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Scientific Methodology

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SpaceEngineerSS edited this page Dec 20, 2025 · 1 revision

Scientific Methodology 🔬

OrbitView is built on industry-standard astrodynamic principles. This page explains the math and physics powering the simulation.

1. Orbital Propagation (SGP4)

OrbitView uses the SGP4 (Simplified General Perturbations 4) model to predict the position and velocity of satellites.

  • TLE Data: The model takes Two-Line Element sets (TLEs) as input.
  • Reference Frame: Calculations are performed in the TEME (True Equator, Mean Equinox) coordinate system and then converted to ITRF (International Terrestrial Reference Frame) for Earth-fixed visualization.

2. Doppler Shift Calculation

The Doppler effect for satellite radio signals is calculated using the relative velocity vector ($\vec{v}{rel}$) between the satellite and the ground observer: $$f{received} = f_{source} \times (1 - \frac{v_{range}}{c})$$ where $v_{range}$ is the rate of change of the distance between the observer and the satellite.

3. Atmospheric Decay Model

OrbitView implements a simplified NRLMSISE-00 inspired decay model. It estimates the change in the semi-major axis over time based on:

  • B Drag Term:* Provided in the TLE.
  • Altitude-Dependent Density: Modeled using an exponential atmosphere approximation.
  • Solar Activity: Estimates are adjusted for average F10.7 solar flux.

4. Pass Prediction Logic

A "Pass" is defined as any interval where the satellite's elevation relative to the observer is greater than 0°.

  • AOS (Acquisition of Signal): When elevation rises above the horizon.
  • TCA (Time of Closest Approach): Maximum elevation and minimum range.
  • LOS (Loss of Signal): When elevation drops below the horizon.
  • Visibility: A pass is marked "Visual" if the satellite is sunlit and the observer is in local darkness.

For technical validation reports, see the Scientific Validation section in the README.

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