars. However, since these vehicles are fission-powered, the risk of meltdown is nonzero - and is actually higher during launch into Earth orbit, when the rocket beneath the payload can explode. Using chemical propulsion would require more launches to orbit, and launch costs are a significant fraction of total mission costs.

But while nuclear propulsion is not vital to a Mars mission in the near term, nuclear power almost certainly is. The only known alternative to nuclear power is solar power, which works well in space and can be used in the human habitat during the outbound transit.

But solar power is perhaps less useful on the Martian surface. Consider: first, the luminous intensity of sunlight in Mars orbit is less than half that in Earth orbit. Second, there is no sunlight at night. Solar panels are already only one-quarter as effective on the Martian surface as in Earth orbit.

Even more importantly, there is the matter of dust storms - which not only appear without warning, but can last for weeks or even months. The concentration of sunlight reduces by another factor of four. There is no way to store months’ worth of solar power using batteries or fuel cells. Considering the maze of solar panels adorning Mir or the International Space Station in Earth orbit, attempting to carry sixteen times that much area, to produce the same power output, to the Martian surface, and set it up, is an outlandish proposition. The array would cover several football fields, and outweigh the human habitat itself. To top it off, dust deposition gradually reduces the effectiveness of photovoltaic panels. A human could dust these panels off with a broom every so often, but sweeping several football fields would waste valuable exploration time. The Viking landers were powered by nuclear reactors that kept them transmitting for three years, while the Pathfinder with its solar panels ran out of power within three months.

Anti-nuclear activists filed several lawsuits to protest the launch of the nuclear-powered Cassini space probe on the grounds that a launch failure would pollute the planet. In reality, the few pounds of plutonium oxides onboard were chemically inert, having a half-life of 88 years (not hundreds of thousands of years like ground-based nuclear waste), and would release only about one ten-thousandth of the radiation of an atomic bomb - and into the ocean, at that.

The fact is, the risks to Earthlings of using nuclear electric power on any space mission are trivial. By choosing NASA as a scapegoat for the nuclear-related maladies caused by reactors on Earth, these activists would only condemn the human race to the surface of Earth.