TDM (Tracking Data Message) - VALAR Documentation

For the complete documentation index, see llms.txt.

The Tracking Data Message (TDM) is a standardized ASCII text format for exchanging spacecraft tracking observations between ground stations, control centers, and orbit determination systems. Unlike OEM which contains computed ephemeris, TDM contains raw or processed measurement data from tracking sensors such as radar, optical telescopes, and ranging systems.

Doppler observables: TDM blocks containing DOPPLER_INSTANTANEOUS rows are ingested as range-rate observations alongside angle and range measurements. See Doppler (Range-Rate) Measurements below for the supported keywords, two-way convention rules, default sigma, and error codes.

Key Components

A TDM file contains a hierarchical structure:

Header: File-level metadata including format version, creation date, and originator
Segment(s): One or more independent tracking data segments, each containing:
- Metadata Section: Observation context (participants, time system, measurement types, reference frame)
- Data Section: Time-tagged measurements in chronological order

Each segment represents a distinct tracking pass, observation session, or measurement configuration. A single TDM file can contain multiple segments for different tracking stations or observation periods.

Structure Overview

TDM Hierarchy

TDM File
├── Header (format version, creation date, originator)
└── Segment 1
    ├── Metadata Section (META_START to META_STOP)
    └── Data Section (DATA_START to DATA_STOP)
└── Segment 2
    ├── Metadata Section
    └── Data Section
└── ... (additional segments)

Segment Structure

Each segment is self-contained with its own metadata and data:

Metadata defines the observation context and applies to all measurements in the data section
Data contains timestamped observations in the format: KEYWORD = EPOCH VALUE

Metadata Fields

Required Metadata

Field	Description	Example Values
TIME_SYSTEM	Time system for all epochs	UTC, TAI, GPS
PARTICIPANT_1	First participant in tracking path	Ground station ID, spacecraft ID
PARTICIPANT_2	Second participant in tracking path	Spacecraft ID, ground station ID
MODE	Data transmission mode	SEQUENTIAL, SINGLE_DIFF
PATH	Signal path between participants	1,2 (one-way), 2,1,2 (two-way)

Observation-Specific Metadata

Depending on the measurement type, additional metadata is required:

Angle Observations

ANGLE_TYPE: Geometry convention (AZEL, RADEC, XEYN, XSYE)
REFERENCE_FRAME: Coordinate frame for angles (EME2000, ITRF, topocentric)

Range Observations

RANGE_UNITS: Units for range measurements (km, m, s, RU)
TRANSMIT_BAND: Frequency band (S, X, Ka)
RECEIVE_BAND: Receiving frequency band

Optional Metadata

TIMETAG_REF: Time tag reference point (TRANSMIT, RECEIVE, BOUNCE)
INTEGRATION_INTERVAL: Data averaging period (seconds)
CORRECTION_ANGLE_1: Correction applied to first angle component
CORRECTION_ANGLE_2: Correction applied to second angle component
CORRECTION_RANGE: Range correction applied

Corrections fields indicate whether measurements have been preprocessed to remove systematic errors, biases, or atmospheric effects.

Measurement Types

TDM supports a wide variety of tracking observations:

Angle Measurements

Keyword	Description	Units	ANGLE_TYPE
ANGLE_1	First angle component	degrees	Azimuth (AZEL), RA (RADEC), X-East (XEYN)
ANGLE_2	Second angle component	degrees	Elevation (AZEL), Dec (RADEC), Y-North (XEYN)

Common ANGLE_TYPE values:

AZEL: Azimuth and elevation (local horizontal frame, typical for radar and RF tracking)
RADEC: Right ascension and declination (inertial frame, typical for optical telescopes)
XEYN: X-East and Y-North (topocentric Cartesian)
XSYE: X-South and Y-East (alternative topocentric)

Range Measurements

Keyword	Description	Units
RANGE	One-way or two-way range	km, m, s, or range units (RU)

Range measurements can be:

One-way: Signal travels from transmitter to receiver (PATH = 1,2 or 2,1)
Two-way: Signal transmitted, reflected, and received (PATH = 1,2,1 or 2,1,2)

Doppler (Range-Rate) Measurements

DOPPLER measurements in a CCSDS 503.0-B-2 TDM are line-of-sight range-rate observations — the time derivative of the slant range between a ground station and a spacecraft. Unlike angle (AZEL/RADEC) or range observations, a Doppler sample reports how fast the geometric distance to the target is changing at a given epoch (m/s). Doppler observables flow through the same orbit determination pipeline that consumes range and angle measurements: VALAR converts the producer-side observable into the internal one-way / two-way MEAN range-rate convention used by the measurement model, normalises the timetag to receive-time, and emits a normalised record carrying band, transponder-delay, and correction-state metadata for downstream OD.

Supported Doppler observables

The CCSDS standard defines three Doppler-family keywords. VALAR accepts only DOPPLER_INSTANTANEOUS and rejects the other two with explicit error codes.

Keyword	Status	Notes
DOPPLER_INSTANTANEOUS	Accepted	Range-rate sample at the stated epoch (km/s on the wire, converted to m/s on emission)
DOPPLER_INTEGRATED	Rejected	Raises `TRK_DOPPLER_INTEGRATED_UNSUPPORTED` — different observable model
DOPPLER_COUNT	Rejected	Raises `TRK_DOPPLER_COUNT_UNSUPPORTED` — phase-count observable, not in scope

INTEGRATION_INTERVAL constraint

DOPPLER_INSTANTANEOUS rows are accepted only when the block-level INTEGRATION_INTERVAL is absent or ≤ 1 s. A larger window means the value is a window average; timestamping it as if it were instantaneous introduces a systematic time shift of order Tc/2, which can translate into kilometre-scale along-track position bias in LEO. Larger windows are rejected with TRK_INSTANTANEOUS_INTEGRATION_WINDOW_TOO_LARGE. The 1 s threshold matches the operational envelope of modern commercial and institutional Earth-orbit receivers (KSAT, SSC, Leaf Space, Viasat RT Logic, post-2015 ESTRACK).

Default sigma values

When the producer does not provide a per-observation σ in the TDM and no per-sensor σ is configured for DOPPLER in the sensor catalog, VALAR applies a per-band default. The emitted record carries sigmaDefaulted=true for audit.

Band	Default σ (m/s)	Source
X	1.0×10⁻³ m/s	X-band reference noise
S	5.0×10⁻³ m/s	Scaled from X-band per typical S-band carrier-noise ratios
Ka	5.0×10⁻⁴ m/s	Scaled from X-band per typical Ka-band carrier-noise ratios

Applied when no per-observation σ is in the TDM AND no sensor catalog σ is configured for DOPPLER. The emitted record carries sigmaDefaulted=true for audit.

Two-way Doppler convention

CCSDS 503.0-B-2 does not mandate which convention a producer uses for two-way Doppler. The two valid forms differ by a factor of two and the keyword alone does not distinguish them — silently assuming one when the producer uses the other introduces a 100% bias in the observable. VALAR resolves the convention per sensor via the twoWayDopplerConvention field on the sensor configuration. See the Sensors page for where to set it.

Setting	Definition	Adapter behaviour
MEAN	Observable is the arithmetic mean of uplink and downlink instantaneous rates (DSN convention)	Accept; emit observable as-received (km/s → m/s)
SUM	Observable is `d/dt` of the round-trip range (e.g. GMAT’s native form)	Accept; halve observable at emission to normalise to the internal MEAN convention; provenance logged
UNDECLARED	No per-sensor configuration	Magnitude-based auto-detection — accept with warning when `\|ρ̇\| ≤ 10 km/s`, reject otherwise

Behaviour per setting:

MEAN: ingestion succeeds without warning; the value is consumed verbatim by the measurement model.
SUM: ingestion succeeds; the observable is halved before emission and the per-record provenance flag records the conversion. Downstream OD sees a MEAN-convention observable.
UNDECLARED with |ρ̇| ≤ 10 km/s: ingestion succeeds with a TRK_TWO_WAY_CONVENTION_ASSUMED_MEAN warning. The 10 km/s sanity bound matches the maximum plausible LEO line-of-sight velocity for a MEAN-convention observable (circular-orbit velocity at LEO ≈ 7.6 km/s).
UNDECLARED with |ρ̇| > 10 km/s: ingestion fails the block with TRK_AMBIGUOUS_TWO_WAY_CONVENTION. The magnitude is consistent with a SUM-convention observable that the adapter cannot safely halve without an explicit producer declaration.

Doppler error codes

The Doppler ingestion contract is fail-closed: every reject path surfaces a specific error code. Codes are scoped at three fatal levels — file-level (entire file rejected), block-level (block rejected, sibling blocks continue), and observation-level (row rejected, sibling rows continue). Two warning codes log vendor-assumption cases without rejecting.

Code	Cause	Remediation
`TRK_AMBIGUOUS_CORRECTIONS`	Producer correction-state inputs (`CORRECTIONS_APPLIED` plus `STEC` / `TROPO_*` data rows) form an inconsistent combination.	Reconcile the producer’s TDM: declare `CORRECTIONS_APPLIED = YES` with co-timestamped correction rows, or set `NO` with no correction rows.
`TRK_AMBIGUOUS_TWO_WAY_CONVENTION`	Two-way block has no `twoWayDopplerConvention` configured and observable magnitude exceeds the 10 km/s MEAN-convention sanity bound.	Configure `twoWayDopplerConvention = SUM` or `MEAN` on the sensor in question.
`TRK_TWO_WAY_CONVENTION_ASSUMED_MEAN` (warning)	Two-way block has no `twoWayDopplerConvention` configured but observable magnitude is within sanity bound; defaulted to MEAN.	Configure `twoWayDopplerConvention` explicitly on the sensor to silence the warning.
`TRK_DOPPLER_INTEGRATED_UNSUPPORTED`	Observation row uses `DOPPLER_INTEGRATED`, which VALAR does not accept.	Re-emit the data with `DOPPLER_INSTANTANEOUS` rows.
`TRK_DOPPLER_COUNT_UNSUPPORTED`	Observation row uses `DOPPLER_COUNT`, which VALAR does not accept.	Re-emit the data with `DOPPLER_INSTANTANEOUS` rows.
`TRK_INSTANTANEOUS_INTEGRATION_WINDOW_TOO_LARGE`	`DOPPLER_INSTANTANEOUS` row carries `INTEGRATION_INTERVAL > 1 s`, risking a `Tc/2` time-shift bias.	Re-emit with `INTEGRATION_INTERVAL ≤ 1 s`, or configure a per-sensor operator override when the producer timestamps at interval midpoint.
`TRK_TDM_PARSE_FAILED`	The CCSDS TDM file failed to parse.	Validate the file against CCSDS 503.0-B-2 syntax and resubmit.
`TRK_UNSUPPORTED_TDM_VERSION`	TDM uses an unsupported version (e.g. legacy -B-1).	Upgrade the producer to emit CCSDS 503.0-B-2.
`TRK_UNSUPPORTED_TIME_SYSTEM`	`TIME_SYSTEM` is not in `{UTC, TAI, GPS}` (e.g. `SCLK`, `UT1`, `TDB`, `TT`, `TCB`, `TCG`).	Re-emit the TDM in `UTC`, `TAI`, or `GPS`.
`TRK_UNSUPPORTED_MODE`	`MODE` is not `SEQUENTIAL` (e.g. `SINGLE_DIFF` differential Doppler).	Re-emit with `MODE = SEQUENTIAL`.
`TRK_UNSUPPORTED_PATH`	`PATH` is not in `{1,2}` (one-way) or `{2,1,2}` (two-way) — e.g. three-way `{2,1,3}`.	Re-emit with a one-way or two-way coherent path; three-way is not in scope.
`TRK_MISSING_PARTICIPANT`	A participant slot referenced by `PATH` is empty.	Populate the missing `PARTICIPANT_*` slot in the block metadata.
`TRK_UNRESOLVED_PARTICIPANT`	Neither participant resolves to a station (or both resolve to the same kind), so direction is undefined.	Verify station / spacecraft identifiers match the mission catalog; three-way Doppler is rejected here.
`TRK_MISSING_BAND`	Model-applied tropospheric or ionospheric corrections are required but `TRANSMIT_BAND` / `RECEIVE_BAND` is missing.	Populate `TRANSMIT_BAND` and `RECEIVE_BAND` (`{S, X, Ka}`) on the block metadata.
`TRK_UNKNOWN_BAND`	A band keyword is present but not in `{S, X, Ka}`.	Re-emit with a supported band.
`TRK_MISSING_TRANSPONDER_DELAY`	Two-way block lacks both pre-applied transponder calibration and metadata constants (`TRANSMIT_DELAY_1`, `RECEIVE_DELAY_1`).	Add `TRANSMIT_DELAY_1` and `RECEIVE_DELAY_1` to metadata, or pre-apply the calibration upstream.
`TRK_UNKNOWN_CORRECTION_KEYWORD`	A non-standard `CORRECTION_*` keyword is not in the closed vendor-alias table.	Use a CCSDS 503.0-B-2 keyword, or request an alias-table extension.
`TRK_NO_EPHEMERIS_FOR_SHIFT`	`TIMETAG_REF = TRANSMIT` requires a reference ephemeris for light-time normalisation, but none is loaded.	Load an initial ephemeris for the spacecraft before ingesting the TDM.
`TRK_CORRECTIONS_ASSUMED_NO` (warning)	`CORRECTIONS_APPLIED` is absent and no correction rows / metadata are present; defaulted to `NO`.	Set `CORRECTIONS_APPLIED` explicitly on the producer side to silence the warning.

Example: One-way X-band Doppler block

A valid one-way DOPPLER TDM block, X-band downlink from a single ground station to a spacecraft, conforming to CCSDS 503.0-B-2:

CCSDS_TDM_VERS   = 2.0
CREATION_DATE    = 2026-06-21T00:00:00.000
ORIGINATOR       = VALAR

COMMENT One-way X-band Doppler downlink, instantaneous range-rate.
COMMENT Tropospheric and ionospheric corrections pre-applied at producer.

META_START
TIME_SYSTEM           = UTC
PARTICIPANT_1         = STATION-A
PARTICIPANT_2         = SAT-1
MODE                  = SEQUENTIAL
PATH                  = 1,2
TIMETAG_REF           = RECEIVE
TRANSMIT_BAND         = X
RECEIVE_BAND          = X
INTEGRATION_INTERVAL  = 1.0
CORRECTIONS_APPLIED   = YES
META_STOP

DATA_START
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:00.000      3.500000
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:10.000      3.487231
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:20.000      3.474102
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:30.000      3.460613
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:40.000      3.446764
DOPPLER_INSTANTANEOUS = 2026-06-21T00:05:50.000      3.432555
DATA_STOP

Field notes:

PATH = 1,2 selects the one-way downlink modality (signal travels from PARTICIPANT_1 to PARTICIPANT_2).
TIMETAG_REF = RECEIVE means the epoch on each data row is the receive time at the ground station; no light-time shift is applied at ingest.
INTEGRATION_INTERVAL = 1.0 is at the boundary (≤ 1 s); larger values would reject with TRK_INSTANTANEOUS_INTEGRATION_WINDOW_TOO_LARGE.
CORRECTIONS_APPLIED = YES with no STEC / TROPO_* data rows is accepted only when metadata CORRECTION_* values are also present. For the more common case where the producer pre-applies corrections via the data section, co-timestamped STEC and TROPO_DRY / TROPO_WET rows accompany each DOPPLER_INSTANTANEOUS row.
Doppler values are in km/s on the wire and are converted to m/s on emission to the internal record.

Frequency Measurements

Keyword	Description	Units
RECEIVE_FREQ	Received signal frequency	Hz
TRANSMIT_FREQ_1	First transmitter frequency	Hz
TRANSMIT_FREQ_2	Second transmitter frequency	Hz

Additional Observations

Keyword	Description	Units
MAG	Visual or radar magnitude	dimensionless
RCS	Radar cross-section	m²
PRESSURE	Atmospheric pressure	hPa
TEMPERATURE	Atmospheric temperature	K
HUMIDITY	Relative humidity	%

Critical Keywords

MODE — Transmission Mode

Defines the signal transmission configuration:

SEQUENTIAL: Measurements taken in chronological sequence (most common)
SINGLE_DIFF: Single-difference measurements (VLBI, GPS)
COHERENT: Coherent ranging
CONSTANT: Constant frequency transmission

PATH — Signal Path

Specifies the route of the signal between participants:

1,2: One-way from Participant 1 to Participant 2
2,1: One-way from Participant 2 to Participant 1
1,2,1: Two-way round trip starting from Participant 1
2,1,2: Two-way round trip starting from Participant 2

PATH order matters for interpreting range measurements. Two-way range includes the round-trip distance, while one-way range is the direct distance.

TIMETAG_REF — Time Tag Reference

Indicates when the measurement timestamp refers to:

TRANSMIT: Time when signal was transmitted
RECEIVE: Time when signal was received
BOUNCE: Time when signal reflected off target (two-way ranging)

This is critical for correctly processing light-time corrections in orbit determination.

Common Use Cases

Orbit Determination: Processing radar and optical tracking to estimate spacecraft state
Orbit Solution Validation: Comparing predicted ephemeris against ground-based observations
Navigation Support: Providing ranging data for real-time navigation
Conjunction Assessment: Sharing raw observations for independent orbit solutions
Data Archiving: Long-term storage of historical tracking campaigns
Multi-Station Campaigns: Combining observations from multiple ground stations

Complete definition of the TDM standard in CCSDS 503.0-B-2 specification.

Sample TDM Files

Example 1: Optical Angle Measurements (RADEC)

This example shows right ascension and declination measurements from an optical telescope tracking a spacecraft in an inertial reference frame:

CCSDS_TDM_VERS   = 2.0
CREATION_DATE    = 2024-12-10T16:30:14.352701
ORIGINATOR       = VALAR

COMMENT Optical telescope tracking data
COMMENT Measurements have not been corrected for atmospheric refraction

META_START
TIME_SYSTEM      = UTC
PARTICIPANT_1    = OPTICAL-STATION-01
PARTICIPANT_2    = 2023-001A
MODE             = SEQUENTIAL
PATH             = 2,1
TIMETAG_REF      = RECEIVE
ANGLE_TYPE       = RADEC
REFERENCE_FRAME  = EME2000
INTEGRATION_INTERVAL = 2.0
META_STOP

DATA_START
ANGLE_1     = 2024-12-10T02:49:31.512      172.016040
ANGLE_2     = 2024-12-10T02:49:31.512       -3.931946
MAG         = 2024-12-10T02:49:31.512       14.535494
ANGLE_1     = 2024-12-10T02:49:33.513      172.024207
ANGLE_2     = 2024-12-10T02:49:33.513       -3.931761
MAG         = 2024-12-10T02:49:33.513       14.621805
ANGLE_1     = 2024-12-10T02:49:35.514      172.032289
ANGLE_2     = 2024-12-10T02:49:35.514       -3.931576
MAG         = 2024-12-10T02:49:35.514       14.708923
DATA_STOP

Example 2: Radar Tracking (AZEL + Range)

This example shows azimuth-elevation angles with two-way range from a ground-based radar:

CCSDS_TDM_VERS   = 2.0
CREATION_DATE    = 2024-12-15T08:00:00.000
ORIGINATOR       = GROUND_STATION_ALPHA

COMMENT Two-way radar tracking pass
COMMENT Range corrected for tropospheric delay

META_START
TIME_SYSTEM      = UTC
PARTICIPANT_1    = RADAR-SITE-A
PARTICIPANT_2    = SPACECRAFT-BETA
MODE             = SEQUENTIAL
PATH             = 1,2,1
TIMETAG_REF      = TRANSMIT
ANGLE_TYPE       = AZEL
REFERENCE_FRAME  = ITRF
RANGE_UNITS      = km
TRANSMIT_BAND    = X
RECEIVE_BAND     = X
CORRECTION_RANGE = YES
META_STOP

DATA_START
ANGLE_1     = 2024-12-15T12:30:00.000       87.234
ANGLE_2     = 2024-12-15T12:30:00.000       45.678
RANGE       = 2024-12-15T12:30:00.000      842.156
ANGLE_1     = 2024-12-15T12:30:02.000       87.456
ANGLE_2     = 2024-12-15T12:30:02.000       46.123
RANGE       = 2024-12-15T12:30:02.000      845.892
ANGLE_1     = 2024-12-15T12:30:04.000       87.678
ANGLE_2     = 2024-12-15T12:30:04.000       46.567
RANGE       = 2024-12-15T12:30:04.000      849.734
DATA_STOP

Multi-Segment TDM Example

A single TDM file can contain multiple segments from different stations or observation sessions:

CCSDS_TDM_VERS   = 2.0
CREATION_DATE    = 2024-12-25T20:00:00.000
ORIGINATOR       = MISSION_CONTROL

COMMENT Multi-station tracking campaign

META_START
TIME_SYSTEM      = UTC
PARTICIPANT_1    = STATION-NORTH
PARTICIPANT_2    = SPACECRAFT-GAMMA
MODE             = SEQUENTIAL
PATH             = 1,2,1
ANGLE_TYPE       = AZEL
REFERENCE_FRAME  = ITRF
RANGE_UNITS      = km
META_STOP

DATA_START
ANGLE_1     = 2024-12-25T10:00:00.000      120.234
ANGLE_2     = 2024-12-25T10:00:00.000       30.567
RANGE       = 2024-12-25T10:00:00.000     1250.123
DATA_STOP

META_START
TIME_SYSTEM      = UTC
PARTICIPANT_1    = STATION-SOUTH
PARTICIPANT_2    = SPACECRAFT-GAMMA
MODE             = SEQUENTIAL
PATH             = 1,2,1
ANGLE_TYPE       = AZEL
REFERENCE_FRAME  = ITRF
RANGE_UNITS      = km
META_STOP

DATA_START
ANGLE_1     = 2024-12-25T14:00:00.000      240.678
ANGLE_2     = 2024-12-25T14:00:00.000       25.123
RANGE       = 2024-12-25T14:00:00.000     1380.456
DATA_STOP

Usage in VALAR

When working with TDM files in VALAR:

Sensor Configuration Required: Ground station or sensor metadata must be configured in VALAR before importing TDM files. This includes station location, antenna characteristics, and measurement biases.
Automatic Processing: VALAR validates TDM structure, parses metadata, and associates measurements with the correct spacecraft and sensors.
Orbit Determination: TDM measurements are used as observations in weighted least-squares orbit determination to estimate spacecraft state vectors.
Residual Analysis: After orbit determination, VALAR computes observation residuals (measured minus computed) for quality assessment.
Multi-Station Support: TDM files with multiple segments from different stations are automatically handled.

Sensor configuration in VALAR must match the PARTICIPANT_1 field in TDM metadata. If the sensor ID is not found, the TDM import will fail.

Best Practices

Data Quality

Include COMMENT fields: Document observation conditions, corrections applied, and data quality issues
Specify corrections: Use CORRECTION_* keywords to indicate preprocessing
Provide metadata: Include INTEGRATION_INTERVAL and measurement uncertainties when available

File Organization

One segment per pass: Separate distinct tracking passes or observation sessions into different segments
Consistent time systems: Use UTC for operational tracking data
Appropriate reference frames: Use ITRF for ground-based AZEL, EME2000/GCRF for RADEC

Measurement Types

Match ANGLE_TYPE to sensor: Use AZEL for radar/RF, RADEC for optical telescopes
Specify PATH correctly: Ensure PATH matches actual signal propagation
Use TIMETAG_REF appropriately: TRANSMIT for radar, RECEIVE for optical

Interoperability

Follow CCSDS conventions: Adhere to standard keyword names and units
Validate before sharing: Ensure TDM syntax and semantics are correct
Document non-standard fields: If using custom keywords, explain them in comments

Comparison with Other Formats

Feature	TDM	OEM	OPM
Data Type	Raw observations	Computed ephemeris	State snapshot
Temporal Scope	Observation period	Time series	Single epoch
Source	Ground sensors	Propagation/OD	OD output
Purpose	Input to OD	Trajectory sharing	State exchange
Measurement Types	Angles, range	Position, velocity	Position, velocity, elements
Multi-Segment	Yes (multiple stations)	Yes (multiple intervals)	No

Reference Frames and Time Systems

Supported Reference Frames

TDM supports any reference frame appropriate for the measurement type:

ITRF/ITRF2020: Earth-fixed frame for ground-based AZEL measurements
EME2000/GCRF: Inertial frames for RADEC measurements
Topocentric: Station-centered frames (local horizontal)

Time Systems

Standard time systems for TDM:

UTC: Coordinated Universal Time (most common for operational tracking)
TAI: International Atomic Time
GPS: GPS Time
TDB: Barycentric Dynamical Time (deep space missions)

Ensure your time system matches the precision requirements of your orbit determination. For sub-meter accuracy, distinguish between UTC, TAI, and dynamical time systems.

Technical References

VALAR’s TDM processing is built on industry-standard astrodynamics models, following:

CCSDS 503.0-B-2: Tracking Data Message standard
CCSDS 502.0-B-3: Navigation Data Messages (for reference frame definitions)
IERS Conventions: Earth orientation and time systems
Vallado’s Fundamentals of Astrodynamics and Applications

For detailed measurement modeling and observation types, consult the CCSDS TDM Specification.

Core Concepts

File Formats

Documentation Index

​Key Components

​Structure Overview

​TDM Hierarchy

​Segment Structure

​Metadata Fields

​Required Metadata

​Observation-Specific Metadata

​Angle Observations

​Range Observations

​Optional Metadata

​Measurement Types

​Angle Measurements

​Range Measurements

​Doppler (Range-Rate) Measurements

​Supported Doppler observables

​INTEGRATION_INTERVAL constraint

​Default sigma values

​Two-way Doppler convention

​Doppler error codes

​Example: One-way X-band Doppler block

​Frequency Measurements

​Additional Observations

​Critical Keywords

​MODE — Transmission Mode

​PATH — Signal Path

​TIMETAG_REF — Time Tag Reference

​Common Use Cases

​Sample TDM Files

​Example 1: Optical Angle Measurements (RADEC)

​Example 2: Radar Tracking (AZEL + Range)

​Multi-Segment TDM Example

​Usage in VALAR

​Best Practices

​Data Quality

​File Organization

​Measurement Types

​Interoperability

​Comparison with Other Formats

​Reference Frames and Time Systems

​Supported Reference Frames

​Time Systems

​Technical References

Key Components

Structure Overview

TDM Hierarchy

Segment Structure

Metadata Fields

Required Metadata

Observation-Specific Metadata

Angle Observations

Range Observations

Optional Metadata

Measurement Types

Angle Measurements

Range Measurements

Doppler (Range-Rate) Measurements

Supported Doppler observables

INTEGRATION_INTERVAL constraint

Default sigma values

Two-way Doppler convention

Doppler error codes

Example: One-way X-band Doppler block

Frequency Measurements

Additional Observations

Critical Keywords

MODE — Transmission Mode

PATH — Signal Path

TIMETAG_REF — Time Tag Reference

Common Use Cases

Sample TDM Files

Example 1: Optical Angle Measurements (RADEC)

Example 2: Radar Tracking (AZEL + Range)

Multi-Segment TDM Example

Usage in VALAR

Best Practices

Data Quality

File Organization

Measurement Types

Interoperability

Comparison with Other Formats

Reference Frames and Time Systems

Supported Reference Frames

Time Systems

Technical References