ashfordeOU ISA Standard Atmosphere (cross-cutting/units-atmos/isa-atmosphere)
Use when the task is the international standard atmosphere: temperature, pressure, and density at altitude for performance and flight mechanics calculations.
Domain quick reference
- ISA sea level: 288.15 K, 101325 Pa, density about 1.225 kg/m3.
- Troposphere: temperature lapses 6.5 K per km up to 11 km.
- Lower stratosphere: isothermal at 216.65 K from 11 to 20 km.
- Pressure integrates the hydrostatic balance with the lapse rate.
Workflow
- Pick the altitude and the needed state variable.
- Read temperature with isa_temperature_k.
- Read pressure with isa_pressure_pa.
- Read density with isa_density_kgm3.
- Confirm the sea-level anchor with isa_sea_level.
Pitfalls
- Using a linear pressure falloff instead of the lapse-rate integral.
- Reading a constant temperature above the tropopause as a lapse.
- Taking the model beyond its 20 km range.
Behavior contract (gate 3)
The temperature, pressure, and density logic is exercised by the gate 3 contract test: scripts/test_isa_atmosphere.py against scripts/isa_atmosphere_logic.py (stdlib unittest, offline). Run: python3 scripts/test_isa_atmosphere.py
Compliance
- Standards referenced, not reproduced: ECSS text is copyright ESA; the ISA model here is common reference data, summary-only per standards-map.yaml.
- compliance: STANDARDS-REF, gated: false.