Orbital docking, closing the gap

[Algomeysa]

Ok, Ive figured out how to get into a pretty much identical orbit as the thing I want to dock with, I'm just trailing it by 15 kilometers, but, despite reading various online tutorials, watching youtube videos, etc. I'm still not getting it: How do I close the gap without completely ruining my orbital characteristics? When those "Intersection 1", "intersection 2" lines come up, which way should I be burning my engines to close the deal? How close do I need to be before I go into "docking mode?"

Edited August 14, 2014 by Algomeysa

[Taki117]

Ok, if you are trailing by 15km you should burn Orbit prograde just a tad to lower your orbit (Not so much that you clip the atmosphere, that would be bad) then when the close approach nodes come up put a maneuver node on the purple one (This is generally the one I adjust for) so that you have plenty of time until intercept. Play around with the different handles and see how it affects your orbit. If you can get within 2km that's good, if you can get within 1km that's better, and if you can get to .2km that's perfect. After executing the node you should be no more than about 5km from your target, at that point you want to zero your relative velocity and burn towards your target (The pink circle) a general rule of thumb is no more than 1/100th your distance in speed. For example, if you are 1km away you shouldn't be moving more than 10m/s.

[LethalDose]

Ok, if you are trailing by 15km you should burn Orbit prograde just a tad to lower your orbit (Not so much that you clip the atmosphere, that would be bad)

I think you meant burn retrograde to lower your orbit. Burning prograde will raise your orbit, and ultimate increase the gap.

[Taki117]

I think you meant burn retrograde to lower your orbit. Burning prograde will raise your orbit, and ultimate increase the gap.

I did mean retrograde, thank you for catching that. Truth be told, either method would work, but burning Orbit Retrograde would be faster, allowing you catch up in fewer orbits and with less expenditure of dV.

[Mr Shifty]

If you're only 15 km away and your orbit is identical to the other vessel (relative velocity ~ 0 m/s), just point your vessel toward the target marker on the NavBall and burn to increase your speed toward the target.

[Kryxal]

That's the fast way but wasteful of delta-v ... you should be able to adjust your orbit to land right on top of it in an orbit with a small retrograde burn.

[Blind Dead McJones]

15km is still a bit too far to do the docking approach. 10km is about the limit. Like everyone else said, you still need to do a very small adjustment to rendezvous and put yourself within 10km or so (even closer if you can manage).

[Alias72]

I assume your in LKO (Low Kerbin Orbit.) and so everyones statement is perfectly adequate but I thought I might add something.

If you and the target are in a higher orbit then you can attempt a docking approach from farther out. the reason is that the greater your orbital radius the more linear your system becomes. If you are ever trying to perform an intercept between two deep space vehicles you may be able to begin a direct approach method from as far away as the mun is from Kerbin.

[impyre]

For rendezvous:

1. Match orbital inclination. (While intercepts can be done at odd angles {I've done it plenty}, it's much easier to plan intercepts if the inclinations match.
   
2. Get your orbit to line up in at least one point with the target orbit. This is easiest if your Pe aligns with their Pe, or Ap to Ap. If it isn't perfect, that's fine because you can fine tune in a bit.
   
3. Set a maneuver node at the target altitude.
   
4. Adjust prograde/retrograde until the closest approach is within 10km. Then shift the node left or right to fine tune it. You should be able to easily get within docking distance (<2km) that way.
   
5. Execute the burn.
   
6. Travel until near the closest approach, then (using the target navball) kill relative velocity and fine-tune approach.
   
7. Tips: Treat the final approach as you would a landing. Don't come in too hot. Orient to retrograde, and burn "outside" of retrograde. (This is because burning near the retrograde marker tends to "push" it away from the current heading.) You want to try to keep the retrograde marker closely aligned with the target retrograde marker. Also, RCS will make fine-tuning of intercepts much easier. Also, you can use thrust limiters in place of rcs to allow for fine-tuning.
   

Edited July 29, 2014 by impyre

[MarvinKitFox]

Tip.

Don't try to enter the identical same orbit.

Go for one that has the same inclination, same shape, but is about 1km lower.

You will be moving very slowly relative to your target, but constantly gaining orbital position on it.

(bigger altitude difference will make the difference in speed greater, making for a quicker but less neat intercept)

If you are behind and want to catch up, you want to be a bit lower in orbit.

If you are ahead and want your target to catch you, you want to be a bit higher.

Just a bit, mind you.

Once you are closer than 10km (messy) or better closer than 2.5km (in physics range) you can just aim right for target and give a gentle nudge.

[LethalDose]

Tip.

Don't try to enter the identical same orbit.

This is what I usually do: go into a different orbit. It actually makes things trickier.

If I'm launching from the surface to a rendezvous, I'll let the target go over head, then launch into a lower orbit in the same plane to catch up, then rendezvous with a simple Hohmann transfer

If I'm getting captured around the same body the target is orbiting, I'll match orbital planes with the target, reduce periapsis to be tangential to the target's orbit (touching at just one point), then burn retro at periapsis so I meet up with the target in an orbit or two.

At 15 km, you could burn straight at the target. It probably won't be very efficient, but it'll get you there.

[Maelstrom Vortex]

Am I the only one who doesn't use nodes and just flys by navball?

[impyre]

I use the navball by itself 90% of the time. But i also use enhanced navball and kerbal engineer, which allows you to keep a pretty good eye on things. I only use nodes occasionally, but when explaining things like this I always suggest maneuver nodes first, and navball as a tip/hint because it's where I started (and because not everyone uses enhanced navball mod).

[Oafman]

I often RV without creating any nodes, as eyeballing simple hohmanns is not hard, but I'll always use the map for the closest approach markers. In fact, I basically do the whole thing on the map screen, until I get within a few km.

Re the OP, it is of course very tempting, when you're learning how to RV, to first try to put yourself in the exact same orbit as your target. I bet most of us did it the first few times - I certainly did.

But it's the wrong thing to do. The only time you should be putting yourself in an identical orbit to your target, is when you are in exactly the same place as your target - ie when you perform the final touches and move in very close. As others have said, the first thing you should actually do is to match planes. Once that's done, everything gets so much easier.

[Algomeysa]

Thanks for the tips, all. I tried to utilize your advice ---- and, I also realized, sometimes it's just being more patient, slight differences can add up if you don't mind sped-up orbits for several days. Of course, if KSP ever institutes air/food/water limits, that might be a problem....

Now I'm within a few hundred meters. I just have to figure out how to dock.... back to more youtube videos.

-------------------

In this instance, what I'm trying to do is dock in low-orbit with a refueling station, in order to gas up for an eventual Kerbin escape into solar orbit.

Maybe I should be aiming higher; put the refueling station higher, somewhere between low orbit and the Mun, and then dock with it.

[DasValdez]

Thanks for the tips, all. I tried to utilize your advice ---- and, I also realized, sometimes it's just being more patient, slight differences can add up if you don't mind sped-up orbits for several days. Of course, if KSP ever institutes air/food/water limits, that might be a problem....

Now I'm within a few hundred meters. I just have to figure out how to dock.... back to more youtube videos.

-------------------

In this instance, what I'm trying to do is dock in low-orbit with a refueling station, in order to gas up for an eventual Kerbin escape into solar orbit.

Maybe I should be aiming higher; put the refueling station higher, somewhere between low orbit and the Mun, and then dock with it.

404 Represent! (heh)

You can keep docking simple... go to the target ship (press "]"), right click the docking port and choose "control from here". Point that puppy straight N (0 degrees) on the navball.

Go back to your docking ship (press "["), right click the target docking port and do "set as target".

On the docking ship, control from it's docking port, and point it straight south (180 degrees).

Now, get "above" ("north" of) the target ship, line up the middle of the nav ball with the pink target market, and nudge "down" towards the target at around 1ms. When thing's go crazy and start wobbling without your control, turn off SAS (press "t") and take your hands off the keyboard. Seriously. If you were close enough with your alignment, the ports will mag-latch and the view will zoom out to a single happily larger orbital object.

For a fueling station, if you're just starting out you may want to park it at a bit higher orbit (100-120k) to give you some wiggle room below and above your station... that will allow you to go into relatively lower orbits (to catch up) or higher orbits (to let it catch you). Running a station right on the edge of atmo means your ships will need less m/sdv to get there, but you won't have any margin to catch up if your launch puts you trailing the station.

[Sirrobert]

Orbital mechanics are funny sometimes

To catch up with something, you need to slow down a little (to get in a lower orbit, which moves faster than the higher orbit).

And to let something catch up, you have to speed up

[Alshain]

Thanks for the tips, all. I tried to utilize your advice ---- and, I also realized, sometimes it's just being more patient, slight differences can add up if you don't mind sped-up orbits for several days. Of course, if KSP ever institutes air/food/water limits, that might be a problem....

Now I'm within a few hundred meters. I just have to figure out how to dock.... back to more youtube videos.

-------------------

In this instance, what I'm trying to do is dock in low-orbit with a refueling station, in order to gas up for an eventual Kerbin escape into solar orbit.

Maybe I should be aiming higher; put the refueling station higher, somewhere between low orbit and the Mun, and then dock with it.

Once your within 200m, you can target a docking port by right clicking it and right click the docking port your docking with and choose Control From Here. This will adjust the orientation that appears on the Navball, unless it's already along the ship pods alignment. Use the I, J, K, and L to move up down left and right instead of rotation (youtube videos will gloss over that). H and N move forward/back.

[Pixel of Life]

First of all, you want to get your initial encounter as close to perfect as possible. Practice this, because it really makes things so much easier. I can get my closest approach to within 1km pretty much every time.

Next, as you're about to hit the closest approach point, cancel your relative velocity. Burn towards the target until your closest approach has decreased by a couple hundred meters. Cancel relative velocity again when you hit the closest approach. Repeat until you're close enough, then use RCS to execute the actual docking maneuvers.

The trick to getting a perfect orbital rendezvous is making lots of small adjustments. Overly aggressive maneuvering is a sure-fire way to throw your orbit out of whack. Just take it nice and easy - as you get more experience you will learn to do it more quickly, and at some point it just becomes second nature.

[kfunk]

For rendezvous:

7. Tips: Treat the final approach as you would a landing. Don't come in too hot. Orient to retrograde, and burn "outside" of retrograde. (This is because burning near the retrograde marker tends to "push" it away from the current heading.) You want to try to keep the retrograde marker closely aligned with the target retrograde marker. Also, RCS will make fine-tuning of intercepts much easier. Also, you can use thrust limiters in place of rcs to allow for fine-tuning.

from boating... approach the dock at the speed you'd like to hit the dock

[O-Doc]

Am I the only one who doesn't use nodes and just flys by navball?

I find this easy to do from launch to docking. It requires you to understand what is going on with the navball. Everything else is "training wheels" to help visualise what going on in the navball. Here's my foolproof guide to using navball to dock.

NB: Technical terms not used.

To head towards the target be in target mode and burn half way between the open(no x) pink circle and the closed(with x) yellow circle. When the closed yellow is on the open pink circle burn on that to speed up or flip 180 degrees and burn to slow down. This is all you need to know to get a rendezvous AND to dock. Once you get used to this mechanic then you can refine the process to take into account your angular velocity to increase fuel efficiency throughout the process.

Edited July 31, 2014 by O-Doc

[Algomeysa]

And thanks for the tips on docking, all. After a lot of effort, I did manage to dock. I got within 2 kilometers, killed my velocity. Closed the gap with the RCS H key, mostly. Sometimes with a little regular thrust. Then I kept killing my velocity. I'm sure I was doing it pretty inefficiently, and I was running on fumes. So I switched to the fuel tanker, turned on its auto-grabber, and did the same from that end. Eventually, I did manage to dock.

Transferring fuel is amazingly satisfying. I managed to fill up my main tank plus the two boosters I never jettisoned.

Then I separated the ships, and moved the tanker to a safe distance.

Just one problem.....my beautifully-refueled ship, I'm just drifting, waiting for the optimum place to begin my burn....

So.....I started time-warp to speed things up a bit....

...and....and.....my ship instantly explodes?! Why?!

[fuzzdemon]

I understand this game is under development but I wanted to ask if this docking will ever get fixed, obviously there must be some bug when you dock bang in the middle and it just bounces off, once is understandable but 42 times is a p*ss take.

[LordFerret]

Algomeysa, before you time-warped did you turn SAS off? I've had a few ships which would develop wobble (space station too) with SAS left on. There's a few posts here on the forums about that. Also, are you sure your craft didn't collide with your other ship?... the one you thought you had moved safely out of they way? Been there and done that too.

[LordFerret]

fuzzdemon - What's your velocity/speed when your docking ports 'bang' together? I find all I need do is very slowly come to just within touching, and the dock ports attract and pull together (even with with very large ships).