Science and Exploration

CuriousMars: Triple Sample Set for SAM, as NASA Cheers Revived Plutonium Production

By Craig Covault
March 22, 2013
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CuriousMars: Triple Sample Set for SAM, as NASA Cheers Revived Plutonium Production
Red-hot plutonium 238 pellet is removed from Energy Dept nuclear reactor. For the first time in 25 years Energy Dept. is restarting plutonium production to power NASA deep space missions. Credit: DOE
Credit: DOE

Restarting science operations after 3 weeks of computer problems, the Mars rover Curiosity will be using its robotic arm and the Goddard Sample Analysis at Mars (SAM) laboratory to process a triple-dose of drilled subsurface rock in a more intense search for organic carbon before April 4, when Mars will move behind the Sun blocking communications until May 1.
“We are still looking forward to that run” before solar conjunction, Paul Mahaffy, SAM principal investigator told CuriousMars.

The objective is to find a stronger carbon signature to add to other evidence that has already confirmed that the Yellowknife Bay would have had a habitable environment 3 billion years ago for Martian microorganisms (CuriousMars March 14).

Mars is now 222 million mi. (357 million km.) from Earth and about 129 million mi. (208 million km.) from the solar backside as it moves behind the Sun cutting off communications from April 4-May 1. Credit: NASA/JPL-Caltech

In other Curiosity developments this week:

–The rover’s computer problems have been resolved. The A side computer memory that started the difficulty Feb. 28 has been patched and restored enabling it to fully backup the B side now commanding all operations. A minor problem put the rover in an additional Safe Mode early this week, but that difficulty was easily fixed.

–Another major Mars mission development this week is the announcement by Jim Green, NASA’s director of planetary science, that for the first time in 25 years the Deptartment of Energy (DOE) has begun producing Plutonium 238 to provide nuclear power for future NASA Mars surface operations and outer solar system missions.

–Also new findings announced by the teams operating Curiosity’s Mastcam, its Canadian Alpha Particle X-ray Spectrometer and the Russian DAN neutron spectrometer provide additional evidence for water and past habitable terrain between Curiosity’s landing site and its current Yellowknife Bay research area.

Researchers have used the Canadian Alpha Particle X-ray Spectrometer (APXS) instrument to determine elemental compositions of rock surfaces. This graphic presents results simplified across diverse elements by dividing the amount of each element measured in the rocks by the amount of the same element in a local soil, called “Portage.” Note the blue spike from vein-rich rocks with elevated abundances of sulfur and calcium. Credit: NASA/JPL-Caltech/University of Guelph

Back on Mars, the rover manipulator arm will be used to drop the powdered equivalent of three individual samples into SAM to be heated to about to 1,535 deg. F (835 deg. C).

Mahaffy and his team hope this triple dose will boost the signal strength of possible organic carbon molecules contained within the rock powder or provide more insight to the simple organic molecules that they do see.

Since first drilled out of the John Klein bedrock at Yellowknife Bay in mid February, the gray powdered sample material has remained housed in the rover’s turret mounted CHIMRA filtering device.

The first two SAM processing runs, each using a baby aspirin sized pinch of 150 micron powdered rock, produced a weak wisp of organic carbon measured by the rover’s instruments, except for a major spike in carbon dioxide from the material when heated.

The Russian Dynamic Albedo of Neutrons (DAN) instrument on NASA’s Mars rover Curiosity detects even very small amounts of water in the ground beneath the rover, primarily water bound into the crystal structure of hydrated minerals. This graphic shows how much of the detected water is very close to the surface (blue) and how much is deeper (red) within the top 20 inches (0.5 m). Credit: NASA/JPL-Caltech/IKI

The SAM instrument specifically found simple organic molecules, but not a strong organic signal from past Martian life. Curiosity detected the simple carbon-containing compounds chloro- and dichloromethane. These species were detected by the gas chromatograph mass spectrometer (GCMS), one of three instruments that make up SAM.

The rover’s CheMin and SAM found within the gray rock sample the elements of carbon, hydrogen, nitrogen, oxygen, phosphors and sulfur, which dominate living cells on Earth.

“There does need to be a source of carbon there somewhere,” Mission Scientist John Grotzinger said. “But if it is just carbon dioxide you can have a “Chemolitho autotrophic organism” that literally feeds on rocks. Such organisms will metabolize and generate organic compounds based on carbon in the carbon dioxide.”

On this image of the rock target “Knorr,” color coding maps the amount of mineral hydration indicated by a ratio of near-infrared reflectance intensities measured by the Mast Camera (Mastcam) on NASA’s Mars rover Curiosity. The color scale on the right shows the assignment of colors for relative strength of the calculated signal for hydration. The map shows that the stronger signals for hydration are associated with pale veins and light-toned nodules in the rock. Credit: NASA/JPL-Caltech/MSSS/ASU

“The fact that Mahaffy was able to show in the SAM instrument that there was a major carbon dioxide spike” that vented from the subsurface rock powder “is what we are really excited about,” Grotzinger said. That is because such a spike indicates a key building block for past life on Mars, he said.

By using the infrared-imaging capability of the Malin Space Science Systems Mastcam and the Russian DAN instrument that shoots neutrons into the ground to probe for hydrogen, researchers said they found more hydrated minerals near the clay-bearing rock than at locations Curiosity visited earlier. They presented those new results this week at the 44th annual Lunar and Planetary Science Conference near Houston, Texas.

The rover’s Mastcam can also serve as a mineral-detecting and hydration-detecting tool, reported Jim Bell of Arizona State University. “Some iron-bearing rocks and minerals can be detected and mapped using the Mastcam’s near-infrared filters,” Bell said.

Cracked open by the one ton weight of Curiosity, color coding of the rock called “Tintina,” maps the amount of mineral hydration (water content) indicated by a ratio of near-infrared reflectance intensities measured by the Mastcam on NASA’s Mars rover Curiosity. The color scale on the right shows the assignment of colors for relative strength of the calculated signal for hydration. Credit: NASA/JPL-Caltech/MSSS/ASU.

Ratios of brightness in different Mastcam near-infrared wavelengths can indicate the presence of some hydrated minerals. The technique was used to check rocks in Yellowknife Bay, some crisscrossed with bright veins.

“With Mastcam, we see elevated hydration signals in the narrow veins that cut many of the rocks in this area,” said Melissa Rice of the California Institute of Technology, Pasadena, Calif. “These bright veins contain hydrated minerals that are different from the clay minerals in the surrounding rock matrix.”

The Russian Space Institute (IKI) Dynamic Albedo of Neutrons (DAN) instrument on Curiosity detects hydrogen beneath the rover. At the rover’s very dry study area on Mars, DAN detected hydrogen as mainly ancient water molecules bound into minerals.

This close-up view of “Tintina” was taken by the rover’s Mars Hand Lens Imager (MAHLI) on Sol 160 (January 17, 2013) and shows interesting linear textures in the bright white material on the rock. This is the same rock as above with red hydration signature. Credit: NASA/JPL-Caltech/MSSS.

“We definitely see signal variation along the traverse from the landing point to Yellowknife Bay,” said DAN Deputy Principal Investigator Maxim Litvak of the Space Research Institute, Moscow. “More water is detected at Yellowknife Bay than earlier on the route. Even within Yellowknife Bay, we see significant variation,” he said in a NASA release on the data.

Findings presented at LPSC by the team with the Canadian Alpha Particle X-ray Spectrometer (APXS) on Curiosity’s arm indicate that the wet environmental processes that produced clay at Yellowknife Bay did so without much change in the overall mix of chemical elements present, something that has been seen on Earth in Hawaii and Iceland.

The elemental composition of the outcrop Curiosity drilled into matches the composition of basalt. For example, it has basalt-like proportions of silicon, aluminum, magnesium and iron. Basalt is the most common rock type on Mars. It is igneous, but it is also thought to be the parent material for sedimentary rocks Curiosity has examined.

The Mastcam showed researchers interesting internal color in this rock called “Sutton_Inlier,” which was broken by the rover driving over it. The Mastcam took this image during the 174th Martian day, or sol, of the rover’s work on Mars (January 31, 2013). The rock is about 5 inches (12 centimeters) wide at the end closest to the camera. This view is calibrated to estimated “natural” color. Brilliant white bluish color shows the “new Mars” beyond the totally red hue at some Martian locations elsewhere. Credit: NASA/JPL-Caltech.

“The elemental composition of rocks in Yellowknife Bay wasn’t changed much by mineral alteration,” said Curiosity science team member Mariek Schmidt of Brock University, Saint Catharines, Ontario, Canada.

A dust coating on rocks had made the composition detected by APXS not quite a match for basalt until Curiosity used a brush to sweep the dust away.

“By removing the dust, we’ve got a better reading that pushes the classification toward basaltic composition,” Schmidt said. The sedimentary rocks at Yellowknife Bay likely formed when original basaltic rocks were broken into fragments, transported, then re-deposited as sedimentary particles, and mineralogically altered by exposure to water.

This chart graphs measurements made by the Russian Dynamic Albedo of Neutrons (DAN) instrument against the distance the rover has driven, in meters. In active mode, DAN shoots neutrons into the ground and senses how they are reflected. Neutrons that collide with hydrogen atoms bounce off with a characteristic decrease in energy. By measuring the energies of the reflected neutrons, DAN can detect the fraction that was slowed in these collisions, and therefore the amount of hydrogen water related minerals. In the passive mode, DAN relies on galactic cosmic rays as a source of neutrons. Credit: NASA/JPL-Caltech/IKI

The findings indicate two major periods of water in the Yellowknife Bay area Rice said.

“We can say the first event was the emplacement of rocks [3-3.5 billion years ago] that had the high phyllosilicate (clay) abundances,” said Rice. “These signs of high alteration mean those rocks likely [formed in] an environment favorable to life,” she said.

“We know there was something that happened afterward, where the rocks were fractured and where water flowed through those fractures leaving behind calcium sulfate minerals,” Rice said.

“A determination about how much time passed between the emplacement of the water-formed rocks and then a second episode of water flowing through cracks in the rocks can not be determined with Curiosity’s instrument suite,” she said.

Another LPSC highlight was the announcement by Green that DOE is restarting plutonium production.

This is a significant milestone for NASA which was nearly out of nuclear material to power its new Advanced Stirling Radioisotope Generator (ASRG) power systems for future planetary missions. These new Stirling cycle systems are much more efficient and complex than the passive RTG radioisotope thermoelectric generators used in spacecraft like Curiosity and the Cassini Saturn orbiter.

Like a simple RTG, the ASRG converts heat energy to electricity. But, unlike RTGs the new system has moving parts, NASA says. Inside the device, a moving piston is driven by the heat of the nuclear fuel source. The piston moves a magnet back and forth through a coil of wire more than 100 times per second to generate electrical current in the wire. To prevent physical wear, the piston is suspended in a helium gas bearing, meaning it does not actually touch the inside of the mechanism.

Graphic shows some components and complexity of the Advanced Stirling Radioisotope Generator (ASRG). Nuclear generated heat and fluid circuit pushes magnet through coil more than 100 times/sec. Credit: NASA.

NASA says the 130 watt Stirling systems will be about 4 times more efficient than traditional RTGs, requiring less plutonium 238 per mission.

“We are building two ASRG flight units, F-1 and F-2, to be completed in FY-2016. The units will go into bonded storage without fuel until we make a flight selection,” Green told the LPSC. “The plutonium story is a good one,” he said.

DOE has worked closely with NASA and moved forward with a plan to test their existing reactors to generate plutonium. Technicians at Oak Ridge National Laboratory, Tenn. take encapsulated neptunium 237, an artificially created chemical element that does not occur naturally, and put in a reactor at the site.

In the reactor, the neptunium 237 is bombarded with neutrons for a month, capturing a neutron and turning itself into plutonium 238. When the reactor rods are pulled, technicians are able to extract small amounts of plutonium.
“We anticipate that by the end of 2013 to have a complete schedule and cost plan for DOE to make 3.3–4.4 lb. (1.5-2 kg.) of plutonium 238 per year for NASA,” said Green.

“When we add the new material with our old plutonium, some of which is 20 yr. old, it really allows us to get the appropriate energy density for fuel,” he said. “When you add 2 kg. of old plutonium 238 with 1 kg. of new plutonium, that will revive our supply and allow us to complete a number of plutonium powered missions over this decade and position us well into the decade of 2020s,” said Green.

He and NASA Associate Administrator for Science John Grunsfeld, made the announcement by video link from NASA Headquarters in Washington to a packed the LPSC audience near Houston. Although Green and Grunsfeld are the two primary NASA managers in charge of planning and budgeting for planetary exploration, they were not permitted to attend the world’s largest forum of planetary mission managers, scientists and engineers because of NASA budget sequester restrictions.

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Credit NASA/JPL-Caltech

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