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Phoenix tries to deliver first sample to instrument deck BY STEPHEN CLARK SPACEFLIGHT NOW Posted: June 7, 2008 An image beamed back to Earth from the Phoenix Mars lander early Saturday shows the platform's robotic arm has dumped a load of dirt near the opening of a tiny high-temperature oven, but a sensor inside the instrument did not detect any soil traveling through the narrow portal.
But an infrared sensor inside the TEGA instrument was unable to confirm any soil made its way into the tiny oven, which measures one inch long with a diameter comparable to pencil lead, according to mission officials. Each oven is designed to heat samples in cycles ranging from relatively low temperatures to more than 1,800 degrees Fahrenheit. The four days of heating cycles are designed to first search for water, and then break down more complex mineral compounds. "It's a very small oven, but it's powerful in its ability to analyze those soils. We don't get a lot of soil, but we get a very accurate analysis of what goes in," said Peter Smith, Phoenix principal investigator from the University of Arizona. Scientists at the Phoenix mission's control room in Tucson, Ariz., sent commands Friday afternoon for the robotic arm's scoop to release about one cup of soil onto the entrance of TEGA oven No. 4. The sample was retrieved on Thursday from a site scientists have named Baby Bear. The TEGA oven selected to test the first sample was prepared to receive the soil earlier this week. Scientists ordered two doors protecting the oven to unlatch, but one of the doors only partially opened. Officials previously said the issue would have no impact on science operations if enough soil was dumped on the screened pathway to the oven. "We wanted a fair amount of sample because the TEGA door wasn't fully opened. We want to make sure that we can get enough sample in there," said Matt Robinson, robotic arm flight software lead from NASA's Jet Propulsion Laboratory.
Peter Smith, Phoenix principal investigator from the University of Arizona, addressed the TEGA team's struggles with the instrument during a Friday teleconference with reporters. "Just from watching them perform, they have really been stressed a bit, and they have been throughout the entire development of this instrument. It's a very, very, very complicated instrument, if not one of the more complicated instruments ever flown in space," Smith said. Smith said Friday he hoped the instrument would work as planned during the sample collection and analysis phase. "At each step there seems to be some little difficulty that causes them to circle the wagons, and work long hours, and do testing in their laboratory and in our simulated Mars environment here. So they deserve a break," Smith said. Scientists are already examining the instrument's latest anomaly, and early speculation centers on the thick texture of the soil. Soil passing into the oven must go through a screened entrance that only allows in particles smaller than 0.04 inches across. "I think it's the cloddiness of the soil and not having enough fine granular material," said Ray Arvidson of Washington University in St. Louis, co-investigator for the robotic arm. Arvidson said the science team is considering several options to get the soil inside the oven, including using mechanical shakers designed to help feed small amounts soil through the screened entrance to a funnel leading into the oven. The shakers normally vibrate for five minutes during the sample collection process, acting like a hopper used in agricultural activities. Images taken Thursday showed the rust-colored soil inside the arm's scoop, revealing several thick clods with mysterious white streaks that researchers believe could be salts or traces of ice. The white material was observed in two previous test scoops and inside trenches carved out by the arm during digging.
Analysis by the TEGA instrument's calorimeter and mass spectrometer would be able to quickly confirm if there is significant water ice in the sample, according to Smith. "As you might imagine, water is the first thing that's cooked out as you start to heat the oven," Smith said. Confirmation of salt in the dirt will have to wait until the arm drops another sample into a chemistry experiment that adds water to the soil to create a muddy simulation of a wet Martian surface. Salt would also be a significant discovery because it is left behind as water evaporates from the soil, Smith said. Scientists expected to have the first results from the TEGA instrument by early next week, but the ground team has suspended normal operations of the experiment as they investigate how to get soil into the oven. Arvidson said scientists may use the arm to push down on the soil before future sample digs to help break up clods of dirt. Phoenix will spend Saturday taking pictures to study the soil's tendency to form thick clumps, giving scientists further insight into the characteristics of the surface's upper layer, according to a NASA statement.
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