Tracking Data Types for OD
Tracking Data Types for Orbit Determination — This section describes tracking data types and file formats for orbit determination.
Measurement Types Supported
GMAT supports the following measurement types for orbit determination.
| GMAT Measurement Type Name | Measurement Description | Measurement Units |
|---|---|---|
| DSN_SeqRange | DSN Sequential Ranging (TRK-2-34 data Type 7), ramped and un-ramped | Range Units |
| DSN_TCP | DSN Total Count Phase (TRK-2-34 data Type 17) measurements, implemented as a derived "Doppler" type measurement using successive phase measurements | Hertz |
| GPS_PosVec | Earth-fixed position vectors from a spacecraft on-board GPS receiver | Kilometers |
| Range | Two-way transponder range. A round-trip range measurement which includes the Spacecraft Transponder.HardwareDelay | Kilometers |
| RangeRate | Two-way coherent transponder range-rate. This is modeled as the difference between range measurements at the end and start of the Doppler count interval, divided by the length of the count interval. The measurement is time-tagged at the end of the interval. | Kilometers/sec |
The GMAT measurement type names listed are the string names to be used in instances of ErrorModel, AcceptFilter, RejectFilter, and TrackingFileSet, and in the GMAT GMD-format tracking data file to identify each measurement type to GMAT.
Deprecated Measurement Type Names
This version of GMAT deprecates the DSNRange/Range_RU and Doppler/Doppler_HZ measurement type names. They are replaced by the new consistent naming convention introduced in the previous section. The old names will still work in the current version of GMAT, but users are encouraged to transition their scripts to use of the new type names.
The new data type names employ the same name in the GMD file, error model, and tracking file set tracking configuration, eliminating the need for a mapping between the names employed in each resource. For those still using the deprecated data type names, the following table provides a guide.
| GMD File and TrackingFileSet.AddTrackingConfig Measurement Type Name | ErrorModel and StatisticsAccept/RejectFilter Measurement Type Name |
|---|---|
| DSNRange | Range_RU |
| Doppler | Doppler_HZ |
GMAT Tracking Data File Formats
GMAT uses a native ASCII tracking data file format called a “GMAT Measurement Data File”, or GMD file. This file format currently implements the following observation measurement types:
-
DSN Sequential Ranging, TRK-2-34 data Type 7
-
Derived Doppler using successive DSN Total Count Phase Doppler tracking measurements, TRK-2-34 data Type 17
-
DSN transmit frequency ramp records, TRK-2-34 data Type 9
-
Earth-fixed position vectors from a spacecraft on-board GPS receiver
-
Two-way coherent transponder range measurements
-
Two-way coherent transponder range-rate measurements
Each GMD file consists of a series of space-delimited ASCII records. Details of the GMD file format for each observation type are provided in the following sections. A single GMD file may contain one or more of the record types described below, but ramp records must be in a separate file. For further details on the TRK-2-34 data formats, please consult the TRK-2-34 DSN Tracking System Data Archival Format, 820-013 Deep Space Network External Interface Specification.
DSN Sequential Range
DSN TRK-2-34 Sequential Ranging employs the DSN_SeqRange measurement type. DSN_SeqRange is a round-trip range observation measured in range units. The GMD record format for DSN_SeqRange tracking data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Observation type name - DSN TRK-2-34 Type 7 Sequential Range = DSN_SeqRange |
| 3 |
Observation type index number - 9004 = DSN_SeqRange (TRK-2-34) |
| 4 | Downlink Ground station pad ID |
| 5 | Spacecraft ID |
| 6 | Range observable (meas_rng or rng_obs from TRK-2-34 Sequential Range CHDO) |
| 7 | Uplink frequency band indicator - 0 = unknown, 1 = S-band, 2 = X-band, 3 = Ka-band, 4 = Ku-band, 5 = L-band |
| 8 | Uplink frequency in Hz |
| 9 | Range modulo value (rng_modulo from TRK-2-34 Sequential Range CHDO) |
The transmit frequency specified in the TRK-2-34 range data GMD file is only used if a frequency ramp table is not available. If a transmit frequency ramp record file is provided on the TrackingFileSet.RampTable field, the transmit frequency will be determined from the ramp table and the frequency specified in the range data GMD file will be ignored. A sample of GMD data records for TRK-2-34 Sequential Range data is shown below.
% - 1 - - 2 - 3 4 5 - 6 - 7 - 8 - - 9 - 27236.157789352 DSN_SeqRange 9004 45 59 +9.810325186004e+005 1 +2.091414432000e+009 +1.048576000000e+006 27236.158240741 DSN_SeqRange 9004 45 59 +5.813243487947e+005 1 +2.091414432000e+009 +1.048576000000e+006 27236.158692130 DSN_SeqRange 9004 45 59 +1.863046908683e+005 1 +2.091414432000e+009 +1.048576000000e+006 27236.159143519 DSN_SeqRange 9004 45 59 +8.450116485521e+005 1 +2.091414432000e+009 +1.048576000000e+006
DSN Total Count Phase
DSN TRK-2-34 Total Count Phase employs the DSN_TCP measurement type. As shown below, the GMAT Doppler measurement type, measured in Hz, is derived from successive Total Phase Count (TCP) observations.
where
The GMD record format for DSN_TCP tracking data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Observation type name - DSN TRK-2-34 Type 17 Total Count Phase = DSN_TCP |
| 3 | Observation type index number - 9006 = DSN_TCP (TRK-2-34) |
| 4 | Downlink ground station pad ID |
| 5 | Spacecraft ID |
| 6 | Uplink frequency band indicator - 0 = unknown, 1 = S-band, 2 = X-band, 3 = Ka-band, 4 = Ku-band, 5 = L-band |
| 7 | Doppler count interval in seconds |
| 8 | Observation value - Doppler observable derived from Total Count Phase (TCP) TRK-2-34 Type 17 measurements |
A sample of GMD data records for TRK-2-34 Total Count Phase derived Doppler data is shown below.
% - 1 - - 2 - 3 4 5 6 7 - 8 - 27226.011944444 DSN_TCP 9006 15 6241 1 10 -2.2445668331979342e+09 27226.012060185 DSN_TCP 9006 15 6241 1 10 -2.2445668330920730e+09 27226.012175926 DSN_TCP 9006 15 6241 1 10 -2.2445668329843016e+09 27226.012291667 DSN_TCP 9006 15 6241 1 10 -2.2445668328729177e+09
Transmit Frequency Ramp Records
GMAT supports DSN tracking utilizing both constant and ramped transmit frequencies. If the transmit frequency is constant, GMAT will use the transmit frequency specified on the DSN_SeqRange measurement records for the computation of the range observation and a ramp table file is not required. If the transmit frequency is ramped, the user must generate a GMD file of ramp records from TRK-2-34 Type 9 raw data, and provide the GMD ramp table on the TrackingFileSet.RampTable object field. If a ramp table is provided, GMAT ignores the frequency specified on the DSN_SeqRange records and instead computes the transmit frequency from the ramp records.
The record format for ground-based range-rate tracking data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Ground station pad ID |
| 3 | Spacecraft ID |
| 4 | Uplink frequency band indicator - 0 = unknown, 1 = S-band, 2 = X-band, 3 = Ka-band, 4 = Ku-band, 5 = L-band |
| 5 | Ramp type - 0 = snap, 1 = start of new ramp, 2 = medial report, 3 = periodic report, 4 = end of ramps, 5 = ramping terminated by operator, 6 = invalid/unknown |
| 6 | Ramp frequency in Hz |
| 7 | Ramp rate in Hz/sec |
A sample GMD ramp file is shown below.
% - 1 - 2 3 4 5 - 6 - - 7 - 27238.640625000 34 234 2 1 +7.186571173393e+09 +6.010599999990e-01 27238.654513889 34 234 2 1 +7.186571894665e+09 +5.822699999990e-01 27238.659664352 34 234 2 3 +7.186572153775e+09 +5.822699999990e-01 27238.668402778 34 234 2 1 +7.186572593389e+09 +5.590199999990e-01 27238.682291667 34 234 2 1 +7.186573264213e+09 +5.315100000000e-01
Earth-fixed Position Vectors from a Spacecraft On-board GPS Receiver
GPS-derived Earth-fixed position vectors employ the GPS_PosVec measurement type. The fixed frame assumed for the vector components is GMAT's EarthFixed reference frame (see CoordinateSystem). The record format for GPS_PosVec tracking data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Observation type name - GPS_PosVec |
| 3 | Observation type index number - 9014 = GPS_PosVec |
| 4 | GPS receiver ID |
| 5 | Earth-fixed position X component (km) |
| 6 | Earth-fixed position Y component (km) |
| 7 | Earth-fixed position Z component (km) |
The GMAT user should be aware that the GPS_PosVec measurement is currently treated as a vector quantity. The vector components are not treated as independent observations. If any component of a vector observation (X, Y, or Z) is edited from the solution by the user or by autonomous sigma editing, the other components associated with that observation will also be edited out, regardless of their quality.
A sample GMD GPS_PosVec file is shown below.
% - 1 - - 2 - 3 4 - 5 - - 6 - - 7 - 26112.586516203704 GPS_PosVec 9014 800 -3575.594419 -5758.828897 1440.891615 26112.587210648147 GPS_PosVec 9014 800 -3257.134099 -5984.420574 1265.579859 26112.587905092594 GPS_PosVec 9014 800 -2926.558570 -6187.149174 1084.793371 26112.588599537037 GPS_PosVec 9014 800 -2585.076391 -6366.230816 899.311591 26112.589293981480 GPS_PosVec 9014 800 -2233.950454 -6520.997704 709.941434
Two-Way Transponder Range
Two-way range measurements that pass through a Spacecraft transponder use the Range measurement type. Range is a round-trip range observation measured in kilometers. The measurement model in GMAT will include the Spacecraft Transponder.HardwareDelay, but the HardwareDelay may be set to zero. The GMD record format for Range data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Observation type name - Range |
| 3 |
Observation type index number - 9002 = Range |
| 4 | Downlink ground station pad ID |
| 5 | Spacecraft ID |
| 6 | Two-way (round-trip) range observation in kilometers |
A sample of GMD data records for Range data is shown below.
% - 1 - - 2 - 3 4 5 - 6 - 27182.022395833334 Range 9002 117 322 +7.447171160686e+04 27182.022511574076 Range 9002 117 322 +7.447456623065e+04 27182.022627314815 Range 9002 117 322 +7.447742325277e+04 27182.022743055557 Range 9002 117 322 +7.448028087448e+04
Two-Way Range-rate
Two-way coherent range-rate tracking uses the RangeRate measurement type. RangeRate is the difference of the range observation at the end of the averaging interval and the start of the averaging interval, divided by the averaging interval duration. The time tag is at the end of the averaging interval. The GMD record format for RangeRate data is shown in the table below.
| Field | Description |
|---|---|
| 1 | Observation receive time in TAIModJulian |
| 2 | Observation type name - RangeRate |
| 3 |
Observation type index number - 9012 = RangeRate |
| 4 | Downlink ground station pad ID |
| 5 | Spacecraft ID |
| 6 | Uplink frequency band indicator - 0 = unknown, 1 = S-band, 2 = X-band, 3 = Ka-band, 4 = Ku-band, 5 = L-band |
| 7 | Doppler averaging interval in seconds |
| 8 | Range-rate observation in kilometers/second |
A sample of GMD data records for RangeRate data is shown below.
% - 1 - - 2 - 3 4 5 6 7 - 8 - 23430.503148148146 RangeRate 9012 GDS LEOSat 1 10 -11.61467029 23430.503842592592 RangeRate 9012 GDS LEOSat 1 10 -11.45104085 23430.504537037035 RangeRate 9012 GDS LEOSat 1 10 -11.18499007 23430.505231481478 RangeRate 9012 GDS LEOSat 1 10 -10.76465017