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Since our last Invictus progress and design update, many things have changed. In this article, we will share the status of the vehicle at the moment and discuss how the updated design is progressing.
STAGE 1 AND 2 DESIGN PROGRESS
Stage 1 will be the simplest part of the second Invictus. Regardless, it will have to be engineered properly to support the 25 pounds of thrust (111 newtons) from the massively more powerful G80-13T motor. This motor has 2.5x the average thrust of the dual F15-0s used on the Flight 1 vehicle. Additionally, Stage 2 now uses an F15-4 motor for extra impulse over the E12-4.
Prototype of S1 mount. Not final design.
Mount
After the first launch, we learned the importance of properly designed and manufactured mounts when all three of our engine mounts failed in some capacity. Stage 1's cracked, Stage 2's melted and broke, and Stage 3's did the same. For this reason, Stage 1's mount will be 3d printed in 316L stainless steel and attached to the tube with four or eight bolts (still deciding) and reinforced with four hot-glued plastic gusset plates that will help to spread the engines thrust across a larger area of the first stage's tube to avoid a structural failure. We will not be using permanent attachment anymore, as Invictus at its core is a development vehicle for other projects. Testing different designs can be very insightful in model rocketry.
Stabilizer / Retainer
A key issue on the first flight was motor oscillations and movement. This is what cracked the stage 1 mount by providing off axis thrust when only one motor lit. The stabilizer shown on the left is for stage 1. This part will also retain the stage 1 motor in place and stop it from falling out prior to launch, and will be bolted in with no other reinforcements to allow for quick engine swaps. This part is present on both stages in the respective motor sizes for each. We project this new type of engine mount combined with this stabilizer and retainer will help the flight.
The stage 2 mount will be solid with no weight reduction holes in it like the stage 1 mount. It will be printed in resin as stage 2 has much less thrust.
No propulsion elements have been ordered yet. They will not be ordered until all other necessary rocket components are also ready.
Avbay shown in green rectangle.
Avbay
The Invictus Avbay is the portion of the rocket where all avionics will be stowed. This flight computer includes a barometer for measuring air pressure and barometric altitude, redundant gyroscopes and accelerometers to measure orientation and acceleration, and ignition systems for the second stage. It will be based on an Arduino Uno R3 and is currently in the very early design stages. Onkla SXC is helping us develop these avionics and other systems that will be introduced on later Invictus flights. A very early schematic of the flight computer is shown below. It is not current and many parts of it are outdated.
Wires will run all over the rocket from the Avbay and all data captured will be logged to an SD card. Multiple safeties will be in place to prevent any ignition anomaly on the pad and the vehicle will be armed for flight 30 seconds prior to liftoff. The computer will detect burnout of the first stage and then use that data to light the second stage after a short coast period.
Recovery
Arguably the worst failure on Flight 1 beyond the mount damage is the hilariously bad performance of the recovery system. Due to the second and third stage mounts practically exploding the moment they bared any thrust, we had no chance to truly test this system out. However, we highly doubt a single D motor (or F motor for that matter) could fully deploy a large parachute from a 4 inch diameter rocket. Therefore, for flight 2, we will use primarily the ejection charge from the second stages F15-4 and secondarily a dual deploy charge to ensure parachute deployment. Recovery is an often overlooked aspect of model rocketry, but one that cannot be ignored. It is one of the hardest, and we will be very happy if the parachutes so much as deploy on this next flight.
Invictus Flight 2 will be a massive leap from Flight 1 if all goes to plan. As of today, we still are targeting
no earlier than Q1 2025 for liftoff.
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