Making orbital rendezvous less laborious

[cephalo]

The only thing about this game that becomes drudgery for me is trying to guess where to place a maneuver node for an orbital intercept. I've been able to 'bracket' my targets so my choices are not just random, but these types of calculations are what computers are for. I don't want to automate the whole process of a rendezvous, but is there an addon that will at least choose the first available intercept node location?

[Kelderek]

MechJeb can autopilot the entire thing for you if you want and it also has a planner if you want to do the steps yourself.

[ElWanderer]

This doesn't answer your question about calculating an intercept (is this something MechJeb can do?), but are you aware that you can drag manoeuvre nodes along your flight-path? Or that if you right-click you can advance a manoeuvre node to the next orbit? Yes the location of my nodes are usually a guess at first, but it doesn't take long to drag them round and advance orbits until I get near an intercept. Helps if your orbit and that of the target are circular, of course.

[adinfinitum]

The one location that will always work for an intercept is either the ascending or descending node. Raise up one of those two so that it crosses your target's orbit, and then place a maneuver at that node. If you're not to far from the target you should be able to fiddle with prograde and retrograde until you get a rendezvous next pass, otherwise you'll have to set it up so that the target gets a little closer each time.

[cephalo]

This doesn't answer your question about calculating an intercept (is this something MechJeb can do?), but are you aware that you can drag manoeuvre nodes along your flight-path? Or that if you right-click you can advance a manoeuvre node to the next orbit? Yes the location of my nodes are usually a guess at first, but it doesn't take long to drag them round and advance orbits until I get near an intercept. Helps if your orbit and that of the target are circular, of course.

No I did not know that! Thank you, that should save loads of time if I can do that. I knew that you could advance orbits, but I didn't know you can drag the node.

I'm a little afraid of MechJeb. I'm having a lot of fun and I'm not sure if I can resist using autopilot for everything.

[OhioBob]

This doesn't answer your question about calculating an intercept (is this something MechJeb can do?), but are you aware that you can drag manoeuvre nodes along your flight-path? Or that if you right-click you can advance a manoeuvre node to the next orbit? Yes the location of my nodes are usually a guess at first, but it doesn't take long to drag them round and advance orbits until I get near an intercept. Helps if your orbit and that of the target are circular, of course.

^This^ usually works pretty well for me.

There is also this: Orbital Rendezvous Made Easy

[cephalo]

The one location that will always work for an intercept is either the ascending or descending node. Raise up one of those two so that it crosses your target's orbit, and then place a maneuver at that node. If you're not to far from the target you should be able to fiddle with prograde and retrograde until you get a rendezvous next pass, otherwise you'll have to set it up so that the target gets a little closer each time.

Really? That surprises me. I imagine that would fail if the orbits are too similar and out of phase.

[OhioBob]

The one location that will always work for an intercept is either the ascending or descending node.

I always make my orbits coplanar before performing a rendezvous. Makes it much easier.

[KatzOhki]

It's possible to launch directly into a rendezvous or at least near-rendezvous, but I don't know where to find a good tutorial on that.

[adinfinitum]

Really? That surprises me. I imagine that would fail if the orbits are too similar and out of phase.

If the semi-major axes of your orbits are close to the same then you'll only get a tiny bit closer or farther each time. The key is the lower your orbit, the faster you'll catch up to a target in front of you, and the higher your orbit the faster you'll catch up to a target behind you.

If you make your orbits coplanar beforehand then you can move any location on your orbit so that it's an intersection, its just that a lot of times I don't feel like making a plane change if its only a couple degrees difference.

[Alshain]

No I did not know that! Thank you, that should save loads of time if I can do that. I knew that you could advance orbits, but I didn't know you can drag the node.

I'm a little afraid of MechJeb. I'm having a lot of fun and I'm not sure if I can resist using autopilot for everything.

Definitely a useful tip, but if you really want to cut the trouble out of rendezvous, practice launching when the craft you are intercepting is just slightly behind the surface where you are launching from. You can then find an 5km intercept without ever establishing orbit at all (you establish orbit as you approach and slow your relative speed instead). The upside to this is less expended fuel trying to rendezvous and a much faster intercept. The downside to this is you end up approaching the target very fast, so you need to be on your toes.

This gets a little harder if it isn't equatorial, but still possible.

Edited May 12, 2015 by Alshain

[cephalo]

I added the click and drag thing to the wiki. That's really important info and it wasn't there.

[Mr Shifty]

It's possible to launch directly into a rendezvous or at least near-rendezvous, but I don't know where to find a good tutorial on that.

<Good tips>

This gets a little harder if it isn't equatorial, but still possible.

If you're trying to launch-to-match-orbit and your target is on an inclined orbit, it's actually not too difficult. You can only launch twice per (Kerbin) day -- when either the AN or DN of your target's orbit passes overhead -- which means that you can't launch straight to rendezvous unless your target passes overhead at the same time. If your target's AN is passing overhead, you need to launch to 90°-target_inclination. If the DN is passing overhead, you need 90°+target inclination. After launch, rotate 3-4° west of that heading to account for Kerbin's eastward rotation. When you start getting significant horizontal velocity (pitched down to 45° or so), switch to the map screen and observe how well your sub-orbital arc aligns with the target orbit. You can rotate left and right as you ascend to adjust your orbit's inclination to match the target. (This sounds difficult, but is surprisingly easy to do if you try it.) Push your orbit out to the target's altitude, coast to apoapsis and proceed to rendezvous as normal.

Edited May 12, 2015 by Mr Shifty

[Kaezan]

The best way to learn orbital rendezvous is to practice.

Launch a station with 4-5 docking ports. Make it so that you can attach another station and still have space near all ports.

then launch any kind of ship. small, big, probe, manned, unbalanced, refueler. try, fail, try again until you learn. before you know it, you are making orbital rendezvous without even placing a node

[n0xiety]

I'm a little afraid of MechJeb. I'm having a lot of fun and I'm not sure if I can resist using autopilot for everything.

Mechjeb by no means makes the game too easy. You still need to know what you are doing to give it commands. Since it can fail from time to time. And it is really not possible to do some of the precision movements like getting a sattelite into specific orbit using mechjeb. Sure you can get close to it easy. But then its up to you to create the node and make precision movements. On the other hand mechjeb makes boring and repetetive tasks like executing a node that you created or orbit ascent easy. Just create your node and let the mechjeb execute it with precision. Why warp yourself and then use the thrust yourself its just repetitive. If you want to intercept something from ascent even mechjeb can't do it in 1 go atm. It will takeoff at a close encounter and get you into a close orbit near your target. But then you need to use randevous autopilot. Even then the randevous autopilot cannot do moves like randevous with something that is in a polar orbit while you are in equatorial orbit. It will probably try going trough the planet itself and crash you. The thing is manuvers are allready calculated and executed by computers in real life. The only thing the pilot does is either give the manuver info to computer or just sit there and supervise it.

Edited May 12, 2015 by n0xiety

[Empiro]

There's a couple of rules of thumb, but for most Kerbin intercepts (which are equatorial), I launch just before the target passes overhead, and I launch into a lower orbit. This usually puts me slightly behind my target and I will quickly catch up. I have a steam guide here that goes over the easy case (the key is to be in circular orbits, and then drag the maneuver node back and forth to get the perfect intercept):

http://steamcommunity.com/sharedfiles/filedetails/?id=289580294

There's different tricks you can do if you or your target are on significantly different inclinations or if your target is in an elliptical orbit. They're a bit advanced, but we can discuss those here if you wish.

[SanderB]

The first 10 min or so of

deal with an equatorial rendezvous.

The most important things I can think of are knowing how long it takes for you to reach orbit and how far ahead of KSC you are when you do reach orbit. If you have KER, add up the burn times of every stage until the cumulative dV reaches 3,3km/s or so. Based on that you can decide how far back the target needs to be behind KSC for you to properly time your launch.

Then, while launching when you get within 100km of your target you switch the navball to target navigation so you see your relative velocities, and you push your relative retrograde-velocity marker on to your anti-target marker as close as you can, while monitoring your closest approach until they minimize. The retrograde-velocity marker can be pushed by burning on the far-side of the anti-target marker.

At the same time you need to track your distance and the amount of distance you will traverse to cancel out your relative velocity with the V^2/2A formula ((relative) velocity squared divided by double your acceleration) so you don't let your target overshoot you.

As long as you don't need to burn more than 30° away from your retro velocity marker you don't lose more than ~5% of your total mission dV.

And just practice and practice. You need a lot of practice.

2nd demonstration video, demonstrating the relative velocity anti-marker approach in particular.

Edited May 12, 2015 by SanderB

[SDEngineer]

No I did not know that! Thank you, that should save loads of time if I can do that. I knew that you could advance orbits, but I didn't know you can drag the node.

I'm a little afraid of MechJeb. I'm having a lot of fun and I'm not sure if I can resist using autopilot for everything.

Generally with MechJeb, you've already done what it can do well enough to become proficient at it before it unlocks the ability in the tech tree. Besides, at a certain point in your KSP career, it becomes more about building your space program, and less about actually piloting all the missions yourself. I generally personally fly all my "historically significant" missions (all my first landings, major launch of a new interplanetary explorer class ship, etc). But do you really want to do something like personally dock every single fuel tanker transport coming from Minmus to your LKO refuelling station? I don't. Those are what I fly with MechJeb fully automating, since it will go far faster. I'm good at flying and docking, but MechJeb, since it uses time acceleration so well, can fly a Minmus fuel mission to my LKO station and have it docked there in a tenth the time I can do it myself - for a mission profile I've done a half dozen times personally and need to do at least a dozen times every Kerbal year.

[Rickenbacker]

Draw an imaginary, straight line that crosses the outer orbit and just tangents the inner orbit where the orbiting craft is. Then just look at where the two craft are relative to each other. When the outer craft hits the "forward" intersection, make your burn (obviously raise your orbit if you're the inner craft, lower it if you're the outer one). Doesn't have to be too exact, this is only a rule of thumb, but it gets you in the ballpark.

[tomf]

I use preceisenode to fine tune my renevous down to <200m. Using the numpad keys to fine tune the time and size of your burn while mouse overing the intercept marker to see the distance makes it easy to get very close intercepts.

[magnemoe]

MechJeb can autopilot the entire thing for you if you want and it also has a planner if you want to do the steps yourself.

Funny enough its one of the few things mechjeb is bad at (outside of atmosphere in 1.0)

Here is how I do it, this assumes the orbits intercept you you are at say 80 km and target is at 120 its a bit different.

Put an node after the intercept point, this will move the position the closest position as its not then you reach it but the next orbit.

Now put an node on the other side of kerbin, and add some dV to the first node, you see the intercept point move, if the difference is huge like on the other side of the planet you will want to use multiple orbits, use the + on the back reference node to see position after two orbits or more, this depend on your dV budget.

Do the burn, you might want to use RSC for accuracy. Now warp to the opposite node and do an adjustment burn to get as close as possible. RSC is again useful.

i tend to use mechjeb for this and the match speed with target.

next is to burn toward target and brake close to it and dock.

Matching planes with target is not very needed however can smart to do at Ap, this will require an new fine tuning burn.

If you are in higher or lower orbit than target you first has to create an intercept, here its smart to match plane first, then make the intercept node, you might want to move it around even wait some orbits before burning, again do fine adjustment preferable with RSC.

Remember you don't want Pe below 70 km around Kerbin, negative Pe is always bad

[bonyetty]

Launch when your target craft is over kerbal India(brown land looks like India). It will vary with the thrust profile of your launch craft. A bit earlier for low thrust to weight and bit later for high thrust to weight launch craft.

[Rickenbacker]

You can also drag the maneuver node along the orbit by grabbing the circle in the middle, in case you didn't know. Very helpful once you're in the general ballpark.