unclassifiedunclassified lesson 2 basic orbital mechanics a537 space orientation a537 space...

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Lesson 2Lesson 2Basic Orbital MechanicsBasic Orbital Mechanics

A537A537SPACE ORIENTATIONSPACE ORIENTATION



OverviewOverview

• Basic PrinciplesBasic Principles

• Orbits in GeneralOrbits in General

• Specific OrbitsSpecific Orbits

• Launch ConstraintsLaunch Constraints

• PerturbationsPerturbations

• Satellite ManeuversSatellite Maneuvers

• SummarySummary



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



Amount of curve depends on...Amount of curve depends on...

Initial Initial speed speed andand directiondirection




Satellites must have a balance of...Satellites must have a balance of...


OrbitOrbitGravityGravity++SpeedSpeed == No orbitNo orbit No orbitNo orbit



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




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




• Apogee: Highest Altitude, Lowest SpeedApogee: Highest Altitude, Lowest Speed

• Perigee: Lowest Altitude, Highest SpeedPerigee: Lowest Altitude, Highest Speed

PERIGEEPERIGEE FOCUSFOCUSFOCUSFOCUS APOGEEAPOGEE



DSP22300 MILES

23 HR. 56 MIN

GPS10900 MILES11 HR. 58 MIN

DMSP510 MILES101 MINUTES


Orbit size determines satellite Orbit size determines satellite period,period,

Or time for one orbitOr time for one orbit




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




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



• 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


Orbital Element SetOrbital Element Set

Detailed description of the satellite path and positionDetailed description of the satellite path and position



Semi-Major AxisSemi-Major AxisSizeSize

PerigeePerigee

aa

cc

ApogeeApogee



EccentricityEccentricityShapeShape

Eccentricity = c/aEccentricity = c/a

ee11 = 0.75 = 0.75

ee22 = .45 = .45

ee33 = 0 = 0

a

c1

c2

c3



InclinationInclinationTiltTilt

Ascending NodeAscending Node

Inclination Inclination AngleAngle

Equatorial OrbitEquatorial Orbit

Inclined OrbitInclined Orbit




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


135135





Argument of PerigeeArgument of PerigeeRotationRotation


PerigeePerigee





True Anomaly/Epoch TimeTrue Anomaly/Epoch TimePosition/Time StampPosition/Time Stamp


PerigeePerigee



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



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



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



Semi-Synchronous OrbitSemi-Synchronous Orbit

• High InclinationHigh Inclination• 10,900 Miles Altitude10,900 Miles Altitude• Missions: Navigation Missions: Navigation

(GPS/GLONASS)(GPS/GLONASS)




GeosynchronousGeosynchronous

• Period = 24 hrsPeriod = 24 hrs• Any inclinationAny inclination• Does not need to be a Does not need to be a

circular orbitcircular orbit


• 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



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)




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



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



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



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)



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



Atmospheric DragAtmospheric Drag

Perigee remains same, apogee Perigee remains same, apogee decreasesdecreases



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



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



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



Out-of-Plane ManeuverOut-of-Plane Maneuver

These maneuvers change the orientation of the orbitThese maneuvers change the orientation of the orbit


New Equatorial OrbitNew Equatorial Orbit

Ascending NodeAscending NodeManeuver PointManeuver Point



QUIZ



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

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Documents

orbit slide

position slide

focus slide

degreesperiod slide

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time stamp orbits

minutes orbits

closed curve slide