Collision Risk Flashcards
List:
The collision risk parameters
- Probability of Collision (Pc)
- Miss Distance
- Relative velocity
- Time to closest approach (TCA)
- Cross-sectional radius
What are the two types of collision avoidance maneuvers?
- Propulsion Manuevers
- Non-Propulsive Maneuvers
What are examples of collision avoidance maneuvers?
- Radial Manuever
- In-Plane Maneuver
- Out-of-Plane Maneuver
- Phasing Maneuver
Define:
Radial Maneuver
Thrust is applied perpendicular to satellite’s velocity vector.
Changes satellite’s altitude, effecting orbital period and separation at closest approach.
Define:
In-Plane Maneuver
Applies thrust in direction of satellite’s velocity.
Effects semi-major axis effectively raising or lowering the orbit, and modifying TCA.
Define:
Out-of-Plane Maneuver
Burn in direction normal to the oribal plane. Changes inclination
Define:
Phasing Maneuver
Multiple burns to change the satellite’s position in orbit
What are system factors that effect collision maneuver decisions?
- Current orbital state
- TCA estimate
- Probability of collision
- Propellant availability
- Thrust capabilities
What is space weather?
Solar flares and geomagnetic storms
How does space weather effect collision probability?
Can impact sensor performance and lead to fluctuations in error.
How does space weather effect sensors?
- Radiaton damage
- Single Event Upsets (one-off, permanent changes in component)
- Interference with electro magnetic and optical sensors
- Thermal control and sensor drift due to thermal stress
- GPS signal degredation
What are space weather mitigation strategies?
- Radiation shielding
- Redundant systems
- Error correction and filtering
- Space weather forecasting and adjustment
- Regular calibration and maintence.
How does space weather effect laser communication systems?
- Atmospheric disturbances
- Spacecraft orientation and control
- Radiation induced noise
What is the Alfano method?
Technique to assess the collision risk between two orbiting objects considering relative motion and positional uncertainties.
What are key components of the Alfano method?
- State Vectors
- Covariance matrices
- Relative motion analysis
- Probability ellipsoid
- Collision probability calculation
What are the steps of the Alfano method?
- Transform state vectors to reference frame.
- Combine covariance matrices
- Calculate relative position and velocity
- Determine combined hard-body radius
- Compute joint probability density finction
- Integrate PDF over collision volume.
Define:
Collision On Launch Assessment
COLA
Safety analysis to ensure that the trajctory of the launch vehicle does not intersect orbits of existing satellites.
Describe the how covariance matrices are combined in the Alfano method.
To combine covariance matrices, the Alfano method sums their error states to create a single 3D probability distribution function, typically visualized as an ellipsoid. This is a simple sum and is centered on the primary object.
How is the combined collision PDF computed?
What is a screening volume?
A rectangular volume of space around a satellite where any object which passes through is analyzed for a collision probability.
What effect does space weather have on collision avoidance maneuver count?
Spaec weather leads to higher errors in sensors and drastic increasses in collision avoidance maneuvers.
How do non-propulsive satellites effect collision risk?
Non-propulsive satellites are unable to perform collision avoidance maneuvers and lead to uncontrolled satellite risk.
What should happen to non-propulsive satellites?
They should be deorbited.
If a satellite has a high Pc, and its propulsion system isn’t working, what steps can be taken to reduce the Pc?
- Attitude adjustment to increase drag
- Coordination with other satellite operators
- Reduce cross section area for collision.
- Active debris removal
- TCA adjustment to minimize impact onto other satellites.
- Activate end of life systems
What is the error function
How is the error function used in the Alfano method?
The error function is used to simplify the double integral of the collision plane into a single integral for numerical calculation.
How does the numerical implementation of the error function impact Pc?
There are numerous approximations of the error function, and with increasing levels of accuracy comes increasing computation. When trying to minimize conjunction compute time, you have to balance erf accuracy as it impacts Pc.
Formula: Bayes Theorem
Formula: Conditional Probability
