Design
Using the SRAD solid motor our team designed, we designed a rocket that would be able to house 3 payloads: a water ballast in the nosecone that ejects the water at apogee, a deployable platform mechanism for proof of concept, and a scientific payload to see how a non-Newtonian fluid reacts in a microgravity environment. However, the main goal is to get the rocket to 10,000 feet. This is achieved by keeping the caliper of stability, how much the center of gravity is behind the center of pressure, below 2 as well as keeping a smooth surface on the airframe, designing the fins to have a double-wedge cross section, and adding a boat tail to decrease the base drag of the rocket.
Recovery
Being in charge of recovery I had to come up with a mode of deployment for our drogue and main chute, calculate the proper amount of black powder for ejection, how to attach the forward and aft segments to the recovery system, ensure the shock cords can withstand the stress shocks at deployment of the chutes, and how to protect the recovery system from the hot gases of black powder.
Deployment and Ejection:
Dual deployment is pretty much a given with such high altitude rocket, so our drogue chute will be deployed at apogee with the our black powder ejection charge, and the main chute will be held together by a mechanism (Jolly Logic) until it reaches a certain altitude upon descent. So, in our case, we will have one ejection charge for both our drogue and main chutes. Sizing of this ejection charge was done using the equation on the right. Calculating the volume that will be pressurized and force needed to shear 3 shear pins, we can get the amount of black powder we need. I calculated that we only need 1.5 grams of black powder for separation; however, we conducted a ground test for separation with 2 grams for a factor of safety. The ground test didn't have any mass in it from payloads or any other miscellaneous components, so we are doubling the amount of black powder (4 grams) as an extra FoS to account for the extra inertial mass and overcoming any aerodynamics upon ejection. The ejection charge was placed on the forward bulkhead and contains a U-bolt for the recovery system to attach to, 2 spring terminals for the COTS altimeter and barometric pressure sensor, a PVC plug to hold the black powder, and a cap to contain the black powder in the plug. The 2 spring terminals will connect to two initiators that then lead to the black powder for ignition. |
Parachute Sizing:
The sizing of parachutes is very important for the recovery of rockets. The drogue chute needs to be a balance between lateral drift and descent velocity. If the descent velocity is too fast, the main chute will experience too much force and could damage the recovery system. If the descent rate is too slow, the lateral drift increases, which sort of makes the point of the drogue chute pointless. The drogue chute was sized to be 48" giving us a descent rate of 22 m/s at an altitude of 10,000 feet. The main chute was sized to be 62" which gives us a descent rate of 9 m/s, ensuring that we will have a safe touchdown velocity. |
Miscellaneous Recovery Components:
Other required hardware for the recovery system includes the U-bolts for the shock cords to mount to in order to join the forward and aft sections of the rocket. We also need shock cord, quick-links to join the shock cord segments, swivels to reduce twisting and tangling, and a reusable heat blanket to protect the recovery system from the hot ejection gases.
Other required hardware for the recovery system includes the U-bolts for the shock cords to mount to in order to join the forward and aft sections of the rocket. We also need shock cord, quick-links to join the shock cord segments, swivels to reduce twisting and tangling, and a reusable heat blanket to protect the recovery system from the hot ejection gases.
Manufacturing
The slideshow on the right is a collection of photos that document the progression of the manufacturing process of our rocket.
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Testing
Our team conducted water ballast tests and ground tests for ejection charge separation. Our electronics team also performed more minor tests for GPS tracking, barometric sensor testing, and altimeter testing. On the right you can see tests done for our water ballast and ejection charge.
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