HR: 15:30h
AN: P24A-01 INVITED     [Abstracts]
TI: Predicting the Mars Atmosphere for MER EDL
AU: * Kass, D
EM: David.Kass@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 169-237 JPL 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AB: As the two Mars Exploration Rovers (MER) approached Mars, Mars Global Surveyor (MGS) detected a regional dust storm. The storm developed as a local storm descending the Chryse storm track but instead of dying out near the equator, it crossed over the Meridiani landing site into the southern hemisphere and started growing. It eventually became a planet encircling storm, with a global impact on atmospheric temperatures. The storm peaked (in terms of dust loading) around December 18th. While the storm was already decaying, it was still expected to change the atmosphere from baseline "clear" atmosphere used for planning Entry Descent and Landing (EDL). To help insure the successful landing, an attempt was made to model and then predict the atmosphere as the dust from the storm (and associated warming) cleared. Two types of data analyses were performed. The first was to rapidly look at MGS-TES daily global maps and MOC weekly reports. This gave a good qualitative assessment of the activity and help give a global view of the activity. The daily global atmospheric temperature maps from TES were particularly useful in showing where there were atmospheric changes but little measurable dust. The second analysis was to use vertical temperature profiles retrieved from the TES data. An effort was made to minimize the turnaround on the analysis and a 3 day latency was achieved. The retrieved profiles from the orbit nearest to the landing site were averaged over a ~ 10 degree latitude bin. They were then incorporated into an engineering model based on the one described in Golombek et al. [2003]. This is an interpolation scheme/Monte-Carlo distribution generator and not an actual dynamical model. It basically uses the TES data as a mean and applies a variability. For Spirit, there was no attempt to make predictions (the storm was too close to landing), so the most recent profiles were just used as a best guess. This turned out to be adequate, resulting in the final model being within ~ 1 σ of preliminary estimates from the accelerometers. For Opportunity, a series of predictions for the landing day conditions were made. The basic approach was to assume that the dust storm would decay back to seasonal conditions in an exponential fashion (based on other recorded storms). Thus an exponential curve in time was fit to the TES profiles on each pressure surface independently. The value of the fit at the landing date was then used for a prediction. Due to the MGS orbital mechanics, the actual latitude of the measurements varied daily (but remained within +/- 20 degrees of the landing site). The data did, unfortunately for predictions, show a latitudinal trend. To the east of the Meridiani Planum site, there was little geographic variations while to the west, temperatures decreased slowly away from the site. Due to the coverage and temporal variability as the storm decayed, the magnitude of this trend was difficult to estimate. Given the paucity of data and the uncertainty included explicitly in the model, this trend was not explicitly modeled for MER EDL purposes. There was some change in the predictions with time over the four weeks they were made, but much less than in the atmosphere itself. Thus the predictions served their purpose of allowing the engineers to design for the encountered atmosphere instead of trying to track the changes as they occurred. The ultimate validation of the modeling approach was that both rovers landed successfully.
DE: 5409 Atmospheres--structure and dynamics
DE: 5445 Meteorology (3346)
SC: Planetary Sciences [P]
MN: 2005 Joint Assembly