Drew Samtmann's Portfolio - Chandelier-Belt Aft End Motor Ignition System

Chandelier-Belt Aft End Sustainer Motor Ignition System

Because our propulsion sub-team hadn’t properly tested head end ignition yet, we were forced to light our sustainer from the aft end for our first two stage flight.

Project Type
Independent Work on College Design Team

Date
Jan. 2025 - Present

Progress
Completed

Due to rules put in place by the launch site we used for our rockets, for launching a two stage rocket, we were not allowed to “hot stage”. Meaning we were not allowed to forcibly separate the two stages by lighting the sustainer while the booster was still connected. So, we were forced to have a coast phase where a black powder charge would separate the two stages, the sustainer would coast in the air for a moment, then light itself from its own electronics bay down to the motor casing. The ignitor, a thin wire with a combustible charge on the end, is what actually lights the motor grains, allowing them to burn from the top down (forward to aft). There are two ways that this ignitor can reach the grains. The first is through head end ignition, a system where the ignitor goes directly into the top of the motor casing to light the grains. This is by far the most efficient and reliable method, but with how we mount our motor casings, we needed to design and test a new head end ignition system, which our propulsion team was still creating and testing. The other option is to run the ignitor wire down the entire air frame, have it go through the thrust block, the fiber glass cap on the aft end of the rocket, and up through the nozzle to reach the top of the motor grains. This design was our only option but it posed several issues, which is where the “Chandelier-Belt” system comes in.

This black cap sits on the thrust block, gripping onto the motor casing as it holds the ignitor in place during launch via channels and a wooden dowel that keeps the ignitor wire standing upright inside the motor casing. These channels also protect the wire from the black powder explosion that separates the two stages. The design has grips around the side with textured bumps to assist with rotating and removing the cap during assembly. Because this piece would be debris, it also has a concave center to make it less aerodynamic as it falls to the ground.

The belt system is what allows the plastic piece and the ignitor to disconnect from the sustainer entirely. For each wire, 3 small holes are drilled in the thrust block. The wire is to be fed down through the 1st hole from the electronics bay, up through the second hole, and back down through the 3rd hole. Holes 1 and 2 are then epoxied while, using an ice pick file, a knife edge is created between holes 2 and 3 on the forward side of the thrust block. Therefor, when the motor lights, the impulse pops the plastic piece off, taking the ignitor with it, creating tension on that blade between holes 2 and 3 to cut the wire in half, releasing all of it from the sustainer.

Previous Concepts

In some previous designs, we had considered standing a mount on top of the fiberglass bulkhead where the black powder charge wells were attached on the booster, but after looking into it more closely, we saw that the result of this design would effectively be lighting the sustainer from the booster which, as previously mentioned, we could not do.

Landon Hendrickson's

Motor Cap

Before the “Chandelier-Belt” system, Landon Hendrickson, the Launch Operations sub-team lead on OLVT, modeled the team’s first design attempt for the solution to this aft ignition issue. It was this model that inspired the solution that I designed. Landon’s motor cap operated in a very similar way mine, but his cap would grip the motor casing from the inside, use magnetic pogo pin wire connectors as wire disconnects, and have a 3d-printed tower that the wires would run up to hold them upright.

The reason this design had to be redone was because of two crucial details. The first being, the magnetic connectors chosen would have been too large to use for this application. The second being, the tower holding the wires up would break under any force applied to it, meaning it would most likely break during the intensity of a rocket launch.  This design might have had some details to fix, but with a larger rocket and a slightly more tuned 3d printer, this design could potentially still be used.