Me messing up? Or really a bug? (rendesvouz almost impossible because of velocity )

[fastbikkel]

I will try and explain what i mean, hope it is clear.

I am comfortable in making a rendesvouz and docking. Done at least 20 succesful attempts now.

Now...

I wanted to do another one, i made a beautiful maneuver node that would get me within 5.1km of the target (space station at 400km orbit)

Once within range, the navball switched to "radar", as expected.

Now came the trick. I was getting close to the target, i was overtaking it from a lower orbit.

At around 5.3km i retroburned to neutralise the speed difference.

But i was not able to.

At the moment i started to burn i had a velocity diff of around 1000m/s.

When i reached 900m/s the station was moving away from me again.

This is the part i do not understand. I though the speed difference should be 0 if i am to move the same speed. I mean i am used to bring the difference to around 20m/s and then i will creep closer for the actual docking.

So in my case, the neutralisation velocity seemed to be around 940m/s.

But is that something wrong with me? DId i press a button that gives these values?

I tried again to get a 20m/s difffernce, because that is easier. But when i tried that, the target, still in front of me, moved away from me again.

I had to stay around 940 m/s the whole time, making maneuvering on the navball almost impossible. I could get close to the target, but i could not rely on the navball.

I know the value on the navball is always positive, i have been using this for all those succesful attempts and i never ran into these high velocity values.

[*Aqua*]

Are your and your targets orbit in the same plane? They have to or the plane change adds up an your relative speed.

[fastbikkel]

I had a near perfect plane. Over time i have been improving on that, i can now take off on a 90 degree trajectory that will put me on a near level plane.

I also checked it in the map view, i do not think that was gonna be a problem. At least, i had had worse "trajectories" in the past and my way of rendesvouz never was this troublesome.

[Comrade Jenkens]

I've had this happen to me before as well. I'm pretty sure it was a bug.

[PlonioFludrasco]

1000 m/s is quite a big difference at 5 km.

I suggest to start burning about 30s before your closest approach mark, and lower your speed below 100 m/s.

Then gradually slow down to 5 m/s at 1 km from your target, then engage RCS and aim for a docking port.

[*Aqua*]

Can you post a screenshot of the map view? Something must be wrong.

[Kasuha]

That's definitely strange, 940 m/s is pretty much exactly half the orbital speed at that altitude.

Was the distance to the target (under the target marker in main view) displayed correctly?

Are you perhaps using any mods?

[Kerbart]

The space station was at a 400km orbit. What orbit was your craft coming from? If you're coming in from a highly elliptical orbit there might be a large velocity difference (although 1000 m/s sounds like you were coming in either straight from launch or in a return orbit from another planet).

That, or some bug. You're not the first one to mention it. So it's either a bug or you're not the only one making this mistake.

Edited March 3, 2014 by Kerbart

[fastbikkel]

Well when i reached the 940m/s i was staying between 4 and 5km distance.

I did realise a 1000m/s diff is a lot, so i started to burn retro. In 5km distance i felt comfy i could burn off the diff, i had a big engine.

The distance counter stopped when i reached 940m/s (or around this). WHen i was at around 800m/s, the target moved away from me again while i was still behind it.

The only mods i have are "lazor docking tools (docking cam) and an alignment indicator", i think they are called plugins.

I brought my vehicle back for reentry after 5 or 6 unsuccesful attempts, i was getting desperate.

I have no screenshots, KSP crashes often when i press F1, i did not have the guts to do that.

I though i had maybe pressed a button that caused this.

[Kerbart]

Well when i reached the 940m/s i was staying between 4 and 5km distance.

There's two aspects on rendez-vous: at a given point in time, you need have have matching positions, AND matching velocities. Just being close is not enough. If you're matching a 400x400 orbit but you're in a 400x75 orbit then your velocity at apoapsis will be much lower (although not 1000m/s lower, more like 200m/s I think) and similar when you're coming in from a 1000x400 orbit.

[Kasuha]

"lazor docking tools (docking cam)"

There were some problems found with this mod if I remember correctly.

[wasmic]

You should try a closer Closest Approach. Go for, like, 1 km at most. PreciseNode can help with this, although it is completely possible with stock maneuver nodes.

[Comrade Jenkens]

Ok I encountered this round Bop and had to do the final approach by eyeball instead.

When I was perfectly stationary next to the target ship and only 5m away it was telling me that I was moving at 90m/s compared to the target. The navball was correctly switched to target mode.

[Scarecrow88]

I have had this bug on many occasions - no matter what you do you just can't close with low relative velocity. The only way I have found to circumvent it is to exit to the tracking station and then try again. I think this may reload the physics which sorts the glitch out.

[sanoj688]

Really strange.. but if you get close enough to your target so that your navball changes to Target mode, it should be easy and you could rendez vouz blindly: only by looking at the navball.

I'm guessing you already know but.. first cancel out your velocity by burning retrograde (in the navbal's target mode!!!) when you hit 0m/s you are traveling at the same speed as your target. But not for long, unless you are exactly in the same orbit/plane. Anyway, now depending on your distance to your target you want to accelerate towards the target marker. I usually pick a speed that will bring me to my target in no more than a few minutes.

So after you accelerated, go to the map view and see the ETA of the closest approach.

Warp till about 1 minute before the closest approach, use the navball (target mode!!) to burn retrograde which will bring your relative velocity down to 0 m/s. DO NOT OVERSHOOT. In fact, when your relative velocity is about 1-3 m/s, it's good enough.

Now repeat this untill you get really close, remember: You don't want to go too fast so divide the distance to your target by 100 to get a speed that will bring you to your target in about 2 minutes. You don't want to do this too fast.

[TYRT]

Different velocities on same altitude. Impossible. Clearly, It's a bug.

[Kerbart]

Different velocities on same altitude. Impossible. Clearly, It's a bug.

Try a 100×100 orbit and a 100×3000 orbit and dock at periapsis. You will find the velocity difference at the same altitude quite well within the realms of possibilities.

[radonek]

I had same problem after installing lazor docking cam mod.

[fastbikkel]

On the retry (after restarting the game) i did not get the same problem. Made an almost same maneuver again, but this time it worked again like i was used to, weird!

Hope this does not happen too often. I did not even uninstall the lazer cam mod. (i love that camera by the way)

KSP is still in development, i realise that.

I notice a lot of problems with KSP, but mostly it is just crashing to desktop. I had never encountered this velocity issue before.

[DonLorenzo]

I've had this happen once or twice. Was thoroughly confused

[Kasuha]

I did not even uninstall the lazer cam mod. (i love that camera by the way)

KSP is still in development, i realise that.

Note that incompatibility between the game and a mod is not considered game bug. If it happens next time I'd suggest you to try to uninstall the mod and try it without it. Or you may be a little more thorough and figure out sure-fire way how to reproduce the bug, then uninstall the mod and try that approach again. That way you can at least be sure it was or wasn't that mod.

[Kerbart]

I notice a lot of problems with KSP, but mostly it is just crashing to desktop. I had never encountered this velocity issue before.

You might want to take a look at your mods. I've clocked over a thousand hours in KSP and I've think I had one Crash To Desktop. It's behaving pretty flawlessly for me. I don't run a lot of mods (not that I'm against them, I just don't have a high-end machine that can run a lot of mods) and it's really, really stable for me.

[mythbusters844]

I had this bug once too. I even had the Lazor docking cam, so it seems to be caused by it. I had to restart the game to fix it.

[fastbikkel]

You might want to take a look at your mods. I've clocked over a thousand hours in KSP and I've think I had one Crash To Desktop. It's behaving pretty flawlessly for me. I don't run a lot of mods (not that I'm against them, I just don't have a high-end machine that can run a lot of mods) and it's really, really stable for me.

I have had the same amount of crashes before i started installing mods.

Really, i have a round 150mb of crashreports since i bought KSP.

I had removed the plugins before, but noticing no difference, i put them back into KSP.

But i guess that is a different topic? KSP crashes on the most simple actions, screenshot, moving back to the space center. Even when i just load a rocket it crashes.

After about 4 tries in an evening, i usually call it a day.

Also noticed on one occassion a radio dish was gone from my station after restarting KSP. I noticed the dish floating at a distance after i logged in again.

[Kasuha]

You might want to take a look at your mods. I've clocked over a thousand hours in KSP and I've think I had one Crash To Desktop. It's behaving pretty flawlessly for me. I don't run a lot of mods (not that I'm against them, I just don't have a high-end machine that can run a lot of mods) and it's really, really stable for me.

I'm playing without mods and I see no problem crashing KSP to desktop. I got two or three crashes within an hour when I was designing my spaceplane, for instance. I didn't bother trying to create a reproduction scenario yet but crashing your ship around launchpad or runway or maybe just to planetary surfaces a lot seems to suffice. That doesn't have to have anything to do with mods.