Alessandro is back for the second talk of the session (he is also co-chair, so a busy morning for him!) He is now talking about the challenges associated with use of low-thrust systems for collision avoidance in large constellations #orbitaldebris2019
What is the probability of a collision? How many collision avoidance manoeuvres (CAMs) are expected? Good questions to ask.
The simulation approach used the cube method [developed by Liou et al. 2003, NASA] as a pre-filter. Then a propagator is used to find the time of closest approach and the close approach geometry, for use with the CAM.
Cube size of 10 km, time step of 60 seconds [quite demanding from a computational point of view], 20-year projection and 10 Monte Carlo simulations
For each conjunction identified, the method identifies the best set of parameters for a CAM that reduces the collision probability below a desired threshold. Use simulated annealing for this part.
Results for tangential thrust (speed up or slow down with the CAM) applied 8 orbital periods and 4 orbital periods before the close approach. Slowing down immediately reduces collision probability. Speeding up can lead to initial increase in probability before it reduces
Direction and low-thrust duration are determined using a heuristic algorithm.
This is only the initial work. Software is being tested. Future work will look at comparison between analytical and heuristic algorithms for CAM parameters, and different constellations
In Q &A, Alessandro explained that the behaviour observed for a speed-up (tangential thrust that increases speed) was consistent - the initial increase in collision probability occurred in most cases. He is investigating
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