MechJeb - Orbiting Kerbin not working, I get to apoapsis then start falling

[Carbal]

Howdy,

I have learned how to orbit Kerbin and have even made it to Minmus and the Mun and back. I just discovered MechJeb and am trying to learn how to auto-orbit around Kerbin. I have my unmanned probe and enable the Auto Ascent and set the orbit to 100 km (I've also tried 90 and 80). I engage auto pilot and launch off. Once I launch, the probe accurately reaches the apoapsis at 100km, and then I see a node get created and it's correctly set to orbit Kerbin at 100km (give or take a few km). However, when the rocket approaches the node where you should start up the rockets again ...nothing happens. The ship just starts falling back down to Kerbin.

Is that because maybe my ship isn't build very well, or am I missing something? Thanks for any help/ideas!

Answer: As sarmagheddomsgw points out, there likely wasn't enough torque recognized by MechJeb, so I added advanced inline rotation wheels to each of the rocket stacks and it works!

Edited December 26, 2014 by Carbal
Solved!

[Anquietas314]

First, auto-orbit to ~70-75km; you want to arrive in orbit low, because it's more efficient for going elsewhere.

Second, are you running out of fuel in the current stage before you reach apoapsis? MechJeb won't auto-stage unless you tell it to. If you can, post the ship design in question (screenshot should be fine, .craft if it's a complicated one)

[Carbal]

First, auto-orbit to ~70-75km; you want to arrive in orbit low, because it's more efficient for going elsewhere.

Second, are you running out of fuel in the current stage before you reach apoapsis? MechJeb won't auto-stage unless you tell it to. If you can, post the ship design in question (screenshot should be fine, .craft if it's a complicated one)

Thanks for the reply! Noted about the ~75km orbit. I tried again, setting 73km orbit, and same issue. I have fuel as well, so that's not the issue...I have attached screenshots of the ship/probe and can post the .craft if you'd like.

NOTE: Sorry I forgot to mention, I'm in the "Science" career mode but I believe I have the required MechJeb stuff unlocked, I'm pretty far along in R&D but let me know if you'd like a screenshot of my progress there...

Screenshot of the ship:

All is going well, the first two rockets are jettisoned:

Apoapsis reaches target altitude and even creates the node automatically for orbit:

...but then the ship passes the node and falls:

[Anquietas314]

Hmm okay, try disabling RCS - you don't have any on your ship anyway. If you have most of the probe cores you should be fine, but I haven't used mechjeb during a career or science game so I don't know exactly how the tech tree progression works for it. Also, why do you have 17 messages waiting for your attention?!

One possiblity is that your ship just doesn't have enough torque for mechjeb to aim at the maneuver node in time - it's not smart enough to realize it can use a low-thrust engine burn to do the alignment then correct it later in my experience. Solution: slap loads of advanced inline reaction wheels on it (you should need one per column of tanks on that thing for it to steer well.

[Carbal]

Will try disabling RCS, thanks.

Ah, I forgot to delete those messages (they're all completed project/mission messages though :thumbsup: )

I've added one inline rotation wheel to each of the four outer rockets, and one in the main stack. Trying now and will report back.

Edit: Aha!! It works now! I believe it was the inline reaction wheels that did it and allowed enough torque. Thanks so much for your help!

Edited December 26, 2014 by Carbal

[Anquietas314]

You're welcome It's what this forum's here for

[Kryxal]

Just as a side note, it might be worth editing your ascent, because that's a HUGE burn there at the top, and probably limit yourself to terminal velocity.

[tg626]

Although it doesn't appear to have been your issue, it is possible yo run out of electricity before reaching a preprogrammed manouver node.

[Carbal]

Just as a side note, it might be worth editing your ascent, because that's a HUGE burn there at the top, and probably limit yourself to terminal velocity.

Thanks for the tip - with MechJeb how would I do that with AutoPilot?

and tg626, thanks as well. I made sure to put some battery packs on the bottom most fuel tank to ensure I have enough power (after I posted those screenshots, I thought the same thing).

[Kryxal]

I think it's covered by your Smart A.S.S. panel, edit ascent path. Just play around with it, see how it works for you.