Launch!

Sunday, June 28, 2009 at approx. 8:00pm EST the Purdue Hybrid Rocket Technology Demonstrator took to the skies for its inaugural launch! The motor ignited as planned and produced approx. 800 lbf of initial thrust, lifting the 115 lb vehicle with an acceleration of ~6Gs off the mobile launch platform. The external valve actuator worked as planned, the avionics umbilical cords were retracted, and the fins cleared the MLP as designed. For the next 5.5 seconds the motor performed flawlessly as it consumed all of its 14.8 lbs of hydrogen peroxide while accelerating the vehicle to an altitude of ~6100 ft and producing max. velocity of ~Mach 0.6. Due to winds of approx. 10 MPH, the flight-vehicle weathercocked into the wind, taking a trajectory which is normal at such wind conditions.

Apogee occured at T+21 seconds, at which time the drogue apogee charges fired. The shock from the apogee ejection charges produced approx. 30 G's of acceleration which caused the plastic shear pins of the nose cone to break and eject the nose cone prematurely. The main parachute which was tied to the nose cone therefore ejected at apogee and not at the pre-planned 700 ft altitude. Therefore the combination of drogue and main parachute deployment at apogee imposed larger-than-normal forces on the recovery harness. Nevertheless, the recovery harnesses and quicklinks which are rated to over 1700 lbf are able to withstand these kind of loads. The recovery harness which is made of tubular nylon rated to over 2000 lbf would have been more than capable of sustaining these loads.

However, the problem lies in the attachment of the tubular nylon shock cord with the booster airframe section. The shock cord was passed through a hole drilled into the upper wooden bulkhead which separates the booster section from the drogue recovery module. The hole drilled into the wooden bulkhead creates a relatively sharp corner which when combined with the large forces already imposed onto the shock cord, led to the shearing of the tubular nylon. Consequently the booster section was detached from the recovery harness and plummeted to its death. The drogue, main, avionics and nose cone sections which were attached to the main and drogue chutes slowly drifted away and were successfully recovery approx. 2 miles downrange (thanks to the 2 on-board radio trackers they were easily found). The video camera recorded spectacular on-board video and the RDAS units recorded acceleration, velocity and altitude measurements taken throughout the entire flight.

The good news is that fixing the recovery problem is very simple. Instead of passing the tubular nylon through a central hole drilled inside the wooden bulkhead, two flat kevlar shock cords passing through slotted inserts on the periphery of the bulkhead with the addition of a slight radius would prevent this shearing phenomenon to occur.

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Overall, I am very happy that the most difficult part of the flight-vehicle, namely the propulsion system performed flawlessly. In fact, the propulsion system performed beyond expectations since the actual achieved altitude of 6,100 ft was 1,100 ft higher than our simulated altitude of 5,000 ft! The motor delivered more total impulse than what we expected based on the hot-fire tests. I am also very glad that our carbon-fiber aero-structures (fuselage and fins) were able to withstand the propulsive and aerodynamics forces as designed. In addition vehicle stability looked really good throughout the entire ascent phase(boost and coast). All the avionics systems worked as planned, keeping the vehicle vent valve closed during motor operation, communicating with the GSE during launch ops, ejecting charges, logging data and taking on-board video.

This flight-vehicle ranks as one of the largest hybrids ever designed and launched by a US university (in terms of total impulse). I was also informed by our local Tripoli prefect that yesterday's flight marks the largest hybrid powered launch in the state of Indiana to date.

All this was only made possible with the tremendous teamwork and passion that all of you exhibited during the past couple of years. More specifically, a BIG thank you to Brad Appel, Allen Yan, Andrew Rettenmaier, Kevin Tait, Tom Feldman, Pam Slaughter, David Hailey, Dr. Pourpoint, Mike Walker, Nick Piercy, Tim Manship, and many more students for their tremendous contributions. None of this would have been possible without us working together as one team.

Finally, I would especially like to thank Scott Meyer and Professor Heister for their unwavering support. Without their expertise and the ability for us to use the Zucrow rocket test facilities, the Hybrid Rocket Project would have existed only in CAD drawings and powerpoint presentations and would have never taken off the ground.

We hope that this project will help to inspire future generations of students to continue the development of larger and more sophisticated hybrid, liquid and solid propellant launch systems, and that yesterday's flight will one day pale in comparison to the wonderful achievements that are yet to come.

Take care,
John