When is a "Rocket" classified as a Model Rocket?

Internationally, a Model Rocket, is defined as a small rocket designed to reach low altitudes and recovered by a variety of means.

A Model Rocket has the following criteria:

  • The rocket must weigh less than 1,5kg (3.3 pounds)
  • Only utilises commercial, certified Rocket Motors
  • The motor used must contain less than 125 grams of propellant
  • A Single motor cannot exceed 160N-s total impulse
  • Combination of motors cannot exceed 320 N-s total impulse
  • Built from Lightweight Materials (cardboard, plastic, balsa wood, etc)

What is a Model Rocket Motor?

(Read this article that explains what the difference is between a Rocket Motor Rocket Engine)

  • Model Rocket Motors are the "Powerplant" of the rocket which allow them to fly.
  • They are basically very thick paper tubes which contain from back to front, a clay or ceramic nozzle, the rocket propellant, a delay charge, an ejection charge, and a clay or paper cap to keep it all inside the tube.


  • Propellant is what actually causes the forward motion of the rocket.
  • By electrically igniting it, the propellant burns and produces large volumes of very hot gas which escapes though the nozzle at the back at high speed.
  • The propellant in model rocket motors is usually black powder, but it can also be a composite fuel.
  • High power rocket motors use composite fuel almost exclusively to power the heavier rockets since they offer more thrust per amount of fuel although they often require higher temperatures to ignite and sometimes require special igniters to light them.
  • Once the fuel is finished burning, the delay charge begins.


Delay Charge

  • The delay charge is a combustible material which blows a lot of smoke out the nozzle to aid in tracking the rocket and also to let the rocket coast to it's maximum altitude before the ejection charge ignites.
  • The delay charge produces no measurable thrust.


Ejection Charge

  • The ejection charge produces a short burst of hot gas to blow the recovery system out the front of the rocket.
  • In rare cases, it's used to blow the motor casing out of the rocket or to move the motor casing to a different position in the rocket to change its center of gravity to either allow it to glide back to Earth or to make it aerodynamically unstable and allow it to tumble down.