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I am trying to evenly space 3 satellites in polar orbit around Kerbin at 500km x 500km but I am not sure how to do the math.  I am not sure how to lower my orbit enough to make the satellites have enough time to orbit so they can get back up to their original position.  Any tips on how to calculate the altitude at which I need to lower my orbit?

Edited by Diamond
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You need Kepler's 3rd Law for calculating orbital period from parent body mass and semi-major axis. 

My method for doing what you are attempting is to send up a "satellite bus" with all three sats into an orbit with periapsis at the desired circular altitude and an apoapsis that yields an SMA that gives an orbital period 1/3rd longer than the desired circular orbit's period. Each time the bus arrives at periapsis, detach a sat and circularize it. 

I ran the numbers for a 500x500km final orbit, the satellite bus orbit should be 500,000x965,110m to get that 4/3rds orbital period.

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The simplest trick in my book is to launch them together, put them in the desired orbit and then basically increase and decrease orbital periods of 2 of them by 1/3 of the reference orbital period or more by accelerating and decelerating respectively (really depends how much spare delta-v you've got). If you choose 1/3, you gotta put them back on the same period one orbit later, if you choose 1/6, do it after two orbits, and so on.

The reason behind this is that 360/120=3, quite straightforward.

Apply thrust limiter to fine tune the period down to +/- 0.02s, which should give you a pretty stable constellation.

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  • 5 months later...

Hey Diamond, check out the following video.I had the same problem, I couldn't find a decent way to do this and kept looking everywhere on the web. So I went ahead and derived the math and made a video as it seems a lot of people still ask about how to do this.


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  • 1 year later...
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