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  1. GMAT
  2. GMT-5989

SOHO GMAT vs. GTDS initial iteration comparison

    Details

    • Type: Task
    • Status: Closed (View Workflow)
    • Priority: P1
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: R2016a
    • Component/s: Nav
    • Labels:

      Description

      • Start with converged GMAT solution.
      • Set flags so all data accepted
      • Make sure GMAT and GTDS uses the exact identical set of data
      • Look at initial iteration only
      • Create an Excel spreadsheet (we have done this before for Maven and or other s/c. Do we have old spreadsheet?) showing;
        • Epoch (TAIMDJ, UTCG)
        • O, C, O-C
        • Various GTDS corrections to O
        • Various GMAT corrections to C
        • Ground Station used
        • Etc

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            Hide
            sslojkowski Steven Slojkowski added a comment -

            I did a straight ephemeris compare between GMAT and GTDS and got a 2 meter difference over a 20-day prediction.

            I'll take a crack at running the range simulation scripts. If I fail, I'll assign this ticket to DSC.

            Show
            sslojkowski Steven Slojkowski added a comment - I did a straight ephemeris compare between GMAT and GTDS and got a 2 meter difference over a 20-day prediction. I'll take a crack at running the range simulation scripts. If I fail, I'll assign this ticket to DSC.
            Hide
            sslojkowski Steven Slojkowski added a comment - - edited

            The attached spreadsheets show the results of the SOHO GMAT/GTDS initial iteration OMC comparison. To summarize:

            • In the absence of any media corrections, GMAT and GTDS agree on the observed measurement to the level of accuracy of reporting.
            • In the absence of any media corrections, GMAT and GTDS disagree on the computed measurements. This disagreement can be explained as the difference between obtaining the computed measurement in the ECI frame (as GTDS does) versus obtaining the computed measurement in the SSB frame (as GMAT does)
            • Running the MATLAB range simulator on selected measurements yields computed values in good and precise agreement with GMAT (see GMAT-GTDS-MATLAB.xlsx). The MATLAB values differ from the GTDS computed measurement by an amount consistent with that shown in the OMC_Detailed_Comparison spreadsheet.
            • GTDS and GMAT use different tropospheric and ionospheric models, so when these effects are included, the OMC's in GMAT and GTDS differ by amounts consistent with the magnitude of ionospheric and tropospheric effects.
            • GTDS does not apply relativistic observation corrections for satellites propagated in an Earth-centered frame. For this test case, SOHO was propagated in an Earth-centered system, so the OMC comparison between GMAT and GTDS shows the entire effect of the relativistic observation because the correction is absent from the GTDS computed measurements.
            • When both GTDS and GMAT propagate in a Sun-centered frame, the computed measurements including relativity disagree by about 5 to 20 meters. Comparison with the MATLAB range simulator shows agreement with GMAT and disagreement with GTDS.
            Show
            sslojkowski Steven Slojkowski added a comment - - edited The attached spreadsheets show the results of the SOHO GMAT/GTDS initial iteration OMC comparison. To summarize: In the absence of any media corrections, GMAT and GTDS agree on the observed measurement to the level of accuracy of reporting. In the absence of any media corrections, GMAT and GTDS disagree on the computed measurements. This disagreement can be explained as the difference between obtaining the computed measurement in the ECI frame (as GTDS does) versus obtaining the computed measurement in the SSB frame (as GMAT does) Running the MATLAB range simulator on selected measurements yields computed values in good and precise agreement with GMAT (see GMAT-GTDS-MATLAB.xlsx). The MATLAB values differ from the GTDS computed measurement by an amount consistent with that shown in the OMC_Detailed_Comparison spreadsheet. GTDS and GMAT use different tropospheric and ionospheric models, so when these effects are included, the OMC's in GMAT and GTDS differ by amounts consistent with the magnitude of ionospheric and tropospheric effects. GTDS does not apply relativistic observation corrections for satellites propagated in an Earth-centered frame. For this test case, SOHO was propagated in an Earth-centered system, so the OMC comparison between GMAT and GTDS shows the entire effect of the relativistic observation because the correction is absent from the GTDS computed measurements. When both GTDS and GMAT propagate in a Sun-centered frame, the computed measurements including relativity disagree by about 5 to 20 meters. Comparison with the MATLAB range simulator shows agreement with GMAT and disagreement with GTDS.
            Hide
            shughes Steven Hughes added a comment -

            Seems like we can close this?

            Show
            shughes Steven Hughes added a comment - Seems like we can close this?

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                • Created:
                  Updated:
                  Resolved:

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