I'm trying to orbit Kerbin at 100km with 90º of orbit inclination using mechjeb ascend guidance but mechjeb is not making vessel orbit correctly.
The orbit is like 5º offset and the apoapsis and periapsis is not 100k, is 110k and 90k respectively (approximately)

My Vessel and Ascend Guidance settings:

Vessel img 1

Stuff inside the fairing:

Vessel img 2



My Addons/Mods:

KSP: 1.0.5 (Unix) - Unity: 4.6.4f1 - OS: Mac OS X 10.11.4

B9 Animation Modules - 1.0
B9 Part Switch - 1.0.1
B9 Aerospace - 6.0.1
B9 Aerospace - 6.0.1
B9 Aerospace HX Parts - 6.0.1
Chatterer -
Community Resource Pack -
Connected Living Space -
Firespitter - 7.1.5
Interstellar Fuel Switch - 1.18
RasterPropMonitor - 0.24.2
KAS - 0.5.5
KIS - 1.2.6
KSP-AVC Plugin - 1.1.5
KW-Rocketry-Community-Fixes - 0.4.10
Kerbal Joint Reinforcement - 3.1.4
Kerbal Konstructs -
Infernal Robots - 0.21.4
ORIGAMI Antennas - 0.9.5
NearFutureElectrical - 0.6.2
NearFutureSolar - 0.5.5
PlanetShine -
Kerbal Planetary Base Systems - 1.0.6
RCS Build Aid - 0.7.7
RemoteTech - 1.6.9
SCANsat -
TAC Fuel Balancer -
TextureReplacer - 2.4.12
TAC Life Support -
Kerbal Alarm Clock - 3.5
TweakScale - 2.2.6


The NavBall:


MJ ascent guidance Corrective Steering overcompensates for planet rotation, which visibly skews ascent to highly inclined orbits.

TLDR: Launch to inclination of 86, then do some fine-tuning once in orbit. And use orbital data readouts from MJ or KER instead of eyeballing it ;)

86 results in 90

And now the long part...

MJ ascent guidance operates in stages:

  1. Vertical ascent (first few seconds of launch)
  2. Gravity turn (burn until designated AP is reached)
  3. Coasting to edge of atmosphere (only when necessary)
  4. Circularization (burn until designated PE is reached)

Gravity turn gets skewed by Corrective Steering when fighting planet rotation and Circularization plainly ignores inclination.

Note: issue occurs both in 1.0.5 and 1.1 version.

You can work around this issue by:

  • Launching to inclination if 86 degrees, which will result in (almost) polar orbit (dirty hack, but it works)
  • Ordering MJ to change inclination once in orbit
  • Skip Circularization in ascent guidance and replace it with Change Inclination and Circularize maneuvers.
  • Disable corrective steering - however without solid rocket you are very likely to perform rapid lithobraking without this option.

"Manual" inclination fix and circularization burns, remember to leave some time between maneuvers manual circularization

No corrective steering no corrective steering

As for difference in AP and PE, there is plenty of things that will make ascent less accurate

  • atmosphere (drag and aerodynamic forces)
  • weird rocket with weird, unpredictable, drag (MJ likes straight, pointy and rigid rockets)
  • wobbling rockets (they tend to fall apart)
  • rockets that require RCS to fly straight (fixing bad design with corrective steering is still a bad design ;)
  • lagging game (bad and weird things can happen)
  • high thrust ratio (creates wobbling and reduces accuracy of burns)
  • non-equatorial launch site (requires thrust offset, which screws with delta-v)
  • non-equatorial target orbit (MJ have problems with inclinations)
  • other mods (warranty void if used with other mods ;)

In your case you certainly scored on atmosphere, non-equatorial orbit and other mods. It also looks like your rocket will wobble a bit, have too much engine power, relies on RCS to fly straight and, as you are still on 1.0.5, will fly at low framerate. I would dare to say that your rocket stays together only because of Joint Reinforcement mod. Combine that together, and usual inaccuracy of ~200 meters goes into 10km.

Hint: cargo under fairing could use struts from its top to fairing base. In 1.0.5 cargo loves to bend out of fairing, which brakes aerodynamics,

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