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A Rendezvous Conundrum


Question

I understand that at least 90% of my KSP forum posts are complaints about bugs, but this one is particularly annoying.

 

Let's start at the beginning: I built and launched a simple space station. Lacking creativity, I named it Station One.

After a few in-game years without trouble I decided to retire Station One. To service the station during its final missions and to assist in the construction of a new station, I built the Space Shuttle Kollumbia based of @ShadowZone's excellent 1.4 design (as console recently got the rough 1.4 update equivalent, the design worked perfectly: the shuttle completed a rigorous shakedown mission without fail).

Problems started as soon as I rendez-voused with the station. Using the RCS jets, I maneuvered close to Station One's docking port. I decelerated to a halt. Suddenly, I began to accelerate in the radial out direction. My orbital velocity stayed the same, but my relative velocity was changing against the station. I checked the map view and my orbit was elongating. I switched off my RCS and engines, but I kept accelerating. I ended up reverting the flight.

This spontaneous acceleration now occurs during about 50% of my docking attempts (and only during rendezvous, nowhere else.

 

Can anyone help?

Edited by Jebediah Kerman Jr.
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This is still happening.  I experienced the same thing just the other day during a rendezvous maneuver.  Our orbits were completely coplanar, and as I closed within 100 meters, the target vessel suddenly started moving away rapidly.

I gave chase, but was unable to close the distance.  When I checked the map, our orbits were now sub-orbital trajectories, and we were climbing towards a very high apoapsis.

My brother who plays on Xbox One confirmed that this happens on that console as well.

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16 minutes ago, Jebediah Kerman Jr. said:

Suddenly, I began to accelerate in the radial out direction. My orbital velocity stayed the same, but my relative velocity was changing against the station. I checked the map view and my orbit was elongating. I switched off my RCS and engines, but I kept accelerating. I ended up reverting the flight.

This spontaneous acceleration now occurs during about 50% of my docking attempts (and only during rendezvous, nowhere else.

That's weird.  I've never observed that myself, nor have I ever heard of anyone else experiencing the same problem.

A few questions:

  • What platform are you playing on?  And what KSP version?
  • When you say "accelerating", how big an acceleration are we talking about, here?  Do you mean "it gains 0.1 m/s over the course of a minute"?  Or "it's pulling a full gee of acceleration"?  Something in between?  Can you estimate how much dV per second (or per minute, if it's small)?
  • Do you notice this when everything is turned off (no throttle, and RCS is deactivated)?  Or does it only happen when you have RCS turned on?
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2 hours ago, Snark said:

That's weird.  I've never observed that myself, nor have I ever heard of anyone else experiencing the same problem.

A few questions:

  • What platform are you playing on?  And what KSP version?
  • When you say "accelerating", how big an acceleration are we talking about, here?  Do you mean "it gains 0.1 m/s over the course of a minute"?  Or "it's pulling a full gee of acceleration"?  Something in between?  Can you estimate how much dV per second (or per minute, if it's small)?
  • Do you notice this when everything is turned off (no throttle, and RCS is deactivated)?  Or does it only happen when you have RCS turned on?

To answer your questions:

I am playing on an Xbox 1S.

When I say "accelerating", I mean somewhere around 1 m/s. It was enough so I couldn't fight it using my RCS.

Everything was turned off. I even double-checked by pressing the "throttle-down" button. The RCS light was not on.

I hope that clears things up a bit.

Edited by Jebediah Kerman Jr.
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1 hour ago, Jebediah Kerman Jr. said:

When I say "accelerating", I mean somewhere around 1 m/s

So, "1 m/s" is a velocity, not an acceleration.  Did you mean "1 m/s2" acceleration?  i.e. if you wait 10 seconds, you gain 10 m/s velocity?

(Sorry, I really don't mean to be pedantic-- just want to be sure we're on the same page, here, so we don't end up talking at cross-purposes.)

If you've got a phantom acceleration that big, when RCS is turned completely off and you have no throttle, then that sounds like a bug.  Moving to Technical Support.

 

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1 minute ago, Snark said:

So, "1 m/s" is a velocity, not an acceleration.  Did you mean "1 m/s2" acceleration?  i.e. if you wait 10 seconds, you gain 10 m/s velocity?

(Sorry, I really don't mean to be pedantic-- just want to be sure we're on the same page, here.)

If you've got a phantom acceleration that big, when RCS is turned completely off and you have no throttle, then that sounds like a bug.  Moving to Technical Support.

 

Oops. You're right, I meant 1 m/s2

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To elaborate... We'll just say its a saturn 5esque ship to the mun... Everything goes fine until trying to rendezvous ascent vehicle with command module.  Inside about 1km the target (com mod) starts moving away. Upon switching to offending vessel i have no control of anything but throttle.  Engine gimbals do move but no change to craft heading.  Oddly enough after multiple vessel swaps i can still revert flight to vab or launch._. Ive captured a video via ps4 share feature but no idea how to get it here or elsewhere except facebook.  This was an issue prior to, and after a game delete/Reinstall/Save file wipe. Current version as of 27Aug19 but got the initial problem a few weeks ago._   if someone cares to boot this up the chain, feel free to copy paste.

 

Edited by Flip665
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On 8/28/2019 at 3:02 AM, Flip665 said:

To elaborate... We'll just say its a saturn 5esque ship to the mun... Everything goes fine until trying to rendezvous ascent vehicle with command module.  Inside about 1km the target (com mod) starts moving away. Upon switching to offending vessel i have no control of anything but throttle.  Engine gimbals do move but no change to craft heading.  Oddly enough after multiple vessel swaps i can still revert flight to vab or launch._. Ive captured a video via ps4 share feature but no idea how to get it here or elsewhere except facebook.  This was an issue prior to, and after a game delete/Reinstall/Save file wipe. Current version as of 27Aug19 but got the initial problem a few weeks ago._   if someone cares to boot this up the chain, feel free to copy paste.

 

You can upload directly to youtube with your ps4. Not sure if you need to have youtube installed, you do need to link an account though!

Edited by Cruss
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On 6/21/2020 at 7:15 AM, Demordrah said:

This is still happening.  I experienced the same thing just the other day during a rendezvous maneuver.  Our orbits were completely coplanar, and as I closed within 100 meters, the target vessel suddenly started moving away rapidly.

I gave chase, but was unable to close the distance.  When I checked the map, our orbits were now sub-orbital trajectories, and we were climbing towards a very high apoapsis.

My brother who plays on Xbox One confirmed that this happens on that console as well.

I am confirming this is happening on PS4, game and console up to date as of 06/21/2020.

 

Very frustrating, trying to dock ship with mobile processing lab in orbit, everything going fine, closing in to 2 km away, kill velocity relative to target, accelerate towards target at ~5 m/s, close in, eventually get to something like 200 m away and out of nowhere the target goes flying off in a different direction.  

 

I switched focus to the mobile processing lab and couldn't switch back, it says it is 'under acceleration' even though it has no engine and the RCS was turned off.  Had to revert to an earlier save.  

 

The mobile processing lab that I'm trying to dock with has no liquid fuel, and no engine, just some RCS thrusters. Checking the map afterwards, the orbit of the mobile processing lab went from nearly perfect 138 km orbit around Kerbin up to some crazy elongated 190 km apoapsis 130 periapsis.  

 

Hopefully they will fix this. This, on top of the constant lockups make the game look very bad.  

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I can confirm that I have been experiencing the same thing on PS4. It has happened with different types of vessels and near different planets. Now I make sure to *always* do a quicksave before attempting a rendezvous.

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