On Tue, Jan 30, 2018 at 05:07:40PM -0500, Caleuche wrote:
> I mistakenly ran the model with 1.4 meters radius rather than 1.4
> meters diameter, but otherwise modeled a sphere with radius 1.4
> meters, subsonic drag coefficient 0.47 and transsonic drag
> coefficient 0.55, and supersonic drag coefficient 0.47 again (I need
> to fix that, spheres have very high supersonic drag coefficients),
> mass was modeled to be 104 kg for the sphere and 100 kg for the
> astronaut+spacesuit (the same as the traveller reentry kit) but
> going on with it:
>
> Here is the plot from entry interface to touchdown:
> https://i.imgur.com/APikZcR.png
>
> And some of the extracted data:
> https://i.imgur.com/zdxUmZG.png
>
> Peak acceleration is just over 8g at around 20,000 meters altitude,
> and dynamic pressure peaks at that time too, at around 650 kPa

That's not possible.  Drag = dynamic pressure * coefficient * area, so
with your figures the drag should be 2.2 MN, acting on a 204 kg object
thus yielding a deceleration of 1100 gee.  If you're getting 8 gee,
then you must be using a mass of 28 tonnes (or some similarly far-out
number elsewhere in the calculation).

A chunk of solid rock of the same size might have a mass of 28 tonnes,
and it would be physically reasonable for it to get down to 20 km
altitude before slowing significantly, but an astronaut in a bubble
won't.

- Tim