What characteristic defines the thrust curve of a Bates grain?

The characteristic that defines the thrust curve of a Bates grain is that the area of burning propellant remains relatively constant throughout the burn. This design allows for a predictable thrust output over time, resulting in a steady, flatter thrust curve. The Bates grain is designed to have a specific surface area that burns uniformly, giving consistent performance during the burn phase, which is essential for achieving stable flight profiles in rocketry.

While other options may describe thrust behaviors associated with different grain geometries or propellant types, the defining feature of the Bates grain is its ability to maintain a nearly constant burning surface, leading to a more reliable thrust profile. This is crucial for applications requiring stable thrust to ensure controlled ascent and performance.