Nuka-Cola
31,000’ AGL, Mach 3.2, Fully Recovered.
Nuka-Cola was the first high-performance, relatively high-performance flight vehicle I was a part of. One of my good friends, Harry Amadeo, and I were involved in the project. I was responsible for the design and planning/manufacture of primary aerostructures on the rocket, and packing and readying of the recovery system. Harry provided the powerplant for the vehicle, which also served as the lower airframe. Much of the integration and manufacturing was done cooperatively between us.
Design Goals
The design of Nuka-Cola was intended to allow us to gain experience and test designing, manufacturing, and flying to higher altitudes and greater speeds. As a result, the requirements devised for this project were mainly performance related. The project requirements were as follows:
Fly to an apogee of greater than 30,000’ AGL.
Fly at speeds equal to, or in excess of, Mach 3 ASL.
Verify manufacturing, construction, and integration processes.
Test recovery deployment at medium altitudes.
It was planned for the vehicle to fly at the amateur rocketry launch event BALLS 2023, or BALLS 31, which it did. During its flight, the vehicle fulfilled all requirements. Flight data analysis of GPS tracking data and barometric altitude data both verified an apogee of above 31,000’ AGL, and a maximum velocity at motor burnout of Mach 3.2.
Overall System Architecture
In the amateur world, high-performance rockets generally occupy one of two classes. Either, the rocket will have separate powerplant that is a close/tight fit inside a tube, with which the rest of the vehicle structures interface with, called an airframe, or the SRM case itself, in large part, fulfills this role. In the hobby, vehicles that conform to the former description are known as “minimum-diameter”, or MD rockets, while those that conform to the latter are known as “sub-minimum diameter”, or “flying case” designs.
Nuka-Cola is, for the most part, a sub-minimum diameter design, that features a separate fincan, upper airframe, and nosecone. In addition, the upper airframe and nosecone are both coupled by an avionics bay, which itself is a tube that fits inside the upper airframe and nosecone, and houses the avionics. The avionics consist of 2 PerfectFlite StratologgerCF barometric altimeters and deployment computers, and one Featherweight GPS system. The recovery system consists of a 1’ drogue chute in the nosecone and a 3’ chute in the upper airframe. Both parachutes are mounted to structural components using kevlar shock cord.
Aerostructures
The primary aerostructures on Nuka-Cola are the “fincan”, the upper airframe, and the nosecone.
The fincan is a 7.5” long section of 3” ID filament would carbon fiber tube, with fins bonded to the tube. The fins themselves are waterjet and beveled 3/16” economy plate from Dragonplate. All surfaces were prepped (sanding, IPA wipe, water break, repeat) before bonding. Fillets of DP420 provide structural rigidity and strength in the joint.
Fins being attached to the can using fillets made of DP420.
The nosecone was made using a multipart, open-mold process. The geometry of the nosecone itself includes the conical section with a straight cylinder at the base, for the coupler interface with the avionics bay. The mold was FDM printed in multiple conical segments, and then wrapped in mylar release film to ensure easy and smooth release of the part form the mold. The layup was done using US Composites 635 laminating resin and Soller Composites 3K 3” biaxial sleeving. 5 layers of carbon sleeve formed the main load bearing structure of the part, and a single layer of Soller Composites 3” light fiberglass sleeve was applied to make the surface finishing process easier. Once the part was demolded and trimmed, the inner diameter was sanded to fit the avionics bay, and the outer diameter smoothed. The nosecone tip was machined out of 6061-T6 aluminum by PCBWay, and retained through the use of a fiberglass bulkhead and threaded eybolt that threaded into the nosecone tip, therefore compressing the joint.
The completed fincan.
Mold assembled.
Mold wrapped with mylar release film.
Layup in progress, 5 layers of carbon fiber applied.
Nosecone immediately after demolding.
Nosecone demolded and trimmed.
Finished nosecone with nosecone tip attached.
The avionics bay was manufactured in a similar manner. An acrylic tube with an OD of 2.75” was used as the mandrel, and 5 layers of Soller Composites 3” light fiberglass sleeve used to achieve a part OD similar to the ID of the upper airframe section and nosecone straight section. A 1” section of the material used for the upper airframe was epoxied to the center of the avionics tube as the switchband, and to give solid structure for thrust to be transferred from the upper airframe to the nosecone. The upper airframe was a 1’ long section of COTS 3” OD filament wound fiberglass tube from Wildman Hobbies.
Completed avionics bay, with the switchband visible.
Avionics bay integrated with the upper airframe.
Avionics bay integrated with the nosecone.
Nuka-Cola, post-flight in April of 2024. White primer is now visible under the formerly red paint, which now appears as a pink char layer. Upon further inspection, the red paint traveled rearwards during its ablation/liquification during flight, as seen on the motor case's forward and aft ends. Furthermore, tracks on the upper airframe and the nosecone can be seen behind where the bolts and shear pins blocked the adhesion of the ablating paint.