Recovery

How it deploys

Recovery decides whether a vehicle flies twice. When the flight computer decides to deploy, it fires a small pyrotechnic charge (an e-match and a charge) on the pyro channel. The charge drives a piston, the middle piece of the recovery section, which pushes the parachute and the nose cone out of the airframe. The shock cord runs through the middle of the piston and keeps the pieces connected.

The sequence

1. Apogee is seen: the vehicle has stopped climbing and starts to fall.
2. The filtered altitude falls below the deploy height, or the backup timer runs out.
3. The flight computer drives the pyro channel and the charge fires.
4. Opening is recognised by the jolt of the canopy, or assumed after a short time. Ground Control then confirms the canopy from the descent rate.

Debounced and time-gated

Deciding when is the harder problem. Every phase change is detected from the sensors and debounced, so that a single noisy sample cannot advance the state. Each phase also has a time gate: burnout and apogee cannot be declared too soon after liftoff, and deployment needs a minimum apogee, which stops a charge firing on a failed launch. Deployment itself is decided from the filtered altitude, with a backup timer that fires the charge if the altitude path never triggers it. Opening is recognised by the jolt of the canopy, or assumed after a short time, and Ground Control confirms the canopy from the descent rate. Touchdown is declared from near-zero vertical speed held for a while, or by a glide-time limit.

At the pad

Deployment parameters are read from the configuration file, and each has a compiled-in default, so a missing file still leaves a working set.

A servo quick-release was also built and tested; it is not the deployment method.

Specification

Revision

mk7  (mk1 → mk7)

Airframe

75 mm

Release

e-match charge on the pyro channel

Extraction

piston pushes parachute and nose cone out

Deployment

altitude-based with a backup timer, parameters configurable

Confirmation

opening seen by the canopy jolt, canopy confirmed by Ground Control

Also built

servo quick-release, not the deployment method