Radiation Measured by NASA's Curiosity on Voyage to Mars has Implications for Future Human Missions

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May 30, 2013

Trent J. Perrotto 
Headquarters, Washington                              
202-358-1100 
trent.j.perrotto@xxxxxxxx 

Deb Schmid 
Southwest Research Institute, San Antonio 
210-522-2254 
deb.schmid@xxxxxxxx 

RELEASE: 13-165

RADIATION MEASURED BY NASA'S CURIOSITY ON VOYAGE TO MARS HAS IMPLICATIONS FOR FUTURE HUMAN MISSIONS

WASHINGTON -- Measurements taken by NASA's Mars Science Laboratory 
(MSL) mission as it delivered the Curiosity rover to Mars in 2012 are 
providing NASA the information it needs to design systems to protect 
human explorers from radiation exposure on deep-space expeditions in 
the future. 

MSL's Radiation Assessment Detector (RAD) is the first instrument to 
measure the radiation environment during a Mars cruise mission from 
inside a spacecraft that is similar to potential human exploration 
spacecraft. The findings will reduce uncertainty about the 
effectiveness of radiation shielding and provide vital information to 
space mission designers who will need to build in protection for 
spacecraft occupants in the future. 

"As this nation strives to reach an asteroid and Mars in our 
lifetimes, we're working to solve every puzzle nature poses to keep 
astronauts safe so they can explore the unknown and return home," 
said William Gerstenmaier, NASA's associate administrator for human 
exploration and operations in Washington. "We learn more about the 
human body's ability to adapt to space every day aboard the 
International Space Station. As we build the Orion spacecraft and 
Space Launch System rocket to carry and shelter us in deep space, 
we'll continue to make the advances we need in life sciences to 
reduce risks for our explorers. Curiosity's RAD instrument is giving 
us critical data we need so that we humans, like the rover, can dare 
mighty things to reach the Red Planet." 

The findings, which are published in the May 31 edition of the journal 
Science, indicate radiation exposure for human explorers could exceed 
NASA's career limit for astronauts if current propulsion systems are 
used. 

Two forms of radiation pose potential health risks to astronauts in 
deep space. One is galactic cosmic rays (GCRs), particles caused by 
supernova explosions and other high-energy events outside the solar 
system. The other is solar energetic particles (SEPs) associated with 
solar flares and coronal mass ejections from the sun. 

Radiation exposure is measured in units of Sievert (Sv) or 
milliSievert (one one-thousandth Sv). Long-term population studies 
have shown exposure to radiation increases a person's lifetime cancer 
risk. Exposure to a dose of 1 Sv, accumulated over time, is 
associated with a 5 percent increase in risk for developing fatal 
cancer. 

NASA has established a 3 percent increased risk of fatal cancer as an 
acceptable career limit for its astronauts currently operating in 
low-Earth orbit. The RAD data showed the Curiosity rover was exposed 
to an average of 1.8 milliSieverts of GCR per day on its journey to 
Mars. Only about 5 percent of the radiation dose was associated with 
solar particles because of a relatively quiet solar cycle and the 
shielding provided by the spacecraft. 

The RAD data will help inform current discussions in the United States 
medical community, which is working to establish exposure limits for 
deep-space explorers in the future. 

"In terms of accumulated dose, it's like getting a whole-body CT scan 
once every five or six days," said Cary Zeitlin, a principal 
scientist at the Southwest Research Institute (SwRI) in San Antonio 
and lead author of the paper on the findings. "Understanding the 
radiation environment inside a spacecraft carrying humans to Mars or 
other deep space destinations is critical for planning future crewed 
missions." 

Current spacecraft shield much more effectively against SEPs than 
GCRs. To protect against the comparatively low energy of typical 
SEPs, astronauts might need to move into havens with extra shielding 
on a spacecraft or on the Martian surface, or employ other 
countermeasures. GCRs tend to be highly energetic, highly penetrating 
particles that are not stopped by the modest shielding provided by a 
typical spacecraft. 

"Scientists need to validate theories and models with actual 
measurements, which RAD is now providing," said Donald M. Hassler, a 
program director at SwRI and principal investigator of the RAD 
investigation. "These measurements will be used to better understand 
how radiation travels through deep space and how it is affected and 
changed by the spacecraft structure itself. The spacecraft protects 
somewhat against lower energy particles, but others can propagate 
through the structure unchanged or break down into secondary 
particles." 

After Curiosity landed on Mars in August, the RAD instrument continued 
operating, measuring the radiation environment on the planet's 
surface. RAD data collected during Curiosity's science mission will 
continue to inform plans to protect astronauts as NASA designs future 
missions to Mars in the coming decades. 

SwRI, together with Christian Albrechts University in Kiel, Germany, 
built RAD with funding from NASA's Human Exploration and Operations 
Mission Directorate and Germany's national aerospace research center, 
Deutsches Zentrum fur Luft- und Raumfahrt. 

NASA's Jet Propulsion Laboratory, a division of the California 
Institute of Technology in Pasadena, Calif., manages the Mars Science 
Laboratory Project. The NASA Science Mission Directorate at NASA 
Headquarters in Washington manages the Mars Exploration Program. 

For more information about the findings and the Mars Science 
Laboratory mission, visit: 

http://www.nasa.gov/msl 

For more information about NASA human spaceflight and exploration, 
visit: 

http://www.nasa.gov/exploration 

	
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