Below we discuss typical concepts of operations for Recovery. Three recovery CONOPS are as follows (in vague order of common-ness in the rocketry community):
Single Separation, Single Deploy:
This CONOPS is useful for lower-altitude flights. It is as simple as possible: one event separates two sections of the rocket, and recovery webbing keeps the two pieces connected. A chute is quicklinked to the webbing, and inflates upon being deployed from the rocket. Typically, the event occurs near apogee because the rocket has no vertical velocity, decreasing the chance for crazy things to happen upon deployment. However, single sep dual deploy is not as useful for high altitude flights because the safe speed at which rockets should fall under the parachute is relatively slow, meaning that the recovery system requires a larger parachute. For high-altitude flights, this leaves the rocket prone to drifting for up to several minutes, and possibly several miles.
Dual Separation, Dual Deploy:
This CONOPS is more useful for high altitude flights because it decreases the amount of drift as compared to a single deployment. In this scenario, two parachutes are deployed out of the rocket, each out of its own separation in the rocket. In the CONOPS, two events occur, one at or near apogee, and one much closer to the ground (usually 500 - 1000 feet AGL). The first event separates the rocket into two sections. A small drogue chute is typically deployed, although not always necessary. The rocket falls relatively quickly after this deployment until the second event, where the third section of the rocket separates to release the main parachute. Once the main chute is inflated, the rocket descends at a safe landing velocity. Just like before, webbing hold the rocket sections together.
The drawback to DSDD is that electronics are required to detect the altitude at which the second event should occur, and initiate the second event. This system was used by the Team for Scylla.
Single Separation, Dual Deploy:
This is the most complex of the three CONOPS discussed here because it required two parachutes to be deployed out of a single separation in the rocket. It requires the drogue chute to pull out the main parachute at a target altitude. Like DSDD, this requires electronics. It also requires a restraint on the main chute which can be released at the target altitude. A COTS solution to this is the Tender Descender, which the Team has used in years past. The benefit to this system is that it only requires one body section to release two parachutes, which is beneficial if a large section of the body is needed for a payload.
This requires careful packing of all of the chutes and cords in the system, and it is usually not used for mid-power or certification rockets. It has been used in Project Therion, and Charybdis.
Optionally, the any section can be separated completely from the others, but chutes are necessary on all sections. Typically the rocket pieces are kept together to minimize the chance of multiple chutes tangling, and to save on structural mass, especially since larger chutes can take considerable volume.