How is the specific impulse of a rocket motor defined?

Specific impulse is a key performance metric for rocket motors, defined as the total impulse produced per unit weight of propellant consumed. This means it measures how effectively a rocket motor utilizes its propellant to generate thrust. The correct definition identifies the relationship between the total impulse provided by the motor during its operation and the weight of the propellant used. Higher specific impulse values indicate a more efficient rocket motor, as it can produce more thrust for the same amount of propellant weight.

The specific impulse is typically expressed in seconds and is crucial for understanding and comparing the performance of different rocket propulsion systems. A higher specific impulse indicates that a rocket can achieve a higher velocity using less fuel, which is vital for mission design and efficiency in space travel.

In contrast, the other options do not capture the essence of what specific impulse is about:

• Total impulse divided by total burn time describes the average thrust rather than the efficiency of fuel usage.
• Burn time divided by average thrust does not relate to the mass of the propellant and hence fails to capture the concept of specific impulse.
• Thrust divided by motor weight describes thrust-to-weight ratio, which is a different performance characteristic than specific impulse.

Understanding these distinctions helps clarify why option B accurately defines specific impulse in the