ALBERT

Description: The development of space geodetic techniques over the past two decades has made it possible to measure the rotational dynamics of the Earth at the milliarcsecond level, improving our geophysical models of the Earth 's interior and the interactions between the solid Earth and its atmosphere. We have found that the rotational dynamics of Mars can be determined to nearly the same level of accuracy by acquiring Earth-based two-way radio tracking observations of three or more landers globally distributed on the surface of Mars. Our results indicate that the precession and long-term obliquity changes of the Mars pole direction can be determined to an angular accuracy corresponding to about 15 cm/yr at the planet's surface. In addition, periodic nutations of the pole and seasonal variations in the spin rate of the planet can be determined to 10 cm or less. Measuring the rotation of Mars at this accuracy would greatly improve the determination of the planet' s moment of inertia and would resolve the size of a planetary fluid core, providing a valuable constraint on Mars interior models. Detecting seasonal variations in the spin rate of Mars would provide global constraints on atmospheric angular momentum changes due to sublimation of the Mars CO2 polar ice caps. Finally, observation of quasisecular changes in Mars obliquity would have significant implications for understanding long-term climatic change. The key to achieving these accuracies is a globally distributed network of Mars landers with stable, phase-coherent radio transponders. By simultaneously acquiring coherent two-way carrier phase observations between a single Earth tracking station and multiple Mars landers, Earth media errors are essentially eliminated, providing an extremely sensitive measure of changes in the differential path lengths between the Earth tracking station and the Mars landers due to Mars rotation. Time variability of the instrumental phase delay through the radio transponder may represent the limiting error source for this technique. Calibration of the transponder stability to about 0.1 ns or less, over a single tracking arc of up to 12 hr, is sufficient to provide the decimeter-level determination of Mars orientation parameters quoted above. We will provide a detailed description of the multilander tracking technique and the requirements it imposes on both the lander radio system and the Earth-based ground-tracking system. This concept is currently part of the strawman science plan for the Mars Environmental Survey (MESUR) mission and complements many of the other MESUR science goals.

Description: Martian dust plays a key role in determining the current climate of Mars, and is suspected of having had a major influence on the evolution of the surface and the history of climatic conditions on the planet. From spacecraft and ground-based observations, some understanding has been acquired of the styles and frequency of dust motion in the atmosphere and at the surface, of atmospheric dust loading, dust particle properties, and their variability. Limited constraints have also been derived for the volumes and ages of some potential dust reservoirs on the surface. These data are adequate to frame questions about the seasonal and long-term cycles of dust of Mars. Additional data are needed to place quantitative constraints on components of these cycles, on their possible linkage to one another, and to draw conclusions from the dust budget about the climate history of Mars.

Description: The potential for earth-based radiometric observations of a network of Mars surface landers to provide accurate determination of the Mars rotational orientation in inertial space is investigated. An error budget is presented for the carrier phase data type and related to system requirements for the surface landers. Differencing the carrier phase observations for a pair of Mars landers can provide extremely high precision due to common-mode error cancellation. Results of a covariance analysis are presented which show that Mars orientation can be determined to better than 10 milliarcsec, corresponding to decimeter distances at the planet surface. Recommendations on how to incorporate these concepts into future Mars missions, such as the Mars Environmental Survey, are discussed.