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Launch, rendezvous and docking


blizzy78

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(Note: I've also made in-game tutorial mods for rendezvous and docking. Perhaps these are more fun to you than to watch a silent video and read lots of text.)

Hi, I've made a video showing how to launch a spacecraft, rendezvous with another vessel and finally dock with it:

As the video is not narrated, I'm going to explain the different steps in this thread.

A Few General Tips and Tricks

  • Quick save/load - Press F5 to quick save, F9 to quick load. Use it often.
  • Pressing M toggles between vessel view and map view.
  • Press DEL on the numpad to toggle the navball while in map view.
  • Timewarp kills all rotation of a vessel should that be necessary. Press . (dot) to increase timewarp level, press , (comma) to decrease timewarp level. To kill rotation, just enter timewarp for a second, then leave it again.
  • You can also use SAS to kill rotation. Press T to toggle.

Step 1/2: Launch Spacecraft (0:00 min)

In these steps, I'm launching a docking target into a 300 km circular orbit, and then launch another spacecraft into a 100 km circular parking orbit that is then going to rendezvous and dock with the former.

Spacecraft

For this tutorial I'm using a slightly modified version of the stock Kerbal X: At the top, I've removed the parachute and the landing legs, and instead equipped the following:

See 12:37 min in the video for a closeup of those modifications.

I've also modified the staging a little by moving the rocket holders into the same stage as the engines.

Launch

On the launch pad, it is helpful to first activate SAS by pressing T. This will enable the spacecraft to hold its orientation while in flight without flipping over or do other stupid things.

To launch, throttle up fully by holding the Shift key. When at full throttle, press Space to fire the engines and release the rocket holders. The spacecraft should be going up vertically now.

The Kerbal X has 3 booster stages to help its ascent. You can see that in the lower left corner of the screen. As soon as one pair of booster tanks are empty and their attached engines switch off, press Space to detach these. This is done three times with the Kerbal X.

When the third pair of boosters is detached, the spacecraft should still be below 10 km altitude (see the altitude indicator at the top of the screen.)

Going Into Space

Reaching a stable orbit involves going around the planet, which is what we haven't done so far. Nevertheless it is necessary to first go straight up to leave the thick part of the atmosphere that is slowing us down. At 10 km altitude, it's time for a change.

As soon we reach the 10 km mark, we switch off SAS by pressing T. Then slowly turn to the right (which is east on the planet) by pressing D. Notice that the prograde marker 32px-Prograde.svg.png will follow you on the navball at the bottom of the screen. Keep turning the rocket slowly towards east while also maintaining only a short distance to the prograde marker on the navball. Do this until you reach the range of 0 to 20 degrees relative to the surface. (On the navball, the surface is the brown area, while the sky is blue.) When done turning the rocket, press T to activate SAS again. (Note: You can turn the rocket by using WASD on the keyboard. W/S is down/up, A/D is left/right.)

Now switch over to the map view by pressing M. Rotate the view with the right mouse button held down to see your current trajectory (blue line.) You will notice that right now you will eventually crash into the planet again. We're going to fix this in a moment. But first let's bring our apoapsis (the point farthest away from the planet) outside the atmosphere. Let your mouse hover over the "Ap" (=apoapsis) marker on your current trajectory. Notice that the altitude of the apoapsis is rising. Let it continue to rise until 300 km. (You can slow things down by throttling down by pressing Ctrl.) When your apoapsis reaches 300 km, kill all throttle by pressing X.

Press Space now two times to detach the last stage and activate the next engine.

Reaching a Stable Orbit

So far, you've done the hardest part of going into space. But to prevent crashing into the planet you must achieve a stable orbit. In the case of Kerbin, this means not only raising apoapsis outside of the atmosphere, but periapsis (the point nearest to the planet) as well. Note that your spacecraft reaching apoapsis is still a few minutes out (hover over the "Ap" marker on the current trajectory to see that.)

To raise periapsis, we're going to use maneuver nodes. With the left mouse button, click on the current trajectory exactly where the "Ap" marker is. This will create a new maneuver node at that point. There are a few things that can be done with those nodes. To raise periapsis, locate the prograde marker 32px-Prograde.svg.png on the maneuver node and click and drag it out slowly. Notice how a new trajectory will be projected. If you drag the prograde marker for long enough, the projected trajectory will more or less become a circle, with a new "Pe" (periapsis) marker appearing on it. Keep on dragging until the new apoapsis and periapsis markers are more or less at 300 km.

Turn the spacecraft to point right at the maneuver node marker 32px-Maneuver.svg.png on the navball by pressing WASD. When done, press T to activate SAS again.

Now that you have a maneuver node set up, it is time to execute it. To the right of the navball it is indicated how much Delta-v (change in velocity) you need to invest, how long the necessary burn will be, and the time to the maneuver node. For best results, you will want to time the burn to take place 50/50 at the time of the maneuver node. For example, if the necessary burn is 20 sec long, you will want to start burning 10 sec before the maneuver node and kill throttle 10 sec after the maneuver node.

Activate timewarp by pressing . (dot) on the keyboard. Keep timewarping until shortly before the burn start time, then kill timewarp by pressing , (comma.) When it is time to burn, throttle up fully by pressing and holding Shift. Notice the yellow progress bar going down. When the burn is complete, press X to kill all throttle. You can also slow things down a bit at the end of the burn by pressing Ctrl to throttle down a bit. Nevermind the wobbling maneuver node marker on the navball at the end of the burn.

You can delete the maneuver node now by left-clicking it (to select it), right-clicking it (to bring up the delete icon), then click the little X icon.

Congratulations, you should now be in a stable 300 km circular orbit around the planet! Make sure SAS is active by pressing T. This will help when docking with this vessel.

Launching the Docking Vessel

So far we have a docking target in orbit. Now repeat all the previous steps with a second spacecraft, this time bringing apoapsis and periapsis into a 100 km orbit instead.

Step 3: Adjust Relative Inclination (3:00 min)

In the map view, you will notice that the orbits of our two spacecraft are most likely not aligned exactly - they are on different inclinations. (You can skip this step if they are.)

To fix this, first click on the docking target vessel, then click "Set As Target". Notice there will be two new markers on the trajectory line, labeled "AN" (ascending node) and "DN" (descending node.) These are the points where the two orbits intersect (regardless of different altitudes.) Click on the current vessel's trajectory line right where the "DN" marker is. This will add a new maneuver node. Click and drag the normal marker 32px-Normal.svg.png of the maneuver node until there is a significant change of positions of the project "AN" and "DN" markers on the project trajectory. This usually indicates that you dragged the "normal" marker far enough and that the projected relative inclination is close to zero.

Execute the maneuver node as you did before. When done, delete it.

Step 4: Establish Transfer Orbit (4:17 min)

Now it is time to plan our rendezvous with the docking target. Click anywhere on the current trajectory line to create a new maneuver node. Drag out the prograde marker 32px-Prograde.svg.png until the projected orbit intersects the target's orbit. There will be new markers that indicate intersection points. Hover over those to see the projected closest approach distances. Notice that it will most likely be very far away. You can now modify the time of the maneuver node by dragging it around the current trajectory. To do that, grab the maneuver node by its little "ring" and dragging it around. If you're lucky, a little bit of dragging should bring one of the intercepts down to as little as 5 km or even lower. It might also be possible that you have to wait for a few orbits to get a good start (use timewarp to do that.)

When you have a good maneuver node set up, execute it, then delete it. You're now on an intercept course.

Step 5: Setup marker node for braking (5:55 min)

The next thing you will want to do when near the target is brake again. Ideally the relative velocities between the vessels is zero. To do so, create a new maneuver node at the intersection point. However, there is no need to adjust this node, we're just going to use it as some kind of marker in time.

Step 6: Brake (6:52 min)

Timewarp until you get close to the maneuver node - about 30 sec before should be enough for this tutorial. Turn your spacecraft so that it points into the direction you came from, which is the retrograde marker 32px-Retrograde.svg.png on the navball. Activate SAS to keep orientation.

When at the maneuver node point in time, throttle up to brake. Ignore the node's progress bar and burn time. Notice that the navball should be displaying velocity relative to the target (it should read "Target" at the top.) If it doesn't, click at the text until it does. What you will want to do is to bring your velocity relative to the target down to ideally zero. So at the end, the navball should ideally read: "Target 0 m/s"

You should now be in relatively close distance to the target (5 km max.)

Step 7: Approach (7:22 min)

Turn the spacecraft and point it right at the target marker 32px-Target_prograde.svg.png on the navball. Throttle up a little and watch the prograde marker move towards the target marker.

Make sure not to go too fast now. You can kill throttle at any time by pressing X. If you're going too fast, turn the ship around to point at the retrograde marker, then burn to brake.

Making the Markers Match

This is actually quite easy once you get the hang of it. What you will want to do is move the prograde marker onto the target marker on the navball. That means your vessel is moving right in the direction of the target and not just flying by.

The trick is in how the prograde/retrograde markers react when you burn: The prograde marker (direction you're moving in) will always move to the current location on the navball when burn - you're "dragging" it towards yourself by burning. The retrograde marker (direction you came from) on the other hand is always being pushed away from you when burning. So with this knowledge it is quite easy to move the prograde marker onto the target marker (while at the same time the same will happen with both vessel's opposite markers.)

Approach Speed

In this step, you're wanting to approach reasonably fast, but not so fast that you don't have time to react. I personally use a simple formula: Take the distance to the target, multiply it by 10, then use that value in m/s for the approach speed. For example, say you're 2 km away from the target: 2 times 10 is 20, so just use 20 m/s for your approach speed. You can gradually slow down when getting closer.

Position Target and Activate SAS (9:15 min)

In the video I've switched to the target by pressing \ (backslash), turned it some way and activated SAS to keep its orientation. Then I've switched back to the first vessel by pressing \ again.

Step 8: Switch To "Chase" Camera (11:19 min)

Now switch to "chase" camera mode by pressing V repeatedly. While being confusing at first, this camera mode is extremely helpful when docking.

Step 9: Use RCS to Get Closer (12:13 min)

Turn the ship to point at the target and activate SAS. Now also activate RCS by pressing R, then thrust a few times towards the target by pressing H. There is no need to go fast, about 0.3 m/s should be quite enough. You can timewarp if it's too slow for you.

Without turning the vessel, brake again when near the target by pressing N. You should now be really close to the target with ideally zero relative velocity (that is, a standstill between the two.)

Step 10: Move Parallel (12:44 min)

Now you will want to move parallel to the docking axis. Simply turn around the vessel by pressing WASD so that the docking port is on an axis parallel to the target's docking port's axis. This can be done without RCS. Activate SAS again to kill rotation.

Step 11: Move In With RCS (13:26 min)

At this point we are all aligned with the target and just need a little translation with the use of RCS.

Move the camera behind the vessel. Activate RCS again and begin translation: IJKL works the same as WASD, but for RCS translation this time (that is, no rotation.) Keep moving until the axes of both your docking port and the target's docking port align. You can move the camera around to check things from all sides.

To move along the docking axis without translating (that is, "go forwards" or "backwards"), press H or N.

Step 12: Move Forward to Dock (14:42 min)

Now it's time for the final step. Your vessel is sitting perfectly on the docking axis and just needs a little push to finally dock with the target. Press H to do so. A relative velocity of 0.1 m/s is just about right.

Congratulations, you've just docked with the target!

Edited by blizzy78
Added tips and tricks
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Thanks for the tutorial, got some of my issues answered and will try docking again... when I have calmed down from raging after nearly 2 hours of idiotic space ballet with my station and my 'bus' buzzing poor Jeb in the station Cupola.

Issue was I couldnt get the prograde into the target reticle so kept flying past the station, I did start to get the hang of it but then ran out of mono prop.

I wish there was some way of telling when you are going 0.02m/s towards the target , and 0.02m/s away from the target (other than checking range and pro or retro grade marker positions) ... perhaps a change in the colour would be more useful.

... anyway, thank you for taking time to write and demonstrate docking.

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Issue was I couldnt get the prograde into the target reticle so kept flying past the station, I did start to get the hang of it but then ran out of mono prop.

I personally don't pay attention to the markers anymore when I'm really close and relative velocities are low. I just switch to chase camera mode and fine tune relative velocities in any of the three axes. Once done, I move to the docking axis, kill all velocity again, and move forward.

I wish there was some way of telling when you are going 0.02m/s towards the target , and 0.02m/s away from the target (other than checking range and pro or retro grade marker positions) ... perhaps a change in the colour would be more useful.

Oh yes. Sometimes it's a bit difficult to tell when you're just moving slowly on RCS. If you're a little further out it helps to activate timewarp so that with the increased speed it's easier to tell which way you're going.

... anyway, thank you for taking time to write and demonstrate docking.

You're very welcome. Not too long ago I thought I could never dock manually myself, now I find myself doing it all the time without any mods.

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Tutorial helped me a lot too, thanks :)

The problem I have is also getting close to the station in a stable fashion. The last part (final approach with RCS) is easy, but I'm also alwas zipping past the station and so forth. To be fair, I also had only one small mono propellant tank, next time I will slap a larger one on my ship so I can use RCS also during the approach stage a bit more aggressively.

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The problem I have is also getting close to the station in a stable fashion.

The trick is to switch the navball to showing "Target" instead of simply "Orbit". By doing that, the retrograde marker switches from orbital retrograde to velocity relative to the target, which means that when burning towards the marker, you're killing all velocity relative to the target. Best combined with a really close encounter coming from a Hohmann transfer orbit ;)

The last part (final approach with RCS) is easy, but I'm also alwas zipping past the station and so forth. To be fair, I also had only one small mono propellant tank, next time I will slap a larger one on my ship so I can use RCS also during the approach stage a bit more aggressively.

I found that by stopping to use mods to dock and doing it manually, I'm using much less monopropellant to accomplish the same task.

Edited by blizzy78
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If I may add a small suggestion:

SAS (instead of ASAS) leaves your RCS alone while still holding the ship steady. I find this vastly superior to ASAS during the final docking, as it means you can keep SAS on during RCS thrusts. While you might still want ASAS for the initial accent, you could put a normal SAS in the stage you want to dock, and put an ASAS in the stage below that.

This means you'll have ASAS to take control of the winglets and stuf during accent, but won't have it annoy the crap out of you during docking

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I put 8 RCS THruster blocks on my Rocket, and finally got my two Rockets next to each other with 0.0m/s! With Fuel! :D

But the RCS Thrusters aren't working and I can't figure out why T.T

My Ship is a modified Kerbal X Docker, taking yours as an example - and putting a bunsh of random stuff on it as well (cuz i can).

It has an Advanced S.A.S Module Large on it, 8 RCS thrusters, some Solar Panels, battery, Flashlight, Commutron and other random stuff.

But i don't know why i can't move with my RCS thrusters. They just don't respond to me at all!

Help me :C

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  • 2 weeks later...
  • 2 weeks later...

Between this thread and video, and Scott Manley's video, I think I understand the basics of rendezvous. Your tutorial mission plugin made docking easy, this info makes me confident that I can achieve a successful rendezvous without mechanical assistance.

I found a useful mnemonic for knowing how to set your initial pre-rendezvous orbit. If the target is AHEAD, your orbit should be ABOVE. If the target is BEHIND, your orbit should be BELOW. (Have I got that right?) I think that'll make it easier for me to remember. Thanks for the education.

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Okay, perhaps I spoke a little too soon. I understand the basics, but today I learned the difference between theory and practice. I put your docking trainer into a nice very uniform 100k orbit and launched a modified Kerbal X to rendezvous with it. I got within 3.4km but attempts to get closer failed. I guess I need to review further.

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If the target is AHEAD, your orbit should be ABOVE. If the target is BEHIND, your orbit should be BELOW. (Have I got that right?) I think that'll make it easier for me to remember.

I think I got this backwards. If the target is ahead, its orbit should be above yours - and when you speed up to intersect, your orbit will increase to match. And if the target is behind, its orbit should be below you? You basically slow down to let it catch up, and lose altitude to match?

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Honestly, I can't answer that because I don't pay any attention to this detail. I simply change my orbit so that it intersects with the target's orbit, move the maneuver node through time so that I get a close encounter, and then just burn towards the retrograde marker (in "Target" navball mode) when at closest distance.

Thinking about it, the point is not if your target is ahead of you or vice versa, but whose orbit is higher. If your orbit is higher than your target's, you need to come a bit below its orbit to get an intersect. This means that you will be going slightly faster at closest distance. You will want to arrive slightly behind your target so that you can catch up using your higher velocity. On the other hand, if your orbit is lower than your target's, it the complete opposite way.

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