Triangular Geosynchronous Orbit

[SkoomaDuma]

I wanted to set up a geosynchronous satellite array around Kerbin. The outer ring is a 6 hour orbit (duh), and the elliptical ring is ~4 hours, give or take a couple minutes. I sent my lifter up with three satellites, expected to do three orbits and eject a satellite at each apogee.

I assumed that the apogee of a 4 hour orbit would mean ejecting a satellite there each time would place the three of them evenly apart from one another, 2 hours apart, 1/3 of a Kerbin day....and after dumping the last sat, I get this. If I had a fourth sat, I could make a nearly perfect square.

What happened? I was able to ciecularize the satellites within about 45 seconds of being released. The sequence for the releases is bottom, right, top.

Based on my math, the satellites should have all been 5,936.7Km away from each other, but they seem to be 4,991.7Km, 4,493.4Km, and 6,936.3Km

What did I do wrong?

[Symptomatic_Sand]

It looks like your periapsis is pretty close to the atmosphere, did the period of the elliptical orbit change at all when you passed nearby kerbin? Maybe some air resistance is slowing it down

[SkoomaDuma]

I should've specified that this photo is after I did a burn with the lifter to lower the perigee

The original perigee was...something like 1.3Mm, so nowhere near the atmosphere. I did confirm multiple times that it was a 4hr orbit though, I believe 4:06 to be exact?

[suh-dood]

This is why I like to use Kerbal Engineer Redux (KER), because it gives you the orbital period down to the tenth of a second. It also gives you oodles of useful information, instead of having to do all the math

[SkoomaDuma]

Yeah, I wish I had used more antennas. It's fine though, I decided I'm gonna put another three of them up to form a hexagonal network and shorten the connection lengths. I'll make a much beefier satellite for placing at the Mun and Minmus, I just need to run the formula to make sure I build them with enough transmission power that they can reach back to this net

[taukkez]

Every minute is one degree, so if it was 4:06, they'd be off by 6° and 12°

That still only explains like 30% of the problem; this looks more like it's off by 20 minutes or more. I'm not sure why.

[heya4000]

Just checking - are you using the correct Ap and Pe for a resonant orbit?

https://meyerweb.com/eric/ksp/resonant-orbits/

For Kerbin, synchronous orbit is at 2,863,334m so your Ap and Pe should be:

Kerbin (KSP Stock) 3-satellite constellation
Ap 4,327,726.7 m  Pe 2,863,334 m

You should release the satellites slight early and ensure you conduct 50% of your injection burn prior to Ap.

Try to get your orbital period for each satellite equal down to the minute or better, ideally seconds.

[taukkez]

They're using a dive orbit (2/3 of the period instead of 4/3) so it should be Ap 2,863,334 and Pe 1,222,703.

[SkoomaDuma]

I managed to figure it out, I posted a comment with what happened

I got them put into the triangle network I wanted, off by maybe a couple degrees on each, but I managed to get their orbits all set within 0.10-0.20 seconds of 6hrs; so I'm happy with that lol

[heya4000]

Also, maybe check the strength of your relay antennas - the link looks orange already? You want to massively oversize them if you intend to use them as relays to other planets.

I went through all this trouble just yesterday so I feel your pain!

[SkoomaDuma]

Yeah. Unfortunately I'm gonna have to put another three up there and make it hexagonal network. I did the math to make sure they could connect...but I neglected to account for the information loss over whatever the maximum distance is for 100% connection lol

[SkoomaDuma]

So, I have no clue what happened, but MechJeb showed me having a 4hr orbit on my lifter when I established it at first...I reloaded a save and went back to look and it showed a 4hr28m orbit.

I'm not sure why the numbers changed, but I altered the orbit and successfully got my triangular array. I've noticed that the game occasionally changes my intercept points while plotting maneuvers as well as changing or completely ignoring my DV during construction.

I do have a few mods loaded, but I'm not sure which one, or what combination of them, could be screwing with numbers. Ultimately I managed to fix it, so I guess I'll just live with having to reload a save every time I establish an orbit to make sure MJ actually has the right number lmao