Six degree-of-freedom (6-DOF) Flight Simulation Check-cases

Title: Standard Check-Cases for Six-Degree-of-Freedom Flight Vehicle Simulations
Speakers: Dr. Robert Shelton
Mr. Michael Madden
Date/Time: April 21, 2015 (2:00 pm EDT)
Abstract:

The rise of innovative unmanned aeronautical systems and the emergence of commercial space activities have resulted in a number of relatively new aerospace organizations that are designing innovative systems and solutions. These organizations use a variety of commercial off-the-shelf and in-house-developed simulation and analysis tools including 6-degree-of-freedom (6-DOF) flight simulation tools. The increased affordability of computing capability has made high-fidelity flight simulation practical for all participants. Verification of the tools' equations-of-motion and environment models (e.g., atmosphere, gravitation, and geodesy) is desirable to assure accuracy of results. However, aside from simple textbook examples, minimal verification data exists in open literature for 6-DOF flight simulation problems.

The NESC undertook an assessment that compared multiple solution trajectories to a set of verification check-cases that covered atmospheric and exo-atmospheric (i.e., orbital) flight. Each scenario consisted of redefined flight vehicles, initial conditions, and maneuvers. These scenarios were implemented and executed in a variety of analytical and real-time simulation tools. This tool-set included simulation tools in a variety of programming languages based on modified flat-Earth, round-Earth, and rotating oblate spheroidal Earth geodesy and gravitation models, and independently derived equations-of-motion and propagation techniques. The resulting simulated parameter trajectories were compared by over-plotting and difference-plotting to yield a family of solutions. In total, seven simulation tools were exercised.

The check cases and the generated family of solutions are now available for download from the NESC Academy web-site for use in cross comparison with other simulation tools. This webcast will give an overview of the check-cases, the comparison approach, the types of differences remaining in the comparison set, and an introduction to the contents of the “flightsim” website where the check case descriptions and generated results are stored.
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This directory contains links to retrieve the models and resulting data for both atmospheric and orbital flight simulation benchmarks as described in the NASA Engineering and Safety Center Report No. NESC-RP-12-00770, "Check-Cases for Verification of 6-DOF Flight Vehicle Simulations" as well as AIAA 2015-1810, "Further Development of Verification Check-cases for Six-Degree-of-Freedom Flight Vehicle Simulations."

The purpose of this study was to compare multiple solution trajectories to a set of verification check-cases that covered atmospheric and exo-atmospheric (i.e., orbital) flight. Each scenario consisted of pre-defined flight vehicles, initial conditions, and maneuvers. These scenarios were implemented and executed in a variety of analytical and real-time simulation tools. This tool-set included simulation tools in a variety of programming languages based on modified flat-Earth, round-Earth, and rotating oblate spheroidal Earth geodesy and gravitation models, and independently derived equations-of-motion and propagation techniques. The resulting simulated parameter trajectories were compared by over-plotting and difference-plotting to yield a family of solutions.

This web page contains the reports as well as the models and datasets generated by them that were used in the reports. They are made available here in a digital form to facilitate comparison with other simulation tools.

For more information, please contact Dr. Robert Shelton <robert.o.shelton@NASA.gov> at NASA Johnson Space Center, (281) 793-5270.

Reports

A two-volume NESC report has been prepared that describes the process of and the results of comparing several NASA and one open-source flight simulation tools; a link is given below. Two AIAA conference papers were also generated during the course of this assessment and are given below as well.

An interim AIAA conference paper (AIAA 2013-5071) describes the project with some initial results, but some of the checkcase initial conditions and scenarios have changed.

An follow-on AIAA conference paper (AIAA 2015-1810) provides a nice summary of the comparison effort with some example resuults.

The final paper, NASA/TM-2015-218675: "Check-Cases for Verification of 6-Degree-of-Freedom Flight Vehicle Simulations," appears in two volumes.

Volume I
is an executive summary spanning 31 pages and provides an overview of the process and results.
Volume II
runs 614 pages and contains the detailed results of the study, including information about the simulated models, initial conditions, maneuvers, cross- and difference-plots, and discussion of detected differences.

Models

There are seven models provided for use in these various checkcases. These models are encoded using DAVE-ML, an AIAA-developed XML grammar for exchanging dynamic models. (See the DAVE-ML website for more information about this format.) Signal / variable names are encoded according to ANSI/AIAA-S-119-2011, "Flight Dynamics Model Exchange Standard," available from the American Institute of Aeronautics and Astronautics.

Atmospheric check-case models (all atmospheric models in a single .zip file), including

Orbital check-case models (all atmospheric models in a single .zip file), including

All models in a single .zip file

Initial Conditions

All initial conditions as a Microsoft® Excel .xlsx spreadsheet

Trajectory Data