# Change in Inclination/Orbital Plane Increases Semi-Major Axis? Is This Normal?

#### 5kinflute

##### New member
Good morning,

I am simulating an orbit around the lunar / seline celestial body but I ran into a problem where changing inclination / declination massively increases the semi-major axis or apoapsis height even at a slightly small change in inclination / declination angle

I attached an image showing my initial & final orbit of my observation. The satellite is at periapsis with a velocity of 1708 m/s and I applied about 6 N of thrust for a normal + burn to increase declination angle. My goal is to at least have a 45 degree inclination orbit around the moon but this causes my orbit to be more elliptical rather than circular -- and this is a big problem for me now because my altitude is now too high ( I want to maintain at least 100 km altitude )

I decided to jump in Orbiter 2016 and detached from ISS and did a similar burn ( anti-normal - ) and it shows my apoapsis reaching 1.693 M which is a bit a relief for me because I thought I was going crazy... but here I achieved an inclination change all the way down to 139 degrees with unlimited fuel turned on... but in the moon I only got 0.0917 degrees ! if I try to go any HIGHER my orbit becomes hyperbolic!

Is this normal in the moon ? How does other space agencies get around this?

P.S. my source code might have errors which I am still investigating but just wanted to share this post for anyone else having this problem...

UPDATE

After some pondering, walking my dog outside, and tossing / turning in my bed ... the position z vector is actually 0 an orbital plane; non-zero when calculating inclination & declination...it's really all about perspective

$\frac{x^{2}}{a^{2}}+\frac{y^2}{b^2}$

#### Attachments

• inclination change help plz.png
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• y.png
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Last edited:

#### n72.75

##### Well-known member
Orbiter Contributor
Tutorial Publisher
Donator
You sure your burning normal+ with respect to your Orbiter around the moon and not the sun or earth? Double check the HUD.

#### 5kinflute

##### New member
Ah I finally figured out what was going on; I had to ask a dumb question to get there... updated my post..

#### Urwumpe

##### Not funny anymore
Donator
Also, you can of course have a change in your apsis nodes while changing your inclination a lot. A 180° change would essentially be about stopping and then accelerating again in the opposite direction...

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