Building (equatorial) Kerbosynchronous network of satellites...

[TheMontgomery]

Greetings, all.

I've just got my feet wet with RemoteTech, and thus now comes the need to build a functional communications satellite network.

So far I haven't had much luck in finding a good technique by which to deploy my satellites. I'm hoping to get a constellation of 3 or more in Kerbosynchronous orbit, in a roughly equilateral polygon, et cetera, et cetera.

I'm hoping to do it in one flight, for example, having the carrier vehicle attain LKO, raise apoapsis to 2,868.75 kilometers, and transfer to such an orbit as to deploy the satellites at regular intervals... the problem being that I can't figure out, say, where to aim for a periapsis/semi-major axis such that the satellites could be released at regular intervals to cover the entire orbit.

So, any techniques for tackling this, whether it be a single flight and the recommended orbital parameters for letting the sats go, or how to schedule multiple successive launches to effect something similar, etc.

Thanks in advance!

Edited December 8, 2013 by TheMontgomery

[Vrana]

There was a very similar question recently... Read this.

[Murph]

It might be easier to circularize the delivery ship's orbit at 2868, saving the need for the individual satellites to do a large burn to pull their periapsis up after deployment. You can then raise or drop the delivery ship's periapsis a little after each deployment to give it a different orbit period, time warp until it's roughly in the right place, circularise again, rinse and repeat.

[Taki117]

Depending on how **** and/or OCD you are, if you want a truly synchronous orbit you are going to have to edit your save file, otherwise your satellites are just going to move out of position over the course of weeks or months (Depending on how well you placed them initially)

In order to get it perfect find the following and edit.

alt = (desired Altitude Synchronous and Semi-Synchronous values can be found in the wiki)

ORBIT
			{
				SMA = Semi-Major Axis (Desired Value can be found in the Wiki)
				ECC = 0 (This gives you a perfectly circular orbit)
				INC = 0 (This gives you an equatorial orbit)
				LPE = 0 (This determines craft position in orbit, if you want them evenly spaced make sure this is a multiple of the same number, for 4 probes 90 degrees apart your f1st is at 0, 2nd at 90, and so on)
				LAN = 0 (This must be 0 for an equatorial orbit)
				MNA = (This value must be the same for all probes)
				EPH = 23200961.363508 (This value must be the same for all probes AND the same as UT)
				REF = 9 (Don't worry about this)
				OBJ = 1 (Or this)
			}

More Detailed data here!

WARNING: Once you edit the save, if you ever go to your probes again they will be knocked out of whack because if it is not being controlled it gets put "On-rails" and physics no longer apply. As soon as you load it it's location get's updated and the values change.

Edited December 8, 2013 by Taki117

[TheMontgomery]

I should be able to run with that. Thanks all!

[Armchair Rocket Scientist]

I happen to have done this before. Basically, build your launcher with all your satellites on it like so:

Either launch to an LKO parking orbit and then burn to Kerbosynchronous Transfer Orbit, or launch directly to KTO. In either case, your apokee should be almost exactly 2868.75 km (the height of the final synchronous orbit).

Next comes the tricky part. At apokee, you need to burn prograde until your orbital period is a particular integer ratio of the final orbital period. For example, the rocket in my picture is carrying 4 satellites, which are put 90 degrees apart. In my case, my orbital period was 3 hours (for a semisynchronous orbit), but for KSO your final orbital period will be exactly 6 hours. If I'm in an orbit with a period of 3/4 of that, or 4:30, and I release a satellite at apokee which instantly circularizes, then at my next apokee the satellite will have only orbited 270 degrees, leaving me 90 degrees ahead of it, perfect for releasing my second satellite. Alternately, I could make my orbital period 5:15, and release a satellite every two orbits. The closer you make your orbital periods, the longer it will take to release all your satellites, but the less dV they will need to circularize their orbits.

KSP's map screen doesn't show you your orbital period. I strongly recommend using Mechjeb, Kerbal Flight Engineer, or another mod that gives you detailed orbital data. Alternately, given a desired apoapse and orbital period, you can calculate the desired periapse manually.

Even with Mechjeb, you won't be able to get the satellites' orbits perfectly synchronized, and they will eventually drift out of alignment. Real satellites drift out of alignment too (though due to orbital perturbations and not floating point rounding errors), but they generally have someone watching them and sending commands for station-keeping burns etc. However, this is not how most KSP players like to spend their time. Instead, I recommend editing the save file after you get them in approximately the right orbit, and not touching them after that.

[Sirrobert]

Why do your satelites have so many antennas and a ladder? XD

[Armchair Rocket Scientist]

Why do your satelites have so many antennas and a ladder? XD

For cosmetic reasons: I wanted it to look like a real GPS satellite. (They also weigh about the same adjusted for scale: real GPS satellites are a bit heavier than a Mercury spacecraft, my KPS satellites are a bit heavier than a MKI capsule).