BUG: apply gimbaled thrust components to translational dynamics

[ting-hong-shieh]

Summary

• Resolve gimbaled thrust into body-frame e1, e2, and e3 components.
• Apply the same thrust vector in the regular and generalized 6-DoF translational equations.
• Compute the thrust moment as r × F, including nozzle position and thrust eccentricity.

Problem

At the head commit of RocketPy-Team/RocketPy#965, both 6-DoF equation paths reduce the axial thrust component and add pitch/yaw moments when TVC is active. The translational equations still omit the corresponding lateral thrust components: the regular path adds no thrust to its e1 or e2 force terms, and the generalized path uses [0, 0, thrust3].

As a result, a gimbal command changes the rotational dynamics without applying the commanded lateral force to the rocket's translation.

Implementation

Flight._calculate_thrust_vector now produces one body-frame thrust vector using the signs implied by the existing moment equations:

• positive x-axis gimbal: thrust toward -e2
• positive y-axis gimbal: thrust toward +e1

Both equation paths consume this vector. The moment contribution is calculated from the nozzle position and force with r × F, which also retains the existing thrust-eccentricity behavior.

This PR is limited to the physics correction on the branch behind RocketPy-Team#965. It does not rebase the actuator work onto develop or the Flight event/controller changes in RocketPy-Team/RocketPy#968.

Validation

pytest tests/unit/simulation/test_flight.py tests/unit/rocket/test_actuators.py -q
109 passed, 4 skipped

ruff check rocketpy/simulation/flight.py tests/unit/simulation/test_flight.py
All checks passed!

git diff --check
No errors

The new cases cover zero gimbal, positive and negative single-axis commands, two-axis magnitude preservation, and the nozzle moment from r × F.

References

• NASA Glenn: Rocket Control
• NASA/TM-20240012525: Six-Degree-of-Freedom Modeling of a Launch Vehicle