astro.J2

class hohmannpy.astro.J2

Perturbation caused by Earth’s equatorial bulge, known as the J2 effect.

This is a simplified version of NonSphericalEarth intended for us in modeling purely the J2 effect. The J2-acceleration is computed explicitly using general perturbation theory.

Variables:

_initial_gmst (float) – Initial angle of the Greenwich meridian in \(rad\) when propagation began.

Notes

The following assumptions are made for this implementation:

1. The gravitational potential field of the Earth is given by the solution to the geopotential partial-differential equation.

2. Only the J2 zonal harmonic is considered.

3. The GMST of the Earth is initially accurately computed wrt. the Vernal equinox (ignoring nutation) and is then said to linearly rotate at the Earth’s mean rotation rate without precession.

See also

NonSphericalEarth

Generalized version of this perturbation which can model N-order zonal harmonic effects as well as tesseral and sectoral ones.

evaluate(time, state, satellite)

Computes the perturbing acceleration due to the J2 effect.

Parameters:

• time (float) – Current time in seconds since propagation began.

• state (np.ndarray) – Current translational state in ECI coordinates given as (position, velocity).

• satellite (Satellite) – Unused parameter simply based due to @abstractmethod requirements.

Returns:

acceleration (np.ndarray) – Current translational acceleration in ECI coordinates.