Orbit Propagation¶
Orbit propagation is the foundation of most ASTROLAB analyses. Coverage, access, link, power, and lifetime results all depend on reliable spacecraft state evaluation.
ASTROLAB uses Orekit as its astrodynamics backend.
Propagation Families¶
ASTROLAB can work with several propagation families, each suited to a different use case.
| Propagator | Use case |
|---|---|
| Keplerian | Fast ideal two-body propagation and simple checks. |
| Eckstein-Hechler | Analytical propagation with zonal gravity effects. |
| DSST | Long-term semi-analytical propagation and secular trends. |
| Numerical | High-fidelity propagation with direct force integration. |
| TLE/SGP4 | TLE-driven propagation where applicable. |
Analytical Propagation¶
Analytical propagators are fast and stable, but represent limited physics.
They are useful for:
- Fast previews.
- Simple mission design.
- Debugging.
- Visualization.
They are generally not sufficient for drag-driven lifetime estimation.
Numerical Propagation¶
Numerical propagation integrates equations of motion directly.
It can include:
- Gravity field.
- Atmospheric drag.
- Solar radiation pressure.
- Third-body perturbations.
Numerical propagation can be accurate, but it may be slower and exposes osculating orbital element behaviour. This can make long-term trend reporting noisy unless elements are averaged or filtered.
DSST Semi-Analytical Propagation¶
DSST is intended for efficient long-term propagation. It separates long-period and short-period behaviour and is well suited for secular trend analysis.
For ASTROLAB Lifetime Analysis, DSST is the recommended propagation model because lifetime depends mainly on long-term orbital decay rather than instantaneous short-period oscillations.
Osculating and Mean Elements¶
This distinction is important.
Osculating elements describe the instantaneous Keplerian orbit tangent to the current state. They can vary significantly due to short-period perturbations.
Mean elements remove short-period effects and are better suited for long-term trend reporting.
For lifetime reporting:
- Altitude can be treated as an instantaneous geometric quantity.
- Re-entry checks can use conservative low-altitude criteria.
- Semi-major axis, eccentricity, inclination, RAAN, argument of perigee, and anomaly should preferably use mean elements when DSST is selected.
Practical Guidance¶
Use the simplest model that answers the engineering question.
For early design:
- Use coarse time steps.
- Use moderate gravity degree/order.
- Avoid unnecessary perturbations.
For final validation:
- Increase model fidelity.
- Compare with independent tools or known references.
- Document propagation assumptions.