HOW TO: Rendezvous in orbit.

[VincentMcConnell]

A GUIDE ON ORBITAL RENDEZVOUS

By Vincent McConnell.

There are few things one really needs to learn about the prospect of getting one spacecraft to link up with another that is 60 miles overhead and moving at nearly 3,000 meters per second, or 500 meters per second. The basic principles are something you can simply practice with different orbits. This guide will teach you how to orbit a spacecraft nearly perfectly and then to get another spacecraft to pull up to it.

ESTABLISHING A TARGET VEHICLE ORBIT

The first step is, of course, to put a target vehicle in place where it can be docked or rendezvous\'d with. I highly recommend that the average player on Kerbal Space Program gets very good with circular orbits and plane change maneuvers. Both of which are important to a successful link up. Launch into orbit the way you normally would, an eccentric orbit is fine for now. My best advice would be to use fairly weak RCS thrusters. This will ensure that you can bring an orbit down to a nearly exact number.

Let\'s assume for a moment that your orbit is 104x99 KM. The best thing to do is begin pro-grade thrusting with your RCS to turn the closest number into 100KM. In this case, it would be 99. A few pro-grade thrusts will put that up to 100KM. As you would do a circularization burn, you want to circularize this 104x100KM orbit. Wait until you hit the point in your orbit which is 100KM (probably your Periapsis) and begin retro thrusting so that you circularize the orbit from 104 to 100KM. The end result of this will be a 100KM orbit that is off by something in the neighborhood of only about 30 meters.

If your orbit is perfectly equatorial, pay no attention to this next part:

If you notice your orbit is tilted and looks like utter garbage, you are going to want to fix that. The best way to do this is a “plane change maneuverâ€. As you cross the equator of Kerbin or the Mun, you want to thrust either north or south, depending on which way you are moving. If your orbit is tilted downward and you are moving south, you will want to thrust NORTH.

The North and South indicators are directly in between pro and retro. North is characterized by an orange line. You will notice that your orbit begins to tilt back towards the equator. You can always use your main engine for a plane change maneuver if you\'d like.

If you have followed this correctly – there are plenty of guides elsewhere on how to get into orbit – you should be maintaining a circularized orbit of 100KM x 100KM that is near perfectly equatorial.

LAUNCHING YOUR DOCKING VEHICLE

Launching your docking vehicle is essentially the same maneuver. Here is the difference: Your docking vehicle will probably be at a lower altitude of orbit than your target vehicle. For Munar rendezvous, I recommend a rendezvous about 100KM above the Mun. For Kerbin rendezvous, I recommend 200KM. Circularize your docking vehicle\'s orbit at 90KM for the Mun or 190KM for Kerbin and make sure it runs along the same plane as your target vehicle. At this point, you will notice that your docking vehicle, being at a lower altitude, is moving faster than your target vehicle. It may take a few orbits for the two to begin to run along side each other, so engage time compression and wait.

ALIGNING YOUR ORBITAL ALTITUDE

Once your docking vehicle is running at a lower altitude, yet along the side of your target vehicle, it is time to RAISE your docking vehicle\'s orbit to the same orbit as the target vehicle. This will result in the two spacecraft at the same altitude, moving along side eachother at the same speed. To do this, begin prograde burning to put your AP or PE to the same altitude of orbit as your target vehicle. This requires what is known as a Hohmann transfer. A transfer from one orbit to another requires two or more burns. Once you have a PE or AP at the same altitude as your target, warp away until you reach that AP or PE and then pro grade thrust some more. Circularize your orbit to 100KM or 200KM so that you are at the same altitude as your target vehicle and are now running along side it. If this was done correctly, you will notice that your target is probably only a few kilometers away.

FINE CONTROL, FINAL APPROACH, RENDEZVOUS

It is important that you understand your RCS like the back of your hand. It will be your only assistance in this final phase. Point your docking vehicle at your target and begin thrusting towards it. This is a thing best done nice and slowly. You have plenty of time to approach it and the slower the better. There are THREE planes that you want to watch out for at this point. Side to side velocity, up and down and forward and backward velocity. Begin pushing slowly towards it, moving side to side as you do. Hopefully, you know about RCS at this phase, because the purpose of this guide is not to teach you how to control your spacecraft to the basics. As you drift closer towards the target, watch it\'s movement. You will not appear to move, although it is the other way around. The target is not moving, it is you who is moving. As you thrust backwards and forwards, side to side, up and down, the target will begin it\'s slow drift towards the center of your approach. You will notice it starting to get ever so closer. Within meters, you want this to be the slowest approach. Watch all three planes of movement so that you don\'t screw up. Hopefully, if you fine control this, much like a landing on the Mun, you will touch the two spacecraft together and prepare yourself for .15\'s update of docking.

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Here is my first lunar orbit rendezvous, which I just completed tonight!

http://kerbalspaceprogram.com/forum/index.php?topic=9058.0

[Desert-Fox]

@VincentMcConnell

Thank you for the info!

Tried a few times to clear space debris from around Kerban, only had one semi-successful docking, there is only one thing worse than not been able to get to your target... is getting to your target with near empty tanks... lol

Using the time acceleration creates phantom forces and jiggles the spacecraft and target apart, so is wise not to use time laps after you have used the legs to clamp on to your target...

I made a suggestion somewhere on the dev forum, to have some sort of time line markers on your ships orbit line, and the ability to select a target and see the same time line markers on its orbital line. Just so you know when & where you and your target will be at the same time.

Ether scaling when you zoom in and out on your map (I think that would be better) or static time, (but I think static time would get messy & difficult to see clearly from far distances).

Never the less I think this will help to take out some of the guesswork for traveling to other bodies, craft, debris etc.

I think it will help more in the future after the dev\'s start to add more planets, asteroids etc. It could also be an in-game research & upgrade for Kerbal nav systems for later development or full release of the game.

Anyways... thanks for tutorial, I have got most of it down, just need to keep my patience in check... :

[VincentMcConnell]

@VincentMcConnell

Thank you for the info!

Tried a few times to clear space debris from around Kerban, only had one semi-successful docking, there is only one thing worse than not been able to get to your target... is getting to your target with near empty tanks... lol

Using the time acceleration creates phantom forces and jiggles the spacecraft and target apart, so is wise not to use time laps after you have used the legs to clamp on to your target...

I made a suggestion somewhere on the dev forum, to have some sort of time line markers on your ships orbit line, and the ability to select a target and see the same time line markers on its orbital line. Just so you know when & where you and your target will be at the same time.

Ether scaling when you zoom in and out on your map (I think that would be better) or static time, (but I think static time would get messy & difficult to see clearly from far distances).

Never the less I think this will help to take out some of the guesswork for traveling to other bodies, craft, debris etc.

I think it will help more in the future after the dev\'s start to add more planets, asteroids etc. It could also be an in-game research & upgrade for Kerbal nav systems for later development or full release of the game.

Anyways... thanks for tutorial, I have got most of it down, just need to keep my patience in check... :

Glad to help. If you find yourself out of fuel, you can always practice rendezvous with modified RCS tanks. The CFG files with all the part parameters (burn rate and fuel capacity) are in your Parts folder in KSP under the name of the exact part.

[Guest GroundHOG-2010]

Just tryed this, but failed (though I got within 200m).

[MFToast]

Finally got it! Thanks again for the guides, also thanks to creators of MechJeb and RinComp, don\'t think I\'d have been able to do it without all of you!

[Kosmo-not]

How is knowing how to do circular orbits and plane change maneuvers detrimental to a successful rendezvous? I, on the other hand, think knowing how to do these tasks are highly beneficial.

I also disagree with waiting until you are side by side with your target to begin the intercept maneuver. You will end up far ahead of it if coming from below.

*edit*

If my calculations are correct, the elevation angle to commence the intercept burn starting at 80km and going to 100km is 21.4°. That is the angle from the tangent line of your orbit to the target craft.

[VincentMcConnell]

How is knowing how to do circular orbits and plane change maneuvers detrimental to a successful rendezvous? I, on the other hand, think knowing how to do these tasks are highly beneficial.

I also disagree with waiting until you are side by side with your target to begin the intercept maneuver. You will end up far ahead of it if coming from below.

*edit*

If my calculations are correct, the elevation angle to commence the intercept burn starting at 80km and going to 100km is 21.4°. That is the angle from the tangent line of your orbit to the target craft.

The reason that those two things are practically required for rendezvous, especially for the average player, is because it allows all of your controlling (meeting up with the second craft) to be more precise. With circular orbits, you don\'t have to worry about changing velocity too much along your orbit.

Side by side is simply an easier way to do it for most people. As long as your orbit is not too low below the target craft, you won\'t end up too far off. In addition, if you end up a little further off from your target craft, it gives you a lot of time to get the fine tuning maneuvers down and make sure everything is ok.

You know... There is a reason why this worked for me to do a surface to orbit rendezvous from the Mun. Not many people (VERY few) have done that.. These techniques are user friendly and they work.

[Kosmo-not]

What I was getting at in my first statement is that you said knowing how to do circular orbits and plane changes is obviously harmful to the success of a rendezvous. I think you need to pick a word with the opposite meaning of detrimental.

[VincentMcConnell]

What I was getting at in my first statement is that you said knowing how to do circular orbits and plane changes is obviously harmful to the success of a rendezvous. I think you need to pick a word with the opposite meaning of detrimental.

LOL. I did put that, didn\'t I? Stand by.

EDIT -

Done. Don\'t know why I put that and that I also didn\'t catch it in your response. It\'s fixed now. That is rather strange.

[Kosmo-not]

I did the mathemagic, and have come up with a nifty way of rendezvous from circular orbit to a target with circular orbit. From an orbit of 80km, I was able to come within 600m of my target at 100km. the magic number for this setup is 50.4km. That is the straight line distance between you and your target at the orbit transfer point (you can easily measure this by mousing over the pink target box of your target). This corresponds to the 21.4° I posted previously.

*edit*

Here is a reference table for you all. It covers orbit radii from 670km to 800km (70km to 200km altitudes if around Kerbin). The result in the table is the straight line distance between you and your target at the Hohmann transfer point. Values greater than 100km (view distance limit) have been grayed out. I hope this makes rendezvous super easy for a lot of people. Enjoy!

I haven\'t yet tested going from a higher orbit to a lower one, so I hope that part is also correct. Oh, and remember that the target should be ahead of you at burn time when transferring from a lower orbit; behind you if transferring from a higher orbit.

[Guest GroundHOG-2010]

I burn to catch up with the target vehicle when its eather infront of me or behind me, and less that 1km away (or else you use too much rcs).

[Randox]

I burn to catch up with the target vehicle when its eather infront of me or behind me, and less that 1km away (or else you use too much rcs).

You need to bring more RCS

I just did this now for the first time. I will admit, I kept the engine that performed all the orbital corrections attached mostly to expedite the return to Kerbin, but a couple of min thrust burn sped things up (if you call flying by the target twice while spinning out of control in an effort to reverse thrust ASAP speeding things up).

I watched a video on this, and my pods are seriously heavier than what they used. In the picture, the lighter of the two still has a full gas tank for the main engine (its carry a half tank on top that\'s just about empty), and two RCS tanks still full. It performed all the maneuvers, and managed to line them up to something like 10km.

My next challenge is to orient one of them so that the other can get nose to nose with it (the way they are now, they both spin a bit end over end, and it happens much to fast to keep up with manually.

[rustymcclintock]

I did the mathemagic, and have come up with a nifty way of rendezvous from circular orbit to a target with circular orbit. From an orbit of 80km, I was able to come within 600m of my target at 100km. the magic number for this setup is 50.4km. That is the straight line distance between you and your target at the orbit transfer point (you can easily measure this by mousing over the pink target box of your target). This corresponds to the 21.4° I posted previously.

*edit*

Here is a reference table for you all. It covers orbit radii from 670km to 800km (70km to 200km altitudes if around Kerbin). The result in the table is the straight line distance between you and your target at the Hohmann transfer point. Values greater than 100km (view distance limit) have been grayed out. I hope this makes rendezvous super easy for a lot of people. Enjoy!

I haven\'t yet tested going from a higher orbit to a lower one, so I hope that part is also correct. Oh, and remember that the target should be ahead of you at burn time when transferring from a lower orbit; behind you if transferring from a higher orbit.

I think ksp need a tool for this

[Guekko]

Hi!!! First, congrat!!! I tryed many times to make a Rendez-vous and i never success it\'s realy hard to be in the same place, at a good moment, with the good speed!! I could advise you to dl the KOCMOC add-on, it will gives you tool to link different ships in orbit. Go take a look on this link: http://kerbalspaceprogram.com/forum/index.php?topic=7178.0

I ll read more seriously you post and try one more time!!!

Thans you!!

[umter]

Hey, successfully caught up to a craft!

Was initially around 10km away, slowly adjusted using RCS thrusters, managed to get within 300m!

The thing that\'s really getting me worked up is closing the final gap, can you offer any little nifty tricks to fine-tune the final approach?

Thanks

[rustymcclintock]

Hey, successfully caught up to a craft!

Was initially around 10km away, slowly adjusted using RCS thrusters, managed to get within 300m!

The thing that\'s really getting me worked up is closing the final gap, can you offer any little nifty tricks to fine-tune the final approach?

Thanks

I also need some tips on final approach. And do the docking modules in the KOCMOC pack actually work? as in if i hit my satellites docking port with my docking port...do they dock?

[Guekko]

With KOCMOC mod i never sucess to make my satellite meet in orbit and i never test it in kerbin, but in the tools you have 2 pieces who normaly doch each other if they re in contact. So if you can make them be in touch in orbit you normaly could dock it. But as i said i never sucess to make my satellites be in the same place a the same time. I ll make some test on the ground to see if docking realy work, i ll post the answer as soon as i know it