Collision example

[gaffarelj]

A new example can be added that:

• propagates multiple satellites (at least 3)
• in an almost not perturbed orbit (only PM gravity or SH up to D/O2)
  • almost circular orbit (e<0.1)
  • almost polar orbit (i~88deg)
• Use one of the latest integrators for maximum positional accuracy (<1 m)

In this example, two of the satellites should be at the same position at the same time (also called collision). This would showcase the accuracy of the integrator. This example can be linked to #9 when discussing accuracy).

The fact that 3 satellites would be propagated could also be used to showcase the dependent variable that saves the body that is the closest to another one (see this issue).