Rocket Rigor Mortis
The accelerometer is packed into the home made rocket, the nose cone is set. We light the engine’s fuse and wait. Will the engine explode and incinerate the miniature flight computer? The rocket sputters, coughs, and roars to life. It sails gracefully into the air, leaving only a smoke trail behind. The luck ends there: the parachutes don’t fire and the rocket is coming down like a meteorite.
It all started a month ago. My school allows seniors to leave early and work on independent projects. I was a junior, and I helped a group that was finding the best design of model rockets. My job was to design a device that measures acceleration, drop it in the rocket, and then figure out how high the rocket went. The way that accelerometer chips output acceleration is trivial. Higher voltage means a higher acceleration. I only needed some way of converting the voltage into a number, and this was not a problem. I had a PIC microcontroller with an onboard ADC (analog to digital converter) unit. I also had to save the results to somewhere inside the rocket. Since the rocket moves fast, it is necessary to take many samples, generating enormous amounts of data. The solution was to write to an external memory chip quickly enough. I had a whole month to do this, and it theoretically was very simple. I thought I wouldn’t break a sweat.
Two weeks into the process I changed my mind. It was not easy after all. The clock read four in the morning, I had school the next day, and initial plans were not working out. The pins on the three axis accelerometer are so tiny that I couldn’t solder them on. The external memory to which readings are saved was slower than dialup internet. I contemplated on giving up. I could have told the group building the rockets that I couldn’t do it. They could use a stop watch to find the height at apogee. I blamed my setbacks on not having a mentor and never taking physics, let alone an electronics class. I went to sleep that morning feeling defeated.
Yet I felt an illogical, burning desire to finish the job. I didn’t do homework for two whole weeks, pulled too many all nighters, and spent lunchtime hunching over part datasheets. Day by day I made progress. I managed to physically attach the accelerometer and optimize the memory write speed. A divine stroke of intuition helped me fix the memory corruption in the EEPROM. After innumerable compilations, burns, and tests, I finished the device.
On launch day, I watch the rocket hurtle to the ground and make a small crater in my backyard, to the dismay of my mother. Fingers shaking, I attach the device to a laptop. Did the crash landing damage the chip? Did it detect the launch and record anything at all? The laptop slowly outputs the flight data. The acceleration curve exactly matches the thrust curve of the rocket engine. It worked!
None of my grades or science fair ribbons could produce the satisfaction I feel from seeing that graph. I had built something from start to finish entirely by myself – something that I supposedly didn’t have the background to do. I taught myself electronics and embedded programming, and felt as if I were on top of the world. Everyone from a baker to a rocket scientist has felt the intimacy with something they have created – the smallest details, the long nights. That is why I love tinkering and making things.