Hi Karthi,
As per my understanding, you can import your CubeSat CAD Model using the Simulink 3D Animation toolbox in one of the supported file formats and integrate it with your Simulink model.
You can also create a CubeSat model in Simulink and use the Aerospace Blockset to simulate the dynamics and controls of the CubeSat.
To simulate the altitude control of the CubeSat, you can use the magnetometer and sun sensor blocks from the Aerospace Blockset and use the Simulink Scenario Editor to create scenarios as per your required position and orientation of the sun, magnetic field, etc.