General Question Help needed with rendezvous

[Blacklight]

Okay. Newbie question here. After YEARS using Orbiter for simple sight seeing by cheating and making scenario files, I've actually decided to learn how to actually fly in this thing properly.
So far, I'm a pro at docking, undocking, and docking to different ports in the same structure. What I am having issues with is rendezvous. I've been using the Delta Glider starting docked to the ISS scenario and I've been trying to fly to MIR. I do everything fine until it comes down to the part where I have to slow down once I get to the rendezvous point. There are two "Relative Velocity Markers". One that adds to your velocity, and one that minuses it. My problem is that every time I point my ship at the proper velocity marker and hit my engine to slow down, the marker goes skittering all over the place wildly until it gets impossible to keep my ship pointed at it and it seems no matter what I do, I'm never able to get anywhere near zeroing out my relative velocity. If anything, my relative velocity seems to increase wildly even when I do manage to lower my relative velocity. What am I doing wrong ?

 

[Sar]

You can move your velocity direction around with linear thrusters to keep you going towards your target while your relative velocity decreases.

(I think tex has an excellent tutorial vid for rendezvous somewhere, that's where I learned it)

 

[Blacklight]

My problem is that even using linear thrusters, the reletive velocity markers start moving all over the place really fast, especially when I lower the speed. The lower the speed, the more they shoot all over the screen. I never get ANYWHERE near zero either. My relative speed always jumps directly from 1 toward to 1 away, even when using ctrl with the linear thrusters.
The only other thing I'm wondering is that maybe I'm setting the rendezvous up wrong, but following the written instructions that I have, I'm doing everything right. I always end up going whizzing past my target, or the target outraces me.

 

[Bloodworth]

First off, are you talking about the pro/retrograde pipets? If you are, is your HUD in orbit mode, atmosphere mode or docking mode?

As your speed approaches relative zero the pipets will swing around and switch places. This does not mean that your vessel is changing relative direction, only that your speed is approaching zero relative to the planet you are orbiting.

If you are talking about the docking pipets (the ones that have distance from and relative velocity to the target) then you need to keep in mind that it is nearly impossible to come to an absolute zero in relation to another orbiting body until you are actually DOCKED to it. Even if you match it's speed exactly, the different masses of the objects (unless you are using 2 IDENTICAL vessels) will slowly result in slightly different speeds and thus the objects will begin to drift apart.

 

[Blacklight]

I'm talking about the docking pipets. I'm 100% sure of it. I think that something's going on where I'm just coming in too fast. I'm at the proper altitude, but when I try to slow down and maneuver the direction of velocity marker over the target, it doesn't translate. The thing either goes zipping off the screen, zips around all over the place, and doesn't translate over the targer or anywhere near it. It always gets to a certain spot near the target but can go no further towards it. Like I said, I think I may be coming in too hot somehow.

I'll practice some more tomorrow with Tex's tutorial.

 

[Bloodworth]

Is the pipet round with a cross (or just a cross) or is it square with numbers?

Try doing the approach by feel and see what happens to the pipet. Don't respond to what the pipet is telling you, do it visually and see what the pipet does. This will show you what is happening to the pipet when at slow speeds.

 

[johan]

Do you have nonspherical gravity sources turned on? I haven't ever seen it in action, but this is the only way I can think what you're describing can happen.

Actually, come to think of it: another possibility is the mistake I made last night: Instead of closing my main thrusters to zero, I accidentally left the retro thrusters open about 2%, without noticing. This made the pip blast around the screen erratically at slow relative speeds, in almost the way you're describing. Make sure your main thrusters are at 0%.

 

[Evil_Onyx]

It may be that you are trying to translate with an autopilot active. I have seen the HUD do strange things when i left an autopilot on and try to maneuver vessels.

 

[Tommy]

What is the relative velocity when this happens? RVel should be under 200 m/s (under 100 is better) at intersect, BEFORE you start trying to lower it. An approach faster than that will complicate things quite a bit. If your RVel is quite low (under a couple m/s) you will need to be very cautious with linear RCS to get it much lower. That's fine, you don't really need to - once you are down to a couple m/s, turn toward the target and give a bit of forward thrust. The "+" hud indicator should come into view, and then use linear RCS to place the "+" on the target station. Keep RVel low (around 10 to 15 m/s) and use Linear RCS to keep the "+" centered on target until you are closer. Use DockMFD and set the com frequency to the ISS's transponder (use the main transponder for initial rendezvous, not a particular docs IDS).
Have you matched planes correctly? Even a half degree of RInc can make docking very difficult.

The easiest way to null the RVel is to use IMFD. In the "Orbital Ops" section there is a program to cancel the RVel between you and a target.

 

[Blacklight]

Well. I discovered part of my problem was that I had "Nonspherical Gravity Sources" checked. I unchecked it and now my relative velocity markers don't jump all over the place like humming birds looking for flowers. I was finally able to somewhat rendezvous with Mir this time. Docking took me a long time to do. I kept bumping into the station, backing up, and bumping into it like a drunk driver.
I'll bet the Russians inside were either laughing at me or fearing for their life, or both.
I DID manage to dock though.
So. I need to work on docking too. So I'm now practicing starting docked to the ISS, undocking, and then picking another port at random and docking there over and over again until I get used to it.

 

[Tex]

http://www.orbiter-forum.com/showthread.php?t=2055

 

[Tommy]

I've noticed that MIR has a sort of forward "tumble" to it that can make docking very difficult since it's hard to maintain alignment with the port. The ISS is definitely easier to dock with, and can use the standard "prograde" AP to minimize spin.

 

[Blacklight]

Tex: Watched that vid several times in the past few weeks. Excellent tutorial ! :thumbup:

My main trouble with MIR was FINDING the blasted docking port. The whole surface is dark gray and unless the port you're aiming for is pointed EXACTLY right so that the sun shines just right on it, I can't really SEE the ports. I have no issue finding the ports on the ISS though.

 

[johan]

Yeah, I docked with MIR myself last night after doing many successful dockings with the ISS. MAN, it was like driving a car into a garage with the limitation that you have to be on two wheels the whole time!!

It definitely has some sort of tumble that makes it difficult.

 

[KosmoKen]

My main trouble with MIR was FINDING the blasted docking port. The whole surface is dark gray and unless the port you're aiming for is pointed EXACTLY right so that the sun shines just right on it, I can't really SEE the ports. I have no issue finding the ports on the ISS though.

Are you using the Docking HUD? it will highlight whatever docking port you have selected in your NAV1 in the COM/NAV MFD. There's also a docking port revealer made my Artlav somewhere that works nice.

 

[johan]

Are you using the Docking HUD? it will highlight whatever docking port you have selected in your NAV1 in the COM/NAV MFD. There's also a docking port revealer made my Artlav somewhere that works nice.

This makes me wonder why most ships do not have an external light... that would have solved it!

 

[Izack]

Yeah, I docked with MIR myself last night after doing many successful dockings with the ISS. MAN, it was like driving a car into a garage with the limitation that you have to be on two wheels the whole time!!

It definitely has some sort of tumble that makes it difficult.

You think that's hard? Try docking to Kulch's Mir-2... >.>

 

[Blacklight]

It definitely has some sort of tumble that makes it difficult.

Those Russians probably started that spin on purpose.

I guess the fact that I actually succeded in docking with MIR twice was either skill or blind luck.

Man. Just wait until I start practicing flying to other planets !!!