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I came across this video1 about the Mars 2020 Perseverance rover mission, especially the atmospheric entry phase.

It says between about 03:50 and 05:00 that the atmospheric lifting entry at an angle of 16 degrees is achieved by dropping weights on one side of the spacecraft (two 75kg tungsten weights) offsetting center of mass where it has to be, to reach this 16 degrees angle of attack.

One region of the ablative heat shield, always the same region, must dissipate more heat, whatever the roll attitude of the spacecraft.

Is the heat shield a perfect body of revolution? Or is the thickness of the ablative material varying depending on the areas that dissipate more or less heat? If so or not, why or why not?

1Comment le rover Perseverance va se poser sur Mars video is en Français but with Google auto-translated closed captions in English available, viz. https://i.sstatic.net/RWcIT.jpg

enter image description here

underlying concern here is : since two sets of tungsten weights are dropped, one just before atmospheric entry, and the other just after reaching subsonic velocity, optimising heat shield's thickness could reduce heat shield (and first and second ballast) total mass.

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  • $\begingroup$ I wonder why one region has to dissipate more heat, since the pressure would seem to be uniform (at least circumferentially if not radially) across the heat shield. I didn't find any mention of asymmetry at first glance thru NASA web pages $\endgroup$
    – Carl Witthoft
    Commented Feb 8, 2021 at 13:42
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    $\begingroup$ @CarlWitthoft I added image from same source, there is heating asymmetry due to lifting entry. (one side of the heat shield is more normal to incoming atmosphere than the other) $\endgroup$
    – user19132
    Commented Feb 8, 2021 at 15:11
  • $\begingroup$ @qqjkztd thanks - yes that makes sense, as the heat shield is far from being a flat surface $\endgroup$
    – Carl Witthoft
    Commented Feb 8, 2021 at 15:17
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    $\begingroup$ I found this quote about the MSL (Curiosity) heatshield: "A uniform heatshield thickness was specified within mass constraints rather than the usual method of sizing the TPS to surface heating conditions; this strategy was chosen due to the late change in heatshield material" (Edquist et al.) $\endgroup$
    – KarlKastor
    Commented Feb 9, 2021 at 1:09
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    $\begingroup$ @qqjkztd Here's the paper as a free pdf from nasa.gov. $\endgroup$
    – KarlKastor
    Commented Feb 9, 2021 at 23:03

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