What is up with MechJeb?

[Guest]

MechJeb has done some very stupid things today, and in the past, that caused me to lose several craft. I'm using 2.0.9.

I tried having it bring down a lander on Duna and it did some wacky burn that popped it up to 250km using a dumb normal burn and then brought the craft down. I started at a 75km x 75km orbit. Fortunately the lander had so much fuel that it didn't run out until 1000m from the ground.

Thrice today I've brought down some craft manually on Duna, because of the idiocy above, and during the descent decided to hit "retro" on the SASS to help kill my horizontal velocity. All three times MechJeb sent my landers into uncontrollable spins. In fact, it was almost as if the craft lost all control after doing that.

I've seen some other dumb behavior before when landing on the Mun. I hit "retro" on the SASS during a gentle burn and MechJeb stops following the retrograde indicator after it passes 45~60 degrees.

Out in space it works great; set up a node and execute, does it perfectly, no problems. Any time it gets near a planet it goes complete retard. I suppose this is all fine and well because the new KSP SAS is pretty much garbage for holding a precise heading but is brilliant for docking and airplanes, and at least isn't idiotic for landing.

[Torminator]

The only problems I've had is when using retrograde for landings, if I get a little too cautious and my Vspeed goes above zero, retrograde obviously flips around and MJ has a heart attack.

Also, There's a difference between surface retro and orbital retro. I haven't had problems like you're describing though. Have you tried Sarbian's patch?

In the meantime, the translatron works well for eliminating horizontal speed. Just set it to "Keep Vert" and check "Kill H/S". It will maintain whatever speed you enter as a vertical speed, and try to eliminate any horizontal drift.

[Guest]

I'll check out Sarbian's patch. The problems seem to get worse the longer the game is running so maybe it's just a memory leak.

Honestly, I'm just really frustrated because 0.21 killed my space program and I've had to use MechJeb to bring it back to life. Dealing with a "better" feature and bugs in a mod, and figuring out all the quirks in between is painful.

[Guest]

These landings started at 120x120. Maybe you're starting to low?

[Van Disaster]

Yeah, I tend to stop using SASS retro when the marker starts moving unless the craft is really agile, I start using the hand-entered pitch & direction hold and then adjust manually with the flight keys to tune the path a bit. At some point I'll enter a new "base" pitch & keep going until it's vertical. I've tried the translatron's kill H/S, but once again unless the craft is agile it massively overcompensates & I'd rather just use it's keep vert button & manually kill lateral V myself. I realise half of that sounds like stock SAS, but that won't revert to a pre-entered pitch if you let go of everything

Given the last thing I was flying was 1100t and roughly square, you can imagine how well the auto pitching ( and how agile ) that was...

[Starwaster]

I echo the suggestion to try the latest release by Sarbian.

Something else you can try in stock 2.0.9 is on final descent, cancel the auto pilot (assuming here you're using targeted landing) and then click land anywhere. Preferably do this before not during its final burn so as not to pancake.

[Hannu]

I have problems on Duna too. I use 2.0.9 and Sarbian's dll library released 31th August. When I try to land from 62 km orbit it make plane change and first deceleration correctly so, that periapsis is about surface level. Then it should wait some minutes and start to brake. But it goes crazy and try to make "corrections" of hundreds of meters per second. Typically it raises periapsis from atmosphere. I must change to manual control and make deceleration burn by myself. Landing predictions work OK. On 10 km I can command "land somewhere" and MJ lands without problems. The original dll works at same way. I updated it because I hoped solution to my problem. My Mechjeb works well on other planets except occasional glitches, but it does not like Duna for some strange reason.

[Guest]

I tried the patch, specifically looking at how "retro" worked on Duna, and nothing has really changed. Fortunately I knew what was likely to happen and landed the shack safely. When I tried using the auto-land from 75km orbit again it did the same dumb pop-up maneuver. I'll try from 125km and also some of the other tricks here to see what works, but for now I'm happy to see that it's not just me.

E: Still went stupid at 125km. From 175km it actually looked like it would land but it was a few km off target, same thing from 200km.

E2: I did the test again from 200km, set it to land, walked away, came back to a wreck. The lander had some 3km/s of delta-V, it should not have done that. It was also way off target. MechJeb has some serious problems with Duna.

(Also, the enforced G-rating is hilariously terrible.)

Edited September 3, 2013 by regex

[little square dot]

I found that the patch made MJ less stable.

MJ seems to gork out when you're nearing the ol' memory threshold.

I've seen some very odd behaviour, and there have been times when MJ has stopped responding to input altogether, however simply restarting KSP seemed to solve my problems.

[Guest]

Duna brings about special challenges because of the thin atmosphere. However, I would expect if :

1. the craft is in a circular, stable orbit(my favorite is 120x120 for the mun, haven't been to Duna in a while)

2. target info is hand entered into the "enter target coordinates" field of the auto-land

3. Engage auto-land.

then each craft should land within 10 meters of one another, sometimes breaking solar panels and such.

If this is not happening for you, something is awry.

[Guest]

Duna brings about special challenges because of the thin atmosphere. However, I would expect if :

1. the craft is in a circular, stable orbit(my favorite is 120x120 for the mun, haven't been to Duna in a while)

2. target info is hand entered into the "enter target coordinates" field of the auto-land

3. Engage auto-land.

then each craft should land within 10 meters of one another, sometimes breaking solar panels and such.

If this is not happening for you, something is awry.

Something is awry, then, because all of the tests I did this morning followed those steps.

[Guest]

Maybe there is a game setting, like max physics delta time, that is causing glitchyness? I have started playing with my slider all the way to the right. The game runs in slo-mo sometimes, but remains smooth and responsive. Other than that, I could help test the craft on my install if you would like, and report back later.

[Guest]

Maybe there is a game setting, like max physics delta time, that is causing glitchyness? I have started playing with my slider all the way to the right. The game runs in slo-mo sometimes, but remains smooth and responsive. Other than that, I could help test the craft on my install if you would like, and report back later.

I don't think the craft is the issue because different craft act the same. I'll give the physics delta a try, since mine is set to 0.15 IIRC, but I think I might just end up digging into the code, adding some debug symbols, and following the landing from the error log. Either way, auto-land isn't a big deal for me, the retrograde following is.

[Guest]

I understand. The retrograde bug has been with mechjeb for quite some time, even before MJ2. I hope you figure it out.