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Nozzle Generator – Parameter Schema (v0.1)

Context:

  • Unity 2022/2023, URP, C#
  • Block-based ship parts using ScriptableObject component definitions
  • NozzleBlock spawns a prefab that owns a procedurally generated nozzle mesh child
  • Mesh generation is deterministic from parameters and optional seed
  • Mesh generation occurs at edit-time or on parameter change, not per-frame

1. Performance-Defining Inputs

These parameters determine thrust, efficiency, and the primary geometric scales of the nozzle. Together, they define the operating point of the engine and anchor the procedural mesh.

Required

  • PropellantClass (enum)
    • Examples: Solid, LOX_RP1, LOX_LH2, Methalox, Hypergolic, Exotic
    • Controls internal defaults such as effective gamma, characteristic velocity (c*), chamber temperature limits, and cooling feasibility
  • DesignThrust_kN (float)
    • Target thrust at the design altitude
    • Used to derive throat area given chamber pressure and thrust coefficient
  • ChamberPressure_MPa (Pc) (float)
    • Combustion chamber pressure
    • Primary driver of throat size for a given thrust
    • Constrained by propellant class, materials, and cooling method
  • ExpansionRatio (epsilon = Ae / At) (float)
    • Ratio of exit area to throat area
    • Determines exit diameter and vacuum efficiency
    • Strongly influences visual silhouette
  • DesignAmbientPressure_kPa (Pa) (float) or DesignAltitudeClass (enum)
    • Ambient pressure at which the nozzle is optimized
    • Used to estimate thrust coefficient and expansion efficiency
    • Enables flow separation and overexpansion modeling
  • MixtureRatio_O_F (float)
    • Oxidizer to fuel ratio for bipropellant systems
    • Influences effective performance and thermal limits
    • Can be hidden behind a simplified “lean vs rich” slider in UI

2. Geometry and Packaging Inputs

These parameters primarily affect shape, proportions, and visual identity, while preserving the same underlying performance model.

  • NozzleType (enum)
    • Conical
    • Bell (Rao)
    • DualBell
    • Aerospike_Linear
    • Aerospike_Annular
    • Magnetic or EM Nozzle (non-gas-dynamic)
  • LengthFactor (L / L_conical) (float)
    • Typical range: 0.6 to 1.0
    • Shorter lengths correspond to higher tech or bell optimization
  • DivergenceHalfAngle_deg (float)
    • Used directly for conical nozzles
    • Used as a constraint or initial slope for bell contours
  • ThroatRadiusCurvatureFactor (float)
    • Multiplier of throat radius
    • Controls smoothness of converging-diverging transition
    • Affects both visuals and estimated losses
  • WallThickness_mm (float)
    • Used for mesh thickness, mass estimation, and collision bounds
  • NozzleMaterial (enum)
    • Steel, NickelAlloy, CarbonComposite, Ceramic, Exotic
    • Affects mass, cost, temperature tolerance, and cooling constraints

3. Operational Constraints

These parameters define how the nozzle behaves during use, and allow one generator to support solids, liquids, and advanced propulsion.

  • CoolingMethod (enum)
    • Ablative
    • Regenerative
    • Film
    • Radiative
    • Magnetic or Non-Contact (for plasma systems)
  • ThrottleRange_MinMax (Vector2 or min/max floats)
    • Solids typically fixed
    • Liquids moderate
    • Plasma systems wide
  • MaxChamberTemperature_K (float, derived or capped)
    • Derived from propellant, mixture ratio, cooling, and material
    • Used to validate designs and limit performance
  • BurnDurationLimit_s (float)
    • Particularly relevant for ablative or solid motors
  • FlowSeparationRiskModel (enum or bool)
    • Enabled for overexpanded sea-level designs
    • Depends on Pc, epsilon, and ambient pressure

4. Advanced and Future Parameters

These parameters are not required for the initial milestone, but are planned extension points and should be accounted for in the data model.

  • NozzleEfficiencyFactors
    • Divergence loss
    • Boundary layer loss
    • Non-ideal expansion loss
  • Altitude-Compensating Parameters
    • Dual-bell mode switch pressure
    • Aerospike plug contour parameters
  • EffectiveAreaSchedule
    • Expansion behavior as a function of ambient pressure
    • Used for dual-bell and aerospike systems
  • GimbalLimits_deg
    • Mechanical articulation constraints
    • Influences mount geometry and clearance
  • DeterministicSeed (int)
    • Ensures reproducible mesh generation
    • Allows visual variation without performance changes

5. Derived Quantities (Internal)

These are not player inputs but are computed from the above parameters and passed to the mesh generator.

  • Throat area (At)
  • Throat radius (rt)
  • Exit area (Ae)
  • Exit radius (re)
  • Nozzle length (L)
  • Estimated thrust coefficient (Cf)
  • Approximate Isp (sea-level and vacuum)

These derived quantities define the 2D nozzle profile, which is then revolved to generate the final mesh.

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