# Presentation: 371593

## ORBITAL MECHANICSLesson Plan 1 - Part 2

- ORBITAL MECHANICSLesson Plan 1 - Part 2

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

## GROUND TRACKSDefinition

- GROUND TRACKSDefinition

- Sub point
- Point on Earth’s surface defined by an imaginary line connecting the satellite and the Earth’s center
- Ground Track
- Trace of sub points over time

## GROUND TRACKSFactors

- GROUND TRACKSFactors

- Period
- Eccentricity
- Inclination
- Argument of Perigee
- Injection Point

## Ground TracksPeriod

**Ground Tracks****Period**

**- For a non-rotating Earth, the ground **
**   ****track of a satellite is a great circle**
**- Since the Earth spins on its axis and the **
**  ****satellite orbits the Earth, the period of both **
**  ****affects the ground track**

## Ground TracksWestward Regression

- Ground TracksWestward Regression

** ****-  ****Earth rotates east under a satellite  => satellite **
**     ****appears to walk west**
** ****-  ****Earth rotates 360 degrees in 24 hours**
**      ****(15 degrees per hour)**

## Ground TracksWestward Regression

- Ground TracksWestward Regression

** ****0**

**30**

**-30**

**-60**

**-90**

**-****120**

**A**

**B**

**C**

**A - time zero**
**B - after one orbit**
**C - after two orbits**

**60**

## Ground TracksEccentricity

- Ground TracksEccentricity

- Highly eccentric orbit means satellite moves faster at perigee and slower at apogee  =>  ground track will be asymmetrical
- Satellite will ‘hang’ over earth at apogee and move faster than the earth at perigee

## Ground TracksEccentricity

- Ground TracksEccentricity

**Ground Track for Molnyia orbit**
**       ****eccentricity = .7252**

## Ground TracksInclination

- Ground TracksInclination

- Inclination of the orbit determines the maximum latitude the ground track will reach
- Special consideration for synchronous orbits

## Ground tracks Inclination

- Ground tracks Inclination

**60**
**30**

**0**

**30**
**60**

**45N**

**45S**

**Inclination = 45 degrees **
**Eccentricity ~ 0**

## Ground TracksArgument of Perigee

- Ground TracksArgument of Perigee

** ****- ****Establishes the longitude of both perigee and apogee**

**direction of**
** ****satellite motion**

**line of nodes**

**perigee**

**apogee**

**w = argument of perigee**

**ascending node**

## Ground tracksArgument of Perigee

- Ground tracksArgument of Perigee

**Argument of Perigee ~ 90 degrees (blue)**
**argument of perigee ~ 270 degrees**

## Ground tracksInjection Point

- Ground tracksInjection Point

- Assuming no maneuvers after launch, launch sites will determine inclination	    - more on this in launch considerations
- Injection point will determine where the ground track will start

## GROUND TRACKSApplications

- GROUND TRACKSApplications

- Mission Planning
- Helps determine which orbit will best maximize mission effectiveness of satellite
- Intelligence Forecasting
- Determine the over flight/proximity of hostile satellites with respect to key areas

## GROUND TRACKSApplications

- GROUND TRACKSApplications

- Geo-synchronous/Geostationary orbit
- Molnyia
- Sun-synchronous
- Polar

**7**

## ORBITAL MECHANICSLesson Plan 1 - Part 2

- ORBITAL MECHANICSLesson Plan 1 - Part 2

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

## PERTURBATIONS

- Definition
- A disturbance in the regular motion of a celestial body
- Types
- Gravitational
- Atmospheric Drag
- Third Body Effects
- Solar Wind/Radiation Effects
- Electro-magnetic

## PERTURBATIONSGravitational

- PERTURBATIONSGravitational

- Earth’s asymmetrical mass causes a non-central gravitational pull
- Oblateness/J2 Effect
- Inconsistent density
- Results
- Nodal Regression
- Apsidal Line Rotation
- Libration

## PERTURBATIONSGravitational:  Nodal Regression

**Nodes regress west for prograde orbits**

## PERTURBATIONSGravitational:  Nodal Regression

- PERTURBATIONSGravitational:  Nodal Regression

**Sun-synchronous**

## PERTURBATIONSGravitational:  Nodal Regression

## PERTURBATIONSGravitational:  Apsidal Line Rotation

- PERTURBATIONSGravitational:  Apsidal Line Rotation

- Line of Apsides is the line connecting apogee and perigee
- Orbit rotates in orbital plane
- Inclinations of 63.4 and 116.6 are stable

## PERTURBATIONSGravitational:  Libration

- PERTURBATIONSGravitational:  Libration

- Ellipticity of the Earth causes gravity wells and hills
- Stable points:  75E and 105W
- 	-- Himalayas and Rocky Mountains
- Unstable points:  165E and 5W
- 	-- Marshall Islands and Portugal
- Drives the requirement for station keeping

## PERTURBATIONSAtmospheric Drag

- PERTURBATIONSAtmospheric Drag

- Friction caused by impact of satellite with particles in the Earth’s atmosphere
- Reduces satellite’s energy
- Changes the size (semi-major axis) and shape (eccentricity)

## PERTURBATIONSAtmospheric Drag

**Perigee remains same, Apogee decreases**

## PERTURBATIONSThird Body Effects

- Gravitational pull of other massive bodies, i.e.  Sun, moon
- Mainly noticeable in deep space orbits

## PERTURBATIONSSolar Wind/Radiation Pressure

- Solar wind causes radiation pressure on the satellite
- Effects similar to atmospheric drag
- Effects are more pronounced on satellites with large surface areas

## PERTURBATIONSElectro-Magnetic

- Interaction between the Earth’s magnetic field and the satellite’s electro-magnetic field results in magnetic drag

## ORBITAL MECHANICSLesson Plan 1 - Part 2

- ORBITAL MECHANICSLesson Plan 1 - Part 2

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

## Launch Windows
Azimuth Vs. Inclination

- Launch Windows
- Azimuth Vs. Inclination

- LAUNCH CONSIDERATIONS

## LAUNCH CONSIDERATIONSLaunch Windows

- LAUNCH CONSIDERATIONSLaunch Windows

- The period of time during which a satellite can be launched directly into a specific orbital plane from a specific launch site
- Window duration driven by safety, fuel requirements, desired injection points, etc.
- Window is centered around optimal launch time

## LAUNCH CONSIDERATIONSLaunch Windows

- LAUNCH CONSIDERATIONSLaunch Windows

- Opportunities to launch DIRECTLY into orbital plane
- 2 per day if latitude of launch site is less than orbit’s inclination
- 1 per day if latitude is equal to inclination
- None if latitude is greater than inclination

## LAUNCH CONSIDERATIONSAzimuth Vs. Inclination

- LAUNCH CONSIDERATIONSAzimuth Vs. Inclination

- Launching due east, or at an azimuth of 90 degrees will result in an orbital inclination equal to launch site latitude
- Any other azimuth results in a GREATER inclination
- Azimuth selected for initial velocity boost and to avoid populated areas
- Proper azimuth minimizes future plane change requirements

## ORBITAL MECHANICSLesson Plan 1 - Part 2

- ORBITAL MECHANICSLesson Plan 1 - Part 2

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

## ORBITAL MANEUVERS

- Reasons
- Types
- Methods

## ORBITAL MANEUVERSReasons

- ORBITAL MANEUVERSReasons

- Maneuver to higher orbit
- Increase satellite Field-of-view (FOV)
- Counteract atmospheric effects
- Maneuver to lower orbit
- Increase imaging resolution
- Satellite rendezvous
- De-orbit

## ORBITAL MANEUVERSTypes

- ORBITAL MANEUVERSTypes

- In-plane
- Change in size/period
- Change in argument of perigee
- Change in true anomaly
- Out-of-Plane
- Change in inclination
- Change  in RAAN

## ORBITAL MANEUVERSIn-Plane Maneuver Methods

- ORBITAL MANEUVERSIn-Plane Maneuver Methods

- Hohmann Transfer
- Can be used to raise or lower altitude
- Most efficient method
- At minimum, requires completion of half rev of transfer orbit

## ORBITAL MANEUVERSHohmann Transfer

## ORBITAL MANEUVERSIn-Plane Maneuver Methods

- ORBITAL MANEUVERSIn-Plane Maneuver Methods

- Fast Transfer
- Does not require set amount of time
- Highly inefficient
- Prone to error
- Driven by time constraints

## ORBITAL MANEUVERSFast Transfer

## ORBITAL MECHANICSLesson Plan 1 - Part 2

- ORBITAL MECHANICSLesson Plan 1 - Part 2

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

## DE-ORBIT/DECAY

- De-Orbit is the controlled re-entry of a satellite to a specific location
- Used for the recovery of payload
- Manned missions
- Decay is uncontrolled re-entry
- Potential impact anywhere along ground track
- Re-entry Assessment (by CMAS)

## ORBITAL MECHANICSLesson Plan 1 - Part 2SUMMARY

- ORBITAL MECHANICSLesson Plan 1 - Part 2SUMMARY

- Ground Tracks
- Perturbations
- Launch Considerations
- Orbital Maneuvers
- De-orbit/Decay

- And now.....

## STK Lesson Plans

- Orbital Mechanics!
- Types of Orbits
- Placing a Satellite in Orbit
- Conducting Satellite Operations
- Exercises

- The world of Space Operations awaits you!!