The Crash, part 1

This is a post about the most expensive rocket I’ve flown – and the most expensive rocket I’ve crashed. And this will also hopefully be the first of many posts chronicling the rebuilding process.

In college I worked on a few projects with Dr. Ed Wilson at Harding University, with most of my time spent on research involving the use of spectrometers to look at hybrid rocket motor exhaust plumes. So when we heard about NASA’s University Student Launch Initiative (USLI) – a systems engineering contests where university teams designed and built rockets to fly scientific payloads – we decided we wanted to compete.

For the first year of our participation in USLI (2007) we flew a 4″ diameter rocket with a hybrid K motor. However, our design kept getting heavier and heavier, so by launch day there was no chance we’d get close to the target altitude of one mile. The first flight was relatively successful – a solid flight on a K hybrid with safe recovery – but a connection between our spectrograph and the onboard R-DAS flight computer came loose, so we did not get any data. Onboard video from the flight is here.

For the second year of USLI (and my last year of college) we tried to improve on our previous design. Because our previous design was too heavy, we made our 2008 rocket 3.1″ in diameter instead of 4.0″. Because our many stressful hours working on our electronics payload were complicated by a difficult-to-access avionics bay, a major feature of our 2008 rocket was a new, easily-accessible (and see-through) bay design, pictured at left. [Note that some of the labels in the diagram are incorrect - that's an RDAS, not a Gwiz, for one - because this was an early version of the diagram before all the labels were corrected.]

Because the telemetry component of the R-DAS caused so many headaches in the 2007 rocket, and since we didn’t get data from it anyway, we decided to forego the telemetry unit in our 2008 project. Instead, we wired our custom spectrograph directly to the R-DAS, which was to store the data. All in all, it was a pretty complex payload, and in addition to the pricey R-DAS unit, the parts for the spectrograph cost over $1k.

From top to bottom, the 2008 rocket consisted of a 3″ nose cone, parachute section (separation at apogee, followed by release of the main chute by a ChuteTamer unit some time later), see-through electronics bay, spectrograph bay (sealed off from light), and the 48″ long 54mm motor mount. The spectrograph attached to a fiber optic cable that ran down the length of the motor thorugh an aluminum wiring conduit and emerged at the top of one of the fins. From there the fiber optic cable was taped (using high-temp electrical tape, I believe) to the outside of the fin until it was positioned to point directly at the exhaust plume.

Scientifically, the goal was to gather spectra from the flight that would be analagous to spectra obtained in ground testing, as a proof-of-concept for more intensive onboard spectroscopy experiments, which might eventually be useful as non-intruive inflight combustion diagnostics. You can learn a lot from the spectral data, including combustion temperature, propellant components, and the presence of uncombusted particulate matter.

 
Pictured above are the pre-flight prep and the pre-flight USLI safety check.

As the weight of the project crept upwards, we switched plans from using a Contrail 54mm J hybrid to the 54mm K555, the same motor used for the 2007 projected.

Two major lessons from my participation in USLI were: A) Everything takes longer than expected; and B) Test everything possible before risking expensive electronics in-flight. We had originally planned to finish major airframe construction approximately 2 months before the launch in Huntsville, Alabama. That would give us time to attend two launches with the Mid-South Rocketry Society in Memphis, TN (two hours’ drive east of our school in Searcy, Arkansas). We finished up construction and electronics work too late to make it to the first launch, and the second launch was rained out. So instead of flying the rocket first on a hybrid J or an Aerotech J350 – without the spectrograph on board – our first flight of the launch vehicle was to be a fully loaded flight for the competition in Huntsville. (Our crash, and that of another, larger project in 2008, probably contributed to NASA’s [wise] decision to require previous test flights for all competition rockets starting in 2009.)

The lift-off was perfect on the Contrail K555. The red and black rocket lept off the pad and flew straight up into the blue sky. My biggest concern prior to launch was whether our see-through, easily disassembled electronics bay design would survive the stresses of flight. When she hit burnout without shredding, I felt a surge of relief and let out a whoop. And then things went wrong.

To be continued…