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The Future of Deep Space Travel is RAD

In the hour of descent as the Mars Space Laboratory dropped toward martian soil a small gadget whirred. The gadget was a particle catcher.

Mars Science Laboratory approaching the martian atmosphere (artist's concept)
Image Credit: NASA/JPL-Caltech 

The size of a coffee pot, NASA's Radiation Assessment Detector (RAD) hitched a ride on the Mars Space Laboratory to measure the radiation of the martian atmosphere. RAD is the first instrument to measure the radiation on the way to Mars from inside a spacecraft that is similar to one future human astronauts could fly to Mars. The results will be published in the May 31 issue of the journal Science. Today, four members of the research teams reported the results at NASA's press conference in Washington, D.C.

It's in the journey -- and in the destination

Radiation Assessment Detector
for Mars Science Laboratory
Image Credit: NASA/JPL-Caltech/SwRI

"We realized, that taking measurements on the way to Mars would be not so different from the environment the future human astronaut might experience on their spacecraft on their way to Mars." said RAD principal investigator Donald Hassler from the Southwest Research Institute.

The researchers turned RAD on about ten days after the Mars Space Laboratory launched in November, 2011 and collected data about the radiation environment inside the space capsule for seven months.

"NASA is planning on sending astronauts to Mars in the 2030's," said Chris Moore, the deputy director of advanced exploration systems at NASA headquarters, "Before we can send astronauts there, we need to understand the environments and hazards they would face. RAD data will help us design the space habitats in which astronauts will live on their trip to Mars."

There are two types of deep space radiation the RAD system measures: galactic cosmic rays and solar energetic particles. Galactic cosmic rays come from outside the solar system and are thought to originate at supernova remnants and other high-energy explosions. Despite their high energy, they radiate at moderately low levels that vary over the eleven-year solar cycle. In contrast, solar energetic particles during solar storms and coronal mass ejections are very difficult to predict and can last anywhere from hours to days. While spacecrafts do a pretty good job of keeping solar energetic particles out, we don't yet know how to prevent cosmic rays from penetrating the ship's living quarters.

Radiation exposure comparison from Mars trip
Image Credit: NASA/JPL-Caltech/SwRI
Radiation exposure during deep space missions remains an outstanding health concern for astronauts. The RAD measured that the Curiosity rover was exposed to 1.8 milliSieverts per day of radiation from galactic cosmic rays, during its seven month journey to Mars. Only about five percent of Curiosity's radiation exposure came from solar particles, thanks to a calm solar cycle and shielding from the spacecraft.

"In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Cary Zeitlin, lead author and principal scientist at the Southwest Research Institute in NASA's statement.

Based on the new RAD data, engineers at NASA hope to design more effective shielding for future deep space flight. "The radiation environment in deep space is several hundred times more intense than on earth," said Zeitlin, "that's even inside a shielded spacecraft."

Dressing for Mars

There are basically two ways to protect astronauts from radiation, according to Moore.

"Hydrogen is the best radiation shield we know about", said Moore. One way to protect a crew would be to surround their living quarters with walls filled with water. Water, which is rich in hydrogen, absorbs the radiation. Moore said that NASA is also tossing around the idea of arranging food packets around the spacecraft living quarters; food, rich in water, also contains a lot of hydrogen.

Currently, NASA uses polyethylene, a material made up of long chains of hydrogen. "Some of our initial concepts [for new space suits] involve multiple layers of polyethylene plastic," Moore said, "I tried on one of these garments once. It reminds me of samurai armor. Or a very heavy coat."

In 2015, NASA is launching a version of RAD to the International Space Station. With comparable instruments on the ISS and on Mars, researchers will be able to compare radiation levels, calculate health risks, and develop new tools for the future of deep space travel. 


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