What component should be installed after the final flare cartridge is securely in place?

The correct choice is the impulse cartridge because it is typically the next component to be installed in the sequence of assembly after ensuring that the final flare cartridge is securely in place. The impulse cartridge serves a critical function by providing the necessary force to ignite the flare cartridge, initiating the overall process.

Understanding the sequential nature of assembling these components is essential, as each piece plays a specific role in the safety and functionality of the entire system. This order ensures that each phase of the assembly is completed properly, which is particularly important in operations involving flares, where the proper timing and function of each part are crucial for effective performance.

Other components like the safety cap, retaining plate, and payload module may serve significant roles within the system but do not follow directly after the final flare cartridge in the assembly procedure; their roles come either before or after the impulse cartridge is installed. Hence, the impulse cartridge is the logical choice following the installation of the final flare cartridge.