May 30, 2013
The Real Radiation Danger In Going To Mars
There are many barriers that stand in the way of sending a human team to the surface of Mars. But near the top of the list of dangers would have to be the radiation exposure during the round trip voyage through the solar system. Clearly, a detailed understanding of the exposure levels is key in planning any mission to the Red Planet.
To this end, the recent mission that carried NASA´s Curiosity Rover to the surface of Mars carried along with it a radiation sensor housed within the space vehicle that monitored the radiation levels over time. This instrument, known as the Radiation Assessment Detector (RAD), allowed researchers to calculate the total exposure to radiation, as well as how it varied during different parts of the trip.
“In terms of accumulated dose, it´s like getting a whole-body CT scan once every five or six days,” said Dr. Cary Zeitlin, a principal scientist in SwRI´s Space Science and Engineering Division and lead author of the study.
There are really two concerns when it comes to radiation exposure: the long-term absorption of galactic cosmic rays (GCRs), and the short-term exposure to bursts of high-energy solar energetic particles (SEPs). With every 1 sievert (Sv) dose of radiation comes a 5% increase in fatal cancer risk.
“Understanding the radiation environment inside a spacecraft carrying humans to Mars or other deep space destinations is critical for planning future crewed missions,” Zeitlin said. “Based on RAD measurements, unless propulsion systems advance rapidly, a large share of mission radiation exposure will be during outbound and return travel, when the spacecraft and its inhabitants will be exposed to the radiation environment in interplanetary space, shielded only by the spacecraft itself.”
This is a challenge, because traditional designs of spacecraft are ill equipped to handle the high energies of GCRs and SEPs. Additional shielding would be required to adequately protect astronauts traveling outside of Earth´s magnetosphere for any length of time.
“A vehicle carrying humans into deep space would likely have a ℠storm shelter´ to protect against solar particles. But the GCRs are harder to stop and, even an aluminum hull a foot thick wouldn´t change the dose very much,” said Zeitlin. “The RAD data show an average GCR dose equivalent rate of 1.8 millisieverts per day in cruise. The total during just the transit phases of a Mars mission would be approximately 0.66 Sv for a round trip with current propulsion systems."
Time spent on the surface of Mars might add considerably to the total dose equivalent, depending on shielding conditions and the duration of the stay. Exposure values that ensure crews will not exceed the various space agencies' standards are less than 1 Sv.
“Scientists need to validate theories and models with actual measurements, which RAD is now providing. 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,” says Donald M. Hassler, a program director at Southwest Research Institute and principal investigator of the RAD investigation. “The spacecraft protects somewhat against lower energy particles, but others can propagate through the structure unchanged or break down into secondary particles.”
The team has reported these findings in the journal Science.