# How presise could 2 satellites “thread the needle” in orbit?

I have a question about using a magnetic field to propel 2 satellites off each other while traveling in opposite directions on the same orbital plain to intersect either 2:1 or 1:1 on each orbit around the Earth.

My question is as follows:

For whatever reason, I'd like to have two Earth satellites in counter-propagating orbits so that either once, or twice every orbit they would pass very close to each other. In satellite lingo these very close passes might be called conjunctions.

These low Earth orbits can be any eccentricity or inclination, the idea is to arrange them such that over time they would tend to repeat their close counter-propagating high-speed flybys.

What effects would tend to cause successive conjunctions to drift farther apart over time, and which orbits would minimize those such that the close flyby's would continue longer?

• Well, to measure and test general relativity with satellites, which we have done, I would think you would have to very precise about your measurements. Something in the ballpark of millimeters and nanoseconds sounds about right, if you've got a good positioning system. – B.fox Dec 8 '18 at 22:07
• Asking "how hard" it is to build something like this is a very subjective question, especially if it doesn't currently exist. What kind of answer are you looking for? The simple answer is "very hard". – Dragongeek Dec 9 '18 at 0:12
• I've made an edit, have a look. I think this is what you are after. Feel free to roll back or edit further. – uhoh Dec 9 '18 at 15:47
• I've started to work on a nice answer to this, but it will take a day or so. See How to correctly make a fake, counter-propagating TLE? – uhoh Dec 10 '18 at 3:05