How to synchronize an orbit with another ship?

[Brucifer]

I want to try and conduct a little rescue mission for a previous ship that went into orbit and ran out of fuel. The only problem is, I'm having trouble getting my ship to that other ship. I still don't understand the concept of what happens when you click on the other ship and click "set as target" besides the fact that it tells you its orbital plane's intersections with your own. Is there any way to go about doing this, by perhaps synchronizing your orbit with the other ship's orbit? Or is there an easier way to do it?

[blizzy78]

I wrote a tutorial and made a video about just that: Launch, rendezvous, and docking. See my signature.

[capi3101]

When you set the other ship as the target in the map mode, you should see one or two sets of chevrons appear on the orbital path of your craft. These are your "intercept" points, the points where the orbits of the source and target crafts cross one another. They'll also tell you what the distance between the two craft will be at those points. Your job is to get that value down...within 1.0 km if you're just doing a rendezvous, all the way to zero if you're going to try to dock.

You should also see two markers labeled "An" and "Dn". These are the ascending and descending nodes, respectively; when your reach the ascending node, your craft's orbit will begin travelling northward of the target's and vice versa. For a successful rendezvous, you want this to be zero in all cases - and you'd prefer it to say "NaN", which means "Not Applicable Node" (I think), which means your orbits are aligned spot on.

So here's how you get to a rendezvous:

1) Note the locations and altitudes of the target's apoapsis and periapsis. When you launch the source craft, you're going to want your source craft's orbit to have as close to the same apopasis/periapsis altitudes/positions as you can manage. I find that waiting until the target is about 450,000m uprange of KSC helps, but you can play around with that value.

2) Launch and get into orbit.

3) Evaluate how well you did. Start with the ascending/descending nodes. If the value isn't zero, you're going to have to adjust the inclination of your orbit. Assuming you've launched eastward (heading 090) like all good Kerbonauts should, you want to aim southward on the horizon if you'll come up on the ascending node first and northward if the descending node is coming up first.

4) When you reach the node, perform a slow burn (unless you've really botched the launch and have a node of 15 degrees or more, then floor it). Get the value as close to 0.0 as you can. If the node starts pulling well away from your ship, stop the burn - if you're still not at zero at that point, try again later.

5) Meantime, when you come up to your first apsis, aim prograde and make a slow burn, and watch the effect it has on the intersects. If the value increases, stop, turn around and burn. Keep burning until the distance starts going back up again.

6) Keep doing this when you hit the nodes and apses. Eventually you'll figure out which way you need to adjust your orbits to bring the value down. Bear in mind that as long as the distance between the two craft is narrowing on its own, you don't necessarily have to do this every time you reach one of these points.

7) If you get close enough to the target, your game may automatically switch you over to "Target" mode on your velocity display. Unless you've got a close rendezvous on your intercepts, I'd manually switch it back over to "Orbit" mode. You can go back to Target mode once things are getting close.

8) Once you've got a close pass - within a kilometer, preferably within 0.5 kilometers, switch over to Target mode. Your gauge will now display your craft's velocity relative to the target. You want this to be roughly 1 meter per second per 100 meters range to the target; if you're travelling faster than that, aim retrograde and make a slow burn.

9) When you've closed to 2250m, you may notice the game shutter ever so slightly depending on your machine; that's the physics engine picking up the other craft.

10) I've already written up something on how to do the final docking today, if you need that. Here's the link.

Good luck; let us know how things turn out.

[draeath]

NaN means "not a number" - effectively zero