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MSL - RAD Science Reports
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RAD looks at long & short-term Radiation-Dose Variations on Mars
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November 15, 2012
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MSL RAD – the Radiation Assessment Detector of the Mars Science Laboratory has been steadily acquiring data as it continued to operate as planned over the course of the early surface mission.
With a growing set of radiation data obtained on the Martian surface, RAD scientists have presented their initial findings showing interesting correlations of impinging cosmic radiation with weather phenomena at Mars.
With a growing set of radiation data obtained on the Martian surface, RAD scientists have presented their initial findings showing interesting correlations of impinging cosmic radiation with weather phenomena at Mars.
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The chart to the right shows the daily variations in radiation measured by RAD and atmospheric pressure measured by REMS. As the pressure increased, the overall radiation dose decreases. This anticorrelation is caused by the shielding effect the atmosphere has. A thicker atmosphere causes higher pressures and increases the shielding effects the atmosphere has against radiation coming from space. At the pressure maximums, the total radiation level drops about 3 to 5 percent. The diagram nicely illustrates this connection as its shows the Radiation Dose Rate (red) and the atmospheric pressure curve (blue). To fit into the diagram, the pressure readings were divided by four. The radiation dose is given in arbitrary units as work to calibrate the instrument and data to show absolute units is still underway. The plot shows radiation and pressure readings taken from Sol 21 through 26 of the landed mission (August 26 to September 1).
"We see a definite pattern related to the daily thermal tides of the atmosphere," said RAD Principal Investigator Don Hassler. "The atmosphere provides a level of shielding, and so charged-particle radiation is less when the atmosphere is thicker." |
Image: NASA/JPL-Caltech/SwRI
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"Overall, Mars' atmosphere reduces the radiation dose compared to what we saw during the flight to Mars."
In addition to these short-term variations, RAD also detected longer-term variations in radiation due to Solar and Heliospheric Rotation.
The diagram below shows the variation of radiation measured by RAD over a period of 50 Sols starting on Sol 10. The black curve represents the dose of charged particles while the red one shows the total radiation dose of charged particles and secondary radiation of neutral particles such as Neutrons and Gamma Rays. The daily variations as well as long-term changes can be seen in the diagram. The long-term variations are caused by changes in the Heliosphere, a structure of gas and plasma in interplanetary space near Mars, tied to the sun by its magnetic field. It rotates along with the sun over a period of 27 days. The density of the Heliosphere as measured on Mars varies with a period of roughly 27 days. The gaps in the curve are due to rover downtime for software updates and RAD outages due to higher priority activities. Radiation levels are given in arbitrary units which can still reflect the magnitude of the variations.
In addition to these short-term variations, RAD also detected longer-term variations in radiation due to Solar and Heliospheric Rotation.
The diagram below shows the variation of radiation measured by RAD over a period of 50 Sols starting on Sol 10. The black curve represents the dose of charged particles while the red one shows the total radiation dose of charged particles and secondary radiation of neutral particles such as Neutrons and Gamma Rays. The daily variations as well as long-term changes can be seen in the diagram. The long-term variations are caused by changes in the Heliosphere, a structure of gas and plasma in interplanetary space near Mars, tied to the sun by its magnetic field. It rotates along with the sun over a period of 27 days. The density of the Heliosphere as measured on Mars varies with a period of roughly 27 days. The gaps in the curve are due to rover downtime for software updates and RAD outages due to higher priority activities. Radiation levels are given in arbitrary units which can still reflect the magnitude of the variations.
Image: NASA/JPL-Caltech/ SwRI
First Report: Cruise Phase and initial Surface Radiation Data |
August 9, 2012 |
The first Science Data of the Mars Science Laboratory Mission comes from the Rover's RAD - Radiation Assessment Detector Instrument. This is not coming as a surprise, because RAD was the only instrument actively taking science data during the Cruise Phase to Mars.
RAD is a particle analyzer that will be used to characterize the radiation environment on Planet Mars by detecting and measuring galactic cosmic rays, solar energetic particles, secondary neutron and other particles created on the planet and its atmosphere. Refer to this page for a complete instrument overview.
After being launched atop an Atlas V Rocket from Cape Canaveral Air Force Station on November 26, 2011, MSL's RAD Instrument was activated to gather radiation data from deep within the Spacecraft. RAD activation occurred on December 6, 2011. As part of cruise operations, RAD data was downlinked to Earth every 24 hours for subsequent analysis by the instrument team. Because the instrument was hidden inside the Rover and its Aeroshell which was protected by the Cruise Stage, RAD was able to characterize the radiation environment Astronauts would encounter in their way to Mars inside a Spacecraft. This enables it to record so called secondary particles – these are particles that result from collisions of primary radiation particles coming from space with spacecraft materials. Secondary Particles can be more dangerous to humans than primary particles, but often go undetected as previous missions were outfitted with Radiation Assessment Instruments directly exposed to space. Just one week after activation of the instrument, RAD already showed four times the radiation it detected during launch preparations in Florida.
On its way to Mars, RAD was able to observe major events such as Coronal Mass Ejections. "Curiosity has been hit by five major flares and solar particle events in the Earth-Mars expanse," said Don Hassler of the Southwest Research Institute in Boulder, Colorado that manages the instrument. "The rover is safe, and it has been beaming back invaluable data."
While analyzing the data with respect to the instrument's position inside MSL, it was found that only the strongest radiation storms have made it inside to RAD and that charged particles penetrating the spacecraft's shell were slowed down and fragmented by their interaction with the spacecraft's metal skin. "It's not only the walls that matter, however," Hassler noted "The spacecraft's hydrazine tanks and other components contribute some protection, too." Data acquired during Cruise will enable scientists to find out what shielding effects each major component such as tanks, shielding materials and other parts, are providing. On July 13, 2012, the RAD instrument was turned off in preparation for landing.
RAD is a particle analyzer that will be used to characterize the radiation environment on Planet Mars by detecting and measuring galactic cosmic rays, solar energetic particles, secondary neutron and other particles created on the planet and its atmosphere. Refer to this page for a complete instrument overview.
After being launched atop an Atlas V Rocket from Cape Canaveral Air Force Station on November 26, 2011, MSL's RAD Instrument was activated to gather radiation data from deep within the Spacecraft. RAD activation occurred on December 6, 2011. As part of cruise operations, RAD data was downlinked to Earth every 24 hours for subsequent analysis by the instrument team. Because the instrument was hidden inside the Rover and its Aeroshell which was protected by the Cruise Stage, RAD was able to characterize the radiation environment Astronauts would encounter in their way to Mars inside a Spacecraft. This enables it to record so called secondary particles – these are particles that result from collisions of primary radiation particles coming from space with spacecraft materials. Secondary Particles can be more dangerous to humans than primary particles, but often go undetected as previous missions were outfitted with Radiation Assessment Instruments directly exposed to space. Just one week after activation of the instrument, RAD already showed four times the radiation it detected during launch preparations in Florida.
On its way to Mars, RAD was able to observe major events such as Coronal Mass Ejections. "Curiosity has been hit by five major flares and solar particle events in the Earth-Mars expanse," said Don Hassler of the Southwest Research Institute in Boulder, Colorado that manages the instrument. "The rover is safe, and it has been beaming back invaluable data."
While analyzing the data with respect to the instrument's position inside MSL, it was found that only the strongest radiation storms have made it inside to RAD and that charged particles penetrating the spacecraft's shell were slowed down and fragmented by their interaction with the spacecraft's metal skin. "It's not only the walls that matter, however," Hassler noted "The spacecraft's hydrazine tanks and other components contribute some protection, too." Data acquired during Cruise will enable scientists to find out what shielding effects each major component such as tanks, shielding materials and other parts, are providing. On July 13, 2012, the RAD instrument was turned off in preparation for landing.
Credit: NASA/JPL/Southwest Research Institute
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This chart shows the entire Particle Flux Record acquired by RAD from December 6, 2011 to July 13, 2012. Five spikes are clearly visible and correspond to 5 solar particle events. The inset covers ten days in March 2012 during which a X5.4-class Solar Flare occurred. This Coronal Mass Ejection occurred on March 7 was registered by the Advanced Composition Explorer (ACE) Spacecraft shortly thereafter. ACE is located in Sun-Earth Lagrange Point 1 which is 1.5 Million Kilometers from Earth. MSL was significantly further away from the Sun and from Earth at that point, explaining why RAD detected the increased particle flux later than ACE. The graph shows that MSL's hull was able to provide significant shielding from the impinging radiation - the Red Line representing ACE measurements consistently remains above the proton flux average detected by RAD. RAD Data acquired during Cruise is still being processed and detailed data products will be available in the future. |
Credit: NASA/JPL/Southwest Research Institute
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After Landing on Mars aboard the Curiosity Rover on August 6, 2012, the RAD Instrument was activated for post-landing tests ad data acquisition. On August 7, three-and-a-half hours of RAD data were acquired and downlinked to Earth with initial data processing completed for a quick-look data product. This data is raw data and not a representative of the exact data that will be provided during the mission. On August 7, the Remote Sensing Mast was still in its stowed position and obstructed the field of view of RAD. That meant that the window through which charged particles and neutrons/gamma rays of the Martian Atmosphere was slightly blocked, so that individual events could have been missed. On August 7, the magnitude of Solar Events was minuscule so that data that was acquired represents the radiation environment on Mars created almost exclusively by cosmic rays.
Credit: NASA/JPL/Southwest Research Institute
This is the result of the 3.5-hour observation on August 7 with a time resolution of one minute. The chart does not show defined units since this is just a quick-look data product with known errors such as the Mast being in the way. There has also not been any data correction with respect to the MMRTR Background and the Silicon present in RAD's detectors. For reference, the average radiation dose observed during Cruise has been included to show that Deep Space Radiation levels are higher than those on Mars. The spikes in the plot represent individual Heavy-Ion-Hits. These hits will be characterized by obtaining energy spectra over the course of the surface mission. Heavy-Ion-Events are the most dangerous aspects for astronauts and data being gathered by RAD will improve shielding technology and techniques.
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