### Author Topic: ITS drag area during entry?  (Read 1865 times)

#### 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 700-800m² from a vertical cross section, maybe 700m² 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 »

#### 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.

#### 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  :Þ.

#### 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  :Þ.

Cd will be around 1.

#### 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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