Author Topic: ITS drag area during entry?  (Read 1769 times)

Offline Rei

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ITS drag area during entry?
« on: 01/19/2017 08:30 AM »
I'm working on a GNAT simulation involving ITS, and having gotten most of the the kinks out of targeting, I think, I need to handle aerobraking / aerocapture in a reasonable manner (not detailed enough to target specific landing sites, just good enough to get the delta-V calcs right for approach).  So, doing that means having a fair estimate for the drag area of the entering vehicle so GNAT can optimize how high to aim for.

Judging from their document, p.38:

http://www.spacex.com/sites/spacex/files/mars_presentation.pdf

So, for cross section... it looks like the craft is approaching at maybe 75 degrees with respect to its path of motion?  Max diameter is 17 meters (internal? or counting the little winglets?), length 49,5 meters, tapered at the tip... maybe 700-800m from a vertical cross section, maybe 700m at 75? 

As for the drag coefficient.... high angle of attack, hypersonic lifting body... maybe Cd = 2?

Do these numbers sound roughly right?  It's not going to make a huge difference, it's mainly just going to affect how high in the atmosphere it's going to have to target.
« Last Edit: 01/19/2017 08:31 AM by Rei »

Offline envy887

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Re: ITS drag area during entry?
« Reply #1 on: 01/19/2017 12:43 PM »
The body diameter is 12m. The chines extend to a 17m diameter.

You could try bringing one of the 3D models in this thread: https://forum.nasaspaceflight.com/index.php?topic=41318.0 into a modeling program and have it calculate the projected area at whatever angle you want.

Offline Rei

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Re: ITS drag area during entry?
« Reply #2 on: 01/19/2017 01:18 PM »
The body diameter is 12m. The chines extend to a 17m diameter.

You could try bringing one of the 3D models in this thread: https://forum.nasaspaceflight.com/index.php?topic=41318.0 into a modeling program and have it calculate the projected area at whatever angle you want.

Hey, that's a great idea for doing the cross section - I'll do just that!

As for Cd... any better idea, or do you think just going with 2 is reasonable for a lifting body at a high angle of attack?  I mean, i guess I could always mesh it into OpenFOAM and set up a simulation for it there, but I don't have the nenn for that today  :.

Offline livingjw

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Re: ITS drag area during entry?
« Reply #3 on: 01/19/2017 01:46 PM »
The body diameter is 12m. The chines extend to a 17m diameter.

You could try bringing one of the 3D models in this thread: https://forum.nasaspaceflight.com/index.php?topic=41318.0 into a modeling program and have it calculate the projected area at whatever angle you want.

Hey, that's a great idea for doing the cross section - I'll do just that!

As for Cd... any better idea, or do you think just going with 2 is reasonable for a lifting body at a high angle of attack?  I mean, i guess I could always mesh it into OpenFOAM and set up a simulation for it there, but I don't have the nenn for that today  :.

Cd will be around 1.

Offline Rei

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Re: ITS drag area during entry?
« Reply #4 on: 01/19/2017 02:24 PM »
Thanks - I'll just assume you've looked into this a lot more than me and go with your suggestion  ;)  There's just so much literature out there and I haven't had the time to go through it.
« Last Edit: 01/19/2017 02:25 PM by Rei »

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