What is the Spaceport America Cup?
The Spaceport America Cup (SAC) is an international collegiate rocketry competition. Student teams build a rocket that can carry an 8.8 pound payload to either 10,000 or 30,000 feet. This is one of the best collegiate rocket competitions because of their locator at the Spaceport America in New Mexico.
Because we are launching from an “active” spaceport, there’s a lot of flexibility in what we can launch. Not only do they allow all different forms of chemical motors (solid, liquid, and hybrid), experimental motors are encouraged as they have their own category. Making as much of your rocket as you can in house is also encouraged due to the scoring scheme. This focus on scratch built parts and experimental motors often leads to several rockets, especially ones using liquid motors, failing quite spectacularly in their flights which is often very interesting to watch.
While what comprises the 8.8 pound payload is not specified, you can get extra points if it is in a 3u cubesat form factor. This leads to most rockets having a diameter between 4-8 inches and and 8-20 feet long. Some teams fly boxes of chains as dead weight but other teams design and build scientific payloads. Those scientific payloads are judged by the Space Dynamics Lab.
Pre-competition photoshoot with last years rocket (left) and this years rocket (right)
What was I Doing There?
The rocketry team at the University at Buffalo (UB) is part of the Students for the Exploration and Development of Space (SEDS). I’ve been a part of the club since freshman year and learned to build rockets with them. Every year, they build a single large competition rocket. This was our second year competing in SAC and we built a 10 foot tall rocket for the 10,000 foot launch category. Unlike last years rocket, almost all of our components were built in house. The only large part of the rocket not made in house was the rocket motor.
One of the components that we designed and built in house, was a flight computer. This computer took in measurements from our 3-axis IMU and barometer, and determined when we were at apogee so that it could deploy our parachutes. Additionally, it logged telemetry data, our GPS coordinates, and had a radio so that we could view the telemetry in real time. The way you can detect apogee is when your velocity is negative, but a lot of flight computers only have a barometer which gives you altitude. To get velocity from position data, we would need to take numerical derivatives. These will magnify the noise and can lead to false positives/deployments. I implemented a Kalman filter, which combines the sensor data with the dynamics of the system, to provide an estimate of position and velocity better than either the model or the instrumentation alone. At SAC we were asked to give a presentation on the flight computer and I was one of the two people presenting.
In addition to my work on the flight computer, I was also in charge of dealing with the payload. We collaborated with a lab on campus, The University at Buffalo Nanosatellite Lab (UBNL), to test fly a component they want to use on a future mission. When satellites are booted out of rockets they can be booted out individually or dozens at a time. If they are close together, when they are assigned a Two Line Element (TLE), the TLE for one nanosat can be given to a different nanosat. This is called a crossed TLE. By placing a low cost radio rangefinder on the nanosat, and combining the range data with a multiple model estimator about 98% of crossed TLE’s can be eliminated in two ground passes. A paper on this can be found here and this work will be presented at this years (2018) small sat conference (At the time of posting, the conference has not yet begun and I’m not sure if there is an embargo on the paper so I will be delaying posting a free link until after the conference). We were flying the radio rangefinder as the payload on our rocket. High altitude weather balloons can get you good distance testing for space based components, but unlike satellites, balloons don’t move very fast. The ISS for example moves at around 7500 m/s. Our rocket was designed to stay in the subsonic regime but has a max velocity around 330 m/s. While this is an order of magnitude slower than the ISS, it’s an order of magnitude faster than the balloon will fly.
Note: I worked at UBNL for 3 years on both the integration and testing team and then later as the science team lead. As I’m going to the University of Alabama for grad school I have stepped away from UBNL, but It’s a great lab to work in if you are at the University at Buffalo and are a us citizen (ITAR requirements). Here’s a link to their Facebook page.
Our Launch
I was assisting with the setup of our rocket on the launch pad, so I got to stay relatively close to the rocket when it launched and got this video of liftoff.
Our Flight/Recovery
We had a gorgeous launch. It went up completely strait and our deployments occurred as designed. Unfortunately, just after main parachute deployment, the bottom half of our rocket came undone from the top half and fell about 1000 feet to the desert floor below. We recovered both halves, but because of the fall the second stage was not re-flyable. We believe that the Kevlar cord used to hold the sections together rubbed on the fiberglass body tube and got cut.
Our Results
Out of over 100 international teams our payload placed 3rd in the Spacecraft Dynamics Lab’s payload challenge.
As I write this I don’t have access to the final point totals so I don’t know how we did in our category 10,000 feet, commercial off the shelf (COTS) motor but I can say that we did not place in the top 2 in our category.
Want more Gereshes?
If you want to receive the weekly Gereshes blog post directly to your email every Monday morning you can sign up for the newsletter here!
If you can’t wait for next weeks post and want some more Gereshes I suggest
Rollout of a rocket motor test stand