Which statement about the thrust curve of a progressive burn motor is true?

A progressive burn motor is characterized by a thrust curve that begins with low thrust and subsequently increases to higher thrust levels before declining again towards the end of the burn. This allows for a more controlled and gradual increase in engine power, which is beneficial for optimizing rocket performance during the ascent phase.

The correct choice reflects the nature of how these motors operate – they typically employ a specific formulation of propellant that allows the thrust to build up over time, enhancing stability and performance as the rocket ascends. This feature is particularly advantageous when launching heavier payloads or navigating through varying atmospheric conditions, as it provides a smoother acceleration profile.

In contrast, the other options describe thrust characteristics that do not align with how progressive burn motors function, such as starting with high thrust, showing no variation in thrust, or peaking at mid-burn. Understanding the nuances of thrust curves, especially for different types of rocket motors, is critical for effective rocket design and performance prediction.