Propagation and Collision of Orbital Debris in GEO ... · Propagation Methods • Cowell’s Method...
Transcript of Propagation and Collision of Orbital Debris in GEO ... · Propagation Methods • Cowell’s Method...
Propagation and Collision of Orbital Debris in GEO
Disposal Orbits
Benjamin Polzine
Graduate Seminar
Presentation Outline
Need – Approach - BenefitGEO Debris
Continuation of Previous WorkPropagation Methods
Modified Equinoctial ElementsPerturbations
CollisionsBreakup Model
Completed WorkWhat’s Left
Need – Approach - Benefit• Need
– GEO is a high-activity, valuable regime
– Debris remains here for a much longer period of time
– Debris behavior in the nearby graveyard orbit is not yet fully understood
• Approach– Create a high-accuracy propagator that takes into account
major perturbations in this regime
– Verify propagator for accuracy by propagating real TLE’s and comparing outcomes to observed outcomes
– Simulate collisions within and outside the regime
• Benefit– An understanding of debris behavior and danger to GEO
GEO Debris• Decommissioned GEO Satellites are generally
pushed into a Graveyard Orbit– >200 km above GEO
• Earth gravity perturbations– Results in “geopotential wells” that capture satellites
– Operational satellites use East-West station keeping to combat this effect
– Wells have unknown effect on debris population• Do they act as sinks?
Continuation of Previous Work• Continuing the work of Christina Diaz
– Study of collisional evolution of debris in Geopotential Wells and GEO Disposal Orbits
• Modeled in Fortran, Visualized in MATLAB
• Propagation with Cowell’s Method
• Perturbations include: – 16x16 Geopotential, Lunar/Solar Gravity, SRP
• Simulated East/West geopotential wells– Could not catch East-West trapped objects
• Had a suspect upward longitudinal drift
Propagation Methods
• Cowell’s Method– Summary: Direct integration of position and velocity
– Pros: Easy to understand, quick to code
– Cons: Not as accurate as VoP, runs slowly
• Variation of Parameters (VoP)– Summary: Break perturbative force down into changes
of each orbital element over time
– Pros: Accurate
– Cons: Hard to find errors, non-intuitive, breaks down at zero inclination if using COE element set
Modified Equinoctial Elements• A VoP element set
• Seeks to address singularity issues with more common VoP element sets
• Pros– Non-singular for any orbit
– High accuracy (as a VoP method)
• Cons– Non-intuitive elements
– Posigrade/Retrograde must be known
Perturbations• Earth’s Oblateness
– The oblateness of the Earth results in a non-constant gravitational force
– Earth analyzed as a checkerboard of different gravitational effects
– Strongest effects for GEO at J2, J22
Φ , 1 , sin ∗ , cos , sin
Φ ,
Perturbations• Earth’s Oblateness
Verified Propagation My J2+J22 Propagation
Perturbations• 3rd-Body Gravitation
– Pull of non-Earth bodies effect satellite’s orbit
– Strongest sources on an Earth satellite are Sun and Moon
– Dependent on vector between S/C and body
Lunar PerturbationSolar Perturbation
Perturbations• 3rd-Body Gravitation (Sun)
Verified Propagation
My Sun Gravity Propagation
Perturbations• 3rd-Body Gravitation (Moon)
Verified Propagation
My Lunar Gravity Propagation
Perturbations• Solar Radiation Pressure
– Photons expelled from the sun exert pressure on S/C
– Dependent on shape of S/C, orientation, mass distribution, and reflectivity
– Assumptions made• Constant Solar Flux @ 1367 W/m2
• 0 < CR < 2
• Spherical spacecraft model
• A/m ratio
P C Am r
Perturbations• Solar Radiation Pressure
Verified Propagation My SRP Propagation
Collisions• Collisions result in massive fragmentation that
can snowball in size– Adversely effects safety of satellites in GEO regime
– Very long time until deorbit is possible
• Low impact velocity (~1.5 km/s)– Typically same orbit, same direction, low orbit speed
• Use Hanada’s experimental scaling of NASA Standard Breakup Model for GEO regime
Hanada’s Breakup Model• NASA Standard Breakup Model describes a high-
speed collision model for LEO
• Hanada gives modification for low-speed GEO breakups
• Steps– Describe size distribution of breakup (LC)
– Determine A/m distribution
– Fragment dV distribution
• Fragment distribution favors low-mass, low-speed fragmentation
Completed Work• MATLAB Modified Equinoctial Propagator
– High accuracy for the following perturbations:• Earth’s Oblateness (J2, J22)
• Sun Gravity
– Need to be adjusted:• Moon Gravity
• SRP Perturbation
• Collection of GEO Debris TLE data
• Breakup model ~75% complete
What’s Left• MATLAB Modified Equinoctial Propagator
– Address perturbation issues
– Verification vs. TLEs
• Completion of Breakup Model– Verification against Hanada’s output
• Collision Simulation– Collision conditions
– # of fragments to propagate
– Verification of orbital well entrapment
– Behavior analysis
Questions?