|The Phantom Torso, also known as "Fred,"
is an anatomical model of a human torso and head. Fred
contains hundreds of radiation monitoring devices.
(Click for a larger image.)
|Supernova explosions like this one accelerate
atomic nuclei to nearly the speed of light. The resulting
"cosmic rays" pose a potential hazard to astronauts.
for a larger image.)
May 4, 2001Fred has
no arms. He has no legs. His job is keeping astronauts safe.
Fred is the Phantom Torso, an approximately 95-pound, 3-foot-high
mockup of a human upper body. Beneath Fred's artificial skin are
real bones. Fred's organsthe heart, brain, thyroid, colon
and so onare made of a special plastic that matches as closely
as possible the density of human tissue.
Fred, who spent four months on board the International Space Station
(ISS) in 2001, measured the amount of radiation to which astronauts
are exposed. High-energy particles that pass through the human body
can disrupt the way cells function. Although no astronaut has ever
been diagnosed with space radiation sickness, excessive exposure
could lead to health problems.
"We believe the current dose [of radiation to the crew of the
ISS] is too small to be of concern," says Dr. Gautam Badhwar,
the study's principal investigator at the Johnson Space Center.
"The one possibility for radiation sickness might be an EVA
(Extra Vehicular Activity) situation during a solar event, if perhaps
a crew member couldn't be brought back inside safely." But
there's still lots to learn, he added, and that's where Fred can
The Phantom Torso was designed to do three things, explains Badhwar.
First, it determined the distribution of radiation doses inside
the human body at various tissues and organs. Second, provided a
way to correlate these doses to measurements made on the skin. "In
the past we've typically recorded doses only on the skin,"
explains Badhwar, "whereas the risk to crew members is established
by exposure to internal organs." Finally, the Phantom helped
check the accuracy of models that predict how radiation moves through
Three types of radiation can endanger astronauts in space.
The most energetic are Galactic Cosmic Rays (GCRs)the nuclei
of atoms accelerated by supernova explosions outside our solar system.
Cosmic ray nuclei can be as light as hydrogen, as heavy as iron,
or almost anything in between. Because they lack their surrounding
coat of negatively-charged electrons, GCRs are positively charged.
The heavier nuclei carry the greatest charge, explains Badhwar.
"As the charge increases, the amount of energy that the particle
can deposit in tissue increases as well."
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