Most high-power rockets need two parachutes for their recovery. The first one is called drogue parachute and it produces the initial deceleration, whereas the second one, the main parachute, helps the rocket achieve its desired ground-hit velocity.
Before designing the parachutes, a specific research needs to be conducted in order to select the right materials, the fabric (ripstop nylon), the thread (nylon) and the paracords (nylon).
The main process for the design and manufacturing of a parachute begins with the calculation of its diameter (d) and its drag coefficient (Cd). It is also necessary to know the exact mass (M) of the rocket after the engine’s fuel has burned out. Moreover, for the drogue parachute we need to know the speed of the rocket (v) the moment it is deployed, while for the main parachute the rocket’s desired ground-hit velocity. These parameters can be easily computed with the help of Open Rocket, a flight simulation program. The diameter of the parachute can be calculated with the help of specific bibliography.
Next is the design of 8 identical pieces in the shape of equilateral triangles. These pieces are cut using a pattern, which is designed using specific equations and manufactured with the help of a laser-cut. The pieces are then hemmed with a sewing machine and sewed together, using a specific type of sewing (zig-zag).
The next step is cutting a center hole with a radius that is 20% of the parachute’s radius and makes the rocket more stable. Then, 8 cords are sewed on the fabric, which have a length that is 1.15 times the parachute’s diameter.
The recovery sub-system has developed two mechanisms. The first one is the ejection mechanism that frees the nosecone and deploys the drogue parachute. Its casing is a metal cylinder with four small holes and two caps for both ends. In the casing the members place a small canister with a small amount of Black Powder (BP), which is connected with two wires that are also connected to the electronics’ bay of the rocket. This is the part of the rocket that gives the signal to ignite the ejection. Once the BP is burnt, it produces gasses that escape with great pressure in the Recovery bay, thus pushing the nosecone and the drogue parachute out of the rocket. The procedure towards designing the mechanism requires knowing exactly how big the recovery bay is, as well as the weight of the nosecone. Then, the dimensions of the casing, the four holes, as well as the approximate amount of Black Powder needed for the ejection mechanism to work, are calculated with equations.
The second mechanism is called tender descender and it deploys the main parachute at the right moment. It consists of two metal parts, one of which is tied to the drogue parachute and the main parachute’s case, whereas the other one is tied to the rocket. These two parts fit together and create a space to place a small amount of BP, which, again, is connected with two wires that are also connected with the electronics’ bay of the rocket. When the signal to burn the Black Powder is given from the electronics’ bay, the two parts of the tender descender mechanism are divided. Consequently, the drogue parachute draws the main parachute’s case, thus deploying the main parachute.
After the design and manufacturing of both mechanisms, many experiments are needed, in order to make sure that they work properly, as well as decide on the perfect amount of BP.
The main goal of the Recovery sub-system is the safe recovery of the rocket. That’s why, its members’ duty is to design and manufacture proper parachutes, as well as capable mechanisms that operate correctly at the desired moment. Safety plays a significant role for the sub-system’s members, which is why a new ejection mechanism is currently in development. This mechanism will utilize compressed CO2 instead of BP, since CO2 is safer to work with during tests as well as the assembly of the rocket. It is also important to note that the addition of a separable payload creates the need for one more parachute to be designed and manufactured.