What is the function of an altimeter during a rocket's flight?

The function of an altimeter during a rocket's flight is to measure the altitude of the rocket. This instrument is essential for providing real-time information about how high the rocket is ascending during its flight. By measuring altitude, the altimeter helps determine when specific events in the flight sequence should occur, such as deployment of the recovery system. This precise measurement contributes to the overall safety and success of the mission, ensuring that the rocket can return safely to the ground.

The other options relate to different functions that are not the primary purpose of an altimeter. Fuel consumption is monitored by different instruments dedicated to tracking the rocket's fuel management systems. Tracking the rocket's trajectory involves navigation and guidance systems that calculate position and velocity rather than altitude alone. Finally, controlling the rocket's descent is managed by recovery systems such as parachutes or other devices, which operate based on altitude information but do not rely on the altimeter for the altitude measurement itself.