Spacecraft dynamics vs orbital propagator

I am running two different models with the same initial orbital state: one using the Spacecraft Dynamics block and one using the Orbital Propagator. The results from the Orbital Propagator block are a relatively smooth orbit; however, the results from the Spacecraft Dynamics block without any perturbing forces show a non-smooth trajectory that does not align with the orbital propagator output.

Are there any obvious reasons why this might be occurring?

Answer 1

[Jaskirat]

Hello,

I understand that you are getting a different trajectory in the same model while using two different blocks. This is because the Spacecraft Dynamics and Orbit Propagator block have a few slight differences in how they calculate the trajectory.

The Orbital Propagator treats the spacecraft as a point mass, solving only translational motion using Keplerian mechanics, resulting in a smooth trajectory. In contrast, the Spacecraft Dynamics block solves both translational and rotational motion, meaning small attitude changes or numerical integration differences can affect the trajectory. If attitude is not fixed, even without external torques, rotational coupling can introduce slight deviations.

Ensuring that both blocks use the same solver settings may also help reduce discrepancies.

Refer to the following links to check out the differences in working of the two block -

• https://www.mathworks.com/matlabcentral/answers/2138017-how-does-the-spacecraft-dynamics-block-work#answer_1486862
• https://www.mathworks.com/help/aeroblks/orbit-pop-algorithms.html

Hope this helps!