It is common for users to compare the results of different STK propagators or with propagators in other tools. STK has many different satellite propagators, including the J2Perturbation and the High-Precision Orbit Propagator (HPOP) propagators. The HPOP propagator allows you to customize the force model, which allows you to mimic a J2 satellite. To set this up:
- Open the satellite's Property Browser.
- On the Basic > Orbit page, click the Force Models... button under Prop. Specific.
- Set the Maximum Degree to two (2) and the Maximum Order to zero (0).
- Turn off all other forces.
While the orbits should be fairly similar, the HPOP and J2Perturbation propagators will not give you the same results. This is because they are computed differently.
The J2Perturbation propagator only includes the secular drift of the argument of perigee, right ascension and mean anomaly over time. It does not include the periodic oscillations of semi-major axis, eccentricity and inclination (these elements are essentially held constant).
The HPOP propagator includes both the periodic oscillations and the secular drifting of the elements over time. The HPOP propagator uses numerical integration of the equations of motion to generate the satellite’s ephemeris, while J2 computes the ephemeris by analytically evaluating a formula.
To learn more about how the J2 and HPOP propagators work in STK, please check out the Help page: