MARS, the International Journal of Mars Science and Exploration, has just published two articles by Donald Rapp about the hurdles still to be clarified before sending astronauts to the Fourth Planet: “Mars life support systems” and “Radiation effects and shielding requirements in human missions to the moon and Mars”
The latter article contains sobering statements about the current status of space-travel technology (my emphasis):
For Mars missions, we conjecture a 400-day round trip transit to and from Mars, and about 560 days on the surface. The [Galactic Cosmic Radiation] dose equivalent with 15 g/cm2 of aluminum shielding during Solar Minimum is about double the allowable annual dose for each leg of the trip to and from Mars. If a major [Solar Particles Event] occurred during a transit, the crew would receive a sufficient dose to reduce their life expectancy by more than the 3% limit. […]
On the surface of Mars, the accumulated [Galactic Cosmic Radiation] exceeds the annual allowable [amount]. For a 560-day stay on Mars [it] would exceed the career allowable dose for most females and younger males.
May Richard Branson live looooooooong then (and prosper)!