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Axisymmetric mass elements: a mass on the motor axis with its own axial and transverse moments of inertia, and how elements combine.
Motor axis coordinate. Positions are meters along the motor’s axis, measured from the
nozzle exit plane toward the forward closure, so +z points toward the rocket’s nose like the
body frame’s +z (docs/physics/frames.md). Every element is symmetric about that axis, so its
inertia tensor about its own center of mass is diag(I_t, I_t, I_a).
Combining uses the parallel-axis theorem (any dynamics text, e.g. Meriam and Kraige,
Engineering Mechanics: Dynamics, the appendix on mass moments of inertia). For elements with
masses m_k, centers z_k, and inertias I_a,k, I_t,k about their own centers,
m = Σ m_k, z = Σ m_k z_k / m, I_a = Σ I_a,k, I_t = Σ (I_t,k + m_k (z_k − z)²)See docs/physics/motor.md.
Structs§
- Mass
Element - A mass on the motor axis, with its moments of inertia about its own center of mass.