Mars doses

["Leif Peterson, Ph.D." <peterson@bcm.tmc.edu>]

When I managed the astronaut exposure history archives during 1986-95, the
word was that a Mars trip would take about a year and the projected nominal
dose equivalent to the blood forming organs (BFO) at a 5-cm depth was ~30
cSv or more.  Nuclear propulsion (fusion) could significantly cut down the
flight time and hence the dose.  Risks for acute exposures abound on a Mars
mission.  With long flight durations, the risk of exposure to high-energy
protons and helium ions from proton events associated with X-class (and
higher) flares goes up.  The frequency of these proton events goes up in
solar max, but there is more solar plasma in interplanetary space, which
helps cut down on the background cosmic ray dose in the absence of a
significant proton event.  In order to get a handle on the forecasting of
solar flares that originate on the back side of the sun, away from the
Earth, there were plans of putting four heliocentric (around the sun)
satellites with detectors in orbit.  Since NASA is always viewed as "paying
your cable bill" in terms of the Gov't budget, this changed things a little
so everyone gave up on that idea.  

A couple of years ago, there was a NASA study called the "90-day" study that
addressed mission duration and the effects of the interplanetary radiation
levels.  NCRP Report 98 is also a good reference to look for Mars data, but
it is outdated by more complete information from the Langley and Johnson
dosimetry groups.  

Since fusion and space environment modeling are not my areas, I'll stop
there.  I'll stick with health effects from fission devices!

-LP