Mars-bound pioneers will be exposed to radiation levels that could effectively retire astronauts under NASA’s current standards, scientists reported Thursday. The radiation astronauts would face on a round trip would be comparable to getting an abdominal CT scan “about once every five days,” Cary Zeitlin, principal scientist for the NASA-led Martian Radiation Environment Experiment, told CNN.The findings were published Thursday in the journal Science, based on data from a device called the Radiation Assessment Detector that took readings during Curiosity’s trip to Mars. The spacecraft was similar to one that would carry humans, and scientists were interested in measuring galactic cosmic rays and solar energetic particles on the trip.
Zeitlin and his colleagues found voyagers could be exposed to between 554 and 770 millisieverts of ionizing radiation during the trip, depending on the level of solar activity. By comparison, the typical American receives about 6.2 millisieverts a year from natural and man-made sources, including medical diagnostic procedures.
“It is clear that the exposure from the cruise phases alone is a large fraction of (and in some cases greater than) currently accepted astronaut career limits,” they wrote.
In terms of health effects of that exposure, there are a lot of unknowns, Zeitlin said. There’s no effective, practical shielding method that would block all of the high-energy particles from getting to the astronauts aboard a mission to Mars, he said. The problem can be mitigated, Zeitlin said, but not eliminated…
Measurements with the MSL Radiation Assessment Detector (RAD) on NASA’s Curiosity Mars rover during the flight to Mars and now on the surface of Mars enable an estimate of the radiation astronauts would be exposed to on an expedition to Mars. NASA reference missions reckon with durations of 180 days for the trip to Mars, a 500-day stay on Mars, and another 180-day trip back to Earth. RAD measurements inside shielding provided by the spacecraft show that such a mission would result in a radiation exposure of about 1 sievert, with roughly equal contributions from the three stages of the expedition. A Sievert is a measurement unit of radiation exposure to biological tissue.
RAD has found radiation levels on the Martian surface to be comparable to those experienced by astronauts in low-Earth orbit. A person ambling around the Red Planet would receive an average dose of about 0.7 millisieverts per day, while astronauts aboard the International Space Station experience an average daily dose between 0.4 and 1.0 millisieverts, Hassler said.
RAD’s measurements show that Mars’ atmosphere — though just 1 percent as thick as that of Earth — provides a significant amount of protection from the fast-moving particles streaking through our galaxy. (Mars lacks a global magnetic field, which helps shield Earth further.)
The long deep-space journey to Mars is another matter. RAD was turned on for most of Curiosity’s eight-month cruise to the Red Planet, and its data show that any potential Mars explorers would likely get around 1.9 millisieverts per day during the flight.
“We can survive the Mars surface. The hard part is the cruise,” Hassler said.
RAD’s data are far from the full story of radiation on (or en route to) Mars, Hassler stressed. For example, solar storms can blast huge clouds of charged particles into space, affecting radiation levels significantly. Curiosity flew through a few such clouds during its cruise but has yet to experience one on the Red Planet surface.
Potential radiation doses will also change as solar activity waxes and wanes on its regular cycle. Galactic cosmic rays vary by a factor of two over the course of the sun’s 11-year activity cycle, Hassler said. …
via Space (12/4/2012)
Nearly everything we know about the radiation exposure on a trip to Mars we have learned in the past 200 days.
For much longer, we have known that space is a risky place to be, radiation being one of many reasons. We believed that once our explorers safely landed on the surface of Mars, the planet would provide shielding from the ravages of radiation. We didn’t how much, or how little, until very recently. Radiation and its variations impact not only the planning of human and robotic missions, but also the search for life taking place right now.
The first-ever radiation readings from the surface of another planet were published last month in the journal Science. The take-home lesson, as well as the getting-there lesson and the staying-there lesson, is this: don’t forget to pack your shielding. [Mars Radiation Threat to Astronauts Explained (Infographic)]
“Radiation is the one environmental characteristic that we don’t have a lot of experience with on Earth because we’re protected by our magnetosphere and relatively thick atmosphere. But it’s a daily fact of life on Mars,” said Don Hassler, the lead author on the paper, “Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover.”
… The Mars rover Curiosity has allowed us to finally calculate an average dose over the 180-day journey. It is approximately 300 mSv, the equivalent of 24 CAT scans. In just getting to Mars, an explorer would be exposed to more than 15 times an annual radiation limit for a worker in a nuclear power plant.
via Space (2/18/2014)
The best light weight radiation blocker is probably metal foam. This article from a few years ago (2015) says they can even block neutron radiation.
… new lightweight shielding based on foam metals that can block X-rays, gamma rays, and neutron radiation, as well as withstanding high-energy impact collisions.
Though they aren’t very familiar to the public, foam metals have been around for over a century. In its simplest form, a foam is made by bubbling a gas through molten metal to form a light froth that cools into a lightweight matrix. This produces a foam that is lighter than conventional metals, but has comparable strength.
Foam metals sound like a very interesting technology and I wonder if we could use many layers of it delivered by remote controlled robots to encase nuclear disasters such as Fukushima.