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Spacecraft Simulation and Visualisationwith Orbiter 2006

Martin Schweiger

Centre for Medical Image ComputingDepartment of Computer ScienceUniversity College London, UK

3rd International Workshop on Astrodynamics Tools and Techniques

ESTEC, Noordwijk, 4 October 2006

orbitersim.com

martins@medphys.ucl.ac.uk

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Contents

IntroductionOrbiter overviewOrbiter 2006 - new features

Simulation and physics engineDynamic state integrationScenario editor

Visualisation and graphics engine

Launcher and payload examplesPlanetary surfaces

Interactive flightdeck simulation

External trajectory data interfaceFlight recording and playback

Playback of external data

Orbiter demonstration

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Introduction: Orbiter

Real-time space flight simulation and visualisation on the PCUnder development for 6 years, latest version is 2006-P1 Edition.Newtonian physics engine, numerical state integration including gravitational

perturbation effectsCovers: atmospheric, suborbital, orbital, interplanetary flightDemonstrate: launch, rendezvous/docking, re-entry, interplanetary transfers,

gravity-assist, and more.

Visualisation/demonstration tool

Interface to external trajectory data allows use of Orbiter as a visualisationtool, bypassing the internal physics engine

Educational toolHands-on orbital mechanics demonstrator

Development model:Modular structure: core application provides physics and graphics engineExtensive application programming interface (API) available for 3rd partyaddition of plugin modules (spacecraft, launch sites, celestial bodies,instrumentation, autopilots, remote control, networking, etc.)An active development community has created an extensive collection ofhigh-quality models of historic, hypothetical and fictional spacecraft.

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Introduction - New features in Orbiter 2006

Physics engineAdaptive order of integration of linear and angular states (Runge-Kutta andsymplectic integrators to order 8)

Perturbation model now includes gravity-gradient torque simulationUser interface

Scenario editor for easy simulation setupInstrumentation: "glass cockpit" and flight data display in external windows

Visualisation and graphics engineSupport for higher-resolution planetary texturesForce vector visualisation

External trajectory data interfaceSupport for simulation replay from Orbiter-recorded or external trajectory data

Includes animations and annotations

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Topic: Physics engine

Dynamic state integration improved in Orbiter 2006

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Dynamic state propagation: IntegratorsLinear state propagation

Adaptive steplength-dependentintegration order provides accuratedynamic state propagation over a

wide range of simulation speeds.Available user-definable

integrators: Runge-Kuttaandsymplecticup to order 8

Sub-sampling and propagation of

perturbations (Encke's method)provide stability at very large timesteps.

Angular state propagationIntegration of Euler's equation of

angular motion using RK integratorup to order 8.

Adaptive and user-definableintegration rules and sub-sampling

depending on angular velocity

Orbiter linear and angular propagationparameter selection.

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Dynamic state propagation: Integrators

57.813RK8

49.111RK7

38.08RK6

30.56RK5

16.24RK4

14.83RK3

9.72RK2

timing [s]stagesmethod

51.516SY8

32.38SY6

20.24SY4

10.12SY2

timing [s]stagesmethod

Computational complexity of the integrators available in Orbiter.

Runge-Kutta Symplectic

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Dynamic state propagation: stabilityLong-term orbit stability with RKintegrators

Mean drift (top) and standarddeviation (bottom) of the semi-major

axis for a low Earth orbit (meanaltitude 217km) over a period of 10

days, as a function of sampling steplength.

Shown are different orders of the RKfamily of integrators available inOrbiter.

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Dynamic state propagation: stabilityComparison between RK andsymplectic integrators

Standard deviation in semi-major axis

(top) and perigee altitude (bottom) ofa low Earth orbit over a 10-day period

as a function of sampling step length.Shown is the family of symplecticintegrators available in Orbiter.For comparison, RK results are

shown as dashed lines.

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User-defined perturbationsExamples: radiation pressure (orbit

perturbation, solar sail simulation, etc.)

Gravity-gradient torquetorque on objects with anisotropic inertia

tensors due to inhomogeneous

gravitational fieldallows simulation of resonant oscillationsor tidal locking

Nonspherical gravity sourcesSpherical harmonics expansion ofdeformation of planetary gravitationalfields due to oblateness

allows simulation of propagation of nodes(e.g. sun-synchronous orbits)

Dynamic state propagation: PerturbationsSecondary gravity sources

Dynamic inclusion of gravity sources frommultiple solar system objects (allows e.g.simulation of Lagrange point orbits)

[ ]rrLr

)(3

3 =

GM

G

Gravity-gradient induced torqueGat r, given inertia tensor L

=

=

N

n

n

n

n Pr

RJ

r

GMrU

2

)(sin1),(

Perturbations of gravitational potential U,

expressed in spherical harmonics withcoefficients J

n

0:)( UGM

nGM

U

n

n

N

n n

n>

=

rrrrr

Superposition of gravitational potentialcontributions for given threshold U0

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Topic: Simulation setup

Scenario editor for interactive spacecraft configuration

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Simulation setup: Scenario editorInteractive configuration of spacecraft parameters

Orbital elements and state vectorsOrientation and angular velocitySurface location

Composite structures/dockingPropellant status, vessel-specific parameters

Simulation date propagation

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Simulation setup: Scenario editorScenario inventory creationdate setup

orbital elements state vectors attitudeground location

...

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Topic: Visualisation

Spacecraft and launch site models: examples

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Visualisation examples: Custom launchersLaunchers and payload can beadded to the simulation usingcustom meshes.

Engine thrust, ascent behaviour,staging etc. can be defined viaplugin modules.

European launcher examples:

Ariane 1

Ariane 1 model by Jos Manuel Garca Estvez

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Visualisation examples: Custom launchersLaunchers and payload can beadded to the simulation usingcustom meshes.

Engine thrust, ascent behaviour,staging etc. can be defined viaplugin modules.

European launcher examples:

Ariane 1

Ariane 4

Ariane 4 model by Pierre Refoubelet, Frdric Servian,Christophe Etienne, Stphane Colombain

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Visualisation examples: Custom launchersLaunchers and payload can beadded to the simulation usingcustom meshes.

Engine thrust, ascent behaviour,

staging etc. can be defined viaplugin modules.

European launcher examples:

Ariane 1

Ariane 4Ariane 5

Ariane 5 model by Thomas Ruth, with modifications byAndy McSorley

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Visualisation examples: Custom launchersLaunchers and payload can beadded to the simulation usingcustom meshes.

Engine thrust, ascent behaviour,

staging etc. can be defined viaplugin modules.

European launcher examples:

Ariane 1

Ariane 4Ariane 5

VEGA

Vega model by Jos Manuel Garca Estvez

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Visualisation examples: Ground structuresCustom groundstructures forlaunch sites can

be added to the

simulation.

Example: Kourou

ELA1

ELA2ELA3

Kourou site by Pierre Refoubelet, Frdric Servian,Christophe Etienne, Stphane Colombain

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Visualisation examples: Space ShuttleMannedspacecraft:Modelling of flightdeck interior

("virtual cockpit")

Interactive

manipulation offlight controls/instrumentation

Example:

SpaceShuttleAtlantis

Atlantis model by Michael Grosberg, with extensions byDon Gallagher

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Visualisation examples: Planetary surfacesCelestial body surfaces:adaptive resolution as a func-tion of apparent size up to 32kx 16k (equiv. 1.2km for Earth)

support for local high-resolu-tion textures (e.g. launch sites)

support for specular reflectionsfrom water surfaces, cloud

layers, atmospheric haze and

city lights.support for celestial andsurface labels and markers

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Topic: Flight recording and playback

Visualisation of externally provided trajectory data

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Position/velocity stream.pos

Position/velocity stream.pos

Playback from external trajectory dataData format

Sampled position and velocity data (ecliptic or equatorial reference)Sampled attitude data (ecliptic or local horizon reference)Articulation data (engine and animation events, staging, booster separation,

onscreen annotations, playback speed, etc.)

Replay modeMixture of playback-controlled and active spacecraft is possibleUser- or datastream-controlled playback speedUser-controlled camera

Attitude stream.att

Event/animation/

annotation stream

.atc

Attitude stream.att

Event/animation/annotation stream

.atc

Position/velocity stream

.pos

Attitude stream.att

Event/animation/

annotation stream.atc

Foreach

object

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Playback from external trajectory dataData interpolation

C2-continuous interpolation: piecewise linear accelerationGiven state samples r0=r(t0), r1=r(t1)and v0=v(t0), v1=v(t1)at consecutivesampling times t0, t1, the acceleration satisfies

Equations of motion: Integration of state vectors leads to

resulting in parameters

0100 ,,)( tttttttbata =+=

32

000

0

2

00

0

6

1

2

1)()(

2

1)()(

tbtatvrtdtvtr

tbtavtdtatv

t

t

+++==

++==

01

3

1010

2

10010

)]()(2[6

)]2()(3[2

ttT

T

vvTrrb

T

vvTrra

=

++=

+=

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ASTOS trajectory

data

Playback from external trajectory dataExample: Interface to ASTOS trajectorydata

The Orbiter playback interface was designed toaccept data from the ASTOS aerospace

trajectory optimisation software.The ASTOS position/velocity and attitude data

samples can be used as playback input streamsfor Orbiter.

Additional spacecraft-specific events (stageing,animations) and onscreen annotations can beadded via the articulation stream to createcomplete launch demonstrations.This allows to use Orbiter as a visualisation tool

or demonstrator for ASTOS trajectory data.Example: VEGA launch vehicle: launch, orbitalinsertion and payload deployment.

ASTOS trajectory

data

ASTOS trajectorydata files

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SummaryOrbiter is a modular customisable real-time simulation and visualisation tool forspacecraft operation.

Programming interface supports data exchange between Orbiter core and 3rd partyaddon modules.

Versatile: simulation of historic missions or hypothetical concepts; "virtualprototyping"

Built-in physics engine: dynamic propagation of linear and angular state vectorsover a wide range of sampling intervals, including various perturbation sources.

User interface: fast setup of spacecraft parameters via scenario editor; real-timesimulation of flight instrumentation, immersive simulation of manned missions:"virtual cockpits".

Support for mission playback from recorded or externally provided trajectory data,for demonstration and visualisation.

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Resources and acknowledgementsOrbiter main site and addonrepositories:

orbit.medphys.ucl.ac.uk (Orbitermain site and core download)www.orbithangar.com (Orbiter addon

repository)www.avsim.com (includes Orbiteraddon repository)users.swing.be/vinka (spacecraft

wrapper dll for rapid prototyping)

Educational resources:"Go Play In Space" e-book by BruceIrving, available at:www.orbiter.migman.com/orbiter.htmResources for educators, maintainedby Jean-Marc Perreault:www.orbiterschool.com

I would like to thank the following authorsfor contributing addon models to Orbiter

presented here:

Pierre Refoubelet, Frdric Servian,

Christophe Etienne, Stphane Colombain(Ariane 1+4 models and Kourou site)

Thomas Ruth and Andy McSorley (Ariane

5 model)

Jos Manuel Garca Estvez, supportedby Hispaseti.org and Astoseti.org (Vega

model)Michael Grosberg and Don Gallagher(Atlantis model)

Seth Hollingsead, Rolf Keibel and others

(planetary textures)

Some images were taken from Bruce

Irving's web site.

Thanks also to all other authors and

contributors, in particular the beta test

team for their input.