[codyallard28]

• Tickets addressed: Closes Remove gravity from the back-substitution dynamics #648
• Review: By commit
• Merge strategy: Merge (no squash)

Description

Gravity is left out of the back-substitution computations. Gravity is added at the very end of the equations of motion now. The hub solves for the non-gravitational acceleration, state effectors receive it as the rDDotNonGrav_BN_N argument of computeDerivatives, and the spacecraft adds g once to the hub velocity derivative. The accumulated delta-v now integrates only the non-gravitational acceleration, replacing the two gravity-velocity states with one.

Interface changes:

• StateEffector::updateContributions no longer takes g_N.
• The g_N gravity property is removed.

Commits: formatting first, then gravity leaves the effectors, then the delta-v rework, then docs. Each new test lands as a strict xfail and the commit that fixes it removes the xfail.

Verification

• Added test_hinged_rigid_body_gravity_invariance: a hub and two hinged panels at rest in free fall stay exactly at rest.
• Added test_spacecraft_free_fall_delta_v: the accumulated delta-v comes only from the applied force, exactly.
• Re-baselined the VSCMG JitterFullyCoupledGravity truth. (was not handling gravity properly before)

Documentation

Model descriptions updated for spacecraft, hub, gravityEffector, dual hinged rigid bodies, linear spring-mass-damper, spherical pendulum and IMU. Spacecraft and gravityEffector carry the main change.

Future work

None