That was a good catch!

When I updated the air friction function to add mass as a parameter, I inadvertently updated the equation using that function with the older version of the function, so whatever was still in the kernel was the mass used.

Hopefully this looks more reasonable:
First, from entry interface to touchdown:
https://i.imgur.com/B9g1ivF.png

then, the data:
https://i.imgur.com/1da7Jr4.png

Peak dynamic pressure is now very low.

​

​

-------- Original Message --------
 On January 30, 2018 4:40 PM, Tim <xxxxxx@little-possums.net> wrote:

>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
>
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