How precise is possible?

[jarmenia]

I've been working through the campaigns on the wiki. I've managed to setup my com sat network in geostationary orbit but my one comm sat isn't exactly over KSC. KSC is at 74 degrees 34 min W Long and my sat is fluctuating between 73 50 and 75 10 with an eccentricity of .003. Is this acceptable or should I be able to get my sats exactly where they should be? Same with inclination, I've got an inclination of 0.22 degrees. Should I be able to get it exactly at 0 degrees? How close is close enough but still possible in KSP? As a comparison, how precise are the satellites that NASA launches?

[Technical Ben]

There are mods that will give higher accuracy read outs. Though there are both limits to what you can make practical in a rocket, and what the game engine/software can deliver.

[lajoswinkler]

Errors in KSP are higher because everything is much smaller so the curvatures are greater. 0.22° inclination after launch is pretty good.

I'm not sure about the real life launches, but I think their errors are numerically similar to the most precise KSP launches, though they end up with much less orbital deviations simply because everything is larger so the room for errors is much greater.

[FITorion]

NASA considers things in orbits with Kilometers of difference between apo and peri to be in circular orbits. I think within about 10km difference would be it. And since KSP scale is around 1:10 or 1:11 then within 1km should be fine.

As for Geosync. Real satellites progress along the Geosync orbit and are tugged on by many different gravity sources at the same time. Orbits have to constantly be adjusted with thrusters or they'll degrade in rather short order even way up at Geosync. With KSPs one gravity sphere of influence it is possible to get into way more stable and accurate orbits than the real world.

[jarmenia]

Wow, thanks. Looks like I should try and get my comm sat directly over KSC down to the second. Any suggestions on how to plan a burn that's that precise?

[lajoswinkler]

Yes, you can get NaN inclination and so circular orbits that their AP and PE nodes wobble like crazy. Oscar-B fuel tank and LV-1 engine are the best for very precise adjustments.

[SpaceSphereOfDeath]

I use a ion engine at low thrust for precision burns.

my most 'perfect' orbit is 90120x90134x0.005'

[Specialist290]

In general, for geosynchronous orbits, you don't want to worry so much about getting the orbit perfectly circular as getting its orbital period to be exactly 6 hours. As long as that condition is met, it'll more or less always be at the same point in the sky when its at a particular point in orbit, even if it seems to "wobble" a bit from the perspective of the ground.

[Guest crlfe]

For the last tweaking, try using RCS with fine control enabled (capslock). That is probably more delicate than can be measured with the stock instruments...

[Ralathon]

I've been trying to get perfect orbits for my Astraeus constellation:

You can get pretty damn close to perfection by using an autohotkey macro to do extremely small burns. All those orbits are accurate up to 5 significant digits. The problem is that the game has some issues translating between loaded physics and unloaded physics. I noticed the eccentricity and inclinations tend to vary a bit after time warping and reloading when you get really close to an accurate orbit. So that's the limiting factor.

When trying to do something like this it is almost essential that you have some sort of flight computer to point your craft in the relevant directions though. It is hard enough to get the orbits right without the period and eccentricity shifting while burning for an inclination change. I used the remotetech flight computer, but I imagine Mechjeb has the same functionality. And else you can always cook something up with kOS.

[Kerbart]

Well not always. Assuming kOS works. That's a big if, on my machine, kOS sticks to "plus or minus 10°" accuracy and that doesn't quite work. It makes for spectacular launches though.

[Ralathon]

Well not always. Assuming kOS works. That's a big if, on my machine, kOS sticks to "plus or minus 10°" accuracy and that doesn't quite work. It makes for spectacular launches though.

kOS tends to be pretty precise for small and medium craft for me. Did 0.7 change anything with the PID controller or something? (still running 0.65 here).

Anyway, even if it has trouble you can always circumvent it by writing your own attitude control program instead. It's pretty easy to program something like that.

[BluetoothThePirate]

IRL communication sats usually librate back and forth over a couple degrees, at that distance they're basically broadcasting to the entire hemisphere anyway, not super critical. What's really critical is getting the period dead on or else it'll drift. Feel free to mess with it more, but you're already (literally) close enough for government work.