Fine-tuning with persistent.sfs

[RabidMonkey]

I'm running into a bit of trouble doing some fine-tuning on my RemoteTech constellation. I'm trying to get 6 satellites into a hexagonal arrangement in a 6000km orbit, and launched them into as close a position as I can get given our standard floating-point, velocity changes depending on orientation nonsense. To get them locked into a constellation that won't drift into uselessness within a couple years, I'm trying to lock down the orbital parameters in the persistent.sfs file. Did a bit of figuring, and worked out that the target orbital period is 56690s, and (obviously) there should be a 60 degree angle between the sats. Here's an example of one of their entries:

ORBIT
	{
		SMA = 6600000
		ECC = 0
		INC = 0
		LPE = 0
		LAN = 60
		MNA = 0
		EPH = 9448.333333
		REF = 1
	}

I entered the appropriate LAN values as multiples of 60, the EPH values as multiples of 9448.333333 (56690/6), and the "lon" values in the VESSEL section equal to the LAN. This resulted in all 6 satellites being in exactly the same place in the orbit in a giant pile-up. I've found lots of guides for 3 satellites in a kerbosynchronous orbit, but I'm having some trouble working out the equations that will help me calculate the relevant values to get an arbitrary number of satellites at an arbitrary altitude.

Yes, I know I can use HyperEdit to get them there more easily, but I like doing the math. Yes, I know that some people will consider this "cheating", but I rationalize it as automated, preprogrammed station-keeping.

Edited April 3, 2015 by RabidMonkey

[maltesh]

The game ignores surface Longitude and latitude when you're orbiting.

What you want to do is keep all the orbit shape and orbit-orientation parameters the same (Semimajor Axis, Eccentricity, Inclination, Argument of Periapsis, Longitude of the Ascending Node) and only fiddle with the ones that set an object's /position on its orbit/, (Mean anomaly at Epoch, and Epoch).

For six satellites, it's easiest to do one of two things.

1. Set Mean Anomaly at Epoch (MNA) to multiples of À/3 and keep Epoch (EPH) the same.

2. Set Epoch to multiples of your Orbital Period/6, and keep Mean Anomaly the same.

[RabidMonkey]

The game ignores surface Longitude and latitude when you're orbiting.

What you want to do is keep all the orbit shape and orbit-orientation parameters the same (Semimajor Axis, Eccentricity, Inclination, Argument of Periapsis, Longitude of the Ascending Node) and only fiddle with the ones that set an object's /position on its orbit/, (Mean anomaly at Epoch, and Epoch).

For six satellites, it's easiest to do one of two things.

1. Set Mean Anomaly at Epoch (MNA) to multiples of À/3 and keep Epoch (EPH) the same.

2. Set Epoch to multiples of your Orbital Period/6, and keep Mean Anomaly the same.

That got it! Reading your post, I realized - if the LAN was offset by the same arc that would be traversed in the EPH, of course I'l get a pile-up. Set the LAN of them all to 0, left EPH alone, and they're in perfect alignment.

Thanks!

[godefroi]

Also, see my proto-mod, OrbitSnap: http://forum.kerbalspaceprogram.com/threads/113592-WIP-OrbitSnap-Keep-your-RemoteTech-commsats-in-proper-formation%21?highlight=orbitsnap

This mod will keep your satellites in perfect formation, even if you visit them (for example, to re-point dishes). It also eliminates the need to edit the file in the first place; get the orbit close enough, and it "snaps" into perfect position.