Re-entry Modeling

Using GMAT for specific types of missions.

Re-entry Modeling

Postby b.adler1980 » Wed Sep 26, 2012 5:58 pm

Can GMAT simulates the atmospheric re-entry mission?
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Re: Re-entry Modeling

Postby jjkparker » Fri Sep 28, 2012 8:26 pm

GMAT doesn't have any features specific to reentry, but it does have atmospheric density models that work down to 100km or so. It only supports a spherical spacecraft shape model, though.

What exactly are you looking for?
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
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Re: Re-entry Modeling

Postby b.adler1980 » Fri Sep 28, 2012 10:38 pm

thank you parker.
can you guide me to find out how can I use this feature of GMAT (atmospheric density models for spherical shapes)?
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
actually I want to simulate the re-entry part of a manned mission (like apollo mission) includes bellow requirements:
1-obtaining the exact pass and heating rate and acceleration during re-entry by giving entry interface conditions(flight pass angel and velocity) and drag coefficient and ...
like what you can see in this video: http://www.youtube.com/watch?v=bw14h3mgbKI&noredirect=1
2-simulating the attitude of the spacecraft during re-entry including pitch, yaw and roll.
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Re: Re-entry Modeling

Postby jjkparker » Mon Oct 01, 2012 12:25 pm

Yes, GMAT definitely does not have the level of reentry modeling that you need. It's can't predict heating on the spacecraft or changes in attitude due to drag, for example.

The drag models in GMAT are used to predict orbital decay, before reentry. For this, you just need to turn on drag modeling in the Propagator setup:
  1. In the Resources tree, double-click a Propagator resource (e.g. DefaultProp in the default mission) to open it.
  2. In the Drag section, select an atmosphere model from the Atmosphere Model list (for example, MSISE86).
  3. Click Setup and provide values for the space weather parameters.
  4. Click Run to run the mission.

In the script, add lines like these, replacing DefaultProp_ForceModel with the name of your ForceModel resource.:
Code: Select all
DefaultProp_ForceModel.Drag.AtmosphereModel = MSISE86;
DefaultProp_ForceModel.Drag.F107 = 150;
DefaultProp_ForceModel.Drag.F107A = 150;
DefaultProp_ForceModel.Drag.MagneticIndex = 3;
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
Posts: 617
Joined: Thu Jan 07, 2010 9:48 pm
Location: NASA Goddard Space Flight Center, Greenbelt, MD

Re: Re-entry Modeling

Postby hornig » Mon Feb 10, 2014 1:58 pm

Hi,

I also play around with re-entry, but for a Mars mission coming home.
because I don't fully know what the propagator does when the atmospheric model is activated, I try to do it with another approach. I use while loops with a propagator that only propagates for short durations (some seconds). Also in this loop is a script event where I let the standard barometric formula calculate the density of the atmosphere and use it for obtaining the drag force. This is used for correcting the velocities of the capsule directly.
I let the capsule aim for a hyperbolic distance of 6461km so at 90km altitude and start this loop and drag stuff when it reaches RMAG of 100km altitude. The capsule is damn fast, about 14km/s so my calculation is not fully working yet, because deceleration becomes really high and after it decreases to a more reasonable level velocity starts oscillating and doing crazy stuff :D. The aim is to have the capsule leave the atmosphere again and only reducing the speed below exit velocity to be captured in earth's gravity field.

Any tips or examples I could use?

Best regards,

Andreas
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Re: Re-entry Modeling

Postby jjkparker » Mon Feb 10, 2014 2:38 pm

What do you mean when you say:

hornig wrote:because I don't fully know what the propagator does when the atmospheric model is activated


What details do you need to know about our atmosphere models? I think it would be much cleaner to use the built-in models, unless you need to code your own for another reason.

Joel
Joel J. K. Parker
Flight dynamics engineer, GMAT team
http://gmatcentral.org
jjkparker
 
Posts: 617
Joined: Thu Jan 07, 2010 9:48 pm
Location: NASA Goddard Space Flight Center, Greenbelt, MD


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