What is the relationship between a regressive burn motor's thrust and time?

A regressive burn motor, which typically uses a fuel that burns backward from the nozzle towards the propellant, exhibits a decrease in thrust over time. This occurs due to the diminishing amount of fuel available as the combustion process continues and the surface area of the propellant decreases as it burns.

As the motor operates, the regression rate (the rate at which the propellant is consumed) can cause the pressure in the combustion chamber to decline, which directly influences thrust. With less fuel being burned and potentially lower combustion chamber pressure, the overall performance of the motor tends to diminish over the burn duration.

In contrast, other types of propulsion systems might maintain a more stable thrust or increase it under certain conditions, but regressive burn motors are specifically characterized by this decline in thrust over the burn duration.