In the late hours of Aug. 5, the next Mars rover, Curiosity, will begin its seven-minute descent from the top of the Martian atmosphere to the planet's red, dusty surface.

Once landed -- assuming the heat shield separates, the parachute deploys and the thrusters fire -- the six-wheeled, SUV-sized, long-armed rolling robot will begin exploring the Martian landscape using its suite of onboard instruments, including the Radiation Assessment Detector, or RAD.


"Radiation is one of the top five problems we need to understand in order to send humans to Mars or out into deep space," said Hassler, of the Southwest Research Institute in Boulder.

The data collected by RAD will also help scientists better understand how the radiation bombarding Mars might shape the possibility of life on the red planet.

"One of the things our instrument will do is tell us how deep life will have to be below the surface to survive the radiation," Hassler said.

That information could guide any future efforts to drill into the planet's surface in search of life.


Hassler is a veteran of measuring space radiation, but RAD is unique because of its mass. Normally, an instrument with the capabilities that RAD has -- to measure both charged and neutral particles -- would weigh at least 10 pounds and maybe as much as 30. But RAD weighs just three pounds, which allowed the instrument to fit onboard Curiosity and also opens the door to a similar instrument flying on a number of future weight-constrained missions to the moon or to other planets.

And while Curiosity is still more than a month away from its date with the surface of Mars, RAD has already taken six months' worth of measurements as it travels through space. For that journey, RAD, and the rest of the rover, is cocooned in the belly of the spacecraft.

"Curiosity is nestled inside its spacecraft, just like a real astronaut would be," Frank Cucinotta, chief scientist for NASA's Space Radiation Program at the Johnson Space Center, said when RAD was turned on 10 days after launch. "RAD will give us an idea of the kind of radiation a human can expect to absorb during a similar trip to Mars."

And it's been an eventful trip so far. As Curiosity has flown toward Mars, the sun has been especially active, throwing off a handful of intense flares -- and the radiation that goes with them.

During one of the largest flares, which erupted in early March, the dose of radiation measured by RAD was close to the lifetime dose limits for an astronaut, even with all the shielding, Hassler said, meaning that more protection is likely needed for a spacecraft carrying a human.

Once RAD has made it to the surface of Mars, it will continue to gauge radiation levels, taking measurements each hour and downloading the information to Earth once a day.

"If a flare goes off, and you have astronauts on the surface, you want to understand what the effect may be," Hassler said.
