Space

August 13, 2014

Curiosity’s first two years revealing Mars’ history

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Raphael Jaffe
staff writer

The left-front wheel of NASA’s Curiosity Mars rover shows dents and holes in this image taken during the 469th Martian day, or sol, of the rover’s work on Mars (Nov. 30, 2013). The image was taken by the Mars Hand Lens Imager (MAHLI) camera, which is mounted at the end of Curiosity’s robotic arm. By that sol, Curiosity had driven 2.78 miles (4.47 kilometers). An uptick in the pace of wear and tear on the rover’s wheels in the preceding few weeks appears to be correlated with driving over rougher terrain than during earlier months of the mission. Routes to future destinations for the mission may be charted to lessen the amount of travel over such rough terrain.

The successful landing of the Mars Science Laboratory, known as Curiosity, Aug. 5, 2012, was a milestone of America’s preeminence in space exploration.

It will stand for decades as one of the most outstanding things this country has done in science. Dr. Charles Elachi, director of the Jet Propulsion Lab in Pasadena, Calif., recently led a celebration of its first two years. JPL developed, built and operates Curiosity for NASA.

The Mars Science Lab is continuing its exploration of Mars after answering its major science goal of determining if Mars ever offered conditions favorable for microbial life. Clay-bearing sedimentary rocks on the crater floor in an area called Yellowknife Bay yielded evidence of a lakebed environment billions of years ago that offered fresh water, all of the key elemental ingredients for life, and a chemical source of energy for microbes, if any existed there.

“Before landing, we expected that we would need to drive much farther before answering that habitability question,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology, Pasadena. “We were able to take advantage of landing very close to an ancient streambed and lake. Now we want to learn more about how environmental conditions on Mars evolved, and we know where to go to do that.”

rover sampled with its drill. Analysis of these samples revealed the site was once a lakebed with mild water, the essential elemental ingredients for life, and a type of chemical energy source used by some microbes on Earth. If Mars had living organisms, this would have been a good home for them.

Other important findings during the first Martian year include:

* Assessing natural radiation levels both during the flight to Mars and on the Martian surface provides guidance for designing the protection needed for human missions to Mars.

* Measurements of heavy-versus-light variants of elements in the Martian atmosphere indicate that much of Mars’ early atmosphere disappeared by processes favoring loss of lighter atoms, such as from the top of the atmosphere. Other measurements found that the atmosphere holds very little, if any, methane, a gas that can be produced biologically.

* The first determinations of the age of a rock on Mars and how long a rock has been exposed to harmful radiation provide prospects for learning when water flowed and for assessing degradation rates of organic compounds in rocks and soils.

During its second year, Curiosity has been driving toward long-term science destinations on lower slopes of Mount Sharp. Those destinations are in an area beginning about 2 miles (3 kilometers) southwest of the rover’s current location, but an appetizer outcrop of a base layer of the mountain lies much closer – less than one-third of a mile (500 meters) from Curiosity. The rover team is calling the outcrop “Pahrump Hills.”

For about half of July, the rover team at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., drove Curiosity across an area of hazardous sharp rocks on Mars called “Zabriskie Plateau.” Damage to Curiosity’s aluminum wheels from driving across similar terrain last year prompted a change in route, with the plan of skirting such rock-studded terrain wherever feasible. The one-eighth mile (200 meters) across Zabriskie Plateau was one of the longest stretches without a suitable detour on the redesigned route toward the long-term science destination.

 

Computer challenges

Another recent challenge appeared recently in the form of unexpected behavior by an onboard computer currently serving as backup. Curiosity carries redundant main computers. It has been operating on its B-side computer since a problem with the A-side computer prompted the team to command a swap in 2013. On Feb 28, the B-side computer was switched on in safe mode, as an A-side flash memory had an error, causing it to keep rebooting in a loop. The switch was made by a hardware command. The B-side computer element was fully operational by March 4, 2013. There was a similar glitch in late March, which was resolved the same way on March 25, 2013.

Work in subsequent weeks of 2013 restored availability of the A-side as a backup in case of B-side trouble. In July, 2014 fresh commanding of the Rover was suspended for two days while engineers confirmed that the A-side computer remains reliable as a backup.

 

Wheel damage

Each of Curiosity’s six aluminum wheels is independently actuated and geared, built for climbing in soft sand and rolling over rocks.

However, JPL engineers have seen a large amount of wear and tear on the wheels. This damage comes in several forms. For example, there are punctures in the wheel skin between what are called “grousers” — traction bars that take on the form of a zigzag pattern on the wheels. Grousers help improve wheel performance and provide a better grip on the Martian terrain.

The wheel skin itself is very thin aluminum. The wheels can sustain significant damage without impairing the rover’s ability to drive. Embedded cap rock which is resistant to weathering and erosion is the source of the punctures. Rover drivers are using imagery from the navigation cameras and NASA’s Mars satellites to pick drive paths that avoid those rocks.

Curiosity’s recent driving has crossed an area that has numerous sharp rocks embedded in the ground. Routes to future destinations for the mission are being charted to lessen the amount of travel over such rough terrain, compared to smoother ground nearby. Since wheel damage prompted a slow-down in driving late in 2013, the mission team has adjusted routes and driving methods to reduce the rate of damage.

For example, the mission team revised the planned route to future destinations on the lower slope of an area called Mount Sharp, where scientists expect geological layering will yield answers about ancient environments. Before Curiosity landed, scientists anticipated that the rover would need to reach Mount Sharp to meet the goal of determining whether the ancient environment was favorable for life. They found an answer much closer to the landing site. The findings so far have raised the bar for the work ahead. At Mount Sharp, the mission team will seek evidence not only of habitability, but also of how environments evolved and what conditions favored preservation of clues to whether life existed there.

To help prepare for future human missions to Mars, Curiosity includes a radiation detector to measure the environment astronauts will encounter on a round-trip between Earth and the Martian surface. The data are consistent with earlier predictions and will help NASA scientists and engineers develop new technologies to protect astronauts in deep space.

In 2016, a Mars Lander mission called InSight will launch to take the first look into the deep interior of Mars. The agency also is participating in the European Space Agency’s 2016 and 2018 ExoMars missions, including providing “Electra” telecommunication radios to ESA’s 2016 orbiter and a critical element of the astrobiology instrument on the 2018 ExoMars rover.

Additionally, NASA recently announced that its next rover going to Mars in 2020 will carry seven carefully selected instruments to conduct unprecedented investigations in science and technology, as well as capabilities needed for humans to pioneer the Red Planet.




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