help with docking tutorial - computing intersect orbit

[coder1024]

With the built-in docking tutorial, once you've aligned your orbit with the stranded vessel, you need to compute a maneuver so your orbit intersects the stranded vessel. I've tried experimenting with prograde and moving the maneuver point around and can never get anything which satisfies the tutorial step. The markers jump around like crazy making it hard to know how to manipulate them in order to get them to line up.

Any suggestions?

http://postimg.org/image/lcl9flrnr/

[micr0wave]

The red markers on your pic look pretty close to each other, fine tune your maneuver node to get them closer, once you have them close enough, execute your maneuver and coast to the point of closest approach (those red markers), there you match up speed with your target and start the docking process.

For more efficiency (i'm not the right person for that though) you could widen your orbit to just touch the target's orbit and then grab your node (clickhold in that white circle) and move it around to get a good intercept.

[vixr]

The center wheel on my mouse allows for some pretty fine control of the node...

[mhoram]

I would like to encourage you to learn about the hohmann transfer.

This is the most fuel efficient way to reach the target orbit (for simple cases like this one).

This basically means that your transfer orbit (the brown dotted line) has its Periapsis touching your current orbit (the blue one) and its Apoapsis touches the target orbit (the yellow one).

So I recommend that you reduce the burn amount of the maneuver node until it's Apoapsis touches the yellow orbit. This also means that the red markers are much further away from each other.

To correct this, adjust the position of the maneuver node to a later point on your current orbit, until the red markers are now closer to each other.

You might have to repeat this step until the red markers are close enough to each other.

Welcome to the forum!

[cephalo]

Keep in mind that in addition to adjusting the various burn directions, you can also drag the whole maneuver node along the orbital path. That's crucial for easily setting up a rendezvous. They don't mention that in the tutorial.

[Wemb]

I would like to encourage you to learn about the hohmann transfer.

This is the most fuel efficient way to reach the target orbit (for simple cases like this one).

The downside of the Hohmann transfer is that because your new Ap just 'touches' the orbit of the target, timing is even more important - so a Hohmann transfer will be cheap in terms of dV and an important and useful side effect will be that when you do meet the orbit of the target ship - and, hopefully, if you've timed it right, the target itself - circularising your orbit should put you into a matching orbit as that of your target - meaning that minimising your relative velocity with the target can be done in a familar and easy way.

So you lose the flexibility in choosing a more complex intersect (as in your original picture). You may need to orbit a few times before you and your target are in good positions to allow a Hohmann transfer.

MechJeb is good for demonstrating this.

Wemb

[Reactordrone]

You may also need to go forward an orbit or two to get a good intercept if you follow the tutorial directions so try clicking on the + symbol on the node after you've raised the apoapsis.

[DancesWithSquirrels]

I try to set an orbit that goes ever so slightly past the target orbit, with two crossings, then drag the node (white circle) around until I'm close. Then tweak the prograde or retrograde till my intersect is less than a kilometer. After executing the maneuver I play around with my RCS to get it even closer.

[TeeGee]

1) Get into a circular orbit that is smaller the the target

2) make sure you are on the same inclination. How you can check that out is to select your target in your map, set it as your target. You will see a yellow ring with the letters AN and DN. AN = ascending node, DN = Descending node. What does that mean? It means that at that orbit you are on, you will cross it and either head ABOVE it or BELOW it. Ascending means you'll be going ABOVE your targets orbit after that point and visa versa with the DN.

3) What you want is to make the AN and DN = 0 degrees. How to do this is to create a maneuver node at the AN or DN (it doesnt matter at all which one) that burns either UP or DoWN relative to the perpindicular of kerbins equator. This is called burning normal or antinormal. Just play with the maneuver node normal and antinormal until you see the AN AND DN get closer to 0 or NaN.

4) Once you match inclination, you should fast forward timewarp and watch your craft approach your target. Being on a LOWER orbit means you're moving FASTER relative to your targets orbit. This is because you are travelling in a smaller circle which means LESS distance you need to cover in comparison to your target.

5) Once you are RIGHT NEXT to your target, point your craft PROGRADE and do a very low level thrust burn until you see your map orbits CRISS CROSS, showing you those 2 symbol thingys, one is purple and the other is orange. This shows you your 2 closest approaches to your target ( you see 2 because you are in an ORBIT aka a CIRCLE, If you draw 2 circles that overlap you see 2 points where the circles intersect that is what those 2 arrows (purple and orange) represent).

6) KEEP CHECKING your closest approach numbers on either the purple or orange arrows until you get it as close to 0 km as possible. The means that at that point you will be 0 km away from your target.

7) Burn very slowly please. Make very fine adjustments, you don;t need to go full blast up in orbit to make a homan transfer.

8) Once you get 0 km ish seperation, wait until JUST before you reach that closest approach point on your map.

9) this is a part that is tricky. You need to make your RELATIVE speed to your target 0. On your navball you will see number on the top that have the words orbital and the number in m/s. CLICK this indicator until you see TARGET and a number in m/s, THAT is your relative speed to your target currently. That is what we want to make 0 m/s.

10) When you've clicked on the indicator and see target, your prograde and retrograde indicators MOVE to new spots on the navball. The shows you your HEADING in comparison to your target. Since you have a target relative velocity now AND your heading relative to your target, you can now match your orbit.

11) Point your craft retrograde and start burning SLOWLY as you get closer and closer to your closest approach. You'll notice that your relative target speed is DROPPING and that your orbit is starting to match your targets. DO NOT SWITCH your speed indicator to orbital or surface! Keep it on target!!

12) You'll also notice that your closest approach indicator is MOVING AWAY from you now. Whenever that happens, CUT your engine and wait until you get CLOSE again then burn. Keep doing this until your target speed indicator shows 0 m/s.

13) Congrats, you've rendezvoused.

14) Get out of map view.

15) Point your ships nose to your target. If you have SAS you can just click Target. TURN OFF your main engine. Turn ON your RCS and thrust FORWARD until you see the target indicator go UP to about 2 m/s. KEEP THE YELLOW PROGRADE marker IN the purple target marker. If you see it drift out, adjust with RCS to bring it back in.

16) As you get closer to your target, start to slow down to 1m/s then reach 0 m/s when you are about 12 meters away.

17) Docking is a skill you need to master on your own. My only advice to you is to make sure you are in LOCKED camera mode and try to orient your craft parallel to your target docking port OR switch to your target, take control of it, then point its docking port to your newly arriving ship.

18) Dock via RCS.

[rofltehcat]

Let me explain the intersect with images. Others have already explained it pretty well but I think with screenshots you'll probably have an easier time understanding their instructions. It is really just based on "low orbits go fast" and "high orbits go slow" (angular velocity).

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Picture 1: Create a maneuvre node (fire prograde) that increases your orbit to just about touches the target orbit in one spot. As you can see your target will be ahead of you quite a bit at the closest intersect. This is exactly how you want it when approaching from a lower orbit. (If you approach from a higher orbit you want it to be a bit behind you at closest intersect).

Pic 2: Execute that node, then warp to just after the closest approach.

Pic 3: You now see the next closest approach. As you can see at the next closest approach you would be very far ahead of your target. Thus you have to increase your orbit. The best spot to do this is your current contact point between your orbit and the target orbit. So you point prograde and fire your rockets to increase your orbit.

(Note: The tutorial bugged out on me because I did this manually, without a maneuvre node. You should probably do this with a maneuvre node designed so the outcome looks like in Pic 4, but I usually do this step without a node when not using mod auto pilots.)

Pic 4: This is how your next closest approach (or maneuvre node) should look. You can still fine-tune it but arriving at roughly 2 km is okay. You can then fast-forward to about a minute or so before the closest approach. (Note: Sometimes the closest approach still shifts but if it does it'll just mean you'll have to do more correction burns later. For the beginning this will suffice.)

Pic 5: This is taken near the closest approach. Note that the navball's mode is switched to target. The direction the ship is pointing in is set to retrograde. You can now fire your rockets until your relative velocity to the target is close to 0 (power down slowly when close to end). Technically, this already counts as a rendezvous for career mode quests but you'll have to still get closer before actually starting to use RCS.

Instructions for small ships (doesn't work that well for large ships):

So you'll be moving at roughly 0 m/s relative to the target and you'll be ~300 m - 2.5 km away. You then point your ship towards the target (on the navball, not by sight!) and accelerate towards it (green marker should be close to or inside pink marker) until your relative velocity is 8-12 m/s. Then you point your ship back to retrograde (so you can again eliminate relative velocity once needed). Wait a bit (you can do a slow warp but be prepared to abort it) and watch the distance to your target carefully. It should decrease. The instant your distance starts increasing again you gently activate your engine and eliminate relative velocity. Repeat these steps until you are just about 300 m or so from the target and moving at roughly 0 m/s relative velocity.

Then it is time to switch to RCS and the actual docking.

Edited July 17, 2015 by rofltehcat

[AaronLS]

Remember you can drag your maneuver around your orbit. Move it around and check intersection distances. You may need to add a very small amount of burn time or radial burn to get a crossing interesection depending on what part of your orbit you burn from of the target is not circularized.

Move it around till you see a close approach. If you dont see a close approach then you need to wait another orbit in the phased orbits to get closer. Note the plus button on a maneuver node when right clicking allows you to delay the node an extra orbit, however this is canceled if you drag the node.

So usually I get into the phased orbit, make a node that intersects, drag it around and tweak burn times to find the closest intersection.

I can usually get an intersection within 200m or 0.2km. Note the two orbits are very different, so what will happen is as I approach the target is use the navball in target mode to start burning retrograde but slowly enough that I'm letting the target still approach. You can burn angled out slightly from retrograde and you'll see the retrograde marker "pushed" towards the target marker. If you get retrograde marker lined up with target marker then it is coming straight at you. I usually dont line them completely because I dont want a collision.

If done right these two burns, first to create intersection, second to match target's speed (which will read 0m/s on target navball), will together get you on target's orbit ready for docking.

Edited July 17, 2015 by AaronLS