Less than three weeks into its nearly nine-month journey to Mars, NASA’s Mars Science Laboratory (MSL) is already on the job, assessing radiation levels en route to the Red Planet.

The Radiation Assessment Detector is the first of 10 science instruments on the MSL, nicknamed Curiosity, to begin collecting data and the only one that’s expected to be turned on before the rover touches down on Aug. 6, 2012.

PHOTOS: When Discovery News Met Mars Rover ‘Curiosity’

Curiosity’s primary mission is to determine if Mars has or ever had the right chemistry and environment for microbial life, but some studies will be used by NASA to figure out if the Red Planet can support future human life as well.

The Radiation Assessment Detector, or RAD, is one of those. The instrument is measuring energetic particles inside the spacecraft, a test run for what an astronaut would experience on his or her way to Mars.

Already, measurements inside the spacecraft show a four-fold increase in the amount of radiation, compared to what was measured inside the spacecraft before launch, RAD lead scientist Don Hassler, with the Southwest Research Institute reports.

SCIENCE CHANNEL: Mars Exploration Timeline

The instrument measures high-energy cosmic rays, as well as particles from the sun and other sources. Of particular interest are the impacts of coronal mass ejections, which stream off the sun during solar flares.

As these particles hit the spacecraft, they trigger secondary cascades of radioactive particles inside the capsule. Scientists want to learn more about the particles’ impact to design better shielding to protect future astronauts.

Positioned in the left-center of the rover, the coffee can-sized RAD will operate nearly continuously throughout the cruise to Mars, radioing its data to Earth about once a day.

NEWS: How a Mission to Mars Could Kill You

Upon arrival at Mars, RAD also will measure neutrons and gamma ray measurements coming from the planet’s atmosphere and from material beneath the rover.

As of noon Wednesday, the spacecraft had covered 31.9 million miles of its planned 352 million-mile journey to Mars.

Images: Artist’s rendering of Mars Science Laboratory in the cruise-phase of its mission. Credit NASA; Radiation Assessment Detector, pictured right, already is collecting data. Credit: Southwest Research Institute.