2.2 Orbit Perturbations
2.2.1 Gravity Field
The basic parameters for the orbit modelling purpose of the mission.
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Multipole expansion gravitational potential is used up to the terms J3, the model JGM-3 (Joint Earth Gravity Model).

2.2.2 Air Drag
2.2.2.1 Modelling
Air drag depends on two essential parameters: atmosphere density and the ratio of effective surface that is perpendicular to the velocity vector of the CubeSat to the mass of the spacecraft. In addition, the drag force also depends on the drag coefficient, the parameter that is not well defined but for the modelling purpose it could be used for some well-defined shapes. In general, higher atmospheric density results in exponential decree of orbit lifetime, and higher the ration area to mass longer the lifetime. The density of the atmosphere depends on the Sun activity, and it is measured in terms of the parameter F10 and correlates well with it: it has large value if the Sun is active, and it is small when it is not. When the Sun is active the atmosphere heaths up and its density in the upper layers gets denser, and the other way around. Activity of Sun is shown in figure
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The density of the atmosphere up to 900 km is shown in figure (Rocket&Space Technology) for three different values of F10.
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For the modelling purpose the drag coefficient is used for a well-defined shape, cube, and its value is c=1. The CubeSat is tumbling after ejection. This means that the mean surface area facing the velocity of the CubeSat is somewhat larger than the area of its side plane, which 0.12 m2. In the modelling increased by the factor 1.3 (maxima area is around 1.6 factor greater).
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where r is distance of the CubeSat from the centre of Earth and h from its surface. A is the area of the CubeSat and M its mass, ρ(h) is density of the atmosphere and C is the drag coefficient (Ballistic Coefficient). In the modelling gravitational potential is assumed to be spherically symmetric. v ⃗ is the CubeSat velocity. Lifetime of orbits for the densities in figure

Lifetimes of 500 km orbits for three values of F10
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Lifetimes of 600 km orbits for three values of F10
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For low value of F10 (at nearly zero active Sun) lifetime of orbits is very large, for 600 km orbit it is nearly 340 years, but this is within a small interval of the minima in figure 2.1-6. In general, realistic is the medium density for which 600 km orbit has lifetime of slightly more than 20 years.

2.2.2.2 Ballistic Coefficient
For this analysis the value of C is taken 1, for a cube, and it is used for the whole-time interval until the CubeSat fall into the dense atmosphere.

2.2.3 Solar Radiation Pressure
This pressure has no effect on the CubeSat, at least for the mission that it is designed for.

2.2.4 Third Body Perturbations
No effect by the third body, or at least negligible probability to encounter it.

2.2.5 Other Mission Relevant Perturbations
Probable perturbation might come from impact of atmosphere on rotation of the CubeSat.