[meteorite-list] Michigan Scientists Simulate the Effects of Blowing Mars Dust on Phoenix Lander

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 15 Jun 2007 12:48:31 -0700 (PDT)
Message-ID: <200706151948.MAA06151_at_zagami.jpl.nasa.gov>

http://www.ns.umich.edu/htdocs/releases/story.php?id=5903

U-M scientists simulate the effects of blowing Mars dust on
NASA's Phoenix lander, due for August launch

University of Michigan
June 14, 2007

ANN ARBOR, Mich. - Gusting winds and the pulsating exhaust plumes from the
Phoenix spacecraft's landing engines could complicate NASA's efforts to
sample frozen soil from the surface of Mars, according to University of
Michigan atmospheric scientist Nilton Renno.

Set to launch Aug. 3 from Florida, the $414 million Phoenix Mars Lander
will use descent engines to touch down on the northern plains, where
vast stores of ice have been detected just below the surface. A robotic
arm will scoop frozen soil and dump it into science instruments that
will analyze its chemical content to see if it has the potential to
sustain microbial life.

With funding from NASA and the spacecraft's manufacturer, Lockheed
Martin, Renno and his students are conducting a series of experiments to
determine how much dust the 12 descent engines will kick up and whether
martian winds could interfere with efforts to deliver soil to the
onboard mini-lab.

Renno, an associate professor in the College of Engineering's Department
of Atmospheric, Oceanic and Space Sciences, is a member of the Phoenix
science team.

"I proposed that my engineering students look into some of the
challenges that the Phoenix team will face when the spacecraft arrives
at Mars," Renno said. "I wanted the students to contribute to the
success of the mission in a meaningful way."

In a laboratory at the U-M Space Research Building, his team built a
Phoenix thruster test chamber that looks a bit like a Plexiglas shower
stall. But instead of a shower head, the enclosure is fitted with a
high-pressure gas nozzle pointing down at a floor covered with 5 inches
of reddish sawdust. The pungent wood dust simulates Mars soil, and the
nozzle represents one of the 12 Phoenix landing thrusters.

Instead of liquid rocket fuel, the U-M researchers use nitrogen gas at
pressures up to 400 pounds per square inch. They fire short bursts into
the soil to mimic the pulsating Phoenix landing engines, filling the lab
with dust and a loud, staccato blast like machine-gun fire.

Renno's team will repeat the thruster experiment in Ann Arbor a few more
times before dismantling the apparatus and taking it to NASA's Ames
Research Center at Moffett Field, Calif., for July tests inside a large
vacuum chamber that more closely simulates Mars conditions. In the
California tests, crushed walnut shells will be used to mimic the
behavior of soil on Mars, where the surface gravity is 38 percent of
Earth's gravity.

Renno and U-M doctoral candidate Manish Mehta said there are several
concerns about the Phoenix thrusters. They said the supersonic exhaust
jets could: buffet the spindly, three-legged probe during the critical
final seconds before landing; scour the landing site and strip it of
loose soil; and possibly contaminate the martian soil with hydrazine,
the liquid fuel used in the thrusters.

"These experiments are mainly run to provide insight to the Phoenix
team, so they know what to expect and can somewhat prepare for it," said
Mehta, who will use the results in his doctoral dissertation. U-M
aerospace engineering senior Neal Rusche and other students from Renno's
Multidisciplinary Engineering Design course also are on the team.

Another set of Phoenix experiments underway in Renno's lab examines the
8-foot robotic arm's ability to deliver soil samples from its scoop into
onboard science instruments.

Mission engineers had planned to dump soil samples into the mini-lab
intakes from a height of 10 centimeters, about 4 inches. Renno said
winds of up to 11 mph are expected much of the time at the Phoenix
landing site during the three-month main mission, which begins with
arrival on May 25, 2008.

"We calculated that if you deploy the soil 10 centimeters above the
instrument intake, most of the particles will be blown away and will not
fall inside the instrument," Renno said. "So now we want to test that in
the lab to see if the calculations are really true."

In coming weeks, Renno and his students will release wood grains of
various densities inside a small U-M wind tunnel and photograph the
blowing particles with a high-speed camera. Ebony, bamboo and balsa will
be used to represent ice, soil and dust.

If the tests show that even relatively weak winds could hinder Phoenix
sample delivery, one option is to move the scoop closer before dumping.
But that also increases the risk that the robotic arm might strike the
spacecraft.

"These tests are valuable in two ways," said Leslie Tamppari, Phoenix
project scientist at NASA's Jet Propulsion Laboratory in Pasadena,
Calif. "One is to alert us that we want to get the scoop as close as
possible to deliver the samples."

Though the original plan was to dump samples from a height of 10
centimeters, it should be possible to do it safely from 3 centimeters
(1.2 inches), she said.

"And if we learn that the winds pick up every day in the afternoon but
are calm in the morning - as you might expect - then we would probably try
to deliver the samples in the morning, so we minimize losses," Tamppari
said.
Received on Fri 15 Jun 2007 03:48:31 PM PDT