rendesvouz for dummies (again)

[Clear Air Turbulence]

Sorry for bugging the forum with so many n00b questions. Feel free to ignore.

I have a simple rdzv question.

I have been able to figure out how to get into fairly close intersects. At the moment my space station and I are intersecting each other less than a kilometre apart.

But the velocity difference is a problem. If you intersect at only 1000 metres, but the other guy is traveling 150 - 160 m/s quicker, or slower than I, it's no help.

What's the best strategy?

Edited October 6, 2015 by Clear Air Turbulence

[Torgo]

When I'm closing in on my target, assuming I'm travelling faster, I'll point retrograde and burn until the difference in speed between my target and I drops to 0. Make sure to use the target function on the navball. If it says orbit, click on it until it says target. You need a target selected, of course.

If your target is catching you, you burn prograde instead.

Once down to 0, use the target indicator on the navball. Burn towards it at a slow rate. Then burn retro as you get closer. You can get right up close using this method. The key is to make sure you have target relative speed selected.

[Clear Air Turbulence]

Wow, thanks. I will try.

This is fun. I am running without mechjeb. It kind of ups the stakes

[Torgo]

I use Mechjeb now, but made sure I figured out how to do it on my own. Outside of actual docking, rendezvous is the toughest thing to learn. You really need to think 4 dimensionally to make it work right. Quick save will be your very best friend in the world while you figure it out.

[Starhawk]

The navball is the key.

Once you are approaching your target, but not yet at the closest point, do the following:

Make sure the navball is in target mode. (Click the speed indicator to switch modes).

Point retrograde (the navball is showing you your relative velocity to the target).

Burn when the target is near to closest approach.

Watch you speed indicator - your goal is to bring the relative velocity to zero.

Once you are 'stationary' relative to your target you can maneuver closer if needed or use RCS and proceed to dock.

Happy landings!

[Harry Rhodan]

Once down to 0, use the target indicator on the navball. Burn towards it at a slow rate.

http://forum.kerbalspaceprogram.com/threads/92480-Illustrated-Tutorial-for-Orbital-Rendezvous

Look at point 7. It's much more efficient to push your retrograde marker onto the target's retrograde marker or the other way around..

[Kryxal]

Doing it efficiently comes after learning to do it at all, but it's nice being able to combine the steps - that is, slow down AND make the intercept closer at the same time.

[Alshain]

Doing it efficiently comes after learning to do it at all, but it's nice being able to combine the steps - that is, slow down AND make the intercept closer at the same time.

Learning it the right way in the first place prevents you from learning bad habits the wrong way that you just have to break later.

It isn't any harder than the "full stop" method so you shouldn't learn the full stop method. You spend fuel to stop and then spend fuel to get going again, or you could spend less fuel adjusting your heading. It's really a no brainer. Don't bring your velocity to zero, just push the retrograde on the target retrograde and keep it there while slowing down as you approach. Real easy.

If you want to talk learning to be better later, getting a rendezvous before establishing an orbit at all is the next step. That is actually quite a bit more difficult, you have to wait for the target to be in just the right place before launch and then find your rendezvous while ascending and then slow down very quickly to establish your orbit as you approach. It is quite the challenge and I do not suggest it for beginners until you understand fully how the closest approach markers on your orbit work and change as you burn. However, this is how it is done in the real world. They don't establish an orbit and then spin around the planet a dozen times till they get close.

Edited September 29, 2015 by Alshain

[Scarecrow88]

The bigger the difference between your two orbits, the bigger the difference in speed will be at the point of intersection. Unfortunately this is a double edged sword, because if your orbits are too closely matched while your craft are some distance apart it will take longer to get the intersect.

[Clear Air Turbulence]

Thanks for the advice. I have managed to get within 40 m of my space station, and we are at rest relative to each other, so I guess now it's time for docking to begin.

One question: from time to time in the approach, with SAS enabled, I find that my prograde, retrograde, target and anti-target markers go dead. I can't click on them. SAS is still working, and I have full electric charge. Then they suddenly appear again. Why would that be?

[OhioBob]

One question: from time to time in the approach, with SAS enabled, I find that my prograde, retrograde, target and anti-target markers go dead. I can't click on them. SAS is still working, and I have full electric charge. Then they suddenly appear again. Why would that be?

I've noticed that that often happens when the velocity relative to target goes to zero or near zero. It usually comes back as soon as I give the vehicle a little impulse. Don't know why it happens or how to avoid it.

[Superfluous J]

It happens because if you're going really slowly compared to the target "prograde" will swing wildly around as your craft turns to aim at it, causing your craft to turn towards where it has moved. Which will of course cause it to swing wildly the other way, causing the craft to turn into the new direction.

You can't avoid it because doing so would at best waste monoprop and electric charge, and at worst shake your ship to bits.

[dborgo]

I find that when intersecting orbits are very different, and thus very high relative speeds to each other at the intersection, the best way to cancel that relative speed is to place a maneuver node at the point of intersection. Then use the maneuver node to match your vessel's orbit with the orbit of the ship you are rendezvousing with. By manipulating the maneuver node, you should be able to place your periapsis and apoapsis right on top of the targets periapsis and apoapsis. Make sure the ascent and descent nodes are zeroed as well, and make the burn when you reach the maneuver node. You will now be on nearly identical orbits and now can make fine adjustments for the approach and docking. Usually you can switch to making small RCS burns and translations (IJKLHN keys) to keep your velocity vector on target.

[ibanix]

To save yourself a huge amount of time when doing final approach docking, I strongly recommend the Docking Port Alignment Indicator mod.

Short version for using:

1) Rotate the craft until the large orange cross-hair is dead center to the targeting brackets

2) Use the IJKL RCS keys to push the prograde/retrograde marker toward the direction of the yellow lines

3) Slowly move the prograde/retrograde marker back toward dead center as the yellow line approach the center

4) Zero out the yellow lines on dead center

5) Use H or N RCS keys to approach and dock

[Lukaszenko]

Also the Kerbal Alarm Clock mod has a nice function (closest approach) to help you speed up the intercept. Set your target and then set an alarm for closest approach. It scans the next few orbits (you decide how many) and tells you how far and when you will be. If there is no reasonable distance in the upcoming orbits, I usually warp to the point where orbits intersect and burn pro or retrograde and watch the distance indicator change in real time until it gets to where I want it. Then I set the alarm a few minutes early and change to some faraway spacecraft that allows me full warp. This probably works best when orbital planes match, btw.

[Clear Air Turbulence]

To save yourself a huge amount of time when doing final approach docking, I strongly recommend the Docking Port Alignment Indicator mod.

Short version for using:

1) Rotate the craft until the large orange cross-hair is dead center to the targeting brackets

2) Use the IJKL RCS keys to push the prograde/retrograde marker toward the direction of the yellow lines

3) Slowly move the prograde/retrograde marker back toward dead center as the yellow line approach the center

4) Zero out the yellow lines on dead center

5) Use H or N RCS keys to approach and dock

I will check it out! thanks!

[Friend Bear]

Sorry for bugging the forum with so many n00b questions. Feel free to ignore.

I have a simple rdzv question.

I have been able to figure out how to get into fairly close intersects. At the moment my space station and I are intersecting each other less than a kilometre apart.

But the velocity difference is a problem. If you intersect at only 1000 metres, but the other guy is traveling 150 - 160 m/s quicker, or slower than I, it's no help.

What's the best strategy?

This is most common, especially when approaching quickly (as opposed to making many orbits and slowly coming into contact). 150m/s is not that hard to kill. You might be trying to burn it too late.

Also, in conjunction with the instructions below, if you end up being at 0m/s relative to the target even 3000m away, just point at it and gun it at 50m/s or slightly faster, time warp, repeat as you get closer (since, because both of you are orbiting and rotating around each other, you will not always head directly towards the target). That is why when you are far away, a higher speed when trying to go straight to it is important. Only difference, however, is at higher speeds, you are doing a lot less trimming, discussed below, and doing a lot more point at target and forward thrust, then, when you are starting to move away from the target, pointing at retrograde and thrusting until 0m/s again; rinse, repeat.

This is also why the movie Gravity was wrong when she thought she could point and move towards something 300 miles away at a low speed...One of the many things wrong with that movie. How difficult is it to ask an astrophysicist before spending millions on something outrageously lame and off. K done, sorry.

All you need to do is:

1) make sure the target station is targetted.

2) make sure the m/s section on the navball says "Target" (you can change it one of two ways. If there is something targeted, it does so automatically when you are within something like 4000 m, or you can simply click that little window until it says "Target")

3) point at your new retrograde. This retrograde will be your movement/forward momentum relative to the targeted vessel.

4) burn as you get close. Do a slow burn a few hundred m out to gauge but as you get on top of it, kill your momentum and have your m/s relative to the target read 0.

Then, docking:

I'm just going to copy/paste what I posted for someone about docking here so ignore the numbers, I'm too lazy to edit:

It took me a second to realize but your prograde is everything. Once you figure it out, docking is as simple as a letting a cow stand in the middle of a room that is exactly the size of the cow, and the room doesn't let the cow sit or move in any direction.

1) Target your destination.

2) Rendezvous using thrusters and get within 500 or fewer meters from target.

3) Right click on the docking port you want to connect to (on the other vessel) and select it as the new target.

4) Aim at retrograde and kill your thrust. Depending on your vessel mass and your thrust to weight, you may use main thrusters at low or RCS. Only go towards it.

5) Aim at the new target (or any direction you need to go to make it to that target, if the vessel happens to be large and you need to make your way around it, for example).

Here is the magic:

When you are at low speeds relative to the target (5 m/s or fewer (higher is possible, too)), you do not have to turn to face the retrograde/prograde to make it an as perfect as possible forward movement. In fact, turning too much, with or without RCS, changes the direction of travel a lot of the time.

Instead, point at the direction you want to go, period; whether that is the target or beyond it.

Make your prograde aim that direction as much as you can by engaging thrusters/RCS forward ONLY. Try to stay under 10m/s. If you are not heading directly towards that target and you are heading, say, just left of it, then engage your linear, left facing RCS to correct your forward movement and scoot your prograde over into the direction you are facing/want to travel. As you slow down when you approach, you start having to micromanage in the same way.

(FYI: In docking mode, Linear is when the button under staging is blue, the other is green and this allows you to turn the vessel rather than scoot up, down, left, right without harming forward movement or needing to change the direction you are facing)

Heading downward when you don't want to? Use your downward facing RCS.

If I remember, the new keymapping will have you using WASD, Shift, and Ctrl for docking procedures. Space bar switches between blue and green mode (linear vs whatever the other one is).

Poof! (magic)

6) Re-aim and re-adjust as necessary to dock.

7) Make sure SAS is turned off when trying to connect to the other port, but have it on the rest of the time.

*Also, if I have to turn, I like to turn off RCS and use only reaction wheels. This reduces the amount your ship changes its forward direction.

Docking port alignment indicator is really nice to have, but when you dock as much as some of us have, it is unnecessary, except for large craft where you camera angles make it hard to tell whether you are actually pointed directly at the docking port. But this is combated with the ability, even necessity, of right clicking and selecting the target docking port as the target, not just the target vessel. This makes is so when you point at the target in the navball, you are pointing directly at the docking port.

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For some reason I can't turn of Italicized and I don't want to retype it =P. Sorry.

Edited October 1, 2015 by Friend Bear

[Clear Air Turbulence]

Thank you. I found that the points about really understanding the navball & what the prograde/retrograde markers do in tracking mode really helped. slowly, rendezvous is becoming a much easier thing to do!

[eddiew]

Nobody seems to have said this yet, but remember you can have your station point its docking port towards yours. Just switch to it, set your ship's port as target, and turn it prograde. Then you can turn your ship to point straight at the station and go in for docking - assuming your docking port is on the axis of thrust

Yet to need any kind of mod assistance when using this method, and usually don't need RCS. If you can have the station hold target automatically with SAS, that's even better ^^