  This paper provides an overview of the radiation aspects of manned space
flight to Moon and Mars. The expected ionizing radiation dose for an astronaut
is assessed along the Apollo 11 flight path to the Moon. With the two dose
values, the expected and the measured total dose, the radiation shielding and
the activity of the Sun are estimated. To judge the risk or safety margin the
radiation effects on humans are opposed. The radiation from the Sun has to be
set to zero in the computer model to achieve the published radiation dose value
of the Apollo 11 flight. Galactic and cosmic particles have not been modelled
either. The Apollo 11 astronauts must have been lucky that during their flight
the Sun was totally quiet in the solar maximum year 1969 - and also their
colleagues of the subsequent Apollo flights, i.e. until 1972, where the
published dose values still require a quiet Sun. The here built mathematical
model allows assessing the total dose of a journey to Mars by only changing the
flight duration. Even if in the meantime much thicker and/or active radiation
shielding is proposed the radiation risk of manned space flight to Moon and
Mars remains still huge.
