test_gravityRotatingPlanet

Tests that the gravity effector keeps the extrapolated planet orientation a rotation.

test_gravityRotatingPlanet.test_extrapolated_orientation_is_orthonormal(stepSeconds)

Verify the extrapolated planet orientation remains a proper rotation matrix.

A first-order update of the matrix elements loses orthonormality by about (omega * dt)^2 / 2, which is a few percent after an hour of extrapolation.

test_gravityRotatingPlanet.test_point_mass_orbit_is_independent_of_planet_spin(stepSeconds)

Verify a point-mass orbit does not depend on the planet orientation.

The point-mass field is spherically symmetric, so a spinning planet must give the same trajectory as a non-spinning one. A non-orthonormal orientation scales the evaluated field and breaks this.

test_gravityRotatingPlanet.test_stored_orientation_and_rate_are_consistent(stepSeconds)

Verify the stored planet orientation and rate are [PN] and [PN_dot] of the same epoch.

The planet spins about the inertial z axis and its message is written once at t = 0, so at the final time the orientation is a rotation by OMEGA_PLANET * SIM_TIME and the rate satisfies dcm_dot = -dcm [omega x] with the inertial angular velocity omega.