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BUG: rocket with a late-starting thrust curve never leaves the rail (#411) (#1085)
A motor whose thrust curve starts at t > 0 never left the rail: the rail phase's only time nodes were [t=0, max_time], so LSODA (max_step defaults to inf) took one huge step over the entire burn and the rocket never accelerated. __setup_phase_time_nodes now forces solver stops at ignition and burn-out when burn_start_time > 0, leaving ordinary motors byte-for-byte unchanged. Also moves Codecov's coverage config out of .github/workflows/codecov.yml (where Actions was trying to execute it as a workflow, failing on every run) to .codecov.yml. Closes #411
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‎CHANGELOG.md‎

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### Fixed
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- BUG: rocket with a late-starting thrust curve never leaves the rail [#1085](https://github.com/RocketPy-Team/RocketPy/pull/1085)
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## [v1.13.0] - 2026-07-21
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### Added

‎rocketpy/simulation/flight.py‎

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# Add last time node
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phase.time_nodes.add_node(phase.time_bound, [], [], [])
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# A thrust curve that starts at t > 0 leaves the rocket stationary at
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# ignition-minus, so the solver (max_step defaults to inf) can take one
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# huge step clean over the burn and the rocket never lifts off (#411).
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# Force solver stops at ignition and burn-out so the burn is always
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# sampled. Guarded to burn_start > 0, so ordinary motors are untouched.
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motor = self.rocket.motor
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burn_start = getattr(motor, "burn_start_time", 0) or 0
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if burn_start > 0:
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for t_burn in (motor.burn_start_time, motor.burn_out_time):
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if phase.t < t_burn < phase.time_bound:
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phase.time_nodes.add_node(t_burn, [], [], [])
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# Organize time nodes
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phase.time_nodes.sort()
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phase.time_nodes.merge()

‎tests/integration/simulation/test_flight.py‎

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import numpy.testing as npt
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import pytest
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from rocketpy import Flight
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from rocketpy import Flight, Rocket, SolidMotor
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plt.rcParams.update({"figure.max_open_warning": 0})
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def test_flight_with_delayed_burn_leaves_rail(example_plain_env):
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"""Regression test for #411: a motor whose thrust curve starts at t > 0 must
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still lift the rocket off the rail. Previously the solver stepped over the
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burn (``max_step`` defaults to ``inf``) so the rocket never left the pad
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(``out_of_rail_time`` came out as 0).
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Parameters
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----------
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example_plain_env : rocketpy.Environment
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A plain environment object, this is a pytest fixture.
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"""
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motor = SolidMotor(
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thrust_source=[(8.0, 1500.0), (9.0, 2000.0), (14.0, 2000.0), (20.0, 0.0)],
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burn_time=(8, 20),
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dry_mass=1.815,
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dry_inertia=(0.125, 0.125, 0.002),
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nozzle_radius=33 / 1000,
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grain_number=5,
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grain_density=1815,
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grain_outer_radius=33 / 1000,
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grain_initial_inner_radius=15 / 1000,
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grain_initial_height=120 / 1000,
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grain_separation=5 / 1000,
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grains_center_of_mass_position=0.397,
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center_of_dry_mass_position=0.317,
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nozzle_position=0,
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throat_radius=11 / 1000,
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coordinate_system_orientation="nozzle_to_combustion_chamber",
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)
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rocket = Rocket(
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radius=127 / 2000,
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mass=14.426,
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inertia=(6.321, 6.321, 0.034),
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power_off_drag=0.5,
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power_on_drag=0.5,
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center_of_mass_without_motor=0,
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coordinate_system_orientation="tail_to_nose",
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)
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rocket.add_motor(motor, position=-1.255)
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rocket.add_nose(length=0.55829, kind="vonKarman", position=1.278)
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rocket.add_trapezoidal_fins(
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n=4, root_chord=0.120, tip_chord=0.060, span=0.110, position=-1.04956
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)
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rocket.set_rail_buttons(0.082, -0.618)
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flight = Flight(
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rocket=rocket,
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environment=example_plain_env,
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rail_length=5.2,
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inclination=85,
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heading=0,
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max_time=60,
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)
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# Ignition is at t = 8 s; the rocket must leave the rail shortly after,
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# not remain at the pad the whole flight.
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assert flight.out_of_rail_time > 8.0
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assert flight.out_of_rail_velocity > 10.0
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assert flight.apogee - example_plain_env.elevation > 1000.0
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@pytest.mark.parametrize(
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"flight_fixture", ["flight_calisto_robust", "flight_calisto_robust_solid_eom"]
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)

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