Lesson 26 - Exterior Ballistics / Guidance

Propulsion and propulsion types

Power required to propel a warhead from launch to aim. Uses the following:

• Gravity

• Reaction

• Impulse (ejector and gun type)

Gravity propulsion

• Uses potential energy from launch to aim point

• All free fall and glide bombs

Reaction propulsion

• On-board energy source creates thrust to aim point

• Ex: turbo jet and ram jet engine, missiles, torpedoes

Impulse propulsion

• ALL energy provided via launching impulse mechanism

• Ejector-type: compressed gas, mechanical force, or EM force used in BOTH launch and propulsion

• Gun-type: burning propellant creates hot gas used in BOTH launch and propulsion

Exterior ballistics and types

Natural phenomena that impact a weapon in flight

• Gravity

• Drag

• Win

• Drift

• Coriolis effect

Skin drag

Caused by projectile surface friction as projectile moves through air

Shape drag

Caused by low pressure behind a body due to the flow of air around it’s shape 

Wave drag

Loss of energy due to shock waves separating the boundary layer from the body at speeds near or greater than the speed of sound

What is drift due to?

• Combination of gyroscopic forces and relative wind

• PROJECTILE ROTATION

What causes Coriolis effect?

Rotation of earth

What are the purposes of using weapon control surfaces for guidance systems?

• Attitude control (stable flight path)

• Flight path control (maneuvers to aim point)

Guidance systems phases

• Boost (inertial): launch signal to stable flight

• Midcourse (guided): inputs may be required to bring missile on course and stay there

• Terminal (guided): systems required to maneuver at their maximum capacity to overtake and engage its target

What is the longest guidance system phase?

Midcourse (guided)

Guidance system types

• Control guidance

• Homing guidance

• Track via missile (TVM)

• Self contained

Control guidance

Launch platform controls weapon guidance to aim point

Homing guidance

Weapon sensor detects target, and uses homing logic to maneuver to aim point

Track via missile

Combines control and homing guidance

Self contained

Internal guidance to aim point

Control guidance: command guidance

Launch platform tracks target and interceptor

Control guidance: wire guided

Launch platform tracks target and weapon

Homing guidance types

• Active

• Semi-active

• Passive

Homing guidance: active

• Missile carries illuminator (transmitter) and receiver

• Ex: Harpoon, SM-6, AMRAAM

Advantages and disadvantages of active guidance

• Advantage: “fire and forget”

• Disadvantage: acquisition range limited due to XMITER size, target may detect/engage weapon

Homing guidance: semi-active

• Launch platform illuminates target. Missile detects reflected signal

• Ex: sea sparrow

Advantages and disadvantages of semi-active guidance

• Advantage: weapon remains undetected

• Disadvantage: target may not reflect energy in direction of weapon, illuminating platform must remain locked on through intercept

Homing guidance: passive

• Missile detects target energy

• Ex: HARM, Sidewinder

Advantages and disadvantages of passive guidance

• Advantage: weapon remains undetected

• Disadvantage: target may “go dark”

Homing logic types

• Preset: cannot be changed midcourse

• Variable homing: adjusts during travel