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MechJeb Misbehaving During Launch


Zeiss Ikon
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I'm running 1.3.1 RO(RSS/RP-1/Principia).  I've launched to orbit several times in previous careers with manual or partially manual control.  My current vessel is this one:

wMzqGyy.png

This is a single LR-79 with dual LR-105 verniers, and (currently, upgraded since the photo) six Tiny Tim boosters to give a thrust aid while clearing the launch clamps.  Upper stages don't matter for this, I don't think, but second stage is two AJ10-37 with nitrous oxide RCS, and inside the fairing is a single AJ10-37, also with nitrous oxide RCS, pushing a Sputnik PS-1 with four Sputnik antennae plus Geiger-Mueller counter and four tiny solar panels.  Even with the low SLT, there ought to be (and according to MechJeb on the pad, is) plenty of dV to make LEO -- but that's not the problem.

When I launch, MechJeb correctly auto-stages the launch clamps (once I figured out that the Clamp Autostage field isn't percent, it's a fraction, so .95 means 95% thrust, not just under 1%), ignites the boosters, and then stages them away after they burn out -- but doesn't start its own timer that should initiate the pitch program to start the gravity turn after (zero, ten, or fifteen) seconds from clamp release.  Instead of counting down, the status displays "Vertical Ascent 10.0 s" (or whatever value I've input) for a minute or more as the rocket ascends vertically, until I revert the launch (I'm testing this in sandbox, after noticing the problem in my career at the cost of a launch vehicle and several simulations -- no reverts there).  Reinitializing stage analysis changes nothing.

VNbXv7m.png

Here, I had selected a 15 second delay on the pitch program, and as you can see, the MET shows 1:08 and MechJeb is still waiting to start the pitch program

The last time MechJeb actually did initiate the pitch program, pitch failed to follow the velocity vector closely enough after transition to PEG and the vessel broke up due to aero forces when it reached ~12 degrees AOA at around Mach 1.5 at around 14 km.  Since that launch, after reducing the amount of permitted AOA to 7 degrees, MechJeb hasn't even started the pitch program.  Restoring the default 10 degree value changes nothing.

My install was done based on @Bornholio's Golden Spreadsheet, so far as CKAN would let me follow it (at one point, CKAN installed a bunch of dependencies much earlier than they appear on the sheet)and everything else seems fine within the limits of performance of my computer (4 GHz isn't as fast as it seemed it was going to be, by the time you add FAR, E.V.E., and so forth), though I'll note that I haven't been happy with MechJeb operation at any time since installing, and had previously chalked it up to my own inexperience (until installing this RO/RSS/RP-1/Principia game, I'd run stock with only Better Burn Time).  Even now, given I haven't done anything beyond LEO and then with satellites that had little or no ability to maneuver and/or ran out of battery in a few orbits, I haven't had any need for MechJeb other than to try to launch into a specific inclination or altitude -- I can manually pilot into orbit about three times in four with as little as 9500 m/s on the pad, so when MechJeb misbehaved, I assumed I'd set something wrong, reverted, and relaunched on manual.

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I'm playing in RSS/RO/RP-1/Principia (and a bunch of other mods pulled in by those or recommended in the Golden Spreadsheet).  In RSS, you need a hybrid of the old-KSP "burn vertically to some altitude, then start tipping" and the current gravity turn, along with some specific guidance late on the way -- because most craft flying to LEO burn continuously to apogee (which becomes perigee after burning some more to raise the perigee above the atmosphere).  The manual pitch program in MechJeb's PEG ascent guidance does that -- burns straight up for a while (recommended, to around 100 m/s), then does a "by the clock" tip-over, which, if set up correctly, will segue into an "unguided gravity turn" if launching to "current inclination" -- that is, launching due east and letting gravity turn your path southward (or northward, if you're at Woomera or other southern hemisphere site).

Regardless, I found the cause and solution of the problem (though I still consider it a bug, in that MechJeb's PEG module doesn't warn for an invalid entry).  With my four stage rocket, I'm not allowed to enter a stage count of "4" in the "Num Stages" field (just above the button to "Reinitialize Stage Analysis") -- apparently, I have to enter "2" there (despite the fact that Orbiter One needs all four stages -- Tiny Tim boosters, LR-79 booster core, 2xAJ10-37 stage, and final 1xAJ10-37, which apparently will have a few tens of m/s to spare at a 230x230 km orbit).  Do that, even after launch, and the vertical ascent countdown picks up counting down from clamp release, manual pitch program engages, and when its countdown elapses, MechJeb transitions to "unguided gravity turn" as it should.

In the process, I also found a setting that lets me shrink MechJeb's UI, so it doesn't cover 60% of my KSP window when I'm flying an orbital ascent...

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I'm not familiar with the mod package you have lined up, so I'll stay away from most of this.   But the one thing that did pique my curiousity, is you never mentioned anything about your ascent profile.  What are it's settings.   If MJ is doing a countdown with vertical ascent, you might have some setting really wonky in your ascent profile, forcing MJ to fly a very weird but technically correct profile.    If that's not the issue, I really got noting else for ya. 

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2 hours ago, Gargamel said:

Do tell.....

In the MechJeb "settings" box, there's a "UI Scaling Factor" (IIRC -- I don't have the game open at the moment).  Just enter a factor to multiply the UI scale -- for instance, 0.8 will give an 80% size UI (which is as small as I'd go unless you have a huge monitor and pixel count on tap).  I've got mine at 0.9 at present, and it leaves a lot more screen real estate -- I can keep the "ascent guidance" and "edit ascent path" and still see the dV, Orbit Info, [X} Science Here and Now, and more or less make out the stock resource display (it goes under the main MechJeb window, which I haven't yet found a reliable way to relocate).

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