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"We
have one solar maximum left to learn what we need to know
before we send humans back to the Moon."
–-Prof. Robert Lin, Chairman of the Solar Sentinels
Working Group, SPD, June 2006
Sept.
1 , 2006: In his 1970s book, Space, James
Michener depicted a fictional Apollo mission that lost its
crew to radiation from a massive solar flare. He based his
tale on what easily might have been but for lucky timing:
a massive flare on Aug. 7, 1972 occurred between Apollo 16
(April) and Apollo 17 (December), mankind's last journeys
to the Moon.
 The
event still resonates today. NASA is preparing to send astronauts
back to the Moon and on even longer journeys to Mars. With
crews "out there" for extended periods, "the
chances go way up that they'll be caught in the middle of
a storm," says David Hathaway, a solar physicist at NASA's
Marshall Space Flight Center.
Right:
Apollo 16 astronaut Charlie Duke on the Moon in April 1972.
[More]
"The
educated view about the August 1972 flare is that a crew on
the surface of the Moon would have gotten really sick."
Or worse. Dr. Lawrence Townsend of the University of Tennessee
and his colleagues calculated that energetic particles from
a super flare, like that recorded by Sir Richard Carrington
in September 1859, could kill.
Not
only humans are at risk. Miniaturized modern electronics are
more susceptible to radiation damage than their predecessors
were 40 years ago. A recent example: Japan's Nozomi Mars probe
was crippled by an intense solar energetic particle event
in April 2002. Future NASA probes are going to be vulnerable,
too.
"NASA
needs reliable forecasts of space weather," says Hathaway.
The
problem is, scientists are still learning to make these forecasts.
"It's often said that space weather forecasting is 50
years behind Earth-weather forecasting. We need to catch up."
A
good "catch-up" opportunity is just around the corner.
Solar Cycle 24 is beginning and it is expected to reach maximum
between 2010 and 2012. During that time, there will be an
abundance of solar flares and coronal mass ejections (CMEs)
for astronomers to study.
"NASA
astronauts are scheduled to return to the Moon around 2020,"
notes Robert Lin, a solar physicist at UC Berkeley. "We've
got only one solar maximum left to learn what we need to know"
to protect those crews.
Lin
recently chaired a team commissioned by NASA in 2004 to study
a "Solar Sentinels" mission that would help scientists
learn to predict solar storms in time to warn astronauts.
Their report has just been published: link.
Above:
the cover of the just-released Solar Sentinels report. [More]
They
note that several new spacecraft are already planned for studying
the Sun during Cycle 24, including the Solar Terrestrial Relations
Observatory (STEREO), Solar-B, and the Solar Dynamics Observatory.
These missions will take 3D pictures of solar explosions,
map the unstable magnetic fields of sunspots (the source of
flares), and probe the sun's inner magnetic dynamo.
But that may not be enough. Additional
eyes and sensors are needed, the Sentinels team argues, to
help address two key questions: (1) How are solar energetic
particles accelerated from the Sun? And (2) how are CMEs born?
In particular, they recommend the following:
Inner
Heliospheric Sentinels--four identical probes stationed
inside the orbits of Venus and Mercury. These spacecraft would
sample freshly accelerated solar energetic particles close
to the Sun.
 Right:
The four Inner Heliospheric Sentinels will face unique thermal
and power challenges as they orbit the Sun, some well inside
Mercury's orbit. [Larger
image]
Near-Earth
Sentinel—a single probe orbiting Earth. This Sentinel
would carry a coronagraph, a special telescope for observing
the Sun's faint corona where CMEs get their start.
Farside
Sentinel—a single probe to watch the farside of the
sun. Together with other spacecraft, this sentinel would provide
a complete picture of the sun--not just the half we see from
Earth.
"The
Sentinels would be based on existing technology so they could
be built and launched in time for the next solar maximum,"
says Lin. The Sentinels themselves aren't intended as a day-in/day-out
operational warning system. "But what we learn from it
will naturally form the basis for a true operational network."
NASA's
Science Mission Directorate is considering the Sentinels recommendations.
Meanwhile, Solar Cycle 24 is beginning.
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Author: Dave Dooling
| Editor: Dr.
Tony Phillips | Credit: Science@NASA
|
