Arming Switches

Arming switches are used to disconnect charges or charge-deployment circuits from energy sources while the rocket is being moved to the pad, to prevent the charges from accidentally deploying while the rocket is being handled or there are people nearby. The challenge in designing the arming switch is that it must be accessible while the rocket is out on the pad, without taking apart the rocket. This usually leads the the switches coming slightly out of the rocket or there being a small hole to access them. One of the challenges to balance with arming switches is dual redundancy. On the one hand, you want switches in a way that one cannot fail and cause charges to deploy before expected, but at the same time you want switches in a way that if one fails there is still a connection to the charges. It is important when choosing arming switches that you choose ones that can be both activated and deactivated, in case there is a need to take the rocket off the pad. There are two main styles of arming switches, physical and wireless.

Physical Arming Switches

Physical arming switches are the most common, least expensive, and (generally considered to be) the most reliable. Physical arming switches can range from anything as simple as a toggle switch to as complex as a remove-before-flight arming pin.

Like with most safety systems, you want to keep them as simple as possible. Switches should be commercially available and tested products that involve as few parts as possible, with no reliance on micro-controllers or software.

Wireless Arming Switches

Wireless arming switches involve sending a radio signal to the rocket that tells an onboard microcontroller to turn on the electricity. These are newer and less common, and many launches restrict them to certain types or sizes of rockets, or only allow them for one of two redundant switches. While being more expensive and taking up more space than a physical arming switch, they do offer the advantage that they do not require any holes cut in the outside of your airframe.

One advantage that Wireless Arming Switches offer is that they can consider sensory input in their arming decision. For instance, the Eggtimer Proton only allows you to wirelessly arm the avionics if it detects that the rocket is vertical. 

Wireless arming switches can be activated with your phone, a Bluetooth device, a radio, etc.

Wireless arming switches can either be independent, where they go inline with the battery/charge wires and just stop/allow the flow of current, or integrated, where the wireless command tells the deployment avionics microcontroller that it can now deploy charges.