Preliminary Atmospheric Hazard Assessment for Mars Science

Laboratory Entry, Descent and Landing

Scot C. R. Rafkin

Southwest Research Institute

rafkin@boulder.swri.edu

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Outline

• The MER Experience.

• MSL Entry, Descent, and Landing (EDL) Atmospheric Environment Requirements.

• Assessment Plan.

• Preliminary Results.

• Summary.

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Experience with MERs

• Atmospheric hazard assessment started late in the game.

• A lot of time & effort spent on areas that were ultimately found to be hazardous.

• Start MSL assessment earlier to avoid wasted effort.

• Provide more time to evaluate high priority sites.

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MSL EDL Atmospheric Requirements• Between 0 and 5 km AGL

– <30 m/s horizontal wind– <10 m/s vertical wind (not directly addressable in this study).

• Between 5 and 10 km– “…the system is less sensitive, but winds that differ

significantly from the above values may present a problem, as may wind fields that contain large spatial or temporal variations.”

• “No particular constraints on wind gusts are presently known or anticipated…”

• Restrict to +/-60o latitude.

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Assessment Plan• There is no global wind observation data set. Must rely on

models.

• Analyze variable dust simulation from Ames GCM.– Identify height (AGL) to 30 m/s horizontal wind.

– Identify maximum wind 0 to 5 km AGL and 5 to 10 km AGL.

– Analyze over range of Ls (120-150) and time of day (landing during afternoon).

• Hazard Assessment is a multi-step process involving a suite of large-scale, mesoscale, and engineering level model simulations, plus a team of scientists and engineers working to analyze model and observational data.

• This is Step 1: Preliminary analysis of one simulation from a single model.

• Significantly more effort is required to close this task.

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Disclaimer

Investigators should neither abandon a potential landing site nor assume a landing site is safe based on the following results. Regions that are presently shown to be hazardous may turn out to be acceptable based on further modeling, analysis, and refinement of MSL system performance. Likewise, regions that presently appear acceptable may turn out to be hazardous, particularly once smaller scale effects, which are not considered in this study, are factored into the analysis. However, investigators are advised to take these results into account when deciding on whether to further invest time and resources into a particular location.

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RESULTS

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• A substantial fraction of the planet experiences 30 m/s winds below 1 km AGL at some point from Ls122-152.

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• A substantial fraction of the planet has winds near or above 30 m/s in the lowest 5 km at some time from Ls122-Ls152. Of these, some are substantially above 30 m/s.

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• From 0-10 km AGL, maximum winds above 30 m/s are quite common, particularly in the southern hemisphere middle latitudes where 60+ m/s is not uncommon. There is a correlation between topography height and wind speed.

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Is There a Seasonal Component to the Winds?

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• Some variation as a function of Ls, but overall pattern is robust and independent of season.

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Is There a Diurnal Component to the Winds?

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~5 Sols

• The thermal tide substantially modulates winds at all latitudes especially north of 30S, but phase depends on latitude (and longitude--not shown).

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Vertical Winds, Mesoscale Circulations, and Turbulence

• A General Circulation Model (GCM) does not have the ability to simulate mesoscale circulations or the turbulent structures within a planetary boundary layer.

• Getting a grasp on these phenomena requires site-specific modeling, which can be undertaken once the list of potential landing sites is reduced.

• Some general comments are appropriate, however:– Vertical wind speeds of 5-10 m/s are typical within the afternoon

convective boundary layer. If MSL is going to land in the afternoon, it is very likely that the vertical wind requirement will be violated.

– The actual wind is, to first order, a result of the large scale winds plus the regional (mesoscale winds) plus the local turbulence. In regions of complex topography(large craters, canyons) the mesoscale winds can overwhelm the large scale circulations. See Gusev crater and Valles Marineris simulations in Rafkin and Michaels (2003).

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Summary • Over the duration of the landing window a substantial fraction of the planet

experiences winds above 30 m/s in the lowest 5 km.– High southern latitudes are in winter storm track.– Some correlation between strong winds and high topography.– Not a strong function of season (winds about the same Ls122-152)– Northern hemisphere tends to be less windy

• There is a strong diurnal component north of ~30S due to the thermal tide.– The phase of the tide depends on location. – Quantifying wind speed phase needs to be done but requires substantial

investment in time. • There a places, especially in the high northern latitudes, that appear “safe”

regardless of time of day or the season.• None of these results include mesoscale winds or the effect of boundary

layer turbulence, the effects of which can be substantial.