Quick Start

This walkthrough builds a simple BATES-grain SRM from scratch, runs an internal ballistics simulation, and plots the results.

1. Choose a propellant

Machwave ships with several pre-defined solid propellant formulations. Here we use KNDX (potassium nitrate / dextrose):

from machwave import formulations

propellant = formulations.solid.KNDX

For a full list of available solid propellants, see the formulations page.

2. Define the grain geometry

Create a Grain and add one or more segments.

from machwave import grain as grain_models

grain = grain_models.Grain(spacing=10e-3)  # 10 mm spacing between segments

bates_segment = grain_models.geometries.BatesSegment(
    outer_diameter=41e-3,   # 41 mm
    core_diameter=15e-3,    # 15 mm
    length=67.5e-3,         # 67.5 mm
)

for _ in range(4):
    grain.add_segment(bates_segment)

3. Build the thrust chamber

The thrust chamber is composed of a nozzle and a combustion chamber:

from machwave import thrust_chamber as thrust_chamber_models

nozzle = thrust_chamber_models.Nozzle(
    inlet_diameter=43e-3,
    throat_diameter=9.5e-3,
    divergent_angle=12,     # degrees
    convergent_angle=40,    # degrees
    expansion_ratio=8,
)

combustion_chamber = thrust_chamber_models.CombustionChamber(
    casing_inner_diameter=44.5e-3,
    casing_outer_diameter=50.8e-3,
    thermal_liner_thickness=1e-3,
    internal_length=grain.total_length + 10e-3,
)

thrust_chamber = thrust_chamber_models.SolidMotorThrustChamber(
    dry_mass=0.85,          # kg
    nozzle=nozzle,
    combustion_chamber=combustion_chamber,
    nozzle_exit_to_grain_port_distance=0.01,
)

4. Assemble the motor

Combine the grain, propellant, and thrust chamber into a SolidMotor:

from machwave import motors

motor = motors.SolidMotor(
    grain=grain,
    propellant=propellant,
    thrust_chamber=thrust_chamber,
)

5. Configure and run the simulation

Set up the simulation parameters and run it. run() returns a time array and a state object containing all ballistic data:

from machwave import simulation

params = simulation.InternalBallisticsSimulationParams(
    d_t=0.01,                # time step [s]
    igniter_pressure=1e6,    # 1 MPa
    external_pressure=1e5,   # 1 atm
)

sim = simulation.InternalBallisticsSimulation(motor=motor, params=params)
time, state = sim.run()

6. View results

Print a summary of key performance metrics and plot the thrust and chamber pressure curves:

from machwave.services.plots import internal_ballistics as ib_plots

sim.print_results()

ib_plots.thrust_pressure_plot(time, state.thrust, state.chamber_pressure).show()

print_results() outputs initial propellant mass, max/average chamber pressure, burn time, max/average thrust, specific impulse, and total impulse.

For more complete examples, including coupled trajectory simulations and Monte Carlo analyses, see the examples directory.