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.
Tasting
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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