1

GMAT R2018a Release Notes

The General Mission Analysis Tool (GMAT) version R2018a was released in May 2018.This is the first public release since June, 2017, and is the 12th release for the project.

Below is a summary of key changes in this release. Please see the full R2018a ReleaseNotes on JIRA for a complete list.

Milestones and Accomplishments

We're excited that GMAT has recently seen significant adoption for operational missionsupport.

• GMAT is now used as the primary system for maneuver planning and product gener-ation for the Solar Dynamics Observatory (SDO).

• GMAT is now used as the primary operational tool for orbit determination for the Solarand Heliospheric Observatory (SOHO) mission.

• GMAT is now used as the primary operational tool for maneuver planning, orbit de-termination, and product generation for the Advanced Composition Explorer (ACE)mission.

• GMAT is now used as the primary operational tool for maneuver planning, orbit de-termination, and product generation for the Wind mission.

• In April 2018, the Transiting Exoplanet Survey Satellite (TESS) mission launched.TESS is the first mission to GMAT as its primary tool for mission design and maneuverplanning from proposal development through operations.

• In May 2018, GMAT passed an Operational Readiness Review (ORR) for the LunarReconnaissance Orbiter (LRO) for Orbit Determination (OD) and is currently beingtransitioned to the prime system for LRO OD replacing the Goddard Trajectory De-termination System (GTDS).

New Features

Orbit Determination Enhancements

The following new features and capabilities have been added to GMAT's estimationsystem.

• The batch estimator now supports a capability that freezes the measurements usedfor estimation after a user-specified number of iterations. This functionality avoidsestimator chatter that can occur near solutions when some measurements are nearthe sigma edit boundary and are repeatedly removed during one iteration and thenadded back in the next iteration.

• Numerics are improved when calculating Doppler and DSN_TCP measurement resid-uals, improving noise behavior in the residuals.

• The GroundStation object supports a new troposphere model, the Marini model,matching the implementation used in GTDS. One operational advantage of the Marinimodel is that it doesn’t require input of weather data at the Ground station. (Modelsthat do accept weather data may have more accuracy.)

2

• Time is now modeled using three data members, a day number, seconds of day,and fraction of second. High precision time is surgically implemented in appropriatemodels such as Earth rotation, planetary ephemerides and others.

• Range differences are computed using a Taylor series and differenced Chebyshevpolynomials.

• Measurement simulation now accounts for central body occultation when orbiting bod-ies other than the Earth.

• Estimation now supports solving for the Keplerian state estimation with a priori con-straints.

• For BLS estimation, the user may choose to perform measurement editing using ei-ther the weighted root-mean-square (WRMS) of residuals, or the predicted weightedroot-mean-square (WRMSP) of residuals. Residuals of elevation edited data are nowreported.

• The batch estimator report now shows the name of input files used in the configurationand the observation time span. Additionally, spacecraft hardware configurations andnew measurement statistics information are included.

• The GMAT Data File (.gmd) was extened to support more options.

As shown by the new features above, GMAT’s orbit determination (OD) capability hasbeen significantly enhanced. As with all new releases, missions that use GMAT’s ODcapability should perform a baseline set of regression/performance tests prior to usingthe new version of GMAT OD for operational purposes.

Example scripts:

• See Ex_R2018a_CompareEphemeris.script for a new example on performingephemeris compares at non-Earth bodies.

• See Ex_R2018a_MergeEphemeris.script for an example demonstrating mergingephemerides.

Built-in Optimizer

GMAT now contains a built-in optimizer called Yukon, developed by the GMAT team.The optimizer uses an SQP line search algorithm with an active set QP-subproblemalgorithm. Yukon is designed for small scale problems and is not applicable to large,sparse optimization problems.

Improvements

• Tide modeling is improved, and GMAT now supports lunar tides.• STM propagation now includes variational terms from drag models.• The degree and order of STM contributions from harmonic gravity is now settable by

the user and defaults to the maximum order on the gravity file or 100, whichever islower.

• The buffer size that determines the number of plot points stored by the OrbitViewResource is now exposed to the user.

• Significant performance improvements have been made in the IRI2007 ionospheremodel.

• The script editor highlights errors and warnings found on the first pass of parsing.

3

• GMAT now supports body fixed and TOD coordinate systems for Code 500Ephemerides and supports all central bodies in the Code 500 Ephemeris format.

• The CommandEcho command has been added to GMAT to support printing com-mands to the message window and log file as they are executed in a mission se-quence. This command is particularly useful when debugging user scripts.

• The Code500 propagator type now automatically detects the endianness when read-ing Code500 files.

• The STK ephemeris propagator now uses Hermite interpolation, and includes velocityinformation in the position interpolation for segments that contain fewer than 7 rows ofdata. Velocity interpolation for segments with fewer than 7 rows of data is performedby forming the hermite interpolating polynomial for position, and then differentiatingthe position interpolating polynomial to obtain the velocity.

• You can now set the step size of an ephemeris propagator during mission execution(i.e. after the BeginMissionSequence command).

• The startup file now allows optional updating of the user configuration file. This avoidsissues encountered when simultaneous instances of GMAT try to write to the userconfig file at the same time, resulting in a system error.

• The Python data file utility now updates data files used by the IRI2007 model.• The GMAT CMake based build system now supports plugin components developed

by external groups.• GMAT now supports GUI plugin components.

Compatibility Changes

• Batch estimation now requires the use of fixed step integration.• The RotationDataSource on CelestialBody Resources is deprecated and no longer

has an effect.• The Spacecraft EstimationStateType parameter is deprecated.• The EphemerisFile OutputFormat options ‘UNIX’ and ‘PC’ are deprecated. ‘BigEndi-

an’ and ‘LittleEndian’ should be used instead.• The EarthTideModel on the ForceModel Resource has been renamed to TideModel• GMAT now returns error codes via the command line interface to indicate if issues

were encountered during system execution.• When using the Write command to write Resource properties to a ReportFile, only

scalar, real quantities are written. Properties that are either not real or are arrays areignored and a warning is issued.

Upcoming Changes in R2019a

R2018a is the last version of GMAT tested on Windows 7.

Known & Fixed Issues

Fixed Issues

Over 112 bugs were closed in this release. See the "Critical Issues Fixed in R2018a"report for a list of critical bugs and resolutions in R2018a. See the "Minor Issues Fixedfor R2018a" report for minor issues addressed in R2018a.

4

• The STK ephemeris propagator now correctly handles segments with fewer than 5rows of data.

• STK ephemeris files that contain event boundaries now correctly count the number ofephemeris rows represented in the NumberOfEphemerisPoints keyword value pair.

• Comments describing the source of ephemeris discontinuities in CCSDS ephemerisfiles are now written inside of meta data blocks.

Known Issues

See the "All Known Issues for R2018a" report for a list of all known issues in R2018a.

There are several known issues in this release that we consider to be significant:

ID Description

GMT-5417 Adaptive step size control behaves inconsistently when used in GMAT'snavigation system. Fixed step integration is currently required for simu-lation and estimation.

GMT-6202 Spikes of up to 1 mm/sec may be observed in some cases in DSN_TCPand Doppler ionospheric corrections. The IRI2007 model has somejumps in the electron density when moving through time. Spikes arecaused when the start and end signal paths are located on different sidesof these jumps.

GMT-6367 For Macs with a Touch Bar (GUI issue only): there appears to be an issuewith WxWidgets, the third party GUI library used by GMAT, and the MacTouch Bar. Crashes occur frequently and the traceback indicates that theissue lies in Apple code, related to the Touch bar specifically, possiblycaused by a NULL string pointer. Our analysis suggests this issue cannotbe addressed by the GMAT team or by WxWidgets; however, we willcontinue to investigate. In the meantime, the GMAT Console version willcontinue to work, and the GUI version (Beta) will work on Macs withouta Touch Bar.