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. (Click for a larger image.)

May 4, 2001—Fred 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 organs—the heart, brain, thyroid, colon and so on—are 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 help.

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 the body.

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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Additional Resources:

Learn more about the radiation monitoring devices Fred contains.

Learn more about space radiation sickness.