Mechjeb acting stupid

[Wabbit]

So, I have an interplanetary ship with four nukes on the bottim, a lot of RCS quads, and a 3-man capsule with parachutes. I try to get mechjeb to calculate an interplanetary transfer (kerbin - Jool) and it dies, or so I think. It will happily spit out a trajectory and I burn the burn. It turns out that was nowhere near getting me even into SOI. It happens again and again, and gets annoying. Does anyone know what causes this, and/or how to fix it?

Some info:

I am using the latest version of MJ

I am using "Transfer to Another Planet", this happens withboth "at window" and "ASAP" modes

Please, someone help! D:

[AlexinTokyo]

I don't use MechJeb, so I can't give you any advice specifically related to that function, but...

Can you describe your initial conditions? What is your pre-departure orbit (AP/PE Height)? What TWR and ÃŽâ€v does your ship have (you can get this info from a MechJeb panel, I think).

What burn (duration) does MJ come up with for you, and what is the situation after you finish the burn?

My best guess (emphasis, it's a complete guess) is that you're starting a long (low-TWR) burn from a low orbit. This can cause your burn to start so much before the node, that you're actually burning down into the atmosphere, which can cost you a lot of effective ÃŽâ€v.

If this is the case, then you can try a) starting in a higher orbit, redesigning your ship with a higher TWR, or c) splitting the burn into a series of more manageable burns (periapsis kicking, along the lines of what the Mangalyaan did).

[Axelord FTW]

Use Advanced Transfer to Another Planet, for one.

Second, is the planed maneuver even giving you an encounter before the burn?

How long is the burn?

Is your parking orbit at or just above 70km AP/PE?

[Taki117]

Another thing is that if your burn is really long you won't ever get an encounter from the start, that's not how interplanetary works. Have Mechjeb do your transfer burn, then have it fine tune closest approach to target (you may have to wait until you are outside the SoI to do this) and set it to something like 20km (My standard orbit for a planet without an atmosphere). At that point, oce that node is executed (it should only be a few m/s) you should get your encounter.

[Red Iron Crown]

Moving this to General Add-on Affiars, the place for all your mod-related questions.

[sarbian]

I am using the latest version of MJ

Define what you mean by that. The last release or the last dev version ?

And what do you mean by "nowhere near getting me even into SOI" ? Does it give you a trajectory that brings you on the opposite of the system or do you miss the SoI by some million of km ? There is a "fine tune closest approach to target" maneuver to adjust your traj.

[Wabbit]

The burn was about 3 minutes long. 3000-4000 dV to jool. I was on a roughly 100km by 100km circular orbit. And I have fixed the problem, advanced transfer is key.