Can bulldozers save Moonwalkers from solar flares?

Space 30 May 2006

The best way to protect astronauts living and working on the Moon from harmful solar radiation is being debated by lunar scientists.

Burying a habitat module under lunar dirt is one option currently being discussed by scientists on a lunar discussion group. Another option, to protect astronauts from solar flares when working away from their base, might be to set off explosives to create an emergency trench as a shield.

Such options were detailed in the late 1980s but have recently been revived by scientists discussing options for a Moon base as part of an academic exercise for students.

As NASA works toward launching humans to the Moon in the next decade, such discussions may move from the realm of academic exercise to real-life survival strategy.


For long-term stays on the Moon – not just the week-long excursions proposed by NASA – a durable shelter takes priority. One of the major hazards to humans is radiation because the Moon lacks Earth’s magnetic field to deflect incoming solar flares. So one solution might be to build the habitat module in a crater before covering it with soil.

Using a bulldozer or other robot to push soil over a habitat module would not be easy. If the bulldozer’s weight is reduced to one-sixth its Earth weight on the Moon, the force it is able to push with is also reduced by one-sixth.

“That means it gets stuck much easier,” explains Edward McCullough, principal scientist in advanced aero analysis at Boeing Phantom Works in Huntington Beach, California, US.

Secondary particles

Scientists estimate that between 3 metres and 5 m of lunar soil, called regolith, would be necessary to pile on top of a module to adequately protect it against solar radiation. Less than that, and the regolith shielding would cause incoming high energy particles from the Sun to split into secondary particles, which could be just as damaging to humans.

If a solar flare is coming and a crew is outside the habitat module, they may not have time to make it back to the main base. So they could blast a crater or trench that could be used as an emergency shelter to shield them from the potentially deadly radiation.

But it is not clear whether explosives could be stashed at predetermined sites. A 1985 paper by scientists at Los Alamos National Laboratory suggested that it would take over 100 kilograms of dynamite to create a shelter in Martian soil, for example.

Resurfacing debates

“There has to be a safety mechanism in place, a plan that says, in the event of this worst case scenario here’s where you go,” says Andrew Daga, president of Daga Research, a consulting firm in Malvern, Pennsylvania, US.

But blowing things up on the Moon comes with its own set of problems. The fine particles accelerated by a blast will not have Earth’s atmosphere or Earth’s gravity to slow them down.

The issue has resurfaced now because Wendell Mendell, manager in the office for human exploration science at NASA’s Johnson Space Center, posed a question to a group of lunar scientists for a graduate student class in Torino, Italy.

“A lot of these questions have been revisited since the 1950s,” Daga says. “The validity of these ideas is underlined by the fact that they keep coming up.”