Simulator
Simulator — Configures the generation of simulated tracking data measurements.
Description
A Simulator configures the generation of simulated tracking data measurements. These measurements can then be used by a BatchEstimatorInv resource as part of an estimation run.
The Simulator object requires specification of one or more instances of a TrackingFileSet resource which identify the specific tracking data observation strands, data types, desired measurement corrections, and the output tracking data file name. Simulated data will be written in the GMAT Measurement Data (GMD) ASCII tracking data format. You must additionally specify a time span for the simulation run and a time interval between simulated observations. Simulated observations are only generated when a tracking strand meets the visibility constraints of all objects in the strand (for example, the observation must be above the ground station minimum elevation mask). Additionally, you must configure and specify an instance of a Propagator for the simulator. Finally, you can choose to add random Gaussian white noise to the generated measurements or to generate measurements without noise. If the Simulator.AddNoise option is set to On, noise with the standard deviation specified on each measurement strand’s GroundStation.ErrorModel, is added to the measurements.
See Also: TrackingFileSet, RunEstimator
Fields
| Field | Description | ||||||||||||
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| AddData | A list of one or more TrackingFileSets
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| AddNoise | If true, adds noise to simulated observations
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| EpochFormat | Epoch format of both the initial and final epoch
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| InitialEpoch | The initial (start) epoch of the data simulation span. In the GMAT script, the EpochFormat field needs to be set before this field is set.
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| FinalEpoch | The final (ending) epoch of the data simulation span. In the GMAT script, the EpochFormat field needs to be set before this field is set.
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| MeasurementTimeStep | Specifies time step in seconds between two consecutive simulated observations
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| Propagator | Name of Propagator object used for calculation
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Remarks
Navigation Requires Use of Fixed Step Numerical Integration
GMAT navigation requires use of fixed stepped propagation. The Simulator resource has a Propagator field containing the name of the Propagator resource that will be used during the simulation. As shown in the Note below, there are some hard restrictions on the choice of error control specified for the ForceModel resource associated with your propagator.
Note
For simulation, the ErrorControl parameter
specified for the ForceModel resource associated
with the Simulator
Propagator must be set to 'None.' Of
course, when using fixed step control, the user must choose a step
size, as given by the Propagator
InitialStepSize field, for the chosen orbit regime and
force profile, that yields the desired accuracy.
Propagator Settings
The Simulator resource has a Propagator field containing the name of the Propagator resource that will be used during the estimation process. The minimum step size, MinStep, of your propagator should always be set to 0.
Interactions
| Resource | Description |
|---|---|
| TrackingFileSet resource |
Must be created in order to tell the Simulator resource, via the AddData field, which data types will be simulated and to specify the name of the output tracking data file (via FileName) |
| Propagator resource | Used by GMAT to generate the simulated orbit |
| RunSimulator command |
Must use the RunSimulator command to actually create the data defined by the Simulator resource |
Examples
The example below illustrates using the simulator to generate DSN
range measurements. This example is more detailed than usual as it can
actually be run to produce a file, simData.gmd,
that contains a single range measurement for a fictional DSN ground
station. For a more comprehensive example of simulating measurements,
see the Chapter 13, Simulate DSN Range and Doppler Data
tutorial.
%Create and Configure Spacecraft
Create Spacecraft SimSat;
GMAT SimSat.DateFormat = UTCGregorian;
GMAT SimSat.Epoch = '19 Aug 2015 00:00:00.000';
GMAT SimSat.X = -126544963;
GMAT SimSat.Y = 61978518;
GMAT SimSat.Z = 24133225;
GMAT SimSat.VX = -13.789;
GMAT SimSat.VY = -24.673;
GMAT SimSat.VZ = -10.662;
GMAT SimSat.AddHardware = {SatTransponder, SatTranponderAntenna};
%Create and configure RF hardware
Create Antenna SatTranponderAntenna DSNReceiverAntenna DSNTransmitterAntenna;
Create Transponder SatTransponder;
GMAT SatTransponder.PrimaryAntenna = SatTranponderAntenna;
Create Transmitter DSNTransmitter;
GMAT DSNTransmitter.PrimaryAntenna = DSNTransmitterAntenna;
GMAT DSNTransmitter.Frequency = 7200;
Create Receiver DSNReceiver;
GMAT DSNReceiver.PrimaryAntenna = DSNReceiverAntenna;
%Create and configure ground station and related error model
Create GroundStation DSN;
GMAT DSN.AddHardware = ...
{DSNTransmitter, DSNReceiver, DSNTransmitterAntenna, DSNReceiverAntenna};
GMAT DSN.ErrorModels = {DSNrange};
Create ErrorModel DSNrange;
GMAT DSNrange.Type = 'DSN_SeqRange';
GMAT DSNrange.NoiseSigma = 10;
%Define data types
Create TrackingFileSet simData;
GMAT simData.AddTrackingConfig = {{DSN,SimSat,DSN}, DSN_SeqRange};
GMAT simData.FileName = {'simData.gmd'};
% Create and configure the Simulator object
Create ForceModel FM1
FM1.ErrorControl = None %Fixed step integration required for Navigation
Create Propagator prop;
prop.FM = FM1
prop.MinStep = 0 %For Navigation, allow propagator to take arbitrarily small steps
Create Simulator sim;
GMAT sim.AddData = {simData};
GMAT sim.Propagator = prop;
GMAT sim.EpochFormat = UTCGregorian;
GMAT sim.InitialEpoch = '19 Aug 2015 08:00:00.000';
GMAT sim.FinalEpoch = '19 Aug 2015 08:00:01.000';
GMAT sim.MeasurementTimeStep = 60;
GMAT sim.AddNoise = On;
% Mission Sequence - run the simulator.
BeginMissionSequence;
RunSimulator sim;