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Thread: Docking with MechJeb 2.0.8 - General Question of understanding

  1. #1

    Docking with MechJeb 2.0.8 - General Question of understanding

    I am playing around with KSP for about two weeks now and currently I am trying work things out to send a small space station in a 100km orbit around Kerbal.

    So here is what I did: Launched the station core (based on the "Space Station Core" included in the game) into a 100km orbit. This worked fine.

    Now I launch a second craft to dock to the staion and bring the first crew up there. Sidn docking is not that simple for a beginner, tried to use the functions of MechJeb 2.0.8 for it.

    1) Launch: Selected the Staion as the target and used the "Select target for a tmes launch" function in the "Ascent Guidance". Works fine, my craft goes up in a 100km orbit and is about 100° ahead of the staion.
    2) Use the "Redezvous Autopilot" autopilot: It first align planes and then puts me up in a 217km orbit. As I am ahead of my staion, I must go to a higher orbit so that the staion can come closer, understood. After the 217km orbit has been circulized, the next manouver point is the hohman transfer. And here is where I lost the understanding. The autopilot then calculates the time for the next manouver - to return to the 100km orbit to be able to make the final approach with 63years ?!?!!? At that point, the game gets very laggy and I cannot define any manual manouver points for my craft anymore even when I turn off the autopilot.

    So what am I doing wrong here, or is there a point that I have totally missed?


    I started up again and re-launched my station, but then the result was the same, so I am a bit confused now.

    Thx for any input that would help me to understand

  2. #2
    Moving this to Addons Requests and Support, since it is MechJeb related.

    I've heard of at least another person with this issue, so I assume the latest version of MechJeb has an issue with rendezvous.

    I'm a bit confused with the need to circularize the higher orbit, though... It shouldn't be required, but might be faster to get an intersection with your target - to the cost of some fuel.
    I personally prefer to keep either my Pe or Ap intersecting with my target's orbit, and tweak the other side to get close.
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  3. #3
    I have had the same problem a few times myself. My soloution: disengage the autopilot, change the distance to something larger, eg 1000 or 5000 or 10000, u know, larger than you origional value. Rengage the autopilot, and it should work. If it occurs again with your larger value, then just repeat the above steps

  4. #4
    Rocketeer
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    This always happens to me using the Rendezvous Autopilot. When it happens, I fire up the Rendezvous Planner en click the Hohmann Transfer button. It then recalculates the time to correct values. After that, everything works fine. Seems to be a bug in MechJeb.

  5. #5
    Ok, thanks for the info. So it seems as if this is a bug. Will have to test those tips this evening.
    I think I tested it with changing the distance, but this had no effect at all.

  6. #6
    ok. first off I don't know how to make mechjeb dock FOR you. however. there is a super simple way to make mechjeb do half your work for you.

    step1) right click the docking port you want to dock onto and set as target.
    step2) use the advanced SAS pannel to tell mechjeb to point at target. if you end up pointing in the wrong direction, right click YOUR docking port and select "control from here"
    step3) enter docking mode and manuver onto target without having to worry about rotation. don't try to dock above 0.3m/s you will fail if you do.



    if you wish to make your manual docking life EVEN EASIER. install lazor docking cam. it adds a cammera to all docking ports that can be accessed via right clicking, and said camera comes up as a window when activated which has red markers indicating your relative motion and position to help you steer onto target. the kind of thing real astronauts have access to.

  7. #7
    2nd Assistant Lackey Jack Wolfe's Avatar
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    Quote Originally Posted by Cykyrios View Post
    Moving this to Addons Requests and Support, since it is MechJeb related.

    I've heard of at least another person with this issue, so I assume the latest version of MechJeb has an issue with rendezvous.

    I'm a bit confused with the need to circularize the higher orbit, though... It shouldn't be required, but might be faster to get an intersection with your target - to the cost of some fuel.
    I personally prefer to keep either my Pe or Ap intersecting with my target's orbit, and tweak the other side to get close.
    The only time I've seen MJ2 jump to a circularised higher orbit is when the rendezvous target is behind your vessel. Higher cost in fuel for a quicker intercept. So far, after about 20 rendezvous and dockings I have yet to see MJ botch it once.
    So, physics! Physics, eh? Physics! Phyyyysics! Physics, physics, physics, physics, physics. I hope you're getting all this down...

  8. #8
    If you launch a test flight first, let the ascent guidance circularize and turn it self off, then it will be much more accurate when timing for the launch to rendezvous, as close as 1km from target when it circularizes.

  9. #9
    Sorry if all of this is repeat or you've already figured it out but from my experience:
    -It's definitely a bug. If MJ has already completed the Hohmann transfer burn, clicking "match velocities at closest approach" in the rendezvous planner will get the autopilot back on track.
    - For rendezvous with objects in Kerbin orbit don't worry about timing your launches to rendezvous, very rarely will MJ put you close enough to your target to dock right away and you will have to go to a higher phasing orbit anyway, now since you're close but not close enough you have almost a full orbit to slow down or catch up. This feature is generally far more useful for timing your launch for fuel optimized transfers to other planets.
    -If your launch vehicle has the capacity, try launching directly to 217km or wherever MJ is taking you to phasing orbit (not timed to rendezvous), it saves you the step in the rendezvous process and you will spend less time in phasing orbit than if you shoot directly for your target and most likely miss.
    -I generally put my stations around 250-400km and then launch to around half that so my ship is catching up to rather than slowing down to wait for it's target. This is purely anecdotal and I might be wrong but this seems to always get a close initial approach to target (1km-200m, One time i swore the thing was going to hit me and ended up 40m away after burn) and much less time spent in phasing orbit vs. letting your target catch up to you.
    As always YMMV but this has worked fairly well for me.

  10. #10
    I did not had so much time to test yesterday, I only did one try and then it worked without a problem. Software is strange sometimes...

    However, what I noticed that the rendezvous autopilot works a bit differently than I had excpectsd. All docking tutorials I have found always say: The object you want to dock with should be ahead of you and in a slightly higher orbit, so that your vessel can catch up to it. So my station is at 100km, my craft is on 80km and about 60 km behind. Mechjeb always puts me into the 217km orbit, waits until my craft is ahead of the station and then goes down to 100km again. Of course this also works, but it seems as a waste of fuel to me. I will have to try to go to 217km directly and then see how MechJeb behaves then.

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