Centennial

Centennial is a 4-inch dual-stage rocket designed for the 2024 Argonia Cup based in Argonia, Kansas. Competing teams were tasked with designing and launching a dual-stage rocket that could carry as many golf balls as high as possible. All competing rockets were constrained to a total impulse limit of 5200 Ns.

Standing over 11 feet and weighing 34.5 lbs, Centennial is designed to reach an apogee of 12,500 feet while carrying 81 golf balls to score about 113,000 points in the competition. The vehicle is powered by two motors: the Aerotech K1999 in the booster section and the Aerotech K250 in the sustainer.

On March 23rd, 2024, Centennial was successfully launched to 10,243ft at the 2024 Argonia Cup, carrying 81 golf balls.

Structure

Illinois Tech Rocketry hosted an IPRO class for the Argonia Team during the spring semester. Throughout the semester, our IPRO students had a chance to visit Illinois Tech's Student Machine Shop to gain hands-on experience. At the Machine Shop, the students cut fiberglass tubes for the avionics bay coupler and airframe using a band saw and threaded aluminum rods for Centennial’s payload using a CNC lathe.

Our student also got to learn using CAD software like SolidWorks as well as CAM like Rhino to export file for CNC router.

RhinoCAM

Fin step file was imported into Rhino CAM to generate gcode for CNC router

CNC ROUTER

Set up and ran gcode on router to cut the fins

FINISH

Cut tabs from fiberglass sheet and sanded and cleaned fins for final design.

Payload

The payload design for Centennial consists of two partitions within the rocket. The first payload section is within the upper section of the sustainer and can hold a maximum of 44 balls. The section is just under 20 inches long and consists of a 3D-printed structure that is lightweight and modular.

At the onset of our payload design, we created a custom Python algorithm to generate the most efficient packing structure given a cylindrical volume and the dimensions of a golf ball. It then used those geometric constraints to determine the minimum distance a golf ball could be placed. Figure 8 shows the algorithm we used and its corresponding result.

Using the results found from our algorithm, we designed a scaffolding structure to hold the golf balls in place. The structure consists of identical PLA plastic armature pieces. These pieces (shown in Figure 9) have two functions. The first function is to hold the balls via a clipping mechanism for ease of loading, and the second is to provide support for the top and bottom of the adjacent golf balls.

All armature pieces stack on each other while rotating out of phase by 90 degrees on every stack, locking the balls in place. Each stack piece interlocks with another, and a metal rod runs through the center of the scaffolding - connecting each piece. The rod stiffens the structure while allowing the bulkheads to be fastened on either side of the assembly. These bulkheads provide further security and rigidity to the entire structure.

For easy and rapid installment, the entire structure can be slid within the sustainer's body tube and fastened at one end to a bulkhead within the sustainer. It should also be noted that the structure is toleranced, so the balls are just shy of flush with the inner wall of the airframe, providing a final source of rigidity and support during flight.

The second partition within the sustainer is located within the nose cone itself. This payload section can hold an additional 25 balls. The nose cone's packing structure is much simpler and only requires a centering rod and two bulkheads. The centering rod for this section is a threaded rod secured to the aluminum tip of the nose cone and extends to the back of the nose cone's coupler. The first bulkhead slides down to a location where the nose cone's diameter can accommodate a golf ball's diameter. The balls are then loaded into the remaining space. The cavity is then capped by the final bulkhead and secured via a nut onto the end of the threaded rod. Overall, Centennial's payload sections can accommodate up to 69 golf balls within the sustainer section of the rocket.

Avionics

Centennial’s avionics are separated into two different AV bays: one in the sustainer and one in the booster. The booster AV bay is in charge of stage separation and apogee deployment of the booster’s parachute, while the sustainer AV bay is in charge of sustainer ignition, apogee, and main chute deployment. Both AV bays feature a fully dual redundant system incorporating Altus Metrum’s TeleMega and Featherweight Altimeters’ Blue Raven flight computers. To ensure full redundancy, both flight computers use separate batteries and pull pin switches, with the Telemega’s using an extra battery for pyro charges to provide a stable voltage. For the Telemega, pull-pin switches are used to turn on the main battery, pyro battery, and motor ignition to ensure safety. The Blue Raven has a single pull-pin for power but features wifi arming and disarming for pyro charges.

The AV bays are designed to fit within a 10-inch coupler that joins the upper and lower airframe sections and is held in place by a 2-inch switch-band for the pull-pin switches. The flight computers are housed on two 3.5-inch by 9.8-inch rectangular sleds, with eight spacers placed along the edges to ensure structural integrity. The sleds are 3D printed out of PLA and designed to perfectly house all of our electronics, with holes integrated into the print to ensure electronics boards are correctly oriented.

The bulkheads of the AV bay are manufactured from ¼-inch aluminum 6061 plates. Variants such as 7075 were considered, but we opted for 6061 due to 7075’s poor corrosive performance. The bulkheads were designed in SolidWorks and machined using a CNC router to ensure all holes were perfectly positioned and the stepped portion of the bulkhead was entirely flat.

Shock cords attach to each end of the AV bay via a 3/16-inch zinc-plated steel eye bolt rated for 600 lb. Connecting the AV Bay sled to the bulkheads are 3/16-inch chromate-plated steel threaded rods. These rods are secured to the sled through the sled spacers and fastened with epoxy and an anchoring nut. The bulkhead then connects to the rods through lock washers and nuts. All hardware in the AV bays was selected to ensure corrosion resistance and avoid degradation from black powder charges.