JNTU B.Tech III SPACE PROPULSION Previous Question Paper (August/September - 2021 - R18)

Specific impulse (I_sp) is defined as the change in momentum per unit weight of propellant consumed, representing the efficiency of a rocket engine. It is expressed as I_sp = F / (ṁ g₀), where F is thrust, ṁ is mass flow rate, and g₀ is standard gravity.

The Breguet range equation for a cruise vehicle is derived from the work-energy principle and mass conservation. Starting with the instantaneous range increment dR = V dt, and using the lift-to-drag ratio (L/D = W/D), the thrust required is D = W / (L/D). Since F = D = -V_e (dW/dt) / g₀, where V_e = I_sp g₀, we substitute to get:

Integrating from initial weight W₀ to final weight W₁ gives the Breguet range equation:

Stage separation is critical for multi-stage rockets to discard dead weight. The primary systems employed include:

• Pyrotechnic Bolts and Explosive Bolts: These use small explosive charges to sever structural connections instantly, allowing the stages to separate under the influence of residual thrust or separation motors.
• Retro-rockets: Small solid-propellant motors mounted on the spent stage, firing in the opposite direction of flight to decelerate the spent stage and ensure it does not collide with the upper stage.
• Ullage Motors: Small thrusters used to settle propellants in the tanks of the upper stage before main engine ignition, providing a small acceleration to prevent gas ingestion during startup.
• Pneumatic or Spring Pushers: Mechanical systems that use compressed gas or high-tension springs to physically push the stages apart once the structural locks are released.
• Interstage Skirts: Structural adapters that house the separation hardware and protect the engine nozzles of the upper stage until the moment of separation.