Module motor 

The solid motor model: thrust, propellant consumption, and the motor’s mass, center of mass and inertia at any time in the burn.

Consumption by impulse fraction. With a constant effective exhaust velocity c = F/ṁ (NASA SP-8039, glossary p. 95), the propellant burned by time t is in proportion to the impulse delivered:

c = I_total / m_p0,   ṁ(t) = F(t) / c,   m_p(t) = m_p0 (1 − I(t)/I_total)

This is RocketPy’s SolidMotor consumption (rocketpy/motors/solid_motor.py:401-418, motor.py:483-524), and the mass column of ThrustCurve.org’s .rse files follows it (docs/format/rse.md). It is an approximation: the real c drifts with chamber pressure and nozzle erosion (SP-8039 p. 14). All propellant is gone when the thrust curve ends.

Where the propellant is. A Propellant::Column keeps its shape and loses density as it burns, so its center stays put and its inertia scales with its mass (the model of RocketPy’s GenericMotor). Propellant::Grains regress as BATES grains (crate::grains).

The whole motor combines the propellant with the dry mass (case, closures, nozzle, liner) about the instantaneous center of mass (MassElement::combine).

Ambient pressure. A curve measured at reference pressure p_ref gives, at ambient p_a, F = F_ref + (p_ref − p_a) A_e (from SP-8039 eq. 2, F = ṁ u_e + (p_e − p_a) A_e, with the flow unchanged; RocketPy’s Motor.pressure_thrust, motor.py:1173-1191). It holds while the nozzle flows full. See docs/physics/motor.md.

Structs

MotorState

A motor’s thrust and mass properties at one time.

Nozzle

A nozzle, for the ambient-pressure correction of thrust.

PropellantColumn

A propellant charge of fixed shape whose density falls as it burns.

SolidMotor

A solid rocket motor.

Enums

Propellant

How the propellant is laid out and how its shape evolves. Serialized with a model tag ("column", "grains").

Constants

EXHAUST_VELOCITY_RANGE_M_S

The effective exhaust velocity c = I/m_p a solid motor’s curve and propellant mass have to imply, m/s.

STANDARD_SEA_LEVEL_PRESSURE_PA

Standard sea-level pressure (US Standard Atmosphere 1976), Pa.

UNITS_HINT

What a motor whose figures imply an impossible exhaust velocity should check: the hint that ends that refusal’s message, so a program can show it apart from the fact (hpr writes it as a help: line).