[ RadSafe ] Sensor on Mars Rover to Measure Radiation Environment

[ROY HERREN]

http://mars.jpl.nasa.gov/msl/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1081


11.09.2010
Sensor on Mars Rover to Measure Radiation Environment

About eight months before the NASA rover Curiosity touches down on Mars in 
August 2012, the mission's science measurements will begin much closer to Earth. 


The Mars Science Laboratory mission's Radiation Assessment Detector, or RAD, 
will monitor naturally occurring radiation that can be unhealthful if absorbed 
by living organisms. It will do so on the surface of Mars, where there has never 

before been such an instrument, as well as during the trip between Mars and 
Earth.
RAD's measurements on Mars will help fulfill the mission's key goals of 
assessing whether Curiosity's landing region on Mars has had conditions 
favorable for life and for preserving evidence about life. This instrument also 
will do an additional job. Unlike any of the nine others in this robotic 
mission's science payload, RAD has a special task and funding from the part of 
NASA that is planning human exploration beyond Earth orbit. It will aid design 
of human missions by reducing uncertainty about how much shielding from 
radiation future astronauts will need. The measurements between Earth and Mars, 
as well as the measurements on Mars, will serve that purpose.
"No one has fully characterized the radiation environment on the surface of 
another planet. If we want to send humans there, we need to do that," said RAD 
Principal Investigator Don Hassler of the Boulder, Colo., branch of the 
Southwest Research Institute.
Whether the first destination for human exploration beyond the moon is an 
asteroid or Mars, the travelers will need protection from the radiation 
environment in interplanetary space. Hassler said, "The measurements we get 
during the cruise from Earth to Mars will help map the distribution of radiation 

throughout the solar system and be useful in mission design for wherever we send 

astronauts."
RAD will monitor high-energy atomic and subatomic particles coming from the sun, 

from distant supernovas and from other sources. These particles constitute the 
radiation that could be harmful to any microbes near the surface of Mars or to 
astronauts on a Mars mission. Galactic cosmic rays, coming from supernova 
explosions and other events extremely far from our own solar system, are a 
variable shower of charged particles. In addition, the sun itself spews 
electrons, protons and heavier ions in "solar particle events" fed by solar 
flares and ejections of matter from the sun's corona. Astronauts might need to 
move into havens with extra shielding on an interplanetary spacecraft or on Mars 

during solar particle events.
Earth's magnetic field and atmosphere provide effective shielding for our home 
planet against the possible deadly effects of galactic cosmic rays and solar 
particle events. Mars, though, lacks a global magnetic field and has only about 
one percent as much atmosphere as Earth. Just to find high-enough radiation 
levels on Earth for checking and calibrating RAD, the instrument team needed to 
put it inside major particle-accelerator research facilities in the United 
States, Europe, Japan and South Africa.
An instrument on NASA's Mars Odyssey orbiter, which reached Mars in 2001, 
assessed radiation levels above the Martian atmosphere. Current estimates of the 

radiation environment at the planet's surface rely on modeling of how the thin 
atmosphere affects the energetic particles, but uncertainty in the modeling 
remains large. "A single energetic particle hitting the top of the atmosphere 
can break up into many particles -- a cascade of lower-energy particles that 
might be more damaging to life than a single high-energy particle," Hassler 
noted.
The 1.7-kilogram (3.8-pound) RAD instrument has an upward-pointing, wide-angle 
telescope with detectors for charged particles with masses up to that of iron. 
It can also detect secondary neutrons coming from both the Mars atmosphere above 

and Mars surface material below. Hassler's international RAD team includes 
experts in instrument design, astronaut safety, atmospheric science, geology and 

other fields.
Southwest Research Institute, in Boulder and in San Antonio, Texas, and 
Christian Albrechts University, in Kiel, Germany, built RAD with funding from 
the NASA Exploration Systems Mission Directorate and Germany's national 
aerospace research center: Deutschen Zentrum für Luft- und Raumfahrt. The team 
assembling and testing the Mars Science Laboratory spacecraft at NASA's Jet 
Propulsion Laboratory in Pasadena, Calif., installed RAD onto Curiosity last 
month for the late-2011 launch.
RAD measurements during the trip from Earth to Mars will enable correlations 
with instruments on other spacecraft that monitor solar particle events and 
galactic cosmic rays in Earth's neighborhood, then will yield data about the 
radiation environment farther from Earth.
Once on Mars, the rover's prime mission will last a full Martian year -- nearly 
two Earth years. A one-time set of measurements by RAD would not suffice for 
determining the radiation environment on the surface, because radiation levels 
vary on time frames both longer than a year and shorter than an hour. 
Operational planning for Curiosity anticipates that RAD will record measurements 

for 15 minutes of every hour throughout the prime mission.
Radiation levels probably make the surface of modern Mars inhospitable for 
microbial life. The measurements from RAD will feed calculations of how deeply a 

possible future robot on a life-detection mission might need to dig or drill to 
reach a microbial safe zone. For assessing whether the surface radiation 
environment could have been hospitable for microbes in Mars' distant past, 
researchers will combine RAD's measurements with estimates of how the activity 
of the sun and the atmosphere of Mars have changed in the past few billion 
years.
"The primary science goal of Curiosity is to determine whether its landing site 
is, or ever was, a habitable environment, a place friendly to life," said JPL's 
Ashwin Vasavada, deputy project scientist for the Mars Science Laboratory. "That 

involves looking both for conditions that would support life as well as for 
those that would be hazardous to life or its chemical predecessors. Natural, 
high-energy radiation is just such a hazard, and RAD will give us the first look 

at the present level of this radiation and help us to better estimate radiation 
levels throughout Mars' history."
JPL, a division of the California Institute of Technology in Pasadena, manages 
the Mars Science Laboratory Project for NASA's Science Mission Directorate, 
Washington. For more information about the mission, see 
http://mars.jpl.nasa.gov/msl/ .

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov
2010-376