Atmospheric Drag coeffiient usage in GROOPS

[Bemtgenj]

Dear developers,

i have been investigating the impact of the coefficient of drag value on non-conservative forces derived acceleration from 2.00 to 3.00 in different steps.

From the manual
Optional determination steps: Turn temperature on or off. In the first case, the model mentioned above is applied, which estimates variable drag and lift coefficients - in the latter case a constant drag coefficient can be specified.

If temperature is set to No then the script purely uses the drag coefficient set in the the satellite macro modeling? and no other input is needed? I just want to make sure i don't miss anything else. or any other input somewhere.

Thank you for your feedback and help.

Best regards

Jean

[ajs8041]

Dear Jean,

I quickly checked the code and to my understanding your assumption is correct.

The choice of temperature yes/no is saved in the boolean useTemperature. Every program that includes this variable does at some point call (groops/source/classes/) MiscAccelerationsAtmosphericDrag::force. If temperature is switched off, this function uses satellite->coefficientDrag, which is the value provided in the macro model file.

At times, this part of force modeling feels a bit convoluted. If you have reason to assume something is off with your results, feel free to tell me which programs you use exactly.

Best regards,
Andreas

[Bemtgenj]

Dear Andreas,

Thank you for your quick reply.

Initially i did not realize that i had to change the temperature setting. I thought as i set the drag coefficient in the macro model that is the one then that is being used in the processing. So when i initially processed cd=2.00 and cd=3.00 i got exactly the same acceleration results and that seemed not correct at all. Going back into the manual i found the above statement with the temperature setting. I reran the scripts and now they looked much better cd=3.00 acceleration higher than cd=2.00 acceleration. so that meant i was on the right track. I just wanted to make sure i had covered everything and the the results are completely correct.

BR
Jean

[Bemtgenj]

Dear Andreas,

I have an additional question question then with regards to the coefficient of drag. In the case that the drag coefficient is determined internally is here a method to find the actual value(s) that are estimated and used in the processing? Would i find the drag coefficient and its values through the parameter file when is save the normal equations? Or in some other way?

Thank you very much for the help.

BR
Jean

[ajs8041]

Dear Jean,

currently, no related program in the published version of GROOPS supports outputting the aerodynamic coefficient into a file. I am not familiar with your exact workflow, thus it is hard to give you precise hints. You can either write an entire program to output the aerodynamic coefficient (which is going to look very similar to InstrumentAccelerometer2ThermosphericDensity.cpp) or, somewhat dirty, add a simple cout in MiscAccelerationsAtmosphericDrag::force. If you put whatever program you use into a "GroupPrograms" and define a logFile, you could filter that logFile for the aerodynamic coefficient...

Best regards,
Andreas

[Bemtgenj]

Dear Andreas

Thank you very much for the fast reply. This is what i thought was the case as i had not seen anything in the parameter description in the documentation, but i wanted to be sure i did not miss anything. Maybe as a first step i will just add a simple cout line in theMiscAccelerationsAtmosphericDrag::force file

BR
jean