Brett Smith for redOrbit.com – Your Universe Online
Newly released data from the Curiosity rover indicate that Martian radiation levels are very close to being acceptable for future manned missions to the surface of the Red Planet.
While the Curiosity rover spent its first 300 days cruising around the planet’s Gale Crater gathering soil samples and examining rock structures, the onboard Radiation Assessment Detector (RAD) was making detailed recording of the radiation found on the Martian surface.
“Our measurements provide crucial information for human missions to Mars,” said Don Hassler, a Southwest Research Institute (SwRI) program director and RAD principal investigator. “We’re continuing to monitor the radiation environment, and seeing the effects of major solar storms on the surface and at different times in the solar cycle will give additional important data. Our measurements also tie into Curiosity’s investigations about habitability.”
“The radiation sources that are of concern for human health also affect microbial survival as well as the preservation of organic chemicals,” Hassler added.
The Curiosity data indicates a 5 percent increase in fatal cancer risk for a round-trip mission. NASA has essentially established a 3 percent increased risk of fatal cancer as a suitable career limit for astronauts working in low earth orbit. However, the space agency does not currently have a maximum value for deep space missions, and it is working with the National Academies Institute of Medicine to calculate appropriate limits for deep space missions.
Two types of radiation potentially threaten astronauts on Mars: a constant low dose of galactic cosmic rays (GCRs) and the potential short-term exposures to solar energetic particles (SEPs) from solar flares and coronal mass ejections. The lack of a global magnetic field on Mars and the thin Martian atmosphere offer very little protection from this radiation, compared to Earth.
Both GCRs and SEPs react within the atmosphere and, if strong enough, pierce down into the Martian soil, or regolith. There they produce secondary particles that add to the multifaceted radiation environment on the Martian surface.
“The RAD surface radiation data show an average GCR dose equivalent rate of 0.67 millisieverts (mSv) per day from August 2012 to June 2013 on the Martian surface,” Hassler said. “In comparison, RAD data show an average GCR dose equivalent rate of 1.8 millisieverts per day on the journey to Mars, when RAD measured the radiation inside the spaceship.”
This means that the highest exposure level for a manned Mars mission will be during travel between planets, when the astronauts will only be shielded by the spacecraft. During just the interplanetary travel phases of a Mars mission, the total radiation dose would be about 660 mSv for a round trip, based on calculations using current propulsion technology and average solar activity, NASA said.
A 500-day stay on the surface would bring the total dose to around 1000 mSv, or 1 Sv, which is associated with a five percent increase in fatal cancer risk. In comparison, the average CT abdominal scan has a radiation exposure level of less than 10 mSv.
NASA scientists published the results of their analysis on the radiation data this week in the journal Science.