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UNCLASSIFIEDUNCLASSIFIED
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Lesson 2Lesson 2Basic Orbital MechanicsBasic Orbital Mechanics
A537A537SPACE ORIENTATIONSPACE ORIENTATION
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OverviewOverview
• Basic PrinciplesBasic Principles
• Orbits in GeneralOrbits in General
• Specific OrbitsSpecific Orbits
• Launch ConstraintsLaunch Constraints
• PerturbationsPerturbations
• Satellite ManeuversSatellite Maneuvers
• SummarySummary
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Objects in motion Objects in motion wantwant to travel in straight to travel in straight lines at constant speedlines at constant speed
Objects in motion Objects in motion wantwant to travel in straight to travel in straight lines at constant speedlines at constant speed
Basic PrinciplesBasic Principles
But ...But ...Gravity causes the path to Gravity causes the path to curvecurve
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Amount of curve depends on...Amount of curve depends on...
Initial Initial speed speed andand directiondirection
Basic PrinciplesBasic Principles
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Satellites must have a balance of...Satellites must have a balance of...
Basic PrinciplesBasic Principles
OrbitOrbitGravityGravity++SpeedSpeed == No orbitNo orbit No orbitNo orbit
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Orbits in GeneralOrbits in General
The initial speed and direction of an The initial speed and direction of an orbitingorbiting object creates a object creates a closed curveclosed curve
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Orbits in GeneralOrbits in General
All orbits are All orbits are ellipticalelliptical and in a single, stable and in a single, stable planeplane with the earth with the earth acting as one of the fociacting as one of the foci
FocusFocusFocusFocus
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Orbits in GeneralOrbits in General
• Apogee: Highest Altitude, Lowest SpeedApogee: Highest Altitude, Lowest Speed
• Perigee: Lowest Altitude, Highest SpeedPerigee: Lowest Altitude, Highest Speed
PERIGEEPERIGEE FOCUSFOCUSFOCUSFOCUS APOGEEAPOGEE
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DSP22300 MILES
23 HR. 56 MIN
GPS10900 MILES11 HR. 58 MIN
DMSP510 MILES101 MINUTES
Orbits in GeneralOrbits in General
Orbit size determines satellite Orbit size determines satellite period,period,
Or time for one orbitOr time for one orbit
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Orbits in GeneralOrbits in General
A A ground traceground trace is the projection of a satellite’s is the projection of a satellite’s orbit onto the earth’s surfaceorbit onto the earth’s surface
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Orbits in GeneralOrbits in General
Due to the earth's rotation an orbit will shift to Due to the earth's rotation an orbit will shift to the west about 22 degrees/periodthe west about 22 degrees/period
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• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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UNCLASSIFIEDUNCLASSIFIED
• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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UNCLASSIFIEDUNCLASSIFIED
• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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UNCLASSIFIEDUNCLASSIFIED
• Semi-Major Axis - - - - - -- - -Semi-Major Axis - - - - - -- - - SizeSize• Eccentricity- - - - - - - - - -- - -Eccentricity- - - - - - - - - -- - - ShapeShape• Inclination - - - - - - - - - - - - -Inclination - - - - - - - - - - - - - TiltTilt• Right Ascension of the -- - -Right Ascension of the -- - - DirectionDirection Ascending NodeAscending Node• Argument of Perigee- - - - - -Argument of Perigee- - - - - - RotationRotation• True Anomaly- - - - - - - - - - -True Anomaly- - - - - - - - - - - PositionPosition• Epoch Time- - - - - - - -- - - - -Epoch Time- - - - - - - -- - - - - Time StampTime Stamp
Orbits in GeneralOrbits in General
Orbital Element SetOrbital Element Set
Detailed description of the satellite path and positionDetailed description of the satellite path and position
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Semi-Major AxisSemi-Major AxisSizeSize
PerigeePerigee
aa
cc
ApogeeApogee
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EccentricityEccentricityShapeShape
Eccentricity = c/aEccentricity = c/a
ee11 = 0.75 = 0.75
ee22 = .45 = .45
ee33 = 0 = 0
a
c1
c2
c3
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UNCLASSIFIEDUNCLASSIFIED
InclinationInclinationTiltTilt
Ascending NodeAscending Node
Inclination Inclination AngleAngle
Equatorial OrbitEquatorial Orbit
Inclined OrbitInclined Orbit
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Ascending NodeAscending Node
Line of NodesLine of Nodes
Right Ascension of the Ascending NodeRight Ascension of the Ascending NodeDirectionDirection
0 degrees = First Point of Aries0 degrees = First Point of Aries
00
4545180180
225225315315
Inclined OrbitInclined Orbit
135135
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UNCLASSIFIEDUNCLASSIFIED
Ascending NodeAscending Node
Line of NodesLine of Nodes
Argument of PerigeeArgument of PerigeeRotationRotation
Inclined OrbitInclined Orbit
PerigeePerigee
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Ascending NodeAscending Node
Line of NodesLine of Nodes
True Anomaly/Epoch TimeTrue Anomaly/Epoch TimePosition/Time StampPosition/Time Stamp
Inclined OrbitInclined Orbit
PerigeePerigee
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UNCLASSIFIEDUNCLASSIFIED
Low-Earth OrbitLow-Earth Orbit
• Inclined/Polar Orbits Inclined/Polar Orbits • Up to 520 MilesUp to 520 Miles• Missions: Missions: – Manned (Shuttle)Manned (Shuttle)– ReconnaissanceReconnaissance– CommunicationsCommunications
UNCLASSIFIEDUNCLASSIFIED
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Sun-Synchronous OrbitSun-Synchronous Orbit
• Near-Polar InclinationNear-Polar Inclination• 460-520 Miles Altitude460-520 Miles Altitude• Missions: Missions: – Earth Sensing (LANDSAT) Earth Sensing (LANDSAT)
– Weather (DMSP/NOAA)Weather (DMSP/NOAA)
GROUND TRACEGROUND TRACE
5 4 3 2 15 4 3 2 1
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Non-Spherical EarthNon-Spherical Earth (Nodal Regression)(Nodal Regression)
Sun-Synchronous OrbitSun-Synchronous Orbit
360 degree change in orbit orientation
in 365+ days
Summer
Fall
Winter
Spring
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UNCLASSIFIEDUNCLASSIFIED
Semi-Synchronous OrbitSemi-Synchronous Orbit
• High InclinationHigh Inclination• 10,900 Miles Altitude10,900 Miles Altitude• Missions: Navigation Missions: Navigation
(GPS/GLONASS)(GPS/GLONASS)
GROUND TRACEGROUND TRACE
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GeosynchronousGeosynchronous
• Period = 24 hrsPeriod = 24 hrs• Any inclinationAny inclination• Does not need to be a Does not need to be a
circular orbitcircular orbit
GROUND TRACEGROUND TRACE
• Period = 24 hoursPeriod = 24 hours• Inclination near Inclination near
zerozero• Circular Circular
(eccentricity near (eccentricity near zero)zero)• Altitude = 22,300 Altitude = 22,300
milesmiles
GeostationaryGeostationary
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Highly Elliptical OrbitsHighly Elliptical Orbits
• 63.4 /116.6 Degree Inclination63.4 /116.6 Degree Inclination• 200-23,800 Miles Altitude200-23,800 Miles Altitude• Missions: Comm Relay (Molniya)Missions: Comm Relay (Molniya)
GROUND TRACEGROUND TRACE
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The direction of launch determines the orbit inclinationThe direction of launch determines the orbit inclination
Launch AzimuthLaunch Azimuth
OO
3030
4545
3030
4545
You You cannotcannot launch directly into any orbit launch directly into any orbit inclination inclination lessless than your launch site’s latitude than your launch site’s latitude
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Launch AzimuthLaunch AzimuthThe desired orbit inclinationThe desired orbit inclination
determines the azimuth of launchdetermines the azimuth of launch
9090
3535
120120
575728.528.5
3939
Blue = orbit inclinationBlue = orbit inclinationRed = launch azimuthRed = launch azimuth
201201140140
104104
Vandenberg AFBVandenberg AFB
Patrick AFBPatrick AFB
7070
3434
160160180180
8787
Safety constrainspossible
launch azimuths7171
5656
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PerturbationPerturbation
Any disturbance in the regular motion of a Any disturbance in the regular motion of a satellite resulting from a force other than satellite resulting from a force other than those causing regular motionthose causing regular motion
– Non-spherical earthNon-spherical earth– Atmospheric dragAtmospheric drag– Sun/moon gravitySun/moon gravity– Space EnvironmentSpace Environment
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Non-Spherical EarthNon-Spherical Earth (Nodal Regression)(Nodal Regression)
Retrograde Sun-Synchronous (East = 1 degree/day) Retrograde Sun-Synchronous (East = 1 degree/day) Pro-Grade (West up to 9 degrees/day)Pro-Grade (West up to 9 degrees/day)
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Non-Spherical EarthNon-Spherical Earth (Argument of Perigee Rotation)(Argument of Perigee Rotation)
• Orbit rotates in orbital planeOrbit rotates in orbital plane• Molniya orbit inclinations of 63.4 and Molniya orbit inclinations of 63.4 and
116.6 degrees are stable 116.6 degrees are stable
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Atmospheric DragAtmospheric Drag
Perigee remains same, apogee Perigee remains same, apogee decreasesdecreases
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Third Body EffectsThird Body EffectsSun/MoonSun/Moon
• Noticeable in deep space Noticeable in deep space
orbits (requires station-keeping thrusters)orbits (requires station-keeping thrusters)
• Suns gravity causes geosynch satellites Suns gravity causes geosynch satellites inclination to rise inclination to rise
(1 degree/ year)(1 degree/ year)
Moon
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Space EnvironmentSpace Environment• Solar wind cause radiation pressure on the satellite, Solar wind cause radiation pressure on the satellite,
effects similar to atmospheric drageffects similar to atmospheric drag
• Effects are more pronounced on satellites with large Effects are more pronounced on satellites with large surface areassurface areas
• Interaction between the Earth’s magnetic field and Interaction between the Earth’s magnetic field and the satellite’s electromagnetic field results in the satellite’s electromagnetic field results in magnetic drag/static dischargemagnetic drag/static discharge
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Maneuver BasicsManeuver Basics
On-board rocket motors are fired to modify On-board rocket motors are fired to modify the satellite’s orbit to:the satellite’s orbit to:– Attain initial on-orbit stationAttain initial on-orbit station– Maintain assigned positionMaintain assigned position– Modify orbit to meet new mission Modify orbit to meet new mission
requirements requirements
Thrusters
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
Out-of-Plane ManeuverOut-of-Plane Maneuver
These maneuvers change the orientation of the orbitThese maneuvers change the orientation of the orbit
Inclined OrbitInclined Orbit
New Equatorial OrbitNew Equatorial Orbit
Ascending NodeAscending NodeManeuver PointManeuver Point
UNCLASSIFIEDUNCLASSIFIED
UNCLASSIFIEDUNCLASSIFIED
SummarySummary
• Satellites remain in earth orbit by balancing force Satellites remain in earth orbit by balancing force
of gravity and lateral velocityof gravity and lateral velocity
• Five basic orbits used in spaceFive basic orbits used in space operations operations
LEO LEO Sun-Sync Sun-Sync Semi-Sync Semi-Sync
Highly Elliptical Highly Elliptical GEOGEO
• Perturbations affects on satellites Perturbations affects on satellites Non-spherical earth Non-spherical earth Atmospheric drag Atmospheric drag
Sun/moon gravity Sun/moon gravity Space EnvironmentSpace Environment
• Types of satellite maneuversTypes of satellite maneuvers
a