Module parts 

Components other than fins: nose cones, body tubes, transitions, inner tubes, centering rings and bulkheads, launch lugs, rail buttons, mass components, parachutes, streamers and shock cords, each with its mass properties from geometry.

Frame. Each part’s frame has body axes and its origin on the body axis at the part’s forward end (a nose cone’s tip), so the part lies at z ≤ 0 (crate::mass). Radial placements use a distance from the axis and a roll angle from x_B toward y_B.

Standard solids (Meriam and Kraige, appendix B), for mass m:

hollow cylinder, radii R ≥ r, length L:  I_axis = m (R² + r²)/2,  I_across = m ((R² + r²)/4 + L²/12)
solid cylinder, radius a, length h:      I_axis = m a²/2,          I_across = m (3a² + h²)/12

Nose cones and transitions use crate::solids::revolve. Shoulders are hollow cylinders beyond the profile’s end, and a capped shoulder is closed by a disc of the shoulder’s inner radius and wall thickness, flush with its far end. Recovery parts and mass components are packed into solid cylinders (OpenRocket technical documentation v13.05, Table 5.1, p. 75, treats them the same way). A parachute’s mass is its canopy, π D²/4 times the fabric’s surface density (the nominal area of a flat circular canopy), plus its shroud lines, count times length times line density. See docs/physics/mass.md.

Structs

BodyTube

An airframe tube.

CenteringRing

A flat annular ring, or a bulkhead when the inner radius is zero.

InnerTube

A tube inside the airframe: a coupler, a motor mount tube, an engine block or thrust ring. It may sit off the axis, and it may be a cluster: several like tubes side by side, as in a cluster’s motor mount.

LaunchLug

A launch lug: a tube on the outside of the airframe, parallel to it.

MassComponent

A mass of known value: an altimeter bay, ballast, a payload.

NoseCone

A nose cone: a profile with its tip forward, and an optional shoulder aft of its base.

Packing

Where and how compactly a mass or a recovery part is stowed: a solid cylinder.

Parachute

A parachute, packed.

PodSet

Pods beside the airframe: side pods, or outboard motor pods. A pod set attaches to a body tube like a fin set, and its children are the pod’s own body components (nose cone, body tubes, transitions), which stack aft from the pod set’s position along the pod’s axis instead of the body’s.

RailButton

A rail button: a base disc on the airframe, a narrower waist, and a flange that rides in the rail, stacked outward along a radial line, with the screw’s dome head on top of the flange.

ShockCord

A shock cord, packed.

Shoulder

A cylindrical extension of a nose cone or transition that fits inside the adjoining tube.

Streamer

A streamer, packed.

Transition

A transition between two radii, with optional shoulders at either end.

Constants

MAX_INSTANCES

The most copies a row of lugs or rail buttons may have: as crate::FinSet::MAX_COUNT, a bound on the bodies weighed one per copy, so a design file’s count can’t stall the weighing.