3 sats on keostationary at 120 degree phase... how?

[cicatrix]

I'm trying to build a comm network and is figuring out the best way to put 3 satellites on a keostationary orbit exactly at 120 degree phase.

Let's suppose I have 3 satellites on LKO and then what should I do?

[Goody1981]

A way that works for me is to build a craft capable of delivering all 3 satellites at once (ie payload is 3 individual satellites, separated by decouplers or stack separators). Then, get your Ap out to keostationary height (2868.75 Mm).

Coast to Ap, and when you get there bring your Pe up until your orbital period is as close to 4 hours as possible (easy with KER which tells you orbital period, but you can also place a manoeuver node directly in front of you, cross it, and see how long it says until you re-cross it).

4 hours is the key though, as that is 2/3 of the 6 hour orbit you have at keostationary height. Once you have a 4 hour orbit, wait until Ap, then release the first sat. Switch to satellite and circularise so you have a 6 hour keostationary orbit. Switch back to main ship, and wait until Ap again and release second sat, and repeat. Do the same for the third. Then they should all be 120 degrees apart and you get those beautiful green comm-net triangles

[cicatrix]

Ehm... I wish I thought of that earlier... I already have 3 satellites on LKO though... any suggestions?

[Goody1981]

Haha yeah that is trickier... I can’t think of a way that doesn’t involve rendezvousing all of them together, which will use loads of your fuel. Are they spaced out evenly now? Like 120 degrees?

[cicatrix]

Just now, Goody1981 said:

Haha yeah that is trickier... I can’t think of a way that doesn’t involve rendezvousing all of them together, which will use loads of your fuel. Are they spaced out evenly now? Like 120 degrees?

Of course, not. I can use some algebra, of course, but it's nearly night and I don't feel like a mathematician right now.

[Goody1981]

Ha well I guess it depends how much fuel they each have... it’s definitely possible, but will require a lot of orbit-fiddling and fine tuning to get them exactly where you want them... time-wise it would def be quicker to use my earlier method. You could always leave them there and launch separate keostationary ones... call it your LKO network - having more comsats never hurt anyone haha.

If you did want to try I think the most accurate way (to get as close to 120 deg without just eyeballing or pressing a protractor to the screen) would be to rendezvous all the the sats somewhere (doesn’t matter where, just as long as they’re all together) then pretty much just repeat my first method. So get each sat in a 4 hour orbit with keostationary Ap (but be as quick as you can doing the burns, even trying to control all 3 at once by switching between if possible, so they all reach the same Ap at the same time), then have the first one circularise at Ap, wait an orbit then do 2nd, etc

[Snark]

I realize this is moot because you've already got them in orbit, but... why not just launch them to 120 degree intervals in the first place?

Kerbin has a rotation period of 6 hours, meaning that it rotates 60 degrees per hour.  So just launch them two hours apart on identical trajectories, and they'll end up 120 degrees apart as you like.

[MechBFP]

I usually just put 1 sat in KSO and then for my next sat I select the KSO one as my target and do a rendezvous node, but purposely make the rendezvous marker of my ship about 120 degrees off from the target. Then when I get to the marker, I circularize. 

Edited March 28, 2018 by MechBFP

[Fett2oo5]

Honestly, I suggest using HyperEdit mod (you can auto-install it using CKAN), or altering the orbit information of each spacecraft in the .sfs save file.  Those will be the easiest, and more accurate ways to get your 3, already in orbit, satellites to the exact orbit, and exact periods you want.

The way I view HyperEdit is that if I've already gotten an object to the desired orbit and positioned them once, then I will use HyperEdit to fine tune the precision, and/or make the orbital parameters EXACT.  When I know I can do it (and have done it at least once) in KSP given enough real-world time, then I'll use HyperEdit to save myself some real world time.  Otherwise I feel like I'm cheating.

[Zhetaan]

@cicatrix:

Since you already have them in orbit, you will need to adjust the satellites to a phase angle (relative to one another) of 120 or 240 degrees.  The trivial solution to this is to rendezvous them and then send them out at one-third intervals of their common orbit (not every two hours--that only works at launch).  Since I assume that you don't want to do that, then figuring out how much to adjust is dependent on what the phase angle is already, and to get that, you're going to need a readout such as Kerbal Engineer.

This may be easier once you reach synchronous orbit;  I'll leave the details to you. Once you have the current phase angle, you need to figure out how many degrees off you are from the target phase angle (x), add that number to 360, and calculate a phasing orbit that is (360 + x) / 360 of the orbital period (or the difference from 360 depending on which way you need to adjust; again, I'll leave the details to you).

There are a few phasing orbit calculators out there, but if you want to do it by hand, you're using the new orbital period to calculate the semi-major axis of the new orbit, and then using that semi-major axis to calculate a new apsis while holding the other apsis constant (so your phasing orbit is tangent to your original orbit).  It's not difficult if you have good skills in algebra but it can be tedious; if you need help with that, I can show you the process.

[korniton]

 

On 27.3.2018 at 10:20 PM, cicatrix said:

I'm trying to build a comm network and is figuring out the best way to put 3 satellites on a keostationary orbit exactly at 120 degree phase.

Let's suppose I have 3 satellites on LKO and then what should I do?

EDIT: It still works as nothing changes much. I still use this as a help. Watch it, and you can do it in 10 minutes. Good luck!

Edited March 30, 2018 by korniton

[cicatrix]

 

Actually, the video is not very informative.

However, I stumbled upon a wonderful guide from Remote Tech wiki:

https://remotetechnologiesgroup.github.io/RemoteTech/tutorials/keo/

Posting in case someone needs this information.

[ArmoredLipid]

On 3/27/2018 at 1:40 PM, Goody1981 said:

Then, get your Ap out to keostationary height (2868.75 Mm).

I'm pretty sure that KEO is 2,863,334 +/- 0.6 meters. I'm not sure whose information is more recent, though.

[Goody1981]

18 hours ago, ArmoredLipid said:

I'm pretty sure that KEO is 2,863,334 +/- 0.6 meters. I'm not sure whose information is more recent, though.

 I think you’re right actually... I think that 2868.75 Mm is a 6-hour orbit (which is preferable relative to the rest of my post), and that 2863.33 Mm which you mention is a slightly quicker orbit that matches the sidereal rotation and so is the true stationary one.

thanks

[Quadkiller]

Here's an easy approach for getting 3 satellites equally spaced out in Keostationary orbit with very little math.

1. Get the first satellite into Keostationary orbit.
2. Get the second satellite into low Kerbin orbit with an orbital period of 34m 12.324s (5h 59m 9.4s * (2/3) / 7).
3. Plan a maneuver node for the second satellite to rendezvous with the first satellite, but don't perform the maneuver yet.
4. Delay the maneuver node by exactly 7 orbits, the closest approach indicators should be 120° apart now.
5. Execute the maneuver node, then circularize at apogee.
6. For the third satellite, make sure you target the second satellite not the first one. You can double check it is correct based on the closest approach indicators.

In general, the parking orbit can have a period of (sidereal rotation period) * (k / number of satellites) / n, where k and n can be any integers. The numbers 2 and 7 just happen to work out well for Kerbin. Note that changing k will change which satellite in synchronous orbit you have to plan the maneuver with.

Edited October 7, 2022 by Quadkiller
Found better approach