Over the last year, activity at the USC Rocket Lab has been astronomical, and we’re not planning on slowing down any time soon! While we’re diving head first into the 2015 semester, we should take a moment to look back at our accomplishments over the last 12 months. From launching the year off with DCX, to solving our problem with multiple static firings of rubber ducky cases, to our final two launches of Flying Dutchman and Tirebiter (which came within 3 weeks of each other), our commitment to lab has never wavered and our morale has never been higher.
Del Carbon Extreme, or DCX, was the first flight vehicle of last year. Named after RPL’s first launch vehicle, Del Carbon, it was designed with all the technology we had developed over the past decade of being a lab. Comparing DCX and its namesake side-by-side, they look very similar – both are 6 inches in diameter and are within inches of each other in length. However, the technology upgrades (including phenolic liner motor TPS, an oxamide motor, and a minimum-diamter fully-filament wound carbon fiber case) meant that DCX could travel 260,000 ft, compared to DCX’s three launches to around 20,000 ft. Less than ten years after the lab was founded, we had the technology to let us go over ten times as high.
DCX launched out of Black Rock Desert almost exactly one year ago, on October 18th, 2014. It took to the sky in one of the most beautiful launches we had ever seen, until it experienced an anomaly around 9 seconds into the flight. We solemnly watched the nosecone and recovery payload emerge from the case, then the vehicle fall back to Earth.
After collecting the pieces and examining them back in lab, we discovered that the internal thermal protection system (TPS) protecting the carbon-fiber motorcase from the heat of the motor had failed at the forward end, causing the case to burn through and shear into pieces. With that discovery, our goal for the next semester was set: design, build, test, and fly a more reliable thermal protection system.
The Rubber Ducky Cases
Knowing we needed to develop a new TPS, the timeline for the Spring 2015 Semester was optimistic. Our plan of creating three static firings, a full-size flight motor static firing, and two flight vehicles, all using a new technology that had yet to be developed was going to keep us very busy.
To remedy our motor's TPS failure, the lab switched from a phenolic liner technology to EPDM rubber liner, which began our “Rubber Ducky” series, or RD for short. A series of smaller, 4-inch diameter cases were made, each one using iterative rubber technology until just the right liner was found. The first two firings both used the EPDM, one with a fiberglass reinforced liner and one with only a cured sheet of rubber. Both were a complete success, so we chose to pursue the one that was less of a pain to work with – the cured sheet of EPDM.
Next, we stepped up our game and created a larger 4 inch motorcase that used the EPDM, and also a newly developed retention ring that was laid up with the case, rather than being machined and inserted afterwards. This new case, known as RD 5.1x, was as much of a success as the first two RD cases. Between the three firings, we not only collected valuable data from our oxamide motors, but we also created and tested a successful TPS.
DCX-S Static Fire
With the successful Rubber Ducky firings, we were ready to take things to the next level: a full scale 6-inch static fire. DCX-S was a static firing of the newly designed DCXII’s (also known as Tirebiter) motor and motorcase, using the EPDM rubber liner we had just developed. This would be the liner’s true test, because there’s a huge difference between a foot long 4 inch motor, and six foot long, 6 inch motor. It’s like asking your bodyguard to protect you from a toddler and then hoping he can also protect you from a 6 foot tall body builder who’s also on fire. DCX-S would show that the liner and the sealing rings worked on a larger scale. Additionally, DCX-S was fired with a nozzle that used a phenolic insulator with an entirely aluminum casing, drastically reducing the weight of our previous steel carrier nozzles.
At the end of spring break, those of us who weren’t in partying it up in warm, sandy places decided to pack up and head back to our warmer, sandier testing facility. DCX-S fired completely successfully on March 21st, and became the most successful composites static fire for the lab, and quite possibly for amateur rocketry as a whole. With the new liner, new nozzle and an oxamide motor that produced a total impulse of 28,000 pound-seconds, our simulations showed DCXII (“Tirebiter”) could exceed the Von Karman Line. Our decade-long dream of “space or nothing” felt within reach.
Our first flight vehicle of the spring semester was the Flying Dutchman. Dutchman was originally designed to be the first vehicle to use oxamide in the motor as a burn suppressant, but DCX took that honor in the fall. Flying Dutchman instead became the first flight vehicle to implement the EPDM rubber liner technology. The flight of the Dutchman would validate the new TPS under flight conditions; however, an aerodynamic failure led to some crazy acrobatics about 4.5 seconds into flight. The nosecone popped off with the avionics unit still intact, which allowed for its speedy recovery. The rest of the vehicle was found a few hours of thorough searching later, in a broken but consolidated wreck.
It’s still a bit of a mystery what happened to Dutchman. The motor was not the issue, nor the EPDM liner, which performed marvelously, the fin can was still attached, the avionics system did not prematurely eject the nosecone, and the design itself of the vehicle was not flawed. Aerobatic failures can be tricky to solve, because we don’t have the luxury of looking inside the motorcase and seeing what technology failed. We picked up the pieces and returned home with some big questions on our minds.
After the failure of the Dutchman, there was a big choice to make. We only had three weeks remaining in the semester, and we had to decide whether or not to press on in the hopes that whatever caused the Dutchman to fail was something we could fix, or to wait until the fall semester to do more research and try again. Ultimately, in true RPL gusto, the lab decided to go for the goal of being the first undergraduate student-run organization to launch a successful space shot. We put our hopes in DCXII, dubbed fondly as “Tirebiter”, after USC’s old canine mascot George Tirebiter.
This vehicle had the same outer mold line as DCX, but was infused with all the new technological improvements tested in the rubber ducky firings. Tirebiter was much lighter and more reliable than the original DCX, which allowed it to be officially called a space shot. Flying proudly in its nosecone was the lab’s new and improved in-house designed and built HAMSTER (High Altitude Module for Sensing, Telemetry, and Electronic Recovery) avionics system. Everyone in lab had put their hearts, souls, and sleep into the final few weeks of the semester in an effort to get one last chance at reaching space. We drove out to Blackrock Desert in the middle of finals and launched the vehicle May 8th. Sadly, Tirebiter experienced a similar fate as many of its predecessors, suffering an event about 6.5 seconds into flight.
Again, some rather impressive acrobatics were performed, and the vehicle went on a horizontal course until its motor burned out. With the delay of this update, we wished we had some concrete conclusions as to what happened. Unfortunately, while we did have several theories, we were still far from pin-pointing the exact cause of the failure. What we could confirm was that the motor, motorcase, and nozzle performed spectacularly considering that they remained intact and continued to burn throughout the entirety of the event that shredded the vehicle. Unfortunately, due to the failure, the vehicle was no longer aerodynamic and, after dumping a ton of energy into a high G loop, the vehicle did not get very far in altitude or range.
While Tirebiter may have been a way off from space, we have never been closer to reaching our goal. The absolutely gorgeous rocket we brought out to Black Rock back in May was built in 3 weeks, not 3 months like its predecessor, or 2 years like we were forced to wait with Traveler I.
During the spring semester we continually set a ridiculous turn around rate between projects, going no more than 3 weeks between each firing/launch. Holding to that for the construction of a full space shot vehicle, made with the highest quality and equipped with all the bells and whistles, is truly outstanding. We worked tirelessly last semester to finally resolve motorcase issues that have plagued our vehicles for years. Moving into this new year with the momentum of that incredible drive and success, we stand more ready than ever to take on the next challenges with unrivaled vigor and competency.