EIT-Smasatelitter-Gruppe3 · adriangl · Feb 25, 2026 · Feb 11, 2026
diff --git a/.gitignore b/.gitignore
@@ -172,3 +172,11 @@ cython_debug/
 
 # PyPI configuration file
 .pypirc
+
+# Nix
+.direnv/
+result
+
+# IDE
+.vscode/
+.idea/
diff --git a/README.md b/README.md
@@ -1 +1,141 @@
-# SatelittSim
+# SatelittSim
+
+Dette prosjektet simulerer satellitter i bane med fokus på deorbitering og atmosfærisk motstand.
+
+## Rask Start
+
+```bash
+# Kjør basis simulering med 3D visualisering
+python examples/basic_simulation.py
+
+# Valider fysikkmodeller
+python examples/validate_physics.py
+
+# Visualisering med egendefinert STL-modell
+python examples/custom_satellite_model.py
+```
+
+## 3D Visualisering
+
+SatelittSim inkluderer interaktiv 3D-visualisering av satellittbaner ved hjelp av Pygame.
+
+### Funksjoner
+
+- **Interaktiv kamera**: Roter, panorér og zoom banen
+- **Jorden som 3D-sfære**: Blå sfære med radius 6371 km
+- **Banestrek**: Grønn linje som viser satellittens trajektorie
+- **Satellittmodell**: Last inn din egen STL-fil for visualisering
+- **Koordinatakser**: X (rød), Y (grønn), Z (blå)
+
+### Kamera-kontroller
+
+| Handling | Tast / Mus |
+|----------|-----------|
+| Roter visning | Venstre klikk + dra |
+| Panorér | Høyre klikk + dra |
+| Zoom | Scrollhjul |
+| Start/pause animasjon | SPACE |
+| Nullstill visning | R |
+
+### Bruk med egendefinert STL-modell
+
+```python
+from src import Satellite, State, Simulation, SimulationConfig
+from src.visualization import visualize_orbit
+
+# Last inn din 3D-modell
+sat = Satellite(
+    mass=10.0,
+    drag_area=10.0,
+    drag_coefficient=2.2,
+    stl_path="path/to/your/satellite.stl"  # Din STL-fil
+)
+
+# ... kjør simulering ...
+
+# Visualiser med 3D-modell
+visualize_orbit(sim.history, sat, title="Min Satellitt")
+```
+
+### Eksempel: Lage enkel STL-modell
+
+```python
+from pathlib import Path
+import struct
+
+def create_simple_satellite_stl(output_path: Path):
+    """Lag en enkel boks-formet satellitt STL."""
+    vertices = [
+        [-1, -0.5, -0.5], [1, -0.5, -0.5], [1, 0.5, -0.5], [-1, 0.5, -0.5],
+        [-1, -0.5, 0.5], [1, -0.5, 0.5], [1, 0.5, 0.5], [-1, 0.5, 0.5],
+    ]
+    faces = [
+        [0, 1, 2], [0, 2, 3],  # Front
+        [5, 4, 7], [5, 7, 6],  # Back
+        # ... flere flater
+    ]
+
+    with open(output_path, 'wb') as f:
+        f.write(b'STL header' + b'\x00' * 70)
+        f.write(struct.pack('<I', len(faces)))
+        for face in faces:
+            f.write(struct.pack('<3f', 0.0, 0.0, 0.0))  # Normal
+            for idx in face:
+                v = vertices[idx]
+                f.write(struct.pack('<3f', *v))
+            f.write(struct.pack('<H', 0))
+```
+
+### Tips for visualisering
+
+1. **Lagre skjermbilde**: Bruk `save_path="orbit.png"` parameteren
+2. **Justér skalering**: STL-modeller skaleres automatisk for synlighet
+3. **Flere baner**: Bruk `visualize_multiple_orbits()` for sammenligning
+4. **Ytelse**: Reduser `save_interval` for færre punkter i lange simuleringer
+
+## Roadmap
+
+1. **Basismodell**
+2. **Støy og orientering** - Støy-modellering, dynamisk satellittorientering, effektivt tverrsnitt
+3. **Deorbit sanalyse** - Areal vs. deorbiteringstid, maksimale krefter på seilet
+4. **Avanserte krefter** - Magnetisk dreiemoment, Lorentz-krefter, J2-perturbasjon
+5. **Komplekse luftmotstands-simuleringer** - Solaktivitetd, geomagnetiske effekter, dag/natt-variasjoner
+
+---
+
+## Teori
+
+### Kjernemodeller
+
+**Luftmotstand:** `F_d = -½ * ρ * v² * C_d * A`  
+**Tyngdekraft:** `F_g = -G * M_e * m / r²`  
+**Lorentz-kraft:** `F_L = q * (v × B)`  
+**Magnetisk dreiemoment:** `τ = m × B`
+
+### Atmosfæremodeller
+
+Alle modeller produserer lignende resultater over 300 km (NASA Report 1982).  
+**NRLMSISE-00** - Empirisk modell fra Naval Research Laboratory, tilgjengelig via [Pymsis](https://pypi.org/project/pymsis) Python-wrapper og [web viewer](https://swx-trec.com/msis).  
+**Harris-Priester** - Analytisk modell for døgnlig utbuling ved ekvator.  
+**Jacchia** - Empirisk modell for høyder over 300 km (Guiseppe Jacchia, 1965).
+
+### Forutsetninger
+
+Atmosfæremolekyler antas å stå i ro relativt til satellitten (Hughes 2004, s. 250).
+
+### Solaktivitet
+
+- **F10.7 indeks** - Måler solens radioemisjoner (2800 MHz), indikerer UV/EUV-stråling
+- **Ap indeks** - Geomagnetisk aktivitet
+- Høy solaktivitet → økt atmosfæretetthet → raskere baneforfall
+
+### Referanser
+
+**Biblioteker:** [Poliastro](https://docs.poliastro.space/en/stable/quickstart.html) (Python), [Orekit](https://www.orekit.org/) (Java), [Skyfield](https://rhodesmill.org/skyfield/) (Python), [Heyoka.py](https://bluescarni.github.io/heyoka.py/notebooks/sgp4_propagator.html) (C++), [Astroz](https://github.com/ATTron/astroz) (Python)
+
+**Kilder:** NASA Report (1982) - [atmospheric density models](https://ntrs.nasa.gov/api/citations/19820002192/downloads/19820002192.pdf), [Jacchia model](https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/JZ065i009p02775), [isothermal atmospheric modelling](https://www.spaceacademy.net.au/watch/debris/atmosmod.htm), [orbital decay](https://en.wikipedia.org/wiki/Orbital_decay), [satellite orbital decay calculations](https://www.sws.bom.gov.au/Category/Educational/Space%20Weather/Space%20Weather%20Effects/SatelliteOrbitalDecayCalculations.pdf)
+
+### Testing
+
+- Dobling i areal = halv deorbiteringstid (validering ved 300 km)
+- Deorbiteringskriterium: < 100 km
diff --git a/docs/atmosphericmodel.md b/docs/atmosphericmodel.md
@@ -0,0 +1,110 @@
+Ai summary of deep reserach around atmospheric density models for satellite drag, integrating insights from the "Open-Source Thermospheric Density Models for LEO Satellite Drag" whitepaper with a comprehensive review of academic literature and technical assessments.
+
+In Practice we ended upp utilizing the pymsis library, becasue the full models are very complex and the pymsis library provides a convenient interface to access the NRLMSIS-2.0 model, which is one of the most widely used and validated atmospheric density models for satellite drag calculations.
+
+---
+
+This report synthesizes previous research on high-fidelity drag modeling with new insights from the **"Open-Source Thermospheric Density Models for LEO Satellite Drag"** whitepaper.
+
+The objective is to provide a roadmap for a **general-purpose, offline-capable simulation toolkit** that achieves maximum accuracy in orbital decay predictions by optimizing the three pillars of the drag equation: **Density ($\rho$)**, **Drag Coefficient ($C_d$)**, and **Relative Velocity ($v_{rel}$)**.
+
+---
+
+# Integrated Report: High-Fidelity Orbital Decay Modeling
+
+## Density Model Selection ($\rho$)
+The combined data reveals that no single model is superior at all altitudes. A high-accuracy toolkit should implement a **Switched-Model Architecture** or a user-selectable tiered approach.
+
+### Comparative Analysis of Density Models
+| Model | Altitude Strength | Key Advantage | Licensing/Constraint |
+| :--- | :--- | :--- | :--- |
+| **JB2008** | **< 300 km** | Lowest bias at low altitudes; uses 4 EUV proxies. | **Fully Open.** Best for re-entry. |
+| **DTM-2020** | **300 – 500 km** | Least bias/best precision in research version. | **Academic Only** (CNES license). |
+| **NRLMSIS-2.0** | **> 500 km** | Major upgrade in species coupling (O, He, N2). | **Public Domain.** Best for long-term LEO. |
+
+### Key Insights from Combined Data
+*   **The Density Gap:** DTM-2020 densities are **20–30% lower** than NRLMSISE-00/JB2008 due to updated calibration against high-precision accelerometers (CHAMP/GRACE). A toolkit must warn users that swapping models will cause a step-change in decay rates.
+*   **NRLMSIS Evolution:** While NRLMSIS-2.0 is the modern standard, version 2.1 tends to underestimate density by ~10% compared to the original 00 model, especially during geomagnetic disturbances.
+*   **Storm Robustness:** For simulations involving geomagnetic storms, **JB2008** and **DTM** are significantly more robust than MSIS-series models, which frequently underestimate storm-induced density spikes by up to 70%.
+
+---
+
+## Offline Space Weather & Index Simulation
+High-fidelity models require indices ($F_{10.7}, S_{10}, M_{10}, Y_{10}, F_{30}, Dst, Ap$). To remain offline, the toolkit must provide a **Synthetic Proxy Generator**.
+
+*   **Proxy Correlation:** Since $F_{10.7}$ is the only widely predicted index, the toolkit should implement scaling laws to derive $S_{10}, M_{10},$ and $Y_{10}$ (required for JB2008) and $F_{30}$ (required for DTM) from a primary $F_{10.7}$ input.
+*   **Climatological Envelopes:** Store 11-year solar cycle tables (NASA MSFC 5/50/95 percentiles). This allows users to run "Scenario A: Solar Max" without needing a live data connection.
+
+---
+
+## Physical Drag Coefficient ($C_d$) & GSI
+The research highlights that density is only half the battle; the **Drag Coefficient** is highly dynamic.
+
+*   **Composition-Dependent $C_d$:** Use the species composition output from **NRLMSIS-2.0** (Atomic Oxygen vs. Helium concentration) as an input for the **CLL (Cercignani-Lampis-Lord)** GSI model.
+*   **The Adsorption Effect:** Implement a **Langmuir Isotherm** to model how atomic oxygen "sticks" to the satellite. 
+    *   *Low Alt (<400km):* Surface is "saturated," leading to diffuse reflection ($C_d \approx 2.1-2.4$).
+    *   *High Alt (>600km):* Surface is "clean," leading to specular reflection and potentially higher $C_d$ values ($3.0+$) depending on geometry.
+*   **Macro-Modeling:** Move beyond the "cannonball." The toolkit should represent satellites as a **Box-Wing model**. This accounts for "shadowing," where solar panels shield the main body from the molecular flow.
+
+---
+
+## Relative Velocity & Environmental Factors ($v_{rel}$)
+Accuracy is lost if the satellite's inertial velocity is used instead of its velocity relative to the rotating, blowing atmosphere.
+
+*   **Atmospheric Co-rotation:** Account for the Earth's rotation ($v_{rel} = v_{sat} - \omega \times r$).
+*   **Horizontal Wind Model (HWM14):** The new research confirms that thermospheric winds are critical. HWM14 provides these vectors analytically (no live data needed). Integrating HWM14 corrects for the "side-wind" effect that can alter the decay rate by several percent in polar or highly inclined orbits.
+
+---
+
+## Implementation Strategy for the Toolkit
+To build a "Best-in-Class" general-purpose simulator, the following architecture is recommended:
+
+### Phase 1: The Core Propagator
+*   **Numerical Engine:** Gauss-Jackson 8th order or RKF7/8.
+*   **Coordinate System:** ITRF (International Terrestrial Reference Frame) to handle the rotating atmosphere and wind vectors natively.
+
+### Phase 2: Modular Physics Plugins
+*   **Tier 1 (Fast):** Harris-Priester Density + Constant $C_d$.
+*   **Tier 2 (Standard):** NRLMSISE-00 + Sentman $C_d$ + Co-rotation.
+*   **Tier 3 (Research Grade):** JB2008 (Low Alt) or DTM-2020 (Mid Alt) + CLL GSI + HWM14 Winds + Box-Wing Area modeling.
+
+### Phase 3: Uncertainty Quantification
+*   Provide a "Monte Carlo" mode that varies the solar $F_{10.7}$ input within a $\pm 10\%$ range to produce a "Probability of Re-entry Window" rather than a single (likely incorrect) date.
+
+---
+
+## Summary of Sources & Documentation
+
+### Atmospheric Density Model Specifications
+*   **NRLMSIS 2.0/2.1:** Emmert, J. T., et al. (2021). *A Whole-Atmosphere Empirical Model of Temperature and Neutral Species Densities.*
+    *   https://www.researchgate.net/publication/345024073_NRLMSIS_20_A_Whole-Atmosphere_Empirical_Model_of_Temperature_and_Neutral_Species_Densities
+    *   https://kauai.ccmc.gsfc.nasa.gov/CMR/view/model/SimulationModel?resourceID=spase://CCMC/SimulationModel/NRLMSIS/2.0
+*   **JB2008 (Jacchia-Bowman):** Bowman, B. R., et al. (2008). *A New Empirical Thermospheric Density Model JB2008.*
+    *   https://sol.spacew.com/JB2008/
+    *   https://arc.aiaa.org/doi/10.2514/6.2008-6438
+*   **DTM-2020 (Drag Temperature Model):** Bruinsma, S., et al. (2021). *The operational and research DTM-2020 thermosphere models.*
+    *   https://swami-h2020-eu.github.io/mcm/license.html
+    *   https://www.researchgate.net/publication/354128639_The_operational_and_research_DTM-2020_thermosphere_models
+
+### Atmospheric Winds & Space Weather Proxies
+*   **HWM14 (Horizontal Wind Model):** Drob, D. P., et al. (2015). *Earth and Space Science.*
+    *   https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014EA000089
+*   **HASDM (High Accuracy Satellite Drag Model):** Space Force/Air Force Research Lab briefing.
+    *   https://spacewx.com/wp-content/uploads/2024/02/HASDM-slides.pdf
+*   **Solar Indices (F10.7, S10, M10, Y10):** Space Weather Technology archives.
+    *   https://spacewx.com/data-center/
+
+### Gas-Surface Interaction & Machine Learning Research
+*   **Physics-Informed Neural Networks (PINNs) for Drag:** Mehta, P., et al. (2022). *A New Paradigm for Accelerating Physics-Based Models.*
+    *   https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022SW003161
+*   **NRLMSIS 2.1 Performance Analysis:** Guo, J., et al. (2024). *Performance analysis of NRLMSIS 2.1 using GRACE-A and SWARM-C.*
+    *   https://www.sciencedirect.com/science/article/abs/pii/S0273117724005295
+*   **Satellite Drag Coefficient Modeling:** Pilinski, M., et al. (2011). *A Semi-Empirical Satellite Drag Coefficient Model.*
+    *   https://arc.aiaa.org/doi/abs/10.2514/1.50348
+
+### Technical Assessments
+*   **Thermosphere Modeling Capabilities Assessment:** NOAA/CCMC Neutral Density Workshop.
+    *   https://repository.library.noaa.gov/view/noaa/44791
+
+### Implementation Note for Toolkit Developers
+When implementing these models in a general-purpose toolkit, use **NRLMSIS 2.0** or **JB2008** as the baseline for open-source compliance. If you include **DTM-2020**, add a disclaimer noting its **CNES Non-Commercial License**, which restricts use in proprietary commercial simulation software without a specific agreement from the SWAMI consortium.
diff --git a/examples/basic_simulation.py b/examples/basic_simulation.py
@@ -0,0 +1,58 @@
+
+"""Simple satellite deorbit simulation with 3D visualization."""
+
+import numpy as np
+from src import Satellite, State, Simulation, SimulationConfig
+from src.constants import EARTH_RADIUS, EARTH_GRAVITATIONAL_PARAMETER
+from src.forces.gravity import NewtonianGravity
+from src.forces.drag import AtmosphericDrag
+from src.environment.atmosphere import Nrlmsise00Density
+from src.events import DeorbitEvent, TimeLimitEvent
+from src.visualization import visualize_orbit
+
+
+def main():
+    # 1. Create satellite (10kg with 10m² drag area)
+    sat = Satellite(mass=2.0, drag_area=0.01, drag_coefficient=2.0)
+
+    # 2. Initial state: 400 km circular orbit
+    altitude = 400_000
+    r = EARTH_RADIUS + altitude
+    v = np.sqrt(EARTH_GRAVITATIONAL_PARAMETER / r)
+
+    state = State(position=[r, 0, 0], velocity=[0, v, 0], time=0.0)
+
+    # 3. Define forces
+    forces = [
+        NewtonianGravity(),
+        AtmosphericDrag(Nrlmsise00Density())
+    ]
+
+    # 4. Define events
+    events = [
+        DeorbitEvent(),
+        TimeLimitEvent(max_time=86400 * 60)
+    ]
+
+    # 5. Run simulation
+    print(f"Simulating deorbit from {altitude/1000:.0f} km...")
+    sim = Simulation(
+        state, sat, forces, events,
+        SimulationConfig(dt=10.0, save_interval=50)
+    )
+    sim.run()
+
+    # 6. Print results
+    print(f"\nDeorbit time: {sim.final_state.time/86400:.2f} days")
+    print(f"Final altitude: {sim.final_state.altitude()/1000:.1f} km")
+    print(f"Steps: {sim.step_count}, Trail points: {len(sim.history)}")
+
+    # 7. Visualize
+    if len(sim.history) > 1:
+        print("\nOpening 3D visualization...")
+        print("Controls: Left-drag=Rotate, Right-drag=Pan, Scroll=Zoom\n")
+        visualize_orbit(sim.history, sat, title="Satellite Deorbit")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/examples/deorbit_simple.py b/examples/deorbit_simple.py
@@ -0,0 +1,31 @@
+"""Deorbit simulation with scheduled parameter changes."""
+
+from src import SatelliteParams, SimConfig, ScheduledChange, DeorbitSimulation
+
+
+def main():
+    params = SatelliteParams(
+        name="Test-1",
+        mass=100.0,
+        area=1.0,
+        height_km=300.0,
+        f107=70.0,
+        ap=0.0
+    )
+
+    config = SimConfig(
+        dt_days=0.001,
+        print_interval_km=10.0,
+        reentry_altitude_km=180.0
+    )
+
+    changes = [
+        ScheduledChange(time_days=20.0, f107=150.0),
+    ]
+
+    sim = DeorbitSimulation(params, config, changes)
+    sim.run_with_output()
+
+
+if __name__ == "__main__":
+    main()