Entropius

Illustrated Tutorial for Orbital Rendezvous

Recommended Posts

I made a series of illustrated tutorials for orbital rendezvous & docking. There are 4 techniques. For a link to all the images in a single imgur album, click here.

 

Hohmann Transfer Rendezvous:

vuDrtq8.png

 

 

Orbit Phasing Rendezvous (easy radial-burn version):

2RfqPOR.png

 

 

Orbit Phasing Rendezvous (more efficient prograde-burn version):

h1QMVsT.png

 

 

Parallel Orbit Rendezvous:

1uMkHgO.png

 

 

Changes:

  • v7 - Adjusted phrasing in one chart and updated drawing of spacecraft in all 4 charts.
  • v6 - Fixed a typo in the Hohmann transfer's step 6.
  • v5 - Added 2 techniques (for a total of 4).
  • v4 - Spelling error corrected.
  • v3 - Refined instructions for final approach, docking indicators now also includes Navball Docking Alignment Indicator, more notes on how to be efficient.
  • v2 - Split into 2 versions: efficient & easy.
  • v1 - Original version.

 

Edited by Entropius
updated graphics
  • Like 46

Share this post


Link to post
Share on other sites

Very helpful, in-depth, simple, great! I will be using this in the future, thanks!

Share this post


Link to post
Share on other sites

Hi

Great info thanks but can I ask how did you get the docking camera to work this looks oorrsuumm is it a mod, if so I want it how do I get it. plz. I done the tutorial on docking but this feature was not explained.??

 

Share this post


Link to post
Share on other sites
On ‎9‎/‎5‎/‎2016 at 9:32 AM, capt: scarlet said:

Hi

Great info thanks but can I ask how did you get the docking camera to work this looks oorrsuumm is it a mod, if so I want it how do I get it. plz. I done the tutorial on docking but this feature was not explained.??

 

Do you mean the two images in the bottom left of each guide?  Those are from two mods.  The left one that's a grey box with the circles and the two green lines is a mod called Docking Port Alignment Indicator and I'd marry it if it were legal.  The other is Navball Docking Alignment indicator and it adds that neat red indicator to the navball.  I haven't used that one personally but DPAI handles my needs just fine.

 

Also @Entropius you are a gentleman and a scholar but I have to ask.  In what situations would we use one of these methods over the other?

Share this post


Link to post
Share on other sites

One more thing, @Entropius would you be able to add some illustrated guides where your craft starts off landed on the body being orbited?  Like what's the best way to go from Kerbin to intercept a space station in orbit.

Share this post


Link to post
Share on other sites
38 minutes ago, Chiron0224 said:

One more thing, @Entropius would you be able to add some illustrated guides where your craft starts off landed on the body being orbited?  Like what's the best way to go from Kerbin to intercept a space station in orbit.

In that case, you basically just launch into an orbit first and then follow the same instructions.  Ideally, wait until the target's orbit is directly above you and then follow a launch trajectory that will put you on the same inclination as the target.  If you're launching from the equator and the target is on an equatorial orbit(which is often the case when using the stock KSC), you can launch at any time and be in the correct inclination, so you can then try to time it so when you do reach orbit, you're already as close to the target as possible.

Share this post


Link to post
Share on other sites

Oh wow, people are commenting here.  I originally posted this in 2014, and hadn't seen a reply in years, so I never bothered to check on the thread except for making occasional tweaks.

Anyway, regarding the question of the docking camera:  Chiron0224 is indeed right, those are docking alignment mods.  They're not technically cameras though, although there is another mod for that out there somewhere.  I don't prefer true camera mods because docking alignment indicators actually offer more information than a camera would.  For instance, pitch and yaw alignment is much more precise with the mods I discussed (Docking Port Alignment Indicator & Navaball Docking Alignment Indicator).  I personally prefer the former.

Regarding the question of when to use each technique… I can offer some general guidelines (but don't take them as hard-rules either).

  • Hohmann Transfers are a good default option for transferring from one circular orbit to another circular orbit.  But as the starting or ending orbit becomes more eccentric, it gets more annoying/tedious as the maneuver's prograde ∆v must be repeatedly re-adjusted as you drag the maneuver node around.  
  • Orbit phasing techniques on the other hand seem to handle high-eccentricity rendezvous rather nicely so long as you can get the tangent-point lined up right.  But Orbit Phasing's efficiency varies a bit more than Hohmann Transfer efficiency.  Orbit phasing, if done very carefully and patiently, can be almost as efficient given the right circumstances, but can also be significantly worse.  IMO, where Orbit Phasing really shines is when you want to rendezvous with another ship immediately upon arrival at another planet/moon. That's because capture burns typically put you into an eccentric orbit that gives you an phasing orbit with a long period to play with.  Assuming the relative-inclination adjustment is reasonably cheap, the Orbit Phasing can basically be as just efficient as a Hohmann Transfer when arriving at a body.  Regarding the choice between the two flavors of Orbit Phasing, if you can do the more efficient one, always do it.  The less efficient one (the one with the radial burn) is just easier for beginners to setup the tangent point.  There's really no advantage to it beyond that.
  • Parallel Orbit rendezvous is arguably the most simple from a conceptual standpoint.  Ships in higher orbits go slower.  Ships in lower orbits go faster.  If you get two orbits lined up inclination-wise, and have a tiny difference in altitude, very slowly drift near the other… eventually.  You can also think of this being technically equivalent to a Hohmann Transfer with a very tiny transfer-maneuver.  The major downside to this technique is that it's painfully slow.   We're talking a rendezvous that can take literally days.  So from a gameplay standpoint, I don't like this technique at all.  It's only redeeming quality is that it's really useful for docking very low-TWR ships together.  For example, docking with big, heavy, fully loaded fuel-tankers.  It's nice for for that scenario because the fuel tankers can't really spin the ship around 180-degrees easily to burn the main engine for steering the final approach, so small precise burns are nice in that situation.  If the difference between the initial orbits is small enough, final approach can be done via RCS-translation thrusters.  Also some trivia:  I totally made up the name of this technique.  As best as I could tell, this technique is not used in the real world and thus had no name.  So I made a name up.  If anybody does find documentation of this technique having a real-world name, feel free to tell me.

Regarding launching guides, I doubt it's necessary to diagram, it's trivial enough to explain textually:  If your rendezvous target is in equatorial orbit, launch whenever you want to, it makes no difference. If your rendezvous target is in a significnatly inclined orbit you must launch your ship directly into the inclination of the orbit of the rendezvous target.  You'll probably have to do a tiny inclination adjustment once in orbit, but hopefully not much. It's made easier by (1) double-clicking Kerbin (or whatever body you are launching from) in map view so the camera centers on it instead of your ship and then (2) zooming out your camera enough to see the target-ship's orbit.  Then (3) while keeping the camera above the equator, orbit the camera around the planet until the target's orbit appears to become a thin diagonal line.  In other words, you want the camera positioned exactly above where the target's orbital plane slices into the equator's plane.  Then (4) wait for the body to rotate such that the launch-site lines up with the point the camera is facing.  Then you just tilt the rocket northward or southward upon launch by the right amount.  Kerbal Engineer lets you see your relative inclination, and keeping that number near zero helps you fine-tune the inclination as you launch.

Edited by Entropius
  • Like 2

Share this post


Link to post
Share on other sites

This tutorial gave me a lot of inside info and put everything nicely together, when I was learning it back in days. Thank you very much for it!

Today, I just use two simple rules:
1) align inclination with target orbit as first step.
2) if you are on lower orbit - wait until you are behind(following) the target; if you are in the higher orbit - wait until you are in front(followed) of the target.
then just burn prograde at closest point and drag maneuver until close encounter, wait until you are close to target and then match orbits (burn to target/burn to retrograde, rinse and repeat).

But that won't be possible without your awesome tutorial Entropius!

Share this post


Link to post
Share on other sites
On ‎9‎/‎18‎/‎2016 at 2:17 AM, Entropius said:

Oh wow, people are commenting here.  I originally posted this in 2014, and hadn't seen a reply in years, so I never bothered to check on the thread except for making occasional tweaks.

Anyway, regarding the question of the docking camera:  Chiron0224 is indeed right, those are docking alignment mods.  They're not technically cameras though, although there is another mod for that out there somewhere.  I don't prefer true camera mods because docking alignment indicators actually offer more information than a camera would.  For instance, pitch and yaw alignment is much more precise with the mods I discussed (Docking Port Alignment Indicator & Navaball Docking Alignment Indicator).  I personally prefer the former.

Regarding the question of when to use each technique… I can offer some general guidelines (but don't take them as hard-rules either).

  • Hohmann Transfers are a good default option for transferring from one circular orbit to another circular orbit.  But as the starting or ending orbit becomes more eccentric, it gets more annoying/tedious as the maneuver's prograde ∆v must be repeatedly re-adjusted as you drag the maneuver node around.  
  • Orbit phasing techniques on the other hand seem to handle high-eccentricity rendezvous rather nicely so long as you can get the tangent-point lined up right.  But Orbit Phasing's efficiency varies a bit more than Hohmann Transfer efficiency.  Orbit phasing, if done very carefully and patiently, can be almost as efficient given the right circumstances, but can also be significantly worse.  IMO, where Orbit Phasing really shines is when you want to rendezvous with another ship immediately upon arrival at another planet/moon. That's because capture burns typically put you into an eccentric orbit that gives you an phasing orbit with a long period to play with.  Assuming the relative-inclination adjustment is reasonably cheap, the Orbit Phasing can basically be as just efficient as a Hohmann Transfer when arriving at a body.  Regarding the choice between the two flavors of Orbit Phasing, if you can do the more efficient one, always do it.  The less efficient one (the one with the radial burn) is just easier for beginners to setup the tangent point.  There's really no advantage to it beyond that.
  • Parallel Orbit rendezvous is arguably the most simple from a conceptual standpoint.  Ships in higher orbits go slower.  Ships in lower orbits go faster.  If you get two orbits lined up inclination-wise, and have a tiny difference in altitude, very slowly drift near the other… eventually.  You can also think of this being technically equivalent to a Hohmann Transfer with a very tiny transfer-maneuver.  The major downside to this technique is that it's painfully slow.   We're talking a rendezvous that can take literally days.  So from a gameplay standpoint, I don't like this technique at all.  It's only redeeming quality is that it's really useful for docking very low-TWR ships together.  For example, docking with big, heavy, fully loaded fuel-tankers.  It's nice for for that scenario because the fuel tankers can't really spin the ship around 180-degrees easily to burn the main engine for steering the final approach, so small precise burns are nice in that situation.  If the difference between the initial orbits is small enough, final approach can be done via RCS-translation thrusters.  Also some trivia:  I totally made up the name of this technique.  As best as I could tell, this technique is not used in the real world and thus had no name.  So I made a name up.  If anybody does find documentation of this technique having a real-world name, feel free to tell me.

Regarding launching guides, I doubt it's necessary to diagram, it's trivial enough to explain textually:  If your rendezvous target is in equatorial orbit, launch whenever you want to, it makes no difference. If your rendezvous target is in a significnatly inclined orbit you must launch your ship directly into the inclination of the orbit of the rendezvous target.  You'll probably have to do a tiny inclination adjustment once in orbit, but hopefully not much. It's made easier by (1) double-clicking Kerbin (or whatever body you are launching from) in map view so the camera centers on it instead of your ship and then (2) zooming out your camera enough to see the target-ship's orbit.  Then (3) while keeping the camera above the equator, orbit the camera around the planet until the target's orbit appears to become a thin diagonal line.  In other words, you want the camera positioned exactly above where the target's orbital plane slices into the equator's plane.  Then (4) wait for the body to rotate such that the launch-site lines up with the point the camera is facing.  Then you just tilt the rocket northward or southward upon launch by the right amount.  Kerbal Engineer lets you see your relative inclination, and keeping that number near zero helps you fine-tune the inclination as you launch.

 

Thanks for the breakdown.  One more thing I would add to your description of when to use parallel is that I sometimes find that I end up using it if the rendezvous target is orbiting so low that Kerbin's atmosphere prevents me from doing one of the other options, or if fuel is tight and I can't raise and lower orbits too much.

Share this post


Link to post
Share on other sites

I've been playing this game off and on for three years and never realized you could right-click the maneuver nodes to get +orbit and -orbit. Wow!

 

Share this post


Link to post
Share on other sites
On 10/4/2016 at 4:01 PM, Kurld said:

I've been playing this game off and on for three years and never realized you could right-click the maneuver nodes to get +orbit and -orbit. Wow!

 

That's probably because that feature wasn't always there.  I believe they added it in version 0.23.5 (the patch that added asteroids).

If you make use of that feature a lot, I recommend installing Precise Node.  You can go into its settings and tell it to replace the ±1k second buttons with +Orbit and –Orbit.  It's extremely convenient.

Edited by Entropius
  • Like 1

Share this post


Link to post
Share on other sites

Yeah that was about the time I went off on a hiatus.  I've used Precise Node  a LOT.  It's one of my "must have" mods!

Share this post


Link to post
Share on other sites

The last time I had docked was back in .90. After jumping back in 1.2 I was struggling to get the hang of it again. I tried watching Mech jeb do it to see if I could recreate it from that but I was still struggling, until I found your tutorial.

 

With the help of your tutorial I finally was able to dock last night. Not only have I learned how to dock, but now I can do it in a quarter of the time it took me in the first place.

Share this post


Link to post
Share on other sites

Thanks a lot for this guide, best tutorial ever with all options, there is no other tutorial like this out there

Share this post


Link to post
Share on other sites

Thank you! Thanks to these guides i finally managed a rendezvous, so thank you for posting. 

On 9/18/2016 at 1:17 AM, Entropius said:

Regarding launching guides, I doubt it's necessary to diagram, it's trivial enough to explain textually:  If your rendezvous target is in equatorial orbit, launch whenever you want to, it makes no difference. If your rendezvous target is in a significnatly inclined orbit you must launch your ship directly into the inclination of the orbit of the rendezvous target.  You'll probably have to do a tiny inclination adjustment once in orbit, but hopefully not much. It's made easier by (1) double-clicking Kerbin (or whatever body you are launching from) in map view so the camera centers on it instead of your ship and then (2) zooming out your camera enough to see the target-ship's orbit.  Then (3) while keeping the camera above the equator, orbit the camera around the planet until the target's orbit appears to become a thin diagonal line.  In other words, you want the camera positioned exactly above where the target's orbital plane slices into the equator's plane.  Then (4) wait for the body to rotate such that the launch-site lines up with the point the camera is facing.  Then you just tilt the rocket northward or southward upon launch by the right amount.  Kerbal Engineer lets you see your relative inclination, and keeping that number near zero helps you fine-tune the inclination as you launch.

This is what i was having the most trouble with as my orbit would be way off the target's and require a long burn just to adjust the inclination. So thank you for the help!

Also, to mark the launch site i had a kerbal plant a flag at the command center so when i click 'display flags' it shows the launch site flag so i can make the alignments in the tracking station instead of when i launch the vehicle.

Share this post


Link to post
Share on other sites

Thank you for this guide. Learn a lot and will keep it as a reference. 

Share this post


Link to post
Share on other sites

Thanks man. Two years of Kerbal and dozens of savegames, and today I managed the first orbital rendezvous with this guide. Sweet.

Share this post


Link to post
Share on other sites

Thanks. Absolutely wonderful. Nothing like your tutorial anywhere else on that matter. You know how to break things down and as a teacher (maybe you are one BTW), I can tell it's not an easy thing to do.

Edited by Kebral
Addition

Share this post


Link to post
Share on other sites

Wow. Such amazing.

This is the best tutorial I've seen :) Congratulations !

I think presenting the different techniques is really interesting, I didn't know the parallel orbit technique, witch seems to be really efficient and safer than the standard Hohmann transfer, witch can be risky (erm... Space station + shuttle + 400m/s = many spares ).

Thanks a lot for thins very nice work :) !

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now