Expulsion motor

Missile's expulsion motor or eject[ion] motor is an element of a missile's propulsion system for the missiles, launched from tubes or otherwise shaped containers.

Below is a typical principal scheme of an expulsion motor.

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  axial section
• 
  detailed longitudinal section
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  rear end view
• 
  front end view

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  Stinger launch motor

And here is a expulsion/sustainer motors burnout sequence of the Redeye missile launch.

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  gunner finds a target, aims and pulls the trigger
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  expulsion motor burns out, carrying missile away from the gunner
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  sustainer ignites, giving the missile speed and acceleration
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  launch area is covered with a cloudy exhaust plume