RunEstimator

General Mission Analysis Tool

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RunEstimator

RunEstimator — Ingests navigation measurements and generates an estimated state vector

Script Syntax

RunEstimator BatchEstimatorInv_InstanceName

Description

The RunEstimator command ingests navigation measurements and generates an estimated state vector according to the specifications of the input BatchEstimatorInv resource.

See Also: BatchEstimatorInv

Remarks

How GMAT generates “Computed (C)” DSN data

As part of the estimation process, GMAT must calculate the so-called observation residual, “O-C,” where “C” is the “Computed” measurement. As discussed in the RunSimulator help, GMAT calculates the DSN range “C” measurement as

C ∫ t 1 t 3 f T ( t ) d t ,  mod M             (RU)

where

t 1 , t 3 = Transmission and Reception epoch, respectively
f T = Ground Station transmit frequency
C = transmitter dependent constant (221/1498 for X-band and 1/2 for S-Band)
M  =  length of the ranging code in RU

and GMAT calculates the DSN Doppler measurement as

C = − M 2 ( t 3 e − t 3 s ) ∫ t 1 s t 1 e f T ( t 1 ) d t 1   = − M 2 ( t 1 e − t 1 s ) D C I f ¯ T     (Hz)

where

t 1 s , t 1 e = start and end of transmission interval, respectively
f T = transmit frequency
M 2 = Transponder turn around ratio (typically, 240/221 for S-band and 880/749 for X-band)
DCI =  ( t 3 e − t 3 s ) =  Doppler Count Interval
f ¯ T ≡ ∫ t 1 s t 1 e f T ( t 1 ) d t 1 ( t 1 e − t 1 s )   = average transmit frequency 

The value of C and M2 used to calculate the computed range or Doppler measurement depends upon the data type and whether the data being ingested is ramped or non-ramped according to the table below. The value of the transmit frequency used to calculate the computed measurement depends upon whether or not the data being ingested is ramped or non-ramped.

Data Type Value of C (Range) or M2 (Doppler) used to calculate “Computed” measurement Value of transmit frequency used to calculate “Computed” measurement
Estimate Range without ramp table

  • Set based upon Uplink Band in input Range measurement GMD file. C=½ for S-band and 221/1498 for X-band.

  • Use frequency in input range GMD file

  • Ground Station transmit frequency set via Transmitter.Frequency is not used
Estimate Range with ramp table

  • Set based upon Uplink Band in input ramp table. C=½ for S-band and 221/1498 for X-band.

  • Value of Uplink Band in input Range measurement file has no effect.

  • Use frequency in ramp table

  • Frequency in input GMD file is not used

  • Ground Station transmit frequency set via Transmitter.Frequency is not used
Estimate Doppler without ramp table

  • M2=Transponder.TurnAroundRatio

  • Value of Uplink Band in input Range measurement file has no effect.

  • Use Ground Station transmit frequency set via Transmitter.Frequency (Note that for Doppler data, there is no frequency data in the GMD file)
Estimate Doppler with ramp table

  • Set based upon Uplink Band in input ramp table. M2=240/221 for S-band and 880/749 for X band.

  • Value of Uplink Bank in input Doppler GMD measurement file has no effect.

  • Use frequency in ramp table. (Note that for Doppler data, there is no frequency data in the GMD file)

  • Ground Station transmit frequency set via Transmitter.Frequency is not used

Earth Nutation Update Interval

If you want the estimator to calculate a Doppler or range rate type of measurement (e.g., DSN_TCP and RangeRate) residual 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.

Examples

Run batch estimator.

          Create BatchEstimatorInv myBatchEstimator

BeginMissionSequence
RunEstimator myBatchEstimator

For a comprehensive example of reading in measurements and running the estimator, see the Chapter 14, Orbit Estimation using DSN Range and Doppler Data tutorial.

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