Phoenix Mars Lander: How to Hunt for Martian Ice
The Phoenix Mars Lander set to land Sunday may represent a clean slate for NASA?s past failed or canceled Martian missions, but its technological lineage also resembles Frankenstein's monster.
The spacecraft will land on the red planet with baggage that includes a backhoe-like robotic arm, a miniature chemistry set, and a laser-guided weather station.
"Most of the instruments have heritage from other missions," said Michael Gross, Phoenix payload manager at NASA?s Jet Propulsion Laboratory in Pasadena, Calif.
Those heritage technologies developed for previous Mars missions such as Mars Surveyor Lander and Mars Polar Lander came in useful to outfit the $420 million Phoenix mission, which seeks to uncover the history of water on Mars by digging beneath the arctic surface. The spacecraft is set to land on May 25 on a six-month mission to determine whether the region may have once been habitable for primitive life.
Digging the Red Planet
However, Gross and other engineers had to remind themselves that Phoenix?s new science mission came with new demands.
"We were counting on the heritage of the 2001 [Mars Surveyor Lander] arm, and we had to redesign the whole thing," Gross told SPACE.com. "There's a comfort level, but also pitfalls with heritage that you want to make sure you don't walk into."
The original robotic arm lacked the physical power to dig into the frozen Martian tundra, so engineers strengthened the joints and switched the arm material from aluminum to steel. They also replaced the original scoop with the Icy Soil Acquisition Device (ISAD), which has several tricks to deal with the ice-hardened layer beneath the looser regolith soil on the surface.
First the nearly eight-foot (2.3 meters) robotic arm uses a backhoe motion to clear away loose regolith and expose the icy layer. A blade on the front of the scoop can try a bit of scraping, but the real digging for ice samples requires a small drill in the back of the scoop.
The spring-loaded drill is sprung against the ground and turned on, rotating and grinding against the icy soil using the spring?s pressure. Wrist movements push the loosened ice samples into a chamber for further testing.
?Within about a minute or so, it kicks a fair amount of material into the scoop or chamber,? said Peter Smith, Phoenix principal investigator at the University of Arizona, Tucson. Smith added that the drill would do its excavation two or three times.
The robotic arm also has scraper blades on the bottom that can clear away material and continue tearing up the icy regolith, Gross said. The arm can dig down as far as 20 inches (0.5 meters), the deepest that anyone has gone on Mars.
Once Phoenix secures samples, it breaks out the first-ever wet chemistry lab on Mars. The Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) allows scientists to analyze loose regolith soil for levels of acidity, minerals, and conductivity, using single-use beakers the size of teacups where Martian soil dissolved in water can be soaked, stirred, and measured.
MECA will also use atomic-force microscopes that can examine the Martian soil down to 10 nanometers, or 10,000 times thinner than a sheet of paper the smallest scale ever examined on Mars. Signs of clay or other material in the loose regolith could indicate the past presence of water.
Another MECA instrument can detect any lingering wetness in the regolith soil, and examine how heat changes within the soil. The thermal and electrical conductivity probe resembles a spiked ?knuckle? that the robotic arm can dig into the excavated area.
?The upper surface stuff done by MECA can look through the dry environment for remnants of water,? Gross said. ?TEGA [Thermal and Evolved Gas Analyzer] will actually look for the water.?
The robotic arm will feed soil and ice into eight TEGA ovens, each the size of a ballpoint pen ink cartridge. The one-use ovens can then slowly heat the samples up to 1,000 degrees C (1,800 degrees F), which allows scientists to measure and analyze any changes from solid to liquid to gas. The TEGA tool also contains a new spectrometer that can sniff heated gases for their chemical signature.
With six months to study Mars and only a limited number of ovens and beakers, Phoenix researchers plan to take extra care in choosing exactly which bits of Martian soil and ice to test.
?It?s called negotiation,? Smith has said. ?We?ll get in a room and we?ll negotiate. If it comes up to me, I?ll make the decision.?
Most of the Phoenix mission?s new technology rests in the Meteorological Station (MET), which can bounce powerful laser pulses off dust and ice particles in the Martian atmosphere. The reflected pulses will provide information about the atmospheric particles.
The combination of old technology and newer instruments required a lot of ?system engineering making sure everything would play together,? Gross noted. But the proud international heritage of instruments from the United States, Canada, and Germany will hopefully help Phoenix hit Martian pay dirt after its nail-biting descent.
?Once it lands, it doesn't end,? Gross said.
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