What are deployment avionics?

*COTS = Commercial Off The Shelf, i.e. a device that can be bought and is already designed and/or assembled for you.

Deployment avionics are electrical systems that deploy recovery systems (parachutes, streamers, landing legs, etc.) at pre-programmed times during the flight. Most small rockets will use a deployment charge built into the motor so there is no need for deployment avionics.

Deployment avionics can also be useful for having multiple deployment events. Large rockets that go to high altitudes will deploy a drogue parachute at apogee, and then a larger landing parachute closer to the ground. If the landing parachute was opened at apogee, the rocket could drift for miles. 

How do deployment avionics work?

Deployment avionics usually determine where they are in flight with barometric altimeters. Therefore, they need to be in a compartment that is equalized to the outside air pressure. 

The recovery systems are usually deployed with low explosive charges, that pressurize the parachute bay and shoot out the parachute and shock cord like a cannon. A low explosive charge consists of an e-match, surrounded in black powder. Visit the knowledge page on deployment charges for more information.

To operate the deployment avionics, a power source such as a battery must be connected. Different deployment avionics will drain power faster than others, so it is important to test them on the ground before flight.

Many deployment avionics also do things besides deployment. Many will log altitude and other flight data, and some will even transmit that back over radio. 

Common COTS deployment avionics

Eggtimer Series

Eggtimer deployment avionics are some of the most common in high-power rocketry. They are inexpensive and versatile modules that have been proven to work well time and time again. Eggtimer offers multiple different deployment avionics with different features (inexpensive, small size, lots of deployment channels, etc.). The major downside to Eggtimers is that they do not come assembled. You must solder together all of the components, which depending on the model of eggtimer chosen, can be very complicated and may result in a destroyed board if done incorrectly. Since they are assembled by the end-user, many events such as IREC do not consider them to be COTS. 

Stratologger Series

Stratologgers are the second most common deployment avionics after Eggtimers. Like Eggtimers, there are a few variants that do different things, and cost different amounts. Stratologgers come pre-assembled and tested from the supplier, and can run on smaller batteries than Eggtimers. They are, however, less feature-dense than Eggtimers, and concerns have been raised in the past for using them on flights that go past Mach 0.8. While eggtimers have documented mach hardening, Strataloggers do not.