RunSimulator

Content of the Output File for DSN data

After the RunSimulator command has finished execution, one or more output files, as defined in the specified Simulator object, will be created. Each row of data in an output file contains information about one specific measurement at a given time. The format for a given row of data is described fully in the TrackingFileSet resource help.

Currently, GMAT supports two DSN data types, DSN TRK-2-34 type 7 (sequential range) and DSN TRK-2-34 type 17 (Total count phase). As shown in the TrackingFileSet resource help, for a type 7 measurement, a row of data has the following GMAT internal file format.

TAIMJD  DSN_SeqRange 9004 [Downlink Station ID] [S/C ID] [Range Observable (RU)] [Uplink Band] [Uplink Freq (Hz)] [Range Modulo (RU)]

where [Uplink Band] species the frequency band of the transmitting station as shown in the table below.

and where the [Range Observable (RU)], is calculated according to

where

As shown in the TrackingFileSet resource help, for a DSN TRK-2-34 type 17 measurement, a row of data has the following GMAT internal file format.

# TAIMJD_t3e DSN_TCP 9006 [Downlink Station ID] [S/C ID] [Uplink Band] [DopplerCountInterval_seconds] [DopplerMeas_Hz]

where [Uplink Band] has been previously described and where DopplerMeas_Hz, the Doppler measurement, is calculated according to

where

Note that (t3e - t3s) is known as the Doppler Count Interval and is an input field, SimDopplerCountInterval, for the TrackingFileSet resource.

When you simulate DSN range or Doppler, you can choose whether or not the frequency from the transmitting Ground Station is Non-ramped or Ramped. If you wish to model ramped data, you must supply an input ramp table. The format of the input ramp table is discussed in the TrackingFileSet resource help.

The table below shows how the values of Uplink Band, C, M2, and transmit frequency are calculated. The second column shows how the Uplink Band, which is included in the output file for both range and Doppler measurements, is calculated. For S-band, a “1” is output and for X-band, a “2” is output.

The output GMAT Measurement Data (GMD) file contains the observable value which is calculated using the equations shown above. The third column shows how the value of C or M2, which is used to calculate the observation value shown in the GMD file, is calculated.

Finally, the fourth column shows how the transmit frequency, which shows up directly in the GMD file (for DSN range but not DSN Doppler) and is also used to calculate the observation value given in the GMD file, is calculated.

As discussed in the Transponder Help, for both ramped and non-ramped data, the turn around ratio set on the Transponder object, Transponder.TurnAroundRatio, will be used to calculate the media corrections needed to determine the value of the simulated range and Doppler measurements.

Earth Nutation Update Interval

If you want to simulate a Doppler or range rate type of measurement (e.g., DSN_TCP and RangeRate) precisely, you will need to set the Earth nutation update interval to 0 as shown below.

          Earth.NutationUpdateInterval = 0
        

It is good general practice to set the Earth nutation update interval to zero for all measurement types.

Run simulation.

          %Perform a simulation

Create Simulator mySim

BeginMissionSequence 
RunSimulator mySim
        

For a comprehensive example of running a simulation, see the Chapter 13, Simulate DSN Range and Doppler Data tutorial.