SPACE EXPLORATION MERIT BADGE
The Flight of the Model Rocket
- Launch: technically, this is the time that the rocket is travelling
up the launch rod. It is not yet moving fast enough for the fins to stabilize the
flight aerodynamically. The engine ramps up to full thrust, briefly exceeding the
average thrust in order to get the rocket up to speed (about 30 mph) before it reaches
the end of the launch rod.
- Powered Flight: flight time after the rocket has left the launch
rod, while the engine is still burning. During this time the rocket is a "free body",
with three forces acting on it: the thrust of the rocket, gravity (the weight of the
rocket), and wind resistance. Of the three forces, though, the rocket thrust is by far
the dominant one.
- Burn-out: the engine runs out of propellant and the rocket is no
longer under thrust. Since it has just gotten the entire "push" from the engine, though,
the rocket is now moving at its highest speed - as much as 300 miles per hour. It's
going to keep going up for a while.
- Coasting Flight: the flight time of the rocket after the motor has
burned out. During this time the rocket remains a "free body" with two forces acting
on it: gravity and wind resistance. Because the rocket is, by design, very light, the
wind resistance is large in comparison to the weight (it can easily be three times the
weight of the rocket at peak velocity) and plays a major role in the performance of the
- Ejection: during coasting flight a delay fuse is burning
in the rocket engine for a pre-determined time that is specified for the motor (see
NAR's Rocket Motor Coding).
When this delay time is up, the ejection charge fires, forcing the nose off the end of
the rocket and pushing the parachute (or other recovery device) out. The delay time is
chosen to give the rocket just enough time to slow to a stop and reach its peak altitude
before deployment of the parachute.
- Recovery: with the parachute deployed, the rocket is returned
gently to the ground so it can be recovered intact and flown again.
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Updated 8 September 2008