High Frontier can help Mars Direct

I have heard estimates that
ionising radiation levels at the Martian surface, are a factor of three less
than those at the moons surface. The figures that I've heard suggest that Mars may be a factor of two to three less than free space. I suspect the moon would be a factor of two belowspace (half of your surroundings is blocked by the moon), so I think Mars has a slim margin over the moon. That to me makes sense, since the only thing Mars presently has over the moon is an atmosphere only 1% as dense as ours.