Attitude Dynamics — Robotics/Spacecraft Dynamics

Robotics/Spacecraft_Dynamics/Attitude_Dynamics · 3 input / 2 output port(s) at insert · exports to Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog, PLC Structured Text

Description#

The block's own DESCRIPTION_HTML, rendered verbatim — the same text the config dialog's info panel and the library navigator show. Fix a wrong sentence in the block's .cpp (R-D9), never here.

Code facts#

Ports#

Ports the constructor creates. A block whose port list changes with its configuration adds or removes ports at load time; the count above is the one a freshly inserted block has.

Configuration variables#

Every block also carries Sampling Time (s) from ICoreBlockSolverEnvironment: zero or less inherits the solver's rate, a positive value runs the block at that period.

Simulink bridge#

Caveat (shown to the user): rotation only, in ICRF: stateFrame and attitudeFrame are always ICRF and the attitude a quaternion, because the other frames and formats need a date or the central body's rotation. momentsIn on and dateOut off fix the ports at X, V, M in and q, w out; cbPoleSrc is Dialog so a Custom body does not add a port. A fixed mass does not enter the rotation, so mass does not cross; the variable-mass models do not either. "Integration Substeps" is how this block integrates a sample and has no counterpart. The Simulink block is continuous and has no SampleTime

Catalog contract: src/ICoreBlocks/ICoreCoder/ICoreCommandSystem/SimulinkBridge/ICoreSimulinkBlockCatalog.h

Description vs code#

The checker has a blind spot here — it could not resolve something (a grouped port bullet, a computed config name), which is reported and never counted as a pass. A reader has to settle it:

• B0 every stimulus in the sample errored — cross-checks skipped

The verdict above is tools/docs/check_block_descriptions.py (P7.1), which compares LISTS. It cannot read a sentence: "stateless" on a block with a state, an initial-value semantic the recursion does not implement, a "not synthesizable" caveat the HDL banner contradicts. That is the agent audit (P7.3) on BLOCK_DESCRIPTION_AUDIT.md, and this tool's green is not a substitute for one.

File banner (developer view)#

The top comment of the block's .cpp — the maths, the realization and the export strategy, addressed to whoever changes it. It must not contradict the description above (P7.5).

Attitude Dynamics -- a spacecraft's rotation in inertial axes States: the attitude quaternion q = [q0 q1 q2 q3] (ICRF to body, scalar first) and the body rates w = [p q r] in rad/s. Inputs: the position X (ICRF, from the central body's centre), the velocity V (ICRF; unused in this frame) and the applied body moments M.

q' = 0.5 * Omega(w) q (Hamilton; NO normalization term) w' = I^-1 (M + Mgg - w x (I w)) Mgg = 3 mu / |X|^5 * (Xb x (I Xb)), Xb = quat2dcm(q) X (gravity gradient, optional)

MEASURED AGAINST R2026a's aerolibsatdyn/Attitude Dynamics, 2026-09-11 (a built-in block, so measured, not read), with fixed-step ode4 and inputs held over the step:

• this derivative under the same RK4 map follows the block to 2.4e-15 in q and 2.7e-15 deg/s

in w over 200 steps with a non-diagonal inertia, a non-trivial attitude, time-varying moments and a moving position, gravity gradient on, Earth and Moon;

• ⚠ NO NORMALIZATION TERM. The 6DOF (Quaternion) block's K(1 - |q|^2) q is NOT here: with it

the same comparison is 1.25e-12 in q, 500 times worse; without it, rounding.

• the gravitational parameters are the Orbit Propagator's (EGM2008 Earth 3.986004418e14, and

so on -- the same toolbox tables, confirmed body by body through a strong gradient);

• Units only scale the position, so for a named body mu is converted to the length unit and

the dynamics are unchanged (km against m: identical to the last bit); a Custom body's mu is taken in the chosen length unit cubed per second squared, as given (measured in km and ft);

• the initial attitude's FIRST OUTPUT is normalized (a [0.9 0.1 0.2 -0.1] starts at |q| = 1

exactly), but ⚠ a non-unit one is not simply normalized: the block's first integration step then leaves the normalized path by a constant offset -- 3.3e-7 in q for |q0| = 0.88, 1.1e-6 for |q0| = 1.77, the same at every later sample, w untouched -- which no normalization, renormalization or K(1 - |q|^2) gain reproduces (K from 0 to 1e4 scanned). This block starts from q0/|q0|; a unit q0 makes the two identical;

• the initial rate and the w output are in the Angle Units per second;
• V moves nothing in the ICRF frame (a doubled velocity changes w by exactly 0).

NOT A DUPLICATE OF 6DOF (Quaternion) (Equations_Of_Motion/EOM_6DOF_Quaternion): that block is body-axis translation AND rotation from force and moment, with no torque that depends on where the vehicle is. This one is rotation only, in inertial axes, with the central body's gravity gradient; it reuses that family's integrator (ICoreEomRk4) and its direction-cosine and inverse-inertia arithmetic.

CONTINUOUS, STATEFUL, NONLINEAR; no direct feedthrough.

Sample results#

No stimulus produced a sampled output in this rig — Invalid input size at Attitude Dynamics block: ICore Blocks/Home/Attitude Dynamics. That is a fact about the single-block rig, not a verdict on the block: an offline batch fit, a block whose output only appears at onSolverFinish, or one that needs a driven environment cannot be exercised alone.

Category unsampled · sample time 0.1 · 60 steps · commit 93133d604 · produced by docsSample --out <folder> --blocks Gain_Scheduled_Lead_Lag Controller_1D Controller_Blend_1D Controller_2D Controller_3D Observer_Form_1D Self_Conditioned_1D Line_Of_Sight_Access Orbit_Propagator_Kepler Attitude_Dynamics Attitude_Profile_Nadir_Pointing Attitude_Profile_Geographic_Pointing Multitaper_PSD Cross_Power_Spectral_Density Transfer_Function_Estimate Envelope_Spectrum Compose_String Scan_String --steps 60

Sample data: docs/generated/samples/Robotics__Spacecraft_Dynamics__Attitude_Dynamics.json