Mars Explorers Face Huge Radiation Challenge

A radiation sensor inside NASA's Curiosity Mars rover shows that even under the best-case scenario and behind shielding currently being designed for NASA's new deep-space capsule, future travelers will face a huge amount of radiation.

The results, based on Curiosity's 253-day, 348-million-mile cruise to Mars, indicate an astronaut most likely would exceed the current U.S. lifetime radiation exposure limit during one round trip mission.

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"Even for the shortest of missions we are perilously close to the radiation career and health limits that we've established for our astronauts," NASA's chief medical officer Richard Williams told a National Academy of Sciences' medical committee on Thursday.

The Institute of Medicine panel is looking into ethics and health standards for long-duration spaceflights.

Curiosity, which landed inside a giant impact basin near the Martian equator on Aug. 5, 2012, continues to collect radiation data as it conducts its primary mission to look for habitats that could have supported ancient or possible present day microbial life.

Curiosity's Radiation Assessment Detector, known as RAD, measures the amount and energy levels of highly energetic particles in galactic cosmic rays and from the sun. Scientists then converted the data into radiation dosage units known as sieverts, which are associated with increased cancer risk.

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Current U.S. standards limit an astronaut's lifetime radiation exposure to 1 Sievert, or 1,000 milliSieverts, which equates to about a five percent chance increase in developing a fatal cancer.

A new study shows that with currently available propulsion technologies and similar shielding to Curiosity's, astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts and that doesn't include radiation dosages for any time spent on the Martian surface.

"We have a challenge," Williams said during a webcast meeting on Thursday of the spaceflight health and medical ethics committee.

"We have the probability that in pursuing exploration-class missions beyond low-Earth orbit of long-duration that we will exceed the standards that we have already promulgated inside the agency. We need the advice of the committee on how best to go about proactively resolving some of these potential conflicts," Williams said.

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In general, Curiosity's shielding was more effective against particles emitted during solar storms, known as coronal mass ejections, than galactic cosmic rays.

"The galactic cosmic ray, during cruise, is the most dangerous. It's certainly very high energy and it doesn't go away. On the surface, you have some atmospheric protection and obviously it depends on how long you stay on the surface," RAD lead scientist Donald Hassler, with the Southwest Research Institute in Boulder, Colo., told Discovery News.

"It's more difficult to shield against the galactic cosmic rays. The only mission design strategy for that is just to get there as fast as you can. The solar particle events give you more opportunity to potentially shield against them, however, what we're finding is that even these events potentially can contribute significantly to the total radiation dose an astronaut may experience," Hassler said.

During the cruise phase, RAD detected five solar particle events, which accounted for about five percent of the total radiation dose during the trip to Mars.

"In a different year, in a different time in the solar cycle, this percentage might be greater or less. It could be 25 percent or its could be zero," Hassler said.

A second paper describing Curiosity's radiation measurements on the Martian surface has been submitted to Science, which published the team's initial results in this week's issue.

Artist's impression of Curiosity guiding its entry into the Martian atmosphere after being exposed to the high-radiation interplanetary environment for 253 days before arriving at Mars on Aug. 5, 2012.

MAHLI Power

Since NASA's Mars Science Laboratory (MSL) rover Curiosity landed on the red planet, each sol (a Martian "day") of the mission sees a flood of new photographs from Aeolis Palus -- the plain inside Gale Crater where Curiosity landed on Aug. 5. In September 2012, mission controllers sent the command for Curiosity to flip open the dust cap in front of the robotic arm-mounted Mars Hand Lens Imager (MAHLI). Until that point, the semi-transparent dust cap only allowed MAHLI to make out fuzzy shapes -- although it did a great job imaging Curiosity's "head" and it is also famous for capturing Curiosity's first color photograph. But since the true clarity of MAHLI has been unleashed, we've been treated to some of the most high-resolution views of the rover, Martian landscape and, most importantly, we've seen exactly what MAHLI was designed to do: Look closely at Mars rocks and dirt, assembling geological evidence of potential past habitability of Mars.

The Business End

Curiosity is armed with 17 cameras and MAHLI is designed to capture close-up photos of geological samples and formations as the rover explores. MAHLI was designed and built by Malin Space Science Systems and is analogous to a geologist's hand lens -- only a lot more sophisticated. Its high-resolution system can focus and magnify objects as small as 12.5 micrometers (that's smaller than the width of a human hair!). This photograph captured by the rover's Mastcam shows the MAHLI lens (with dust cap in place) in the center of the end of Curiosity's instrument-laden robotic arm.

Lights On!

To aid its studies, MAHLI is equipped with four LEDs to light up the imager's samples.

Mars Dirt

The first photograph to be returned from MAHLI without the dust cover in place was received on Sol 33 (Sept. 8) of Curiosity's mission. Shown here is a view of the ground immediately in front of the rover. Although this photo was a test, mission scientists were able to do a very preliminary study of the large "pebble" at the bottom of the picture: "Notice that the ground immediately around that pebble has less dust visible (more gravel exposed) than in other parts of the image. The presence of the pebble may have affected the wind in a way that preferentially removes dust from the surface around it," they wrote.

How Did Lincoln Help MAHLI?

On Sol 34 (Sept. 9), MAHLI was aimed at Curiosity's calibration target. This target is intended to color balance the instrument and provide a "standard" for mission scientists to refer to. The 1909 Lincoln penny was provided by MAHLI's principal investigatory Ken Edgett. Using a penny as a calibration target is a nod to geologists' tradition of placing a coin or some other object of known scale as a size reference in close-up photographs of rocks, says the MSL mission site.

Dusty Wheels

Although MAHLI will be used to examine microscopic scales, it is showing its prowess at generating some spectacular high-definition views of the rover. Shown here is a mosaic of Curiosity's three left-side dusty wheels.

Hazard Avoidance Cameras

Hazard Avoidance Cameras, or Hazcams, have become "standard issue" for the last three rovers to land on Mars. Mounted on the front and back of rovers Opportunity, Spirit and Curiosity, these small cameras provide invaluable information about the terrain and potential hazards surrounding the rovers. These cameras are not scientific cameras -- they are engineering cameras. Shown here, MAHLI has imaged the four front Hazcams on Curiosity. Interestingly, it was these cameras who returned Curiosity's first dusty image after touch down in August.

Underbelly

Using the flexibility of the robotic arm, MAHLI was able to check the underside of Curiosity. As the camera can focus on objects from 0.8 inch (2.1 centimeters) to infinity, MAHLI has incredible versatility allowing mission controllers to focus on the very small features of Mars to checking the health of the rover to viewing the impressive vistas beyond.

Mystery Object

In October 2012, the Internet was abuzz with speculation about a "mystery object" lying beneath the rover during digging operations at "Rocknest." Sadly, after studying the translucent object, mission scientists deduced that it wasn't anything native to the alien environment, it was actually a piece of plastic that had fallen from Curiosity. Yes, Curiosity is littering the red planet.

Digging In

The MAHLI camera was very attentive while Curiosity dug trenches in the Mars soil at "Rocknest."

Mars Flower?

In early 2013, MAHLI snapped another curious photo. This time, after driving to a rocky outcrop at a location dubbed "Yellowknife," the camera picked out what appeared to be some kind of organic-looking object embedded in the rock. Nope, it's not a Mars "flower" -- more likely it's a concentration of minerals.

Cheese!

In what has become an iconic photo of Curiosity, MAHLI was commanded to capture dozens of high-resolution pictures of the rover. Like an "arms length" shot you may have in your Facebook profile, Curiosity did the same, composing a mosaic of pics taken with its outstretched robotic arm.

Curiosity Cleans Up!

The Mars rover isn't only a scientific superstar, it also has a talent for cleaning. This circular pattern on a Mars rock was brushed aside by Curiosity's Dust Removal Tool (DRT), helping the rover carry out analysis of the rock surface beneath the layer of dirt.