And if I may ask, and to validate my own calculations, exactly how did you come up with 20 kPa peak dynamic pressure? I'd like to pin down the reason I'm getting a different result than you.
​

​

-------- Original Message --------
 On January 30, 2018 5:41 AM, Tim <xxxxxx@little-possums.net> wrote:

>On Tue, Jan 30, 2018 at 12:31:26AM -0500, Caleuche wrote:
>>I'm not clear about some of the reentry procedure, the patent states
>> that the sphere is under very low absolute pressure and is obviously
>> not rigid, the returning astronaut will know it's safe to depart the
>> "vehicle" once the sphere starts to collapse under the higher
>> outside pressure of Earth's atmosphere. But reentry itself will
>> result in fairly high pressures at times
>>
> Not for something this light.  Even if it came in steeply enough to
> peak at 10 gee deceleration, the dynamic pressure would still be less
> than 20 kPa.  You can run the numbers on a (say) 100 kg sphere with
> about 1.4 m diameter to see that the expected peak deceleration for a
> typical shallow entry will be quite a bit less than that.
>
> The patent document states that it was designed to support up to
> 8.5 gees deceleration, with an internal pressure of 1.75 p.s.i.a (about
> 12 kPa).  So their figures are comparable with my back of the envelope
> numbers.  The bladder pressure was chosen to be that low so as not to
> exceed the internal pressure of a space suit and possibly restrict air
> flow during descent.
>
>
> - Tim
>
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