Mini-Pioneer

Mini Pioneer is a 2-3in sub-scale step-down dual-stage designed to test the Interstage Coupler and Head-End Ignition (HEI) design for Pioneer 1. Flown on an AeroTech K750ST and a K185W, Mini-Pioneer 1 was expected to reach 15,000ft and Mach 1.

This rocket was designed as a testbed rocket for all the new subsystems that would go on to make up Pioneer-1. Mini Pioneer uses the same step-down dual stage design as P-1, as well as the same interstate coupler design, and the same method of Head End Ignition. The only real difference between the two is the motor selection to accommodate the lower launch ceilings of local launch sites. Everything else is meant to be as identical as possible to validate our designs.

Design

Motor selection: K750ST with high thrust and neutral thrust curve and K185W, a c-slot motor with long burn time. Initially, J90W was the motor selected, but that motor went out of stock last minute, which required the substitution of the K185W. The main drawback of the K185W over the J90W is that due to it's length in comparison to the J90W, the rocket could experience tumbling if not lit right after stage separation.

Since both stages of Mini Pioneer are minimum diameter, meaning the body tube also acts as the motor mount, the fin is attached on surface of body tube, making the connection between the fin and airframe less rigid. For that reason, I decided to do layup on both sets of fins. Taking lessons learned from Big Red 2, I design a cutout for the layup, used masking tape to secure the carbon fiber and prevent it from fraying, then draw the layup shape from a CAD generated cutout. I also practiced some layups on 3D print fins can before performing actual layup on the rocket.

The original interstage coupler was meant to be machined out of 6061-T6 Aluminum, but due to procurement issues an emergency ISC was 3D printed out of Carbon Fiber Reinforced PLA. The backup ISC was printed at a slight angle to prevent the part from sheering under flight loads, and it held up well in practice.

Launch Results

Mini Pioneer was launched from the Indiana Rocketry Inc. Pence HP Field on April 12th, 2025. The booster got off the rail at around 120 ft/s, and climbed to 3,600ft. However, the two stages failed to separate, and despite the pyrotechnic charges detonating, none of the parachutes deployed, causing the rocket to follow a ballistic trajectory, impacting the ground at over 150 ft/s

Flight Data

Mini Pioneer reached a maximum altitude of 3,643 ft AGL, a max speed of Mach 0.6, and pulled 12 Gs off the launch pad. It came to rest around 500 ft from the launchpad.

Lessons Learned

While Mini Pioneer itself was not a successful launch, some key lessons were learned that went on to be implemented into Pioneer-1. Chief among these was the need to oversize the parachute bays on our rockets. While the parachute bays on Mini Pioneer were in theory large enough to accommodate the selected parachutes, in reality this required them to be packed so tight that the pyrotechnic charges were unable to push the parachutes out of the rocket. Even just a few extra inches would have meant that the parachutes would have had a much looser fit inside the body tube, allowing for easier deployment.

The other key takeaway was the need to simulate all possible flight scenarios prior to launch. While simulations were run for the nominal flight case, simulating a launch with simply a booster burn and stage separation, no sustainer ignition, would have shown the rocket was likely to tumble significantly after the planned stage separation, and the design could have been adjusted accordingly

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