UNCLASSIFIEDUNCLASSIFIED Lesson 2 Basic Orbital Mechanics A537 SPACE ORIENTATION A537 SPACE ORIENTATION

UNCLASSIFIEDUNCLASSIFIED Overview Basic PrinciplesBasic Principles Orbits in GeneralOrbits in General Specific OrbitsSpecific Orbits Launch ConstraintsLaunch Constraints PerturbationsPerturbations Satellite ManeuversSatellite Maneuvers SummarySummary

UNCLASSIFIEDUNCLASSIFIED Objects in motion want to travel in straight lines at constant speed Basic Principles But... Gravity causes the path to curve

UNCLASSIFIEDUNCLASSIFIED Amount of curve depends on... Initial speed and direction Basic Principles

UNCLASSIFIEDUNCLASSIFIED Satellites must have a balance of... Basic Principles OrbitGravity+Speed= No orbit

UNCLASSIFIEDUNCLASSIFIED Orbits in General The initial speed and direction of an orbiting object creates a closed curve

UNCLASSIFIEDUNCLASSIFIED Orbits in General All orbits are elliptical and in a single, stable plane with the earth acting as one of the foci All orbits are elliptical and in a single, stable plane with the earth acting as one of the foci Focus Focus

UNCLASSIFIEDUNCLASSIFIED Orbits in General Apogee: Highest Altitude, Lowest SpeedApogee: Highest Altitude, Lowest Speed Perigee: Lowest Altitude, Highest SpeedPerigee: Lowest Altitude, Highest Speed PERIGEE FOCUS FOCUS APOGEE

UNCLASSIFIEDUNCLASSIFIED DSP MILES 23 HR. 56 MIN GPS MILES 11 HR. 58 MIN DMSP 510 MILES 101 MINUTES Orbits in General Orbit size determines satellite period, Or time for one orbit

UNCLASSIFIEDUNCLASSIFIED Orbits in General A ground trace is the projection of a satellite’s orbit onto the earth’s surface

UNCLASSIFIEDUNCLASSIFIED Orbits in General Due to the earth's rotation an orbit will shift to the west about 22 degrees/period

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Semi-Major Axis Size Eccentricity Shape Eccentricity Shape Inclination Tilt Inclination Tilt Right Ascension of the Direction Right Ascension of the Direction Ascending Node Ascending Node Argument of Perigee Rotation Argument of Perigee Rotation True Anomaly Position True Anomaly Position Epoch Time Time Stamp Epoch Time Time Stamp Orbits in General Orbital Element Set Orbital Element Set Detailed description of the satellite path and position

UNCLASSIFIEDUNCLASSIFIED Semi-Major Axis Size Perigee a c Apogee

UNCLASSIFIEDUNCLASSIFIED Eccentricity Shape Eccentricity = c/a e 1 = 0.75 e 2 =.45 e 3 = 0 a c1 c2 c3

UNCLASSIFIEDUNCLASSIFIED Inclination Tilt Ascending Node InclinationAngle Equatorial Orbit Inclined Orbit

UNCLASSIFIEDUNCLASSIFIED Ascending Node Line of Nodes Right Ascension of the Ascending Node Direction 0 degrees = First Point of Aries Inclined Orbit 135

UNCLASSIFIEDUNCLASSIFIED Ascending Node Line of Nodes Argument of Perigee Rotation Inclined Orbit Perigee

UNCLASSIFIEDUNCLASSIFIED Ascending Node Line of Nodes True Anomaly/Epoch Time Position/Time Stamp Inclined Orbit Perigee

UNCLASSIFIEDUNCLASSIFIED Low-Earth Orbit Inclined/Polar OrbitsInclined/Polar Orbits Up to 520 MilesUp to 520 Miles Missions:Missions: –Manned (Shuttle) –Reconnaissance –Communications

UNCLASSIFIEDUNCLASSIFIED Sun-Synchronous Orbit Near-Polar InclinationNear-Polar Inclination Miles Altitude Miles Altitude Missions:Missions: –Earth Sensing (LANDSAT) –Weather (DMSP/NOAA) GROUND TRACE

UNCLASSIFIEDUNCLASSIFIED Non-Spherical Earth (Nodal Regression) Sun-Synchronous Orbit 360 degree change in orbit orientation in 365+ days Summer Fall Winter Spring

UNCLASSIFIEDUNCLASSIFIED Semi-Synchronous Orbit High InclinationHigh Inclination 10,900 Miles Altitude10,900 Miles Altitude Missions: Navigation (GPS/GLONASS)Missions: Navigation (GPS/GLONASS) GROUND TRACE

UNCLASSIFIEDUNCLASSIFIED Geosynchronous Period = 24 hrsPeriod = 24 hrs Any inclinationAny inclination Does not need to be a circular orbitDoes not need to be a circular orbit GROUND TRACE Period = 24 hoursPeriod = 24 hours Inclination near zeroInclination near zero Circular (eccentricity near zero)Circular (eccentricity near zero) Altitude = 22,300 milesAltitude = 22,300 miles Geostationary

UNCLASSIFIEDUNCLASSIFIED Highly Elliptical Orbits 63.4 /116.6 Degree Inclination63.4 /116.6 Degree Inclination ,800 Miles Altitude200-23,800 Miles Altitude Missions: Comm Relay (Molniya)Missions: Comm Relay (Molniya) GROUND TRACE

UNCLASSIFIEDUNCLASSIFIED The direction of launch determines the orbit inclination Launch Azimuth O You cannot launch directly into any orbit inclination less than your launch site’s latitude

UNCLASSIFIEDUNCLASSIFIED Launch Azimuth The desired orbit inclination determines the azimuth of launch Blue = orbit inclination Red = launch azimuth Vandenberg AFB Patrick AFB Safety constrains possible launch azimuths 71 56

UNCLASSIFIEDUNCLASSIFIED Perturbation Any disturbance in the regular motion of a satellite resulting from a force other than those causing regular motion –Non-spherical earth –Atmospheric drag –Sun/moon gravity –Space Environment

UNCLASSIFIEDUNCLASSIFIED Non-Spherical Earth (Nodal Regression) Retrograde Sun-Synchronous (East = 1 degree/day) Pro-Grade (West up to 9 degrees/day)

UNCLASSIFIEDUNCLASSIFIED Non-Spherical Earth (Argument of Perigee Rotation) Orbit rotates in orbital planeOrbit rotates in orbital plane Molniya orbit inclinations of 63.4 and degrees are stableMolniya orbit inclinations of 63.4 and degrees are stable

UNCLASSIFIEDUNCLASSIFIED Atmospheric Drag Perigee remains same, apogee decreases

UNCLASSIFIEDUNCLASSIFIED Third Body Effects Sun/Moon Noticeable in deep spaceNoticeable in deep space orbits (requires station-keeping thrusters) Suns gravity causes geosynch satellites inclination to riseSuns gravity causes geosynch satellites inclination to rise (1 degree/ year) (1 degree/ year) Moon

UNCLASSIFIEDUNCLASSIFIED Space Environment Solar wind cause radiation pressure on the satellite, effects similar to atmospheric dragSolar wind cause radiation pressure on the satellite, effects similar to atmospheric drag Effects are more pronounced on satellites with large surface areasEffects are more pronounced on satellites with large surface areas Interaction between the Earth’s magnetic field and the satellite’s electromagnetic field results in magnetic drag/static dischargeInteraction between the Earth’s magnetic field and the satellite’s electromagnetic field results in magnetic drag/static discharge

UNCLASSIFIEDUNCLASSIFIED Maneuver Basics On-board rocket motors are fired to modify the satellite’s orbit to: –Attain initial on-orbit station –Maintain assigned position –Modify orbit to meet new mission requirements Thrusters

UNCLASSIFIEDUNCLASSIFIED Out-of-Plane Maneuver These maneuvers change the orientation of the orbit Inclined Orbit New Equatorial Orbit Ascending Node Maneuver Point

UNCLASSIFIEDUNCLASSIFIED QUIZ

UNCLASSIFIEDUNCLASSIFIED Summary Summary Satellites remain in earth orbit by balancing force of gravity and lateral velocitySatellites remain in earth orbit by balancing force of gravity and lateral velocity Five basic orbits used in space operationsFive basic orbits used in space operations LEO Sun-Sync Semi-Sync LEO Sun-Sync Semi-Sync Highly Elliptical GEO Highly Elliptical GEO Perturbations affects on satellitesPerturbations affects on satellites Non-spherical earth Atmospheric drag Sun/moon gravity Space Environment Types of satellite maneuversTypes of satellite maneuvers a