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Case Study Freeflyer

Decent Essays

Hi Jun,

Thank you for evaluating FreeFlyer and your patience while we worked through your issue. Our Tech Support team has spent some time analyzing your Mission Plan’s (MP). We are happy to see you using the Orbit Determination (OD) abilities of FreeFlyer. We do have some suggestions to help in simplifying your MP and evaluating your results.

To recap, you have three separate MP’s; the first is to setup your spacecraft and export the state vector as an ephemeris. Then the second MP is used to apply the Black Jack point solution data file to the ephemeris file using a Kalman Filter tool. The final MP then uses the Tracking Data Editor to generate a new Black Jack point solution data file from the original Black Jack point solution. Although, …show more content…

I have attached the edited version of your mission plan to this email. You can use the same data files that you sent in your original email to create your spacecraft and load the Black Jack point solution file. The first portion of your MP I modified on your MP is I commented out the Report Kalman Filter epoch and the Report Spacecraft’s semi-major axis in the script. I then had FreeFlyer instead plot the Pre & Post residuals vs the epoch for your Kalman Filter. This is seen in lines 11 thru 16 of the attached edited mission plan. Once the mission was reporting the Pre residuals it was evident that your initial Kalman Apriori State started ~5 (km) out of the expected position. This was causing issue with the Kalman Filter accepting the data due to the defined Sigma values of .05 (km); which caused the initial state to not be properly processed in the filter. I have included a description for each additional modified portion …show more content…

o In your spacecraft GUI there is a tab for the propagator step size (Spacecraft1  Motion Model  Propagator  Step Size) set to 300 seconds, where as your Kalman Filter step size is only 60 seconds. The Spacecraft step size should be identical to the Kalman Filter step size. This is mainly due to the Kalman Filter step size taking precedent in FreeFlyer and wanting to ensure that the spacecraft propagation is synced with the Kalman Filter. o Also under the “Motion Model” you are using 22 Zonal and Tesseral potential fields and the “Analytic” density model. Although this is not incorrect you would receive a better estimate if you used the Jacchia Roberts density model and increased your Zonals to a larger number. I have updated the Zonals and Tesserals, in the attached MP, to use 40

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