# Would the orbits intersect during 7 days?

I'm calculating the probability of collision of the satellites. I'm trying to filter the set of orbits to minimize the calculations.

Which conditions may definitely say that the given 2 orbits O1 and O2 of the satellites wouldn't intersect during 7 days propagation?

For example, if the apogee of O1 is lower than the perigee of O2 or the perigee of O1 is higher than apogee of O2.

• if the apoapsis of 0$_1$ at the start of the period is lower than the periapsis of O$_2$ at the end of the perioid and vice versa – JCRM Nov 30 '18 at 21:46
• @JCRM This condition is in the question ) – Leeloo Nov 30 '18 at 21:47
• it's not quite the same, the question doesn't contain the times – JCRM Nov 30 '18 at 21:48
• @JCRM Yes, but, to calculate the periapsis at the end of the period, I have to make the propagation - there is no minimization of the calculations. – Leeloo Nov 30 '18 at 21:49

An apogee/perigee screen is a common first step in conjunction analysis screening. Remember to add a pad at least equivalent to the miss distance you're screening for + twice the expected radial position uncertainty to the apogee/pergiee filters. And use caution with this sort of filter in very low earth orbits where apogee could be changing rapidly due to drag.

So you would reject a pair of satellites as potentially conjuncting if: