Orbiting Sync with ISS

[evensis-]

Hi guys, been mucking around with orbiter for years, but first time posting on the forums! I can get to and from the moon, get into orbit etc. But for the life of me, i just cannot sync up with the ISS. I'm usually missing by about 10km, and practically at the same speed, which is beginning to frustrate me to say the least!

I had a gander at one of the video tutorials for lining up an orbit for the ISS. And happened to notice that the apopasis and periapsis don't move an inch for whoever made the tutorial. Mine are flying around like a fiddlers elbow, and upon a full orbit, they have changed height without fail, without myself doing anything.

I've tried raising and lowering the orbits, but never does a thing to help me, they still move around. I would like to try getting to mars as my next venture with orbiter, but i'm determined to rendevous with the ISS before i attempt that.

Does anyone have any suggestions?

 

[Zatnikitelman]

Welcome to the forum!
It sounds like you have nonspherical gravity enabled, so if you turn it off (in the launch pad), the orbit should stay quite a bit more stable than it is now. I pull off multiple sync with it enabled because over one orbit, the differences average out to what you had one orbit ago (at least from my experience).

But if you say yuo're getting to within 10km, then syncing is not your problem. The first time I successfully synced with something I only got with in like 50km. At that close distance, just use the docking HUD and turn toward the big green CROSS and burn till the number is as close to 0 as you can get it (it drifts around so you'll have to burn->correct->burn->correct or correct as you burn.) once you've done that, just point toward the ISS and burn to get the number under it positive.

While you're heading toward it, depending on your orbits, the number might go negative, or might go very highly positive. Don't worry, if it's negative, just burn towards it more, if it's high, just use the linear thrusters firing in reverse (NUMPAD 9 in translation mode). The green CROSS at this point is a real good indicator of where you're heading in relation to the station. So use LIN thrusters to place the center of the CROSS over where you want to be, I'd recommend the squares out from the docking port you're heading for. Once you're in the squares, cancel out the velocity again (just use LIN, don't worry about turning toward the CROSS) then move toward the docking port.
Welcome!
Zatnikitelman

 

[evensis-]

Ah, well as it stands i have two big crosses, one encased in a circle and another just as a X, without the circle encased.

The video tut i was watching mentioned facing towards the cross encased in a circle, then turning the view around, use linear thrusters to make the X behind the ship line up with the docking squares, then just wait and do a deacceleration burn once close enough. Which left me totally confused when i was still a fair distance from the station. I'm just gonna give it another go now i have non-spherical gravity disabled.

Thanks for the help, will post back and give you my results

well as it stands, DTmin at 0, r inclination at 0, and 2 orbits till intercept! Lets see how it goes.

EDIT:

Fantastic! First dock at the ISS, the difference the non spherical gravity made was quite astonishing! Will have to try it sometime as an added difficulty dock! Rather pleased with myself. Thanks for your help!

 

[Zatnikitelman]

Lol, glad you made it! Considering I goofed up my post quite a bit :sorry::sorry:
To null velocity, burn toward the CIRCLE_CROSS regular cross shows "where you're going."
Sorry!

 

[Kaito]

Congrats!
Cross and Cross with Circle: Cross is your direction relative to ISS. Cross with circle is on the exact opposite side of it. You burn TOWARDS the cross with circle to decelerate (or burn with retro thrusters when you are facing the cross)

 

[evensis-]

Thanks guys and no problem zatnikitelman, I kinda gathered what you meant and gave it a try lol! Also gave it another go with the Ravenstar and same result, perfect dock, also realised that I shouldn't burn towards the circular cross till about ~700m. First time dock was a bit of a shambles as i decelerated at about 4km lol! And used a bit too much fuel doing it! Second time decelerated at ~700m. Then moved towards and docked. The non spherical gravity really makes it difficult!

Now to have a go at IMFD, and go for mars i think. Obviously, a dock at ISS for a refuel before attempting that will now be on the agenda!

 

[James.Denholm]

The funny thing is, I always find it a lot easier to get to Mars than the Moon... so good choice!

And congrats on the docking. Did you manage to re-enter ok?

 

[evensis-]

Yeah, re-entering is a breeze! DG4 and Ravenstar's autopilot makes life a lot easier when holding the AoA, re-entering at the right place has always been a challenge for myself though lol. I always get the moon quite easily with tranx, i'm totally bewildered with IMFD at the moment though, trying to find a decent tut for it.