Deployment Charges

Owned by Jim Heaney (RIT Student)
Last updated: Apr 22, 2021 by James May (RIT Student)

For larger rockets, deployment charges (paired with deployment avionics) are the most common way to deploy recovery systems such as parachutes. 

Deployment charges work by pressurizing the parachute bay until it separates from the rocket, forcing out the parachute and shock cord like a cannon.

SAFETY WARNING

Deployment charges are made using low explosives, including black powder. Do not attempt to make deployment charges unless you are trained to do so, or are working under someone trained to do so. Wear PPE at all times when assembling and handling charges. Do not use or posses black powder in a way that is against NAR or TRA regulations, or against local, state, and/or federal laws. Always keep the wires of a deployment charge shorted together to prevent sparking. Unsafe behavior related to explosives is ground for immediate removal from the team. 

Deployment Charge Components

Deployment charges have two main parts of the charge itself, and one part of where it interfaces with the rocket.

Electronic Match

The electronic match, or "E-match" for short, is the part of the deployment charge that ignites the black powder. The most common and best performing E-match used in rocketry is the "MJG Firewire Initiator." When provided with 1.0 amps of current through is two leads, it will explode, sending shrapnel in a small radius, which can then ignite anything it touches. Firewires can also be used to ignite large motors, but it is recommended against use for small motors, since there is a risk that the shrapnel can damage the grain geometry. 

Black Powder

Black powder is a low explosive that creates a large amount of heat and pressurized gas when ignited. There are multiple grades and types of black powder, but natural black powder is found to work best for deployment charges. It is also important to note that black powder is not gun powder, gun powder cannot be used for deployment charges. 

The Launch Initiative uses FFFFg (4f) black powder for all deployment charges. It is a common powder used in re-enactments and cannons. While other natural powder types can work, they result in reduced performance or a large amount of soot coating your rocket and deployment systems. 

Charge Well

The charge well is the part of the rocket where the charge is secured during flight. Usually, it is just a cylindrical pipe that is glued to the bulkhead of the parachute bay. The charge must be able to sit fully inside the well, and below the top of the cylinder.

Determining Charge Size

The size of a deployment charge depends on the size of the rocket, the altitude of deployment, the recovery system used, etc. While you can do trial-and-error testing to find the right amount, it is best to start with a calculator to determine charge size. It is important to always check your numbers with two different calculators and make sure they provide the same/similar charge size. 

The most common charge calculator used by the team is the BP Estimator.

The calculators usually provide good info, but ground testing is also required for every rocket as well. 

Charge Assembly

Only assemble a charge if you are trained to do so, are wearing proper PPE, and you are in a designated safe location to do so. Failure to follow safety standards for handling of explosives is grounds for immediate removal from the team.

  1. Cut the finger off of a 3-mil rubber glove at the knuckle
  2. Measure out the deployment charge using a scale or graduated cylinder. If using a scale, make sure to tare for the weight of the measurement device.
  3. Pour the powder into the finger of the glove
  4. Remove the protective cover from the FireWire
  5. Strip 0.25" off the ends of each FireWire lead, and wrap them together tightly
  6. Push the FireWire into the black powder so that it is in the center of the powder
  7. Use a zip tie to secure the top of the glove above the powder. Cut any excess glove so that there is only 0.125" of glove above the zip tie.
  8. If the charge will not immediately be put into the well, wrap a piece of blue painter's tape around the zip tie to prevent leaking. Always store charges wires-up.
  9. Place the charge into the charge well, and cover the top of the charge well in blue painter's tape