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The grain's outer radius was smaller than its bore #2

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The grain's outer radius was smaller than its bore #2

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27 changes: 24 additions & 3 deletions custom_rocket.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3,12 +3,30 @@
from rocketpy.motors.tank import MassFlowRateBasedTank
from rocketpy.sensors import Accelerometer, Barometer, GnssReceiver, Gyroscope

# A hollow grain's mass goes as (outer^2 - inner^2), so an outer radius under
# the inner one is a negative mass. RocketPy 1.13 accepts it in silence: the
# motor carried -0.623 kg of fuel and the flight apogeed at 200 m, not 131 m.
GRAIN_OUTER_RADIUS = 0.0843
GRAIN_INITIAL_INNER_RADIUS = 0.0295


def _check_grain_geometry(outer_radius, inner_radius):
"""A hollow grain needs a positive bore strictly inside the outer wall."""
if not 0 < inner_radius < outer_radius:
raise ValueError(
"grain geometry is impossible: need "
"0 < grain_initial_inner_radius < grain_outer_radius, got "
f"inner={inner_radius}, outer={outer_radius}"
)


def create_custom_rocket():
"""
Create a custom rocket with a hybrid motor and an oxidizer tank.
"""

_check_grain_geometry(GRAIN_OUTER_RADIUS, GRAIN_INITIAL_INNER_RADIUS)

tank_shape = CylindricalTank(0.133, height=0.83)
oxidizer_tank = MassFlowRateBasedTank(
name="oxidizer_tank",
Expand All @@ -28,13 +46,16 @@ def create_custom_rocket():
thrust_source=1080,
dry_mass=0,
dry_inertia=(0, 0, 0),
center_of_dry_mass_position=0.015,
# 0.15 in the official scenario, not 0.015. Inert while dry_mass is 0,
# since this is a mass-weighted position, but a 10x error waiting for
# the day that mass stops being zero.
center_of_dry_mass_position=0.15,
burn_time=(0, 30),
reshape_thrust_curve=False,
grain_number=1,
grain_separation=0,
grain_outer_radius=0.00843,
grain_initial_inner_radius=0.0295,
grain_outer_radius=GRAIN_OUTER_RADIUS,
grain_initial_inner_radius=GRAIN_INITIAL_INNER_RADIUS,
grain_initial_height=0.2757,
grain_density=900,
nozzle_radius=0.04425,
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