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How to rendezvous with other orbiting spacecraft


duckunlimited2
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After many days of researching, brainstorming, testing, and general figuring out of stuff, I have designed a Easy-to-follow step-by-step process that will get any two satellites to meet up in orbit; and don\'t worry, there is very minimal math required as per designed.

There are 2 versions of my process: Low-to-High Transfer and High-to-Low Transfer. Both assume that the satellite you want to meet is in a perfect circular orbit and that the spacecrafts orbit is in the same plane as the satellite.

Low-to-High Transfer

1) Set your spacecraft in a circular orbit that has an orbital radius of 63% compared to the orbital radius of the satellite you want to meet up.

- ex: if the satellite you want to meet has an orbital radius of 12,000,000m, you want your craft to have an orbital radius of 7,560,000m or 63% of the meet-up satellite\'s orbital radius.

2) Wait for the satellite, your craft, and the central orbiting body to position themselves, in that order, in a perfectly straight line.

3) Wait for your spacecraft to complete 1 & 3/4 orbits

4) Burn in the direction of travel to raise your Apoapsis up to the same level of orbit as that of the Meet up satellite

-ex: if the meet up satellite has an orbital radius of 12,000,000m, raise apoapsis to that same No.

- For optimal results, do your burn a little later or after you hit 3/4 of that last orbit in step 3

5) wait again for your spacecraft to reach the other side of its orbit at apoapsis

- From here, your spacecraft should meet up with the satellite

6) Burn in the direction of travel to make a circular orbit that matches with the satellites circular orbit

7) Congratz yourself for a job well done!

High-to-Low transfer

1) Set your spacecraft in a circular orbit that has an orbital radius of 159% compared to the orbital radius of the satellite you want to meet up.

- ex: if the satellite you want to meet has an orbital radius of 7,560,000m, you want your craft to have an orbital radius of 12,000,000m or 159% of the meet-up satellite\'s orbital radius.

2) Wait for your craft, the satellite,and the central orbiting body to position themselves, in that order, in a perfectly straight line.

3) Wait for your spacecraft to complete 3/4 orbits

4) Retrograde to lower your periapsis down to the same level of orbit as that of the Meet up satellite

-ex: if the meet up satellite has an orbital radius of 7,560,000m, lower periapsis to that same No.

- For optimal results, do your burn a little early

5) wait again for your spacecraft to reach the other side of its orbit at periapsis

- From here, your spacecraft should meet up with the satellite

6) retrograde to make a circular orbit that matches with the satellites circular orbit

7) Congratz yourself for a job well done!

Do to the fact that while your doing it, you are approximating, you may find that your rendezvous may not be stellar and may find yourself a little too far ahead or behind for a docking attempt. If you find yourself in this situation, follow these correctional maneuvers:

Correctional Rule of Thumbs

To speed your craft up to meet up with the satellite, Retrograde and lower periapsis just slightly. For every orbital period that passes, you will gain on the satellite. The more you lower periapsis, the more you gain on the satellite per orbital period. Once you have sufficiently caught up, bring periapsis back up to to make a circular orbit again at apoapsis.

To slow your craft down to meet up with the satellite, Prograde and raise apoapsis just slightly. For every orbital period that passes, the satellite will gain on you. The more you raise apoapsis, the more the satellite gains on you per orbital period. Once you have sufficiently caught up, bring apoapsis back down to to make a circular orbit again at periapsis.

Seems illogical, but when you lower/raise an orbit, your velocity doesn\'t change much. What changes significantly is the distance you need to cross to complete an orbit. High orbit = more distance = longer orbital period. Low orbit = less distance = shorter orbital period.

This maneuver is best used when you cannot see the satellite\'s distance indicator in the flight screen. It\'s a good way to get the distance indicator into view

The Skipping Maneuver

This maneuver is best used when you can see the satellite\'s distance indicator.

To slow down yourself in order for the satellite to catch up, retrograde a bit to lower your speed. Watch the satellite\'s distance indicator in order to help control the rate at which the satellite closes. As the satellite gets closer, prograde in increments to gently slow the rate the two crafts closes until their in a reasonable distance away from each other to perform docking maneuvers. Once achieved, you can fix your orbit, or attempt a dock.

Important: After you retrograded, your craft, by laws of physics, will start to lose altitude. In order to keep altitude under control, you want to thrust upwards, away from the celestial body your orbiting (do this by placing your indicator on the north pole of your navball and thrust). This type of burn will raise the front half of your orbit, and lower the back half of your orbit without changing your orbital velocity. Periodically thrust up in order to keep altitude (hence the term 'skip'). I find it best to use the main engine to maintain altitude and RCS thrusters to slow the rate of closure.

In order to speed yourself up to catch up with the satellite, prograde instead and periodically retrograde as you get closer. To keep altitude in check thrust straight down (south pole on navball). I think you get the picture.

Aligning A Tilted Orbit

Right after the pivot point (where your two craft\'s orbits meet), you want to thrust in the direction of the satellite\'s orbit. (on the navball, you should be thrusting in between the yellow markers.

With this guide, you now have the ability to create space stations, meet up with other planets, and other things you could imagine. Enjoy

Notes:

you really want both crafts apoapsis and periapsis to be extremely close to the same spot and extremely close to the same altitude. It makes things alot easier.

HarvestR is planning on implementing a feature in the game to help with rendezvous. Since it will be more precise and be a bit more versatile, it probably would outdo this guide. However, it won\'t be released probably in the next few patches.

Be sure to check out WX_Echo\'s Orbital Mechanic calculator. It\'s quite a good tool to help with orbital matters.

Forgot to mention: Altitude and orbital radius aren\'t the same thing. To find orbital radius, take the altitude and add that with the planets radius. (I made that mistake a few times. I\'m just trying to warn you, lol!)

Edited by duckunlimited2
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That would be more difficult. Orbital periods are directly related to their orbital radius. If you are at a certain altitude, your orbital period will be quite specific. It\'s easy to compare them that way and get them to match up. However, a planet\'s spin isn\'t related to the planet\'s radius so comparing would be difficult. Plus atmospheric drag makes it even more complex.

But there should be a way and I will find it . ;)

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I\'ll have to check this out. Also, I think this will be an accomplishable task once we have persistance. Especially since observing the satellite, your craft, and the central orbiting body positioning themselves in a perfectly straight line is not easy.


  • [li]I can confirm that this technique works very well for Munar rendezvous. Considering testing for Kerbin rendezvous.[/li]

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This thread needs more video! Since someone has confirmed it works, I\'ll put it on my mental list of things to do. Perhaps I can make a video.

Does the engine ever 'clean up' old / distant objects?

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This thread needs more video! Since someone has confirmed it works, I\'ll put it on my mental list of things to do. Perhaps I can make a video.

Does the engine ever 'clean up' old / distant objects?

Yes, and no. It\'s hard to tell now (much easier in .14), because you have to physically SEE something to know it exists. However, I do know that you can see a bright object from at least 15 kilometers away, and that an object can orbit the Mun (while you\'re landed on the moon) and that object won\'t get removed.

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I don\'t have a video but I do have pictures. http://kerbalspaceprogram.com/forum/index.php?topic=7317.msg105854#msg105854

In this example, I\'m trying to do a Challenge where I go into Kerbol Orbit and Come back. First try was a bust. The second was more successful. My guide proves very valuable in getting back to Kerbin.

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Hey I found your information about Retrograde and Prograde really useful :) getting circle orbits to match was tricky I had to get the eccentricity to match but I did that by firing either at 180 degree marker or at the north marker near the point which the target orbit is crossed. I am still not sure which way to vector as the line comes close its hard to tell which point of the cross you are so I normally vector 1 way and then vector the other if the orbits diverge .

All of that got me really close! 454meters at the closest! but how the hell you close the last 500meters?? I can just see the other ship I tried vector towards it and I can close but I have no tool telling me how close i am which direction to vector in and the nav ball is less than useless!!! I shot past the ship 3 times, I nearly came close (but way too fast) must have been under 200meter as the information had disappeared? is there away to lock the camera to the ship?

Also I wish I film my attempt because I only remembered to take two screen shot while I was anywhere close to touching.

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Well, honestly you did an superb job. Basically, you need a bit of finesse when your that close. When distances are so big, its okay to go full burn and throttle at its highest, however, the smaller the distance is, the more gentle you need to be in the controls. At distances less than thousand, you basically need an extremely gentle touch.

So, assuming that your going the same speed with 500 meters between the two crafts, I\'d increase/decrease your speed by 10-15m/s (use the skip manuever, and make sure apopasis is only a 10-50 meter deviation). As it gets closer, you want to incrementally burn to slow down the speed at which they close. RCS is a great for this scenario thanks to its gentleness and versatility of direction at which to burn in any orientation.

500 meters, to me, is just at the cusp of the viable distance to do docking maneuvers. I strongly suggest you send a rocket out in orbit, decouple a target part, and play around with RCS, watching how each little push affects the relative position of the craft and target part and the speed the move away from each other. As you get more comfortable, push your craft farther and farther away and attempt to get back to it. This exercise should give you a better idea on how much finesse you need to gently close those 500 meters.

I don\'t know any way to lock the cameras, but the best view is a side view of your craft and satellite. This way, you get a better vantage point to judge its speed and vector relative to your craft.

By the way, I was able to get 70meters away from the satellite. A little RCS docking maneuvers and they were practically hugging!

Cheers!

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I have tried both techniques a few times to rendezvous, but I have failed hard. I have followed every step but I still miss my target craft. I bring my target to 300 000 000m height and my craft to 477 000 000m. I still can\'t make an extremly perfect curcular orbit because as soon as my orbit starts to becomes circular the Ap and Pe points start to rezonate like hell because of a bug, reading and determining their exact position becomes very difficult, so it is understandable that I fail. But still, even with this anoyance the difference between them is usualy about 30-70 000m, which means even if I can\'t match my crafts properly their distance from eachother shouldn\'t be as big as I get (sometimes half orbits). I suspect that besides the technical issue my real problem is that I can\'t make the right timing. It would be great if you could make a tutorial video of this.

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Sorry Rico, I got the High-To-Low Orbit wait time wrong. You should wait for your craft to do 1 & 3/4 orbits like the Low-To-High, (I think that\'s how you end up being half orbit distances away). Yeah, I never tested that specific method until just a few moments ago. It\'s alot easier to test it with .14 released. I fixed the mistake in the guide.

I think the major thing that\'s messing you up is not factoring the planet\'s radius in your calculation. Altitude is not the same as orbital radius.

Ex: You have the target satellite up at 300,000m in Kerbin Orbit. To find the altitude your craft should be, add 600,000m (kerbin\'s radius) with the target satellite\'s altitude. 600,000+300,000=900,000. Then you multiply it by 1.59. You should get 1431000. What you have now is Orbital radius. You want altitude, so subtract Kerbin\'s radius from the number to get your altitude. 1431000-600000=831000m. So, to rendezvous with a satellite 300,000m high, you need to get your craft up at an altitude of 831000m first.

I\'ll see if I can get a video up sometime soon.

Cheers!

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Sorry Rico, I got the High-To-Low Orbit wait time wrong. You should wait for your craft to do 1 & 3/4 orbits like the Low-To-High, (I think that\'s how you end up being half orbit distances away). Yeah, I never tested that specific method until just a few moments ago. It\'s alot easier to test it with .14 released. I fixed the mistake in the guide.

I think the major thing that\'s messing you up is not factoring the planet\'s radius in your calculation. Altitude is not the same as orbital radius.

Ex: You have the target satellite up at 300,000m in Kerbin Orbit. To find the altitude your craft should be, add 600,000m (kerbin\'s radius) with the target satellite\'s altitude. 600,000+300,000=900,000. Then you multiply it by 1.59. You should get 1431000. What you have now is Orbital radius. You want altitude, so subtract Kerbin\'s radius from the number to get your altitude. 1431000-600000=831000m. So, to rendezvous with a satellite 300,000m high, you need to get your craft up at an altitude of 831000m first.

I\'ll see if I can get a video up sometime soon.

Cheers!

I see, this made some light in my head, you are right, I didn\'t consider Kerbin\'s radius, no wonder I failed with both techniques. I will ceartanly try this tomorrow. Thank you for the explanation!

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Were missing by a quarter of an orbit at first, but after reading through this twice, and adding the radius of Kerbin into the equation :-[, i managed to bring myself to just under 1000m away from my target at its closest. But it took a few orbits to make the rough adjustments needed to get me there, and even tho the orbits were more or less as identical as i could make them, we were slowly drifting apart.

Guess I´ve got to try this out some more tomorrow. Challenge is also to make both orbital planes identical, along with the radius and all that.

And it doesn\'t help that I\'m not entirely sure on how to move about to close in that last gap.

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I\'ve attempted this a couple times in .14. Didn\'t work. I blame myself. Probably any number of inaccuracies with my calculations, or with a too-eccentric orbit. I\'ll have to try it again when the full .14 comes out.

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I chased one of my satellites around the Kearth for 2 hours last night! But that was probably because I was using the non updated instructions. The orbital plane alignment is also pretty exasperating but I am committed to my modular space station! Thanks for this tho, there are absolutely no other guides... Ima make this work, I swear to Kerbus!

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Now that 0.14 is out I could try the manuver with the new calculation and I have managed to get 3,4 km near to my target craft for the first try. Thanks for the explanation Duckunlimited2!

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Suddenly, I know what I\'ve done wrong. It turns out I was using altitude, not orbital radius. Silly me. This guide has earned a spot in my notebook!

Here\'s some shots of the rendezvous.

6840305354_5f8c9d623b_z.jpg6840305530_72f9d1bf21_z.jpg6986426073_518f49b558_z.jpg

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This guide has helped me a lot with figuring out some orbital mechanics. I\'ve failed trying to use the more mathematical and complex meetup equations, but just by making controlled burns to come close to my target. The problem that I have is I just can\'t exactly figure out how to raise or lower the inclination of my orbit (not altitude) without screwing up my altitude. I really wish somebody would finally make a video tutorial on orbital maneuvering that went into more detail. Because of this, the closest I\'ve ever gotten is about 8km\'s.

I\'m pretty confident that Squad will add in some kind of tool to help with this sort of orbital navigation once 0.15 is out, and if not I\'m sure somebody would make a plugin for it or whatnot, but I\'d still like to be able to pull it off manually.

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