DockingMFD The Rendezvous Burn

[fullarmor2]

I'm in the Arrow and I launched from Mercury to orbit. I needed to rendezvous with the XR2 which is in a 2200 km orbit(not far from my GasMiner_Station at that orbit) and is crewless, so I can have Doug Brown, one of my pilots, do a space walk to the XR2 so he can get it docked in the bay. So, when I'm closing in after the trans XR2 injection burn from a lower parking orbit, I intend to do the rendezvous burn at about 1km distance from the XR2. I have nav/com set and the docking mfd. My question is, in the docking HUD, how do I know which velocity vector in the HUD to burn towards in order to decrease the relative velocity? I keep burning on the wrong one and it raises my relative velocity, then I have to turn all the way around and burn the other one, which works, but by that time I have botched the rendezvous!:facepalm:

 

[blixel]

My question is, in the docking HUD, how do I know which velocity vector in the HUD to burn towards in order to decrease the relative velocity? I keep burning on the wrong one and it raises my relative velocity, then I have to turn all the way around and burn the other one, which works, but by that time I have botched the rendezvous!

It's easy to understand if you just think about the movement of the objects. If you are closing in on the target, then burning toward the positive velocity vector will make you speed up, and that's not what you want. When closing in on an object, you want to slow down as you approach the target.

I tend to know this by experience/intuition at this point, but in Dock MFD, if your relative velocity is showing as Yellow, then you are currently on a trajectory that is bringing you closer to the target. If the relative velocity is showing as Green, then your trajectory has you moving away from the target.

Note that if your relative velocity difference is small (like 50 m/s or less), then you can face the positive velocity vector and use retro engines instead. I do almost all my rendezvous braking burns that way.

Edit: Here's a video from my youtube channel showing a rendezvous with another XR2. (The video is set to skip ahead so that it starts playing at 812 seconds [13m32s].) Note that at 14:25, I can see that I am closing in on the other XR2. The Docking HUD shows the velocity difference in yellow.

Here is a second example.

[ame="http://www.youtube.com/watch?v=TK5kC4Cy0-U#t=1288s"]Orbiter 2010 - [Part 2] From the Earth to the Moon and back again - YouTube[/ame]

 

[fullarmor2]

This will help. Thanks.

 

[Mister Mxyzptlk]

Another way to rendezvous in a scenario like you have described is to use IMFD orbital function and use auto burn with the velocity match function after you have set all the parameters. Fire auto burn when time to rendezvous according to the sync orbit MFD is about half of your burntime according to the autoburn timer. This is an almost foolproof way to get close enough to dock then switch to the docking mfd.