Monday, July 20, 2015

Quick Look: Touchdown on Venus: Analytic Wind Models and a Heuristic Approach to Estimating Landing Dispersions

I'm working through a lot of recent Venus-related papers, so here's another morsel for you that I will not have time to read in depth (I'm prioritizing articles relating to the Venusian surface). The author created a straightforward model of winds on Venus (using data from the VEGA Balloons and the Pioneer descent probes) to determine entry and descent dispersions for future Venus landers.

From the April 2015 edition of Planetary and Space Science:


Touchdown on Venus: Analytic wind models and a heuristic approach to estimating landing dispersions


The ‘landing ellipse’ or region of uncertainty within which an unguided probe to Venus may be expected to land is calculated. The region can be usefully seen as the convolution of three different factors: an initial circular delivery uncertainty which is smeared at a grazing entry angle onto the planetary sphere, an along-track uncertainty due to atmospheric density and vehicle aerodynamic variations during hypersonic entry, and a descent dispersion due to uncertain and/or variable zonal and meridional winds. This decomposition allows the various contributions to be instructively exposed and conveniently traded-off, without conducting explicit entry and descent dynamics simulations. It is seen that for descent durations and delivery errors typical of past Venus missions, the zonal wind contribution (determined with an analytic fit to Pioneer Venus tracking data) generally dominates, causing a ~200 km E–W (99%) dispersion, with meridional dispersions being about 4 times smaller. However, when entry angles become shallower than about 8°, the along-track dispersions may dominate, with the resulting ellipse becoming longer or wider depending on the entry azimuth. The analytic wind descriptions presented here may be applied to scientific problems, such as the dispersal of volcanic plumes or impact ejecta.

Full Citation:

Lorenz, R. (2015). Touchdown on Venus: Analytic wind models and a heuristic approach to estimating landing dispersions Planetary and Space Science, 108, 66-72 DOI: 10.1016/j.pss.2015.01.003

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