Decent Renevous Tutorial? No Official Manual?

[GungaDin]

I've learned how to get into orbit and even change the shape of my orbit by scouring through Youtube videos but have struggled with rendezvous. I hate having to pick and choose from Youtube videos not as they waste a lot of time and are often very incomplete. Isn't there any kind of official source of information for simulation? For instance - what IS an ascending node and a descending node? How are they supposed to work? In the videos I've watched I get to a certain point and the guy drags the mouse somewhere and shouts - 'there ya go!' with no explanation for what he has just done. Grrrr!

[Talisar]

[GungaDin]

I've looked at Scott Manley's tutorials and they are a good example of what I mean - he seems like a nice and smart guy but never says what the various nodes are intended for and when he does something he says, "there your go, just mess around with that until it's right."

So I'll ask a direct question here : ascending and descending nodes appear once you have selected a target - are they optimal points to establish a new maneuver when attempting a rendezvous?

[Mr.Rocket]

I'm pretty sure ascending and descending nodes are only the right place to change your inclination relative to the target. That just seems what it does for me. Not sure about that here. For rendezvous, once the craft have the same orbital inclination, i only use the prograde and retrogade markers depending if i'm in front or behind the craft in orbit. Those are the green markers in the manuver node.

[Borogove]

So I'll ask a direct question here : ascending and descending nodes appear once you have selected a target - are they optimal points to establish a new maneuver when attempting a rendezvous?

Two orbits around the same massive body each lie in their own plane that passes through the body's center of mass, right? If the two planes aren't perfectly aligned, they meet along a single line. Where that line crosses one of the orbits are the ascending node and descending node.

The ascending node is where the path of an object in one orbit crosses the other orbit in a more-northerly-than-not direction, i.e. it's going up, ascending. The descending node is on the opposite side where it crosses southerly. (North here is a vague direction implied by the planes of all the bodies in the system and the direction they orbit.)

The importance of the AN and DN is that they're the places you can change the plane of one orbit to align it with the other orbit. Manuever from anywhere else and you can't get the planes to match. So at the AN, you want to burn down, southerly, towards the 180 on the navball; at the DN you want to burn up, northerly, towards 0 on the navball. Once you get the relative inclination down below about 0.1 degree, the orbits are basically in the same plane; perfectionists will want to get it to 0 degrees (or, as KSP sometimes reports, to NaN).

This doesn't mean the orbits are the same size, or the same eccentricity, or that the bodies in the orbits are in the right phase for a rendezvous -- just that they're orbiting in the same plane.

The wikipedia page (http://en.wikipedia.org/wiki/Orbital_node) assumes that you're talking about one orbiting body and treating the equatorial plane of the Earth (or whatever) as the other plane, but the principle is similar.

[Cashen]

Let's assume you have two craft in basically circular orbits with different altitudes and aligned in the same orbital plane (as per what Borogrove said above: you MUST have your planes aligned before you can perform a rendezvous.).

Let's assume that the vessel you control is in the lower orbit, at say 80km above Kerbin, and you want to rendezvous with another vehicle in a 120km orbit.

Create a maneuver node anywhere on your orbit, and drag the prograde marker (thrusting in your direction of travel) out until you raise your orbit's apoapsis until it's tangent to your target's orbit. Make sure you "Set as Target" the other vehicle. Then, click and drag the manuver node around on your orbit until you get the encounter markers to line up. You can then do some fine tuning to the node to get the approach distance 0.1km or 0.0km or so.

If you can't get the markers to line up anywhere, wait one full orbit and try it again. Remember that from a lower orbit, you need to catch up a little to the target, but still be behind them. If you're in front of them, you'll have to wait a while. When transferring to a target higher up, you'll want to start from behind them. I usually launch my second vehicle when the target vehicle is already between about 1/8th and 1/4th of an orbit past KSC.

Perform the burn once you have the encounter lined up.

Assuming you did the burn correctly, you're going to get within about 100 meters of the target. If not, you can do a tiny adjustment node about half way there (likely using RCS) to get the encounter closer. This is one you might just have to play with to see what effect the various node markers do.

Creating a note isn't always necessary for when you reach your target, but it can be helpful to see what kind of delta-V and burn time you'll need. More or less, your Navball will now be reporting velocity relative to target, and your prograde and retrograde markers will be in the relative velocity vectors. So you'll want to point yoursef in the retrograde direction and when you reach your target, burn until relative velocity is zero. Celebrate because you performed a rendezvous.

I have much less experience with performing a rendezvous from a higher orbit, but basically you'll want to be slightly in front of the target and you'll be adjusting your orbit down to meet them, so burning retrograde. Everything else more or less applies though. About 80% of my rendezvous experience is from low to high in Kerbin orbit, though I have done some from high to low to reach my stations in Mun and Minmus orbit.

Edited December 31, 2013 by Cashen

[federicoaa]

When you select the target, some extra indicators will appear in the navball. First, you will have the target vector in violet (showing the prograde and retrograde), and in you click the relative to target instead of orbit/surface you will have velocity vector relative to the target, this vector is important when you want to match speeds, as you have to burn retrograde until relative speed is 0.

So, first step to rendezvous is to match the inclination and get into a "phase orbit" (an orbit lower or higer than the target's orbit so you can catch up).

Second step is to intersect the orbit and have an encounter. The most fuel efficient way is with a hohmann transfer, but you can just play with a node until you get an encounter less than a few km.

Third step is to match velocities at encounter. Wait until you are near the minimum separation and burn in the relative velocity retrograde until velocity is near 0

Fourth step is to get closer. Point to target prograde and increase the speed to a few m/s. If you are farther than 1km then go to 20 m/s ~ 50 m/s otherwise dont go faster than 10 m/s. Once you get near, match velocities again (step 3)

Repeat step 4 until you are around 20 m away

[capi3101]

The ascending node is the point at which a craft's orbit crosses a reference plane moving in a direction normal to the reference plane; the descending node crosses moving in an anti-normal direction. They are the most efficient points at which to align the planes; you do it by burning anti-normal (upside down triangle with spokes) at the ascending node or normal (triangle with a dot in the center) at the descending node. More simply, assuming you're in a 090 prograde orbit (i.e. flying east), burn north at the descending node or south at the ascending node.

So for rendezvous, here's what you do:

1) Target your target. This way you'll get the approach chevrons.

2) Adjust your plane until your nodes get to 0.0 degrees - if you get it to NaN degrees, you're spot on. You should have the chevrons for sure at this point.

3) Note the distance of closest approach.

4) At the next apses, set up a maneuver node. Pull prograde and see what it does to your distance of closest approach. If the distance increases, stop and pull retrograde instead. Keep pulling until the distance starts increasing again. If you had to pull retrograde, watch the resultant distance of the periapsis - in Kerbin orbit, you want this to stay above 70,000 m (of course).

5) Repeat this process at the next apsis. Keep this up until you can't make any meaningful adjustments at the apses.

6) If you still don't have an approach within 2,250 m, try making adjustments between the apses, or make a few orbits and see if you can get the distance down. Be ready to adjust at the apses once more.

Try those steps and see if that helps you make the rendezvous.

If you're trying to dock:

1) Once you make rendezvous, burn to reduce your relative velocity to the target ("Target" on the speedometer) to zero. Try to do this as close to the target as possible.

2) Once zeroed, turn to face the pink meatball on your nav ball. Do this on pod torque only; don't use RCS if you can at all help it for this stage.

3) Thrust ahead and watch your distance. Keep your speed to about 0.1 m/s per 10 meters distance (but don't worry too much about this).

4) At 500 meters, zero your relative velocity, realign on the meatball, and thrust ahead.

5) Do this again at 100 meters and 50 meters. At 50 meters if you have not done so already, target the specific docking port you're aiming for. Start using RCS at this point for velocity changes only.

6) At 20 meters, zero out and realign again. Switch to the target craft, set your control point to its docking port, target your source craft's docking port, and align on the pink meatball. Again, do this on torque thrust if at all possible. One you're on the the money and not moving, set the target's SAS on and switch back to the source craft.

7) Retarget the other craft's docking port and set your control point to your docking port. Once you're aligned, go to 10 meters, zero and realign once again. Do it again at five meters if necessary. Keep it slow and steady.

8) Once you're within a meter or two, your docking ports will start attracting one another (provided they're the same size, of course). They'll pull one another in. If there is any remaining misalignment, the two craft will dance a bit with one another but they will ultimately settle down. When the camera shifts, you're docked.

[DennyC]

I agree that it is annoying to have to rely on videos or forum posts to deal with specific questions. These media are great for learning as much as you can about this very captivating and educational game, but they compete with the time you could be doing the game, let alone time needed to deal with life. Several times I have watched 30 minutes of video trying to deal with a single question, and instead gotten a pile of information that is useful, but still leaves me with the original problem. I use the wiki, the videos, the Drawing board and others, spending more time there than in flying. Perhaps someday (months in the future) I might make contributions myself, but I sorely miss a single, centralized "lookup" with text, graphics, a good index and table of contents. I recognize this is not easy to do well, and doing it badly would not be worth the effort. But it would add value (think: $) to the game.

[Soda Popinski]

Not the most efficient way to rendezvous, but conceptually the easiest way. What you'll do is match orbits with each other, then either slow yourself down or speed yourself up at some point to ensure you get a rendezvous point on the next orbit at the spot you burned at.

0) Circularize your target's orbit, using CAPS LOCK (lowers thrust) with prograde / retrograde RCS thrusts (H & N keys) to get it as circular as possible. Note the altitude.

1) Switch back, and set your target

2) Make a maneuver node at the next ascending / descending node, and grab the normal or antinormal (purple handles) and drag up or down until you get 0.0 inclination at the green tabs (or NaN). Your inclination now matches

3) Circularize your orbit at the same altitude as the target (matching orbit, but you'll be behind of ahead)

4) Pick ANY spot along the orbit (preferably on the lit side), and set up a maneuver node or just start burning prograde (if the target is behind you) or retrograde (if the target is in front of you), until the encounter tabs give you a close encounter of less than 1km (0.2 or less is best). Use CAPS LOCK with RCS burns to fine tune it (H for prograde and N for retrograde). Don't burn so much you either dip below the atmosphere (periapsis < 70km) or so far you escape out of Kerbin's SOI (very hard to do as you'll be burning for at least a minute).

5) Once you're at your encounter you'll have to rematch your orbit. You can set up a maneuver node at the intercept point, and drag prograde / retrograde until orbits match, so you should hit a relative velocity pretty close to 5 m/s or less.

6) Switch from map view, and determine if you are heading towards or away from your target. If away, make sure your navball is set to target, and point towards the retrograde marker and burn until it flies off the side - you'll now be heading towards your target. If heading towards or once you are aim towards your target pointing at the purple circle

7) Use RCS thrusters to get the yellow prograde mark in the middle of the purple circle (thrust in the opposite direction of the yellow mark - so if the mark is on the right, thrust left)

8) Adjust approach speed to about 1/100 of your distance - so if you are 500 meters away, approach at about 5 m/s. 100 meters away, 1 m/s.

I also highly recommend getting Navyfish's Docking Port Alignment Indicator. I feel this game really should have this rather basic tool.

[michaelhester07]

I'll throw my method into the mix too.

1. Circularize your orbit at about twice the altitude of your target. It doesn't matter if the target's orbit is circular. This altitude is if you're impatient (which I am). You can go lower if you want to save fuel.

2. Set the object you want to rendezvous as your target. Your map will gain new markers on the orbits. Two of them are "AN" and "DN".

3. Match your orbital planes: Set a maneuver at the AN or the DN node (whichever comes up next) and drag the purple spike on the maneuver up or down until you get the AN and DN to flip sides. That is if you put your maneuver at the AN it switches over to DN. Then slightly drag the spike the opposite direction until the nodes are at a 90 degree angle to where they were.

4. Do the maneuver you planned in part 3.

5. Look at the planet or moon you're orbiting from top down, when you put your craft at 6 oclock and your target is at 8 oclock add a new maneuver just behind your ship in its orbit direction. Drag the retrograde spike until your orbit crosses the target's orbit. You'll see new bugs on the map: The orange ones mark when you first intercept the orbit and where the target is at that point, the purple ones mark when you second intercept the orbit. If they're pink you'll have one intercept. Each marker comes in 2 parts: where you'll intercept, and where your target is. Mouse over them to see which is which.

6. Adjust the position of the maneuver until the bugs are lined up vertical for one of the intercepts. If you mouse over them you'll see the separation. Get this to be at most 10km. If you can't get the bugs to line up advance your orbit half way (time warp) then try again.

7. Perform the maneuver from above.

8. Watch now as you approach the intercept. When you're within 50km of your target the navball speed will switch over to "target" mode. Wait a little longer until you're within 20km of your target.

9. Turn your ship to thrust towards the retrograde marker on the navball (the green one with an X in it). Thrust until target speed is less than 10m/s.

10. Turn your ship towards the target (large circular purple marker) and thrust slightly. Aim on the opposite side of this marker to line up your prograde marker (green, no X) with the toward target marker when you thrust. Once the markers are lined up thrust directly towards the target until 20m/s. Timewarp till you're within 500 meters. If the markers drift apart stop your warp and thrust to re-align them. If you're over 20m/s turn towards the retrograde side and thrust on the side of the Rg marker away from the "away from target marker" to move your retrograde vector towards it.

11. Once you're within 500 meters thrust toward retrograde to zero out your target velocity.

Docking:

12. Target the docking port, and press the V key until you get the chase camera. Align the camera to the front of your ship. Now you can aim it as you were moving the navball.

13. RCS: activate docking mode and RCS. If your ship doesn't have RCS this is a little trickier but doable. Put your ship about 40 meters out from the docking port vector. If you draw a line from the center of the port directly out from it, that's where. Once you're there thrust to kill any velocity you have.

14. Aim towards the docking port: Line up the center of the navball with the target prograde marker (the same one from step 10 above). Thrust toward it with RCS. Use the "strafe mode" thrust on RCS to line up your prograde vector to the target prograde marker. You can turn your camera to the side when you're within 10 meters to see if you're gonna capture right.

15. If you're not going to get the capture thrust backward and let the ship drift to where it would capture, then thrust forward. make sure your navball progrades are lined up and you'll get the capture.

[Stone Blue]

You could try Blizzy's in-game Rendevous Tutorial....

http://forum.kerbalspaceprogram.com/threads/46232-0-21-1-Rendezvous-Tutorial-1-1-0

Blizzy also has a Docking Tutorial, as well as a Mun Tutorial that shows you how to get to another planetary body from Kerbin....

[pebble_garden]

You might find some useful information in my

videos, specifically Part 4 and Part 5. I strove to make the videos as brief and uncomplicated as possible, and show use of the maneuver nodes as a navigation aid.

My Miranda Project Part 1 may also be of help, as it gives a more thorough demonstration of my "pushing the marble" method of using the navball to fly a rendezvous. With this method you can fly to within a few meters of your target using only the main engines, saving the RCS for the final alignment and docking.

Edited December 31, 2013 by pebble_garden

[GungaDin]

Two orbits around the same massive body each lie in their own plane that passes through the body's center of mass, right? If the two planes aren't perfectly aligned, they meet along a single line. Where that line crosses one of the orbits are the ascending node and descending node.

The ascending node is where the path of an object in one orbit crosses the other orbit in a more-northerly-than-not direction, i.e. it's going up, ascending. The descending node is on the opposite side where it crosses southerly. (North here is a vague direction implied by the planes of all the bodies in the system and the direction they orbit.)

The importance of the AN and DN is that they're the places you can change the plane of one orbit to align it with the other orbit. Manuever from anywhere else and you can't get the planes to match. So at the AN, you want to burn down, southerly, towards the 180 on the navball; at the DN you want to burn up, northerly, towards 0 on the navball. Once you get the relative inclination down below about 0.1 degree, the orbits are basically in the same plane; perfectionists will want to get it to 0 degrees (or, as KSP sometimes reports, to NaN).

This doesn't mean the orbits are the same size, or the same eccentricity, or that the bodies in the orbits are in the right phase for a rendezvous -- just that they're orbiting in the same plane.

The wikipedia page (http://en.wikipedia.org/wiki/Orbital_node) assumes that you're talking about one orbiting body and treating the equatorial plane of the Earth (or whatever) as the other plane, but the principle is similar.

Thank you - thank you! I had tripped on the phrases ascending and descending as referring to whether the craft was in the process of 'lowering it's altitude' rather than 'lowering it's latitude'. This helps. So burn at those points in order to get the two orbits in the same plane. Got it.