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Exposure Limits for Astronauts




Exposure Limits for Astronauts 
have been proposed by the Space Science Board Committee on Space Medicine,
with levels about one order of magnitude greater than the maxima allowed for
workers in the nuclear industry:

NASA annual maximum limit for space flight :  50 rem (500mSv)
(compared to 2 - 5 rem occupational limit on Earth)

NASA career limit for different ages and gender :  100 - 400 rem (1 - 4Sv)

(former USSR standards allowed cosmonauts 66.5 rem a year, but not more than
162.5 rem per three years)

...all of the above from the August 1999 issue of SPACEFLIGHT magazine
article by Erik Seedhouse, "Radiation Concerns for Astronauts."

(comment: these limits may force future manned Mars mission planners to
choose nuclear rocket propulsion to shorten the flight duration... as
already acknowledged by some astronauts at a meeting last winter:
> > ----------
> > From: 	Michael C. Baker[SMTP:mcbaker@lanl.gov]
> > Reply To: 	Ans-pie
> > Sent: 	Thursday, February 04, 1999 2:55 PM
> > To: 	Multiple recipients of list ans-pie
> > Subject: 	nuclear space power news
> > 
> > 
> > Feb. 2, 1999
> > 
> > Astronauts at Albuquerque forum push for return
> > of nuclear power in space
> > 
> > By Lawrence Spohn
> > TRIBUNE REPORTER
> >      
> >      Four American astronauts have crossed the politically correct line
> > and said it's time to start talking again about nuclear power in space.
> >      Speaking at a packed session of the Space Technology and
> Applications
> > International Forum in Albuquerque on Monday, the astronauts --
> including
> > Apollo flier John Young -- said they want nuclear power for future
> missions
> > and they want research into it to resume now.
> >      The four said they hope to soon present compelling reasons for
> federal
> > agencies and Congress to support a long-term nuclear-power program to
> > develop energy reactors and propulsion systems for space missions.
> >      Current propulsion systems are chemical-based, and electrical power
> > systems used inside spacecraft get their power from solar panels.
> >      Young, who worked with nuclear generators to power experiments on
> the
> > moon, said it's a tragedy that since then nuclear has become a bad word.
> >      One of the casualties has been putting manned exploratory missions
> of
> > the solar system into an endless holding pattern, he said.
> >      "We should be going back to the moon and Mars, and we should be
> doing it with nuclear power," Young said. "That's exactly what this great
> nation
> > ought to be doing."
> >      In fact, Young said, some NASA missions could never have been done
> > without nuclear power and many proposed for the new millennium would be
> > foolhardy to attempt without it.
> >      The astronauts' comments were cheered by an audience of aging
> > nuclear-power scientists and engineers who over the past four decades
> have seen their research programs achieve technical milestones only to
> have funding cut.
> >      About 650 scientists and engineers are attending the forum, which
> is
> > organized by the University of New Mexico's Institute for Space and
> > Nuclear Power Studies. It is actually five separate space-science
> conferences, under way concurrently at the Hyatt Regency Hotel.
> >      The oldest of the conferences, the 16th Symposium on Space Nuclear
> > Power and Propulsion, merged with the others several years ago when
> federal funding for space nuclear-power research waned.
> >      Young and astronauts Franklin Chang-Diaz, John Grunsfeld and John
> > Herrington said they aim to kick-start that research by writing a paper
> > stating the virtues of nuclear energy in space.
> >      Grunsfeld said chemical and solar energy systems "aren't going to
> get
> > us very much farther" and that whoever the astronauts are who eventually
> are
> > selected to go to Mars, nuclear power will give them "the best possible
> > chance of succeeding."
> >      The astronauts' nuclear campaign is "a grass-roots effort," said
> > Chang-Diaz, estimating that perhaps a dozen in NASA's astronaut corps
> share the view that nuclear power is fundamental to pushing space
> exploration beyond Earth orbit.
> >      But Young complained that while NASA Administrator Dan Goldin
> firmly
> > supports missions to the moon and Mars, he "doesn't want nuclear power."
> >      Opponents of nuclear-powered missions have raised concerns about
> the
> > risks of an explosion on takeoff and the release of radioactive
> material.
> >      Chang-Diaz said the growing pro-nuclear astronaut cadre will be
> working
> > with scientists and engineers at New Mexico's Sandia and Los Alamos
> > national laboratories to develop technical arguments to support their
> effort.
> >      Taking on the political establishment, however, could require a
> massive
> > public-education campaign. The astronauts and several scientists
> suggested
> > that they need to help Americans understand that astronauts, who risk
> > their lives, find nuclear power far superior to other energy sources.
> >      They said nuclear power has many advantages, including that it is
> > fast, relatively simple and reliable.
> >      These are critical considerations, they said, in getting astronauts
> > to their destination quickly, partly to minimize the negative effects of
> > weightlessness on the body but also to minimize radiation exposure.
> >      The astronauts said that background cosmic radiation and solar
> > radiation bursts are far more dangerous to them than on-board nuclear
> reactors or propulsion systems.
> >      Sandia researcher Roger Lenard put the risks bluntly, suggesting
> > "what these astronauts are saying here today is that when the (sand)
> storm hits Mars and the lights (from a solar station) go out, these guys
> don't want to be the ones to prove that, hey, without nuclear power,
> they're all going to die."
> >      He suggested that the last thing weary astronauts would want to do
> > upon arriving at Mars would be to set up and maintain a complex array of
> solar collectors.
> >      "They're there to explore," Lenard said, noting that a nuclear
> > reactor can be turned on virtually with the flip of a switch.
> >      Likewise, he argued, a fast nuclear- propulsion system would get a
> > crew to Mars in one-third to one-fourth the time that a chemical rocket
> could
> > make trip and that because of background space radiation, "going slow
> and
> > taking a long time is the worst thing you can do for these guys."
> >      Los Alamos scientist Deborah Bennett, who worked on previous space-
> > nuclear projects at the lab, suggested the problem really is much
> broader
> > and proposed that the astronauts and scientists create an alliance with
> > nuclear- power companies and scientists.
> >      Another scientist suggested studying France, where nuclear power
> > provides most electrical energy and the population overwhelming supports
> nuclear energy.
--------------

jaro
frantaj@aecl.ca



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