Since KSP 0.25 and MJ 2.4.0, I have been unable to successfully launch vessels into orbit using MechJeb. During the gravity turn, rather than following a nice gradual change in angle, MechJeb overcompensates and ends up actually decreasing the apoapsis instead of increasing it, thus burning all the fuel and never making it to orbit.

To illustrate my issue, I have made two videos. First with MechJeb flying the vessel, then myself manually flying the vessel to show it is a stable craft that can go into orbit.

Note that I move the vessel away from the launch pad early on to prevent debris damage, then I let MechJeb do its magic. I did notice that SAS was overcorrecting when I was flying manually, having to disable it once in a while, so that might play a role in the issue.

MechJeb flying:
http://youtu.be/1Xho_O7Q8ko
Gravity turn is at 1:52

Manual flying:
http://youtu.be/2EEW24L550s
Orbit is at 5:13

It is the exact same vessel.

Hey, I saw a similar behavior and it turns so, that I enabled 'Use stock SAS' under Attitude Adjustments pane. After reverting back to 'Tf auto-tuning' (with the default config) the automated controlling became much smoother and accurate.

Using "Use stock SAS" is asking for trouble most of the time. I should remove it, but I know some like it for planes

Well that sure solves the issue. Why it was activated by default, no idea.
It is indeed useful for planes, but definitely not for rockets.

Just tried with MJ 2.4.0 on KSP 0.24.2 and I have the same issue. Will try with MJ 2.3.1 on KSP 0.24.2.

Issue is not present in MJ 2.3.1 (version string 2.3.0) on KSP 0.24.2.

Video evidence:
http://youtu.be/AcsNOtnOE0Q

Do you use other mods? Could you post a save so I can test it, and the full log ( see here to find the log http://forum.kerbalspaceprogram.com/threads/92229)

I do have other mods installed, but I made sure to have all of them installed on both versions of KSP when I tested, to rule out the possibility of other mods affecting the result. I'll try again with just MechJeb installed and report my results along with the log file.

Here is the VAB craft for KSP 0.25:
https://dl.dropboxusercontent.com/u/61447917/MJ-1.craft

• The leaning before the gravity turn is me moving the rocket away from the launch pad to avoid damaging it with falling debris. It launches straight up.
• I have SAS modules between the Aerospikes and the fuel tanks to allow for proper rotation of the rocket. It works fine in manual mode and with MJ 2.3.1.

Though you are correct on the rocket being unstable due to the broomstick effect, and it is most likely why it is spiraling out of control. I tried to recreate the issue with a different rocket, still using Aerospikes and it launched to orbit, though it did wobble quite dangerously.

I'll use the same rocket to post a side-by-side video of MJ 2.3.1 and MJ 2.4.0 for comparison. While it is not a big issue with stable rockets, all of my (somewhat) unstable rockets I used to launch before cannot be launched anymore using MechJeb due to this wobbling/leaning (manual override still works fine to orbit them).

Issue still occurs when MechJeb 2.4.0 is the only mod.
This is on Windows for the 32-bit version of the game. I have not tested other architectures but I doubt it is linked with the game itself, as it works when MechJeb 2.3.1 is used.

Output log:
https://dl.dropboxusercontent.com/u/61447917/output_log.txt

MechJeb settings are as follow:
Ascent Guidance
Prevent overheats
Corrective steering
Autostage (pre: 0, post: 0)
Auto-warp

Ascent Path Editor
Automatic Altitude Turn
Start: 18 km
End: 69 km
Final flight path angle: 0°
Turn shape: 30%

Everything else is left unticked or with the default value.

From watching your video I have some observations that might be helpful:

• the wobbling/leaning also occurs well before the gravity turn, which indicates that the rocket itself may be hard to stabilize even when trying to fly straight up
• the lower stages use SRBs and Aerospikes, neither of which have thrust vectoring to steer the rocket; using vectoring engines may help the rocket to have a more stable flight path
• the bulk of the mass is concentrated in the lower half of the rocket, which makes it very hard to balance (due to the broomstick effect: KSP wiki article) especially when fuel drains and is further pushed down.

I'm not saying that this is definitely the cause and that there could be nothing wrong with this MJ version, but these aspects I mentioned do all increase the difficulty to keep the rocket steady in flight.

I have made a comparison video of MechJeb 2.3.1 and MechJeb 2.4.0.
http://youtu.be/B7AgvUWUeHU

You can see it has a much harder time in 2.4.0 to get to the correct angle in the gravity turn. The exact same rocket is used in both cases, same game version, only the MechJeb version changes. While it is not critical for this stable rocket, it can drive an semi-stable rocket to oblivion (especially with the broomstick effect previously discussed).

Craft file:
https://dl.dropboxusercontent.com/u/61447917/MJ-3.craft

One thing I noticed while watching my video is the use of SAS in MechJeb 2.4.0 which is not done in MechJeb 2.3.1. Maybe that could be part of the issue, where MechJeb is fighting against the SAS compensation, which results in overcompensation. Just a thought.