Parachute Bay Design Consideration

Parachute bays take up the majority of the volume of a rocket, and special considerations must be made while designing them.


Parachute bays need to be able to vent to the ambient pressure if they fly too high. If they are not vented, the pressure in the sealed parachute bay from ground level will overcome the low pressure at altitude and may prematurely deploy the parachutes. A small vent hole needs to be drilled on the side of the bay opposite the deployment charge, so that the charge does not vent out. It does not need to be as large as the equalization ports drilled in the avionics bay. There is not much documentation on how large or how many of these holes there should be. Just be careful that you do not put too many holes that would drop the effectiveness of the deployment charge.


The volume of the parachute bay is based on the packed dimension of the recovery systems. Make sure to have considerations for couplers on either side of the bay. Some parachutes have a listed volume on their datasheets, but for most, we need to find the volume experimentally. We can do this by packing everything into a tube and seeing how much volume it takes up. If that does not work, you can use OpenRocket to estimate the size of packed parachutes and shock cords, and then add a factor of uncertainty to it. It is not bad to have a too-large parachute bay, but a too small parachute bay will not seal properly or hinder proper deployment.

Deployment Charge Positioning

The positioning of the deployment charges inside a parachute bay is important to how it will work. The charges will have to be on the bulkhead nearest the avionics bay so that the wires can be run cleanly. 

One critical consideration with the deployment charges is their position relative to the split point of the bay. The most common approach is the "cannon configuration" where the charges are at the base of the parachute bay and it splits at the top, so that everything inside is propelled out like a cannon. The second approach is the pull-away method, where the rocket separates at the deployment charges, and the force of the top of the rocket moving away will rip everything out of the tube. The danger with this approach is that the charge will also compress the recovery systems into the bay during separation, leading to concerns that it may not fully eject. Wherever possible, the cannon configuration should be used. 


The bulkheads that deployment systems connect to are known as the parachute bulkheads, and can be read about on this wiki page.