What is two stage recovery?

Two stage recovery involves the deployment of a drogue parachute or streamer at apogee, or at high altitude, and the deployment of a main parachute at low altitude. Two stage recovery cannot be performed by motor ejection alone, but needs either a timer, or an altimeter or altimeter/accelerometer, or motor ejection for the drogue deployment coupled with one of the other ejection initiation systems listed above.

The advantages of two stage recovery are that if the drogue parachute does not deploy, then there is effectively a back-up in the fact that the main parachute can still deploy, and vice versa, if the drogue parachute deploys, but not the main parachute, it does at least ensure the vehicle does not return ballistically. The other advantage is that when the two stage recovery system deploys properly, the rocket is generally recovered only a short distance down range, since the drogue or streamer deployment ensures that the rocket does not drift a long distance, but descends more rapidly than under a large single parachute.

The disadvantages of two stage recovery are that there are more things to go wrong than in a single stage recovery system, and it takes comparatively longer to prepare the recovery system since there are essentially twice as many components to consider, and also there is a need to employ electronic initiation systems, rather than just motor ejection alone.

Two stage recovery is a very popular choice for recovery of rockets in the U.K., and is becoming more popular all the time, due to the size constraints of most launch sites, and also due to two stage recovery preventing rockets from drifting long distances due to windy conditions.