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The Mars Environmental Compatibility Assessment (MECA) instrument was designed, built, and flight qualified for the now canceled MSP (Mars Surveyor Program) '01 Lander. The MECA package consisted of a microscope, electrometer, material patch plates, and a wet chemistry laboratory (WCL). The primary goal of MECA was to analyze the Martian soil (regolith) for possible hazards to future astronauts and to provide a better understanding of Martian regolith geochemistry. The purpose of the WCL was to analyze for a range of soluble ionic chemical species and electrochemical parameters. The heart of the WCL was a sensor array of electrochemically based ion-selective electrodes (ISE). After 20 months storage at -23 degrees C and subsequent extended freeze/thawing cycles, WCL sensors were evaluated to determine both their physical durability and analytical responses. A fractional factorial calibration of the sensors was used to obtain slope, intercept, and all necessary selectivity coefficients simultaneously for selected ISEs. This calibration was used to model five cation and three anion sensors. These data were subsequently used to determine concentrations of several ions in two soil leachate simulants (based on terrestrial seawater and hypothesized Mars brine) and four actual soil samples. The WCL results were compared to simulant and soil samples using ion chromatography and inductively coupled plasma optical emission spectroscopy. The results showed that flight qualification and prolonged low-temperature storage conditions had minimal effects on the sensors. In addition, the analytical optimization method provided quantitative and qualitative data that could be used to accurately identify the chemical composition of the simulants and soils. The WCL has the ability to provide data that can be used to "read" the chemical, geological, and climatic history of Mars, as well as the potential habitability of its regolith.

A collection of high-precision tiltmeters is being operated at Pinon Flat Observatory, southern California, both to compare instruments and to measure tectonic deformation. We report on 1.2 years of data from four of these: two Michelson-Gale long fluid tiltmeters, one long center-pressure tiltmeter, and a shallow borehole tiltmeter. The three long-base instruments are all located on the same baseline, with a precise leveling line running between their end-monuments. At nontidal frequencies, only the two Michelson-Gale instruments show some coherence (gamma 2 = .3 for periods of 2 to 4 days), while the center-pressure instrument is correlated with air temperature at periods from a few days to a few weeks. The most stable tilt record shows a secular rate of 0.28 mu rad/a, which may be real. Over much longer times, leveling to specially stabilized bench-marks should confirm this. Comparing instruments has identified more and less successful measurement techniques; it appears that low-noise data will most probably be produced only by relatively complex and expensive instruments, though even for these, the operating costs over any reasonable lifetime will exceed the capital cost. Even the best existing sensors must be improved to measure continuous tectonic motions.