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In short, you must safely launch a rocket on a H or I motor and recover it in a condition such that it could immediately fly again to get your L1. The rocket must have been constructed entirely by the person going for their certification, and they will usually be asked a series of questions about the construction techniques used by the RSO at the launch. In order to make a safe flight as described, the rocket must be stable and strong enough to withstand the thrust of the chosen motor, have retention to hold the motor into the rocket during coast and recovery, and have a working recovery system.
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