Mechjeb: Edit Ascent Profile on other planets?

[J-Dude]

I'm on Eve right now, trying to climb my heavy escape vehicle up a mountain to eliminate as much atmosphere as possible.

The problem is, the rover part of the vehicle is effectively crawling as it goes, only travelling short distances before wheels need to be repaired. And often, at least one wheel will instantly break upon repair, probably because too much weight is sitting on it. It's hobbled its way up, risen about a hundred meters and half a kilometer away from its original landing spot in the foothills.

So I'm trying to see if I can JUST make it from where I am.

Using SMARTASS to keep the ship angled up, I've managed to engage the ascent guidance after the thickest atmosphere, and ALMOST make it to a 100km orbit. Only 8 seconds of burn between me and an orbit my mothership can collect the vessel from.

But of course, angling straight up forever and doing a gravity turn that late is bound to be inefficient. If I did the turn somewhat earlier, I could optimize the ascent. Ascent guidance could almost certainly do it... it just isn't.

I don't know why, but attempting the autopilot from landed provokes some weird, useless behavior. The ship slowly spirals upward and harsher and harsher angles, until it finally flips over. Usually it catches itself and is upright after a few seconds, but the ascent is by then a total failure for the fuel and momentum wasted.

It's not even in a consistent direction. It almost looks like over-correction and a propagation of error. Even engaging the ascent autopilot ANY time before being CERTAIN you're in the upper atmosphere is likely to provoke this effect.

One wonders if there was a simple issue in the ascent profile gumming things up from the Kerbin Launch, but as this isn't Kerbin, I have no way to edit the profile.

...Or do I?

See, I've SEEN videos of Mechjeb users editing the ascent profiles on other planets... but I can't for some reason. When I open the profile window, I get a blank window I can't close without hitting the button in the Ascent Guidance control panel again.

I'm starting to suspect this isn't normal, though I've deleted and redownloaded the entire game and reinstalled Mechjeb a number of times by now. Do I have a wrong version?

[Signo]

I think that is because of the "force roll climb" option enabled. If you disable it the weird behaviour issue should disappear.

Your craft is very draggy on top due to struts so that is the attitude MJ is trying to overcorrect producing the spiral.

Edited August 8, 2015 by Signo

[J-Dude]

Interesting... I never really knew what that did, only that it's enabled by default.

UPDATE:

Well, it definitely flies true... to a point.

Apart from holding my breath that each stage won't blow half of another stage up on decoupling, at some point it eventually likes to tip in the upper atmosphere and flip over. I think re-enabling the AOA limiter might help with this a LITTLE.

It's probably to do with only having the one reaction wheel on top, but I couldn't see how else to do it. Can't interrupt the fuel passage with those, or mount them on the side. RCS maybe, but that would demand BRINGING RCS propellant, which is unnecessary weight. Uh... canards maybe? I dunno.

Good news is I'm finding flatter ground to drive the whole thing higher. Got it up to 20m/s without busting at one point... still a LONG way to go.

Edited August 8, 2015 by J-Dude

[John FX]

One more thing I would do is set the pre and post autostage values to zero. You don`t want to carry excess weight any longer than you have to.

You may want to see if the Dev version fixes the issue with the ascent profile. You can find it here.

[Signo]

If I may give my full 2 cents: start your G turn around 25000/30000m even if it might look inefficient - keep your AoA limited (3°/5° and remove the limitation as soon as you hit 50000 or give it a couple of tries until you find your craft sweetspot) - obviously disable Force Roll Climb - do not limit acceleration - +1 for John FX point on delays

Last but not least: humans are by far better pilots than MJ, I am pretty sure you can get it done in a better way with pure eyeball.

[Foxster]

If you do fix Mechjeb (delete the MechJeb2 directory and try installing again?) then try my ascent profile. Works fine to get my landers from the ground at sea level to a 100km orbit...

And put some fins on your craft like this...

You might also like to try to redesign it with a bit more dV, 8000 should do you.

Edited August 9, 2015 by Foxster