Re: [TML] More meteoric reentry thoughts Tim 31 Jan 2018 00:40 UTC
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