PIONEER I

Pioneer 1 is ITR's first full-scale step-down dual-stage rocket with targeted altitude of 80,000ft and Mach 2.5.

Design

Pioneer-1's design was optimized around stability at high supersonic speeds, as well as minimizing unneeded mass. This is the thought process behind the step-down dual-stage design, as by having the sustainer be minimum diameter(ID of the body tube is a slip fit with the OD of the rocket motor), the sustainer ends up much lighter than a rocket that had the same diameter at both stages, as the sustainer is both physically smaller, and doesn't need a dedicated motor mount, as the airframe is also the motor mount.

I used the open source program Open Rocket to design and simulate the rocket. Open rocket is a powerful tool that allows instant feedback between design changes and how they affect the flight of the rocket. This allows me to dial in the exact flight profile I want, optimizing things like ignition timing, motor selection, etc.

Pioneer-1 uses Filament Wound Fiberglass tubes as it's airframe, a 5-1 Von Karman profile nose cone, and 3/16 G10 Fiberglass plate for the fins. The rocket is 10.25ft tall, and is 34 pounds on takeoff, including propellent. The booster used a CTI M2245, and the sustainer used a Aerotech K250W

Launching off a 40ft launch rail at the Friends of Amateur Rocketry launch site in the Mojave desert, Pioneer-1 screams off the pad at over 217ft/s, reaching a maximum velocity of 2300ft/s, and an apogee of 80,000ft. It reaches this height in around a minute and a half, and the rocket is in the air for around 15 minutes from launch to landing, depending in launch day conditions.

Motor Selection

Booster: M2245 is chosen for high thrust, neutral burn profile

Sustainer: K250W regressive thrust curve with long burn time

Step Down Interstage Coupler

The centerpiece of this style of dual-stage design is the coupler that attaches the two stages together. In a typical dual stage design, this would simply be a section of coupler tube that would slide into the bottom of the sustainer airframe, but with a minimum diameter upper stage, that's not possible. The solution to this is to have a section for the sustainer to slide into, and a lip for the bottom of the airframe to rest against, which transfers the thrust from the booster motor directly into the airframe, rather than indirectly via the fins, which runs the risk of sheering off the fins if the epoxy isn't bonded well enough to the airframe. In theory, this would be a low risk, but with all the other unknowns at play, I made the decision to add the lip to make the design less dependent on the layup.

The ISC is made of 6061-T6 Aluminum, and is bolted to the top of the booster upper airframe, and has a slip fit with the sustainer lower airframe. Upon stage separation, a pyrotechnic charge pressurizes the internal volume of the ISC, and forces the two apart.

Avionics Bay

While the ultimate goal of the Pioneer program is to implement home grown flight electronics, Pioneer-1 flew on COTS(Commercial off the Shelf) flight computers, namely a Altis Metrum Telemega V5 on the sustainer, and a pairing of another Telemega V5 and a Featherweight Altimeters Blue Raven. The Telemegas are each powered by 2 3.7v 1S LiPo batteries, and the Blue Raven is powered by a 7.4v 2S LiPo. Current Flow is controlled via a series of pull pin switches, which electrically disconnect the flight computers from pyrotechnic charges, ignition leads, as well as controlling the power state of the computers themselves

All of this is mounted to a 3D printed Sled, which is then attached to a frame of 2 1/4 mild steel threaded rods, terminated by 2 G10 Fiberglass bulkheads. All of this is then nested inside a coupler tube, the ends of which nest into the shoulders of the bulkheads. 2 Eyebolts are also mounted to the bulkheads to attach the recovery system to, the load of which is distributed through the bulkheads and threaded rods, ensuring that none of the flight loads are transmitted to the flight electronics.

The Telemega's used a 433MHz radio to communicate with a ground station to transmit live telemetry and GPS data, as well as to do remote programming. The Blue Raven uses Bluetooth Low Energy (BLE) for programming, but does not communicate remotely, so it's only purpose is as a backup to deploy parachutes

HEI (Head End Ignition)

Due to the minimum diameter construction of the sustainer, there are 2 options of running the ignition leads from the sustainer AV bay, either running them externally down the side of the airframe, then down into the bottom of the rocket motor, or doing down through the motor retainer and into the forward closure of the motor itself, in a configuration know as Head End Ignition, or HEI for short. We chose the latter following the design philosophy of having the sustainer be as light as possible, and the cable ducting, epoxy, and extra wiring would have added upwards of an extra pound or two, especially if mirrored to ensure even aerodynamic loading at high supersonic speeds.

In an HEI configuration, a small hole is drilled into the forward closure, and two redundant ignitors are inserted, with a pair of red JST connections facing outwards. This way, when the motor is assembled, the ignitors, they are right at the top of the grain, the same place they would be if they were inserted up through the bottom of the motor. Those ignition leads are then attached to a set of wires that run up through the motor retainer, and to another set of JST connectors that connect to the Avionics Bay

Vacuum Bag Layup

On previous rockets, I've done layups by laying out Carbon Fiber on a flat surface, and squishing epoxy resin into it using a rubber applicator, then smoothing that out onto the fins. This generally works well, but I've run into trouble when applying this technique to the very triangular fins that I use on rockets that fly at supersonic speeds(See the Big Red 2 Layup, not my best work). The shape of the fins tends to want to stretch the weave at odd angles

The solution to this problem is to Vacuum Bag the layup, in which all the entire layup is put in an airtight bag, and all the air is removed, sucking the resin down into the fibers, removing air bubbles, as well as pulling the weave as tight as possible against the fins. This also has the additional benefit that the weave doesn't need to be pulled on so much to position it, preventing fraying at the edges. It also leaves a very smooth finish behind.

A number of other lessons were taken from Big Red 2's layup, namely the benefit of having a precise template for cutting out the carbon fiber, rather than just approximating the shape of the fins, as that significantly reduces the amount of manual trim work, and thus reduce opportunities for fin damage to occur.

RESULT

Launch Results

Pioneer-1 Lifted off the pad on June 7th, 2025. It left the rail traveling at approximately 230ft/s, and ultimately reached a speed of 391ft/s. Around 3 seconds into flight, the rocket experienced a anomalous decrease in acceleration before the rated burn time of the M2245 that propelled the booster, causing the rocket to destabilize and flip over, ultimately breaking up. Some small pieces were recovered so far, including the sustainer AV bay, which allowed us to look at the flight data that was recorded.

Flight Data

The flight data from the recovered computer gave us a lot of valuable information, and allowed us to determine the cause of failure. Pictured above is a map of the launch site, with the launch pad at the red target, and the blue target is where the sustainer AV bay came to rest after being separated from the rest of the rocket.

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