January 6, 2020

Operational management of Collision Risks

The Operational management of collision risks consists in detecting two space objects moving dangerously close to each other (see Figure 1) and then statistically analysing the probability of them colliding.
The situation is considered to be dangerous if the distance between the two objects falls below a certain threshold.


Figure 1
Detection of a close approach between two orbiting objects (explanatory diagram)

Given that on the one hand the orbits change under the effect of the gravitational attraction of the Moon and the Sun, but also under the influence of solar flux and atmospheric drag, which itself depends on the geometry and attitude of the object, but also on solar activity, which causes variations in the density of the residual atmosphere at high altitude, and on the other that the observations used to calculate the orbits of space objects themselves comprise a degree of error, the orbital position of a space object at a given date can only be given with a corresponding level of uncertainty.
This uncertainty as to the position and velocity of the space objects in orbit must be correctly modelled in order to carry out operational management of the collision risks, so as to reduce this risk of collision between two space objects, while minimising the cases in which a manoeuvre will be required.


Figure 2
Calculation of the probability of collision between two space objects, with Gaussian modelling of orbit errors (Explanatory diagram)