The rocket project: a record of the progress of building a rocket

from scratch

An introduction

In the beginning...

The idea to build a rocket, completely from scratch, came from an unexpected source, Advanced Placement United States History to be exact. It was back at the end of my sophomore year, and for the APUSH class, we had to select an end of the year project and discuss the history of whatever we chose. Rather than simply do a boring report, I chose to go above and beyond and actually provide a visual for my project, whatever it may be. With the help of my teacher, I limited my choices down to a project on the history of one of two things: the radio or the rocket. In my naivety, I chose the rocket, thinking it would be far simpler to build a rocket than a radio. Of course today, a year and a half later, I realize that a flying rocket is undoubtedly far harder to create than a working radio. Nonetheless, I have also realized that building rockets is one thing I love to do and hope to do in the future.

The initial stages

I started out working with two other guys in my class, one of whom still even helps me occasionally. We had no clue of where to start, so we began with Google. Very quickly, we decided that the water powered bottle rockets where not the way to go. Aside from being pathetically simple, we wanted something that would be flying into the air higher than the naked eye could see. This was yet another case of naivety, as we would later learn. So, we deemed that researching propellant was the first step, as without a knowledge of how to power our rocket, there was no reason to proceed in the creation of it. After probing the internet for its secrets of homemade rocket fuel, we discovered that the best ingredients could be found in the kitchen and the local Lowe's Home Improvement store. A mixture of sugar, as the actual fuel, and Potassium Nitrate, as the oxidizer, was the candidate of choice, and although we got many strange looks while purchasing an ingredient used in homemade bombs, it was the best deal for our money. The process began with simple, but highly informing experimentation. We tried everything, and multiple times over. Different ratios of sugar to KNO3, more mixing, less mixing, different ignition processes, all to the same result. It just wouldn't work. Our powder mixture would either not ignite or just sit and smoke, certainly not providing enough of the all important thrust we had read so much about. Then we discovered the process of melting the two ingredients together and burning the cooled byproduct. This chemistry experiment was supposed to be safe, but we were still hesitant about cooking up some flammable substances. Eventually, with plenty of safety precautions, we made a small batch. The results were exponentially improved, although it still seemed to take an awfully long time to burn. So, with our fuel seeming satisfactory, we took the next step: building the actual rocket motor.

Coming together, finally

Logically, we started off small. Very, very small, especially in comparison to the rocket motors that people commonly think of. The entire motor measured about 4 inches in length and 5/8 inches in outer diameter. This left us with only a few grams of propellant that would actually be burned. However, we took no chances, and decided that the amount was suitable, as least for now. The motor itself was made out of copper piping, the only thing we could find that was small enough and had thin enough walls. As for the capping, we initially used just plaster of paris, packed and hardened with a hole drilled in one end. We found this to be usable, but inefficient as we had to wash the motor out after each use. After more tests, some even utilizing plain mixed powder again, we were relatively satisfied, aside from the extremely long pressure build up and slow release. From there, we moved onto using an aluminum cap and an aluminum "nozzle." This was made by drilling a small way into the aluminum, then replacing the bit with a smaller size. This resulted in a more easily reusable motor, but it still did not fire much better. Finally, with the project date almost near, we realized we had spent so much time testing the propellant and motor, we forgot all about the actual body. The day before the project was due, after a few more pitiful static fires, we rigged up the ugliest, most amateur rocket one has ever seen.

The very first launch of my rocket.

To infinity and beyond

While we were flying high one day, the next day at school we weren't leaving the launch pad. Unfortunately, during a late night test before school the next day, one of my partners added some rust to the fuel mixture in hopes of boosting performance. Instead, the reaction ruined the motor, and we went to school with an Estes rocket motor in a model rocket to demonstrate that. Misfortune struck again, as we could not get the motor lit, and our project seemed, to the rest of our classmates, like a complete failure. But although school was out, rocket building was not quite finished. We tested more, and made multiple motors in case one got ruined again. From there, I took on the task of making a better body and fins for the rocket. Of course, better was relative to the original and not by much. The second rocket was much shorter and made of heavy duty cardboard tube. Standing only about 5-6 inches tall, and with fins that were nearly half the height of the rocket itself, I discovered later why the flight was so unpredictable. Although all three flights were drastically better than the first due to much heavier duty materials, they still fell short of what I believed the potential to be. So, back to the drawing pad. After the final brutal flight that ended in the body getting torn apart from the thrust of the screws holding in the motor, I threw out the entire project we had going and began from scratch. This meant lots of reading on the various aspects of flight stability, recovery systems, ignition, thrust, max. altitude and many other components. During my original research, I chanced upon a website created by a man by the name of Richard Nakka. Mr. Nakka's website on amateur rocketry (http://www.nakka-rocketry.net/) was an overwhelming trove of information on everything to do with the building of rockets. In fact, he had so much information that, for the most part, we disregarded it. Now, I returned and found exactly what I was looking for. Everything from various size motors designs to the complete schematics of timers to the mathematical theory behind all the designs was put together in one place. And from there, I began building the rocket that I am still working on today.

The second rocket and motor, retired after the retaining screw tore through the body

The first phase

Once again, I began with the motor and propellant, and again, I opted for the smallest possible motor size, although when compared to my original motors, it is much larger. With a 1 inch diameter and measuring around 6 inches in length(without the nozzle) this motor had the capacity of 100 grams of propellant. However, the hardest part of the new motor proved to be the nozzle. A de Laval nozzle, otherwise known as a convergent divergent nozzle, needed to be machined out of steel, and I had no way of doing this myself. Fortunately, I have connections via my dad to the local community college, where they have CNC lathes and other machine tools. Here, my first nozzle was machined in the fall of 2011. However, due to the upcoming winter, it would lay dormant until the spring of 2012, when I could finally begin testing this incredible piece of simplistic geometry. The beauty of a de Laval nozzle is that it requires two main points. The first portion, the convergent section, with an angle of 30 degrees, filters the hot gases and solids that have been ignited in the chamber down to the throat. This region is where the most important parts of producing thrust take place. Prior to entering the throat, the gases are moving at subsonic speeds, and are thus compressible. However, upon entering the throat, the gases are choked, and simultaneously accelerated to supersonic speeds as they exit the throat through the divergent portion of the nozzle. This is the result only if there is high enough pressure and mass flow is great enough and also if the exit pressure is very near to the ambient pressure outside the nozzle. Under these particular conditions, the nozzle will produce the max thrust for its size and dimensions. After a number of tests regarding the propellant grain perfection, I finally did the first static test of the new motor and nozzle on May 18, 2012. I fired it a total of two times that day, the first of which was successful, the second, not so much. A few days later, it was fired again, with very promising results. I also fired it a fourth time a week or so later, again to a success.

The complete motor, after several firings. Also, the blue prints, courtesy of nakka-rocketry.net

Please scroll to focus on motor.

Phase two: rebuilding

During the late spring, I began working on other systems beyond the motor design and propellant chemistry. Starting with the fuselage, I calculated a 1ft. long x 2 in. diameter aluminum pipe should be light enough. I fastened four fins, cut from a thinner gauge aluminum, to each quarter. Before I got too far into fabricating the fuselage, I recognized that some general, but necessary components were also missing. The first of these was the electronic igniter. As much as I enjoyed lighting a long fuse, then sprinting away from a high pressure motor set to ignite, I opted for the much safer route. Although igniters are now very simple to make, initially I had no experience or understanding of electronics and electricity. So, I took a crash course from Google results and learned the essential information about circuits, batteries, series, parallel, amps, volts, current and more - all necessary to make a functional electric igniter. Composed of two copper wire leads and about a cm of nichrome wire, I constructed a simple switch and placed it in a box. Igniter? Check. Of course, this was unsatisfactory and wasn't completely effective, so again with help from Mr. Nakka, I found out how to make a basic pyrotechnic igniter. By encasing the nichrome filament in a 1 inch section of straw, then gluing shut one end, filling the rest with black powder and finally gluing the other end shut, I created a much more effective igniter. This wonderful device had a tenfold effect on not only the safety of my future ignitions, but also the performance of the motor. We suspected that the micro-explosion spewed burning particles of powder down the barrel of the propellant grain. This created a more even and therefore more rapid ignition, since pressure would build up quicker and to higher levels. Compared to igniting the fuel rod at a single point, the pyrotechnic igniter enabled rapid build up to high pressures and resulted in significantly increased performance.

After this, I built two more pieces. First, I constructed a small pouring and testing stand for filling the motor with propellant, as the hot mixture is difficult to accommodate. Secondly, I built the future launch pad, a tripod with a trapezoid surface and a removable rail for guidance. This also doubled as a static testing stand, but it is much more versatile than the wooden one. I made it possible to not only do the typical upside down static fire, but also a horizontal fire at with even an approximately 10 degree angle upwards. This enabled me to get a rough estimate on how much thrust I was producing, since the conventional static thrust stand I could have made was out of my budget then. However, after one horizontal fire, I decided I won't be doing that very often.

Phase three: Starting over, again

As the summer began, I began to like less and less my current body of the rocket. So, I went back to the drawing board and did some more research. I had already played around a bit with the center of gravity and pressure that contribute so much to a rocket's stability. I also began to look into drag more, and the more I thought about it, the less satisfied I was with how the rocket was shaping out to be. So, I threw away the current body. I decided the body must be longer, especially with the size of the payload, motor and parachute. Also, with all the weight I would be adding, I needed to cut off a lot of the unnecessary weight accumulating. I reduced the thickness of the body walls, and I opted for the fins to be welded once the time came. I reshaped the whole process of building the body, based on building from the inside out. I started out with the recovery system, even more electronics. I got a bit of help from one of my original rocket buddies, and we put together a timer. This will be used to ignite a charge near apogee which will eject the nosecone and pull the parachute out. With the size of the electronics, parachute and motor and planning for expansions, I am planning on using at least a two foot tube for the body. Inside this, I figured out a way to secure any motor, with a steel disc screwed into the walls to transfer the thrust from the motor to the rocket, and a series of centering discs and screws to keep the motor center aligned and in place. The nosecone will be machined from a piece of aluminum for increased durability. While I could have completed this already had I gone down to the community college and asked them to machine my parts, I chose to instead wait until spring of 2013 so I can take a class and learn to use a lathe myself. Once I have these completed, I can calculate the center of gravity and pressure, and design fins that are suitable. Then, near the end of my senior year, I will be able to launch my rocket once again.

The completed timer, along with the schematics, borrowed from Nakka-rocketry.net

Began designing new motor and nozzle. I did extensive research on the types of nozzles and how to design them. Initially, I opted to design a bell nozzle, due to the decreased length and therefore weight, as well as increased efficiency. I found a general diagram of the bell nozzle, along with some of the necessary formulas for designing one. However, after further investigation, I realized that coming up with the slope of the bell curve in order to accurately plot points was beyond my current mathematical abilities. I talked to both my physics and math teachers, and eventually, they helped me to find out that I calculated my dimensions wrong and would therefore have to change the dimensions in order to find the missing slope of the parabola. I decided, after this to disregard the bell nozzle and opt back to the simpler de Laval nozzle, since machining would be far to difficult as well. Currently, I have just learned how to find derivatives in calculus and what they can be used for. Again referring to Mr. Nakka's website on the theory behind nozzles and thrust (http://www.nakka-rocketry.net/th_nozz.html), I began exploring the formulas necessary to calculate the exit area, and thus the optimum expansion ratio in order to maximize my thrust for my set conditions. I will be delving deeper into the equations and calculations within the next few weeks as I learn more about the uses of derivatives.

March 23, 2013:

After a long winter of school and sports, I have found some time to begin to work on rocketry again. Due to time and financial constraints, the nosecone will be machined by a friend from school. Later in the summer, I hope to be able to learn how to use a lathe myself. A new, larger motor has been obtained by a friend. Static testing will begin tomorrow with high hopes. This motor, doubling in size, is the anticipated motor for launch. Two new propellant types have also been tested: Dextrose and potassium nitrate, and sucrose and generic lawn fertilizer. The first propellant was too small of a batch to properly heat and combine, so it was tested as open powder. This looks to be a potential source of fuel in the future, if enough dextrose can be purchased. The generic fertilizer, however, was not. Although properly melted and mixed, the grain and samples would not ignite, much to my dismay. This was thrown out. In order to speed up the anticipated launch date (Mid-May), I stumbled upon an inexpensive, very complete onboard computer that I plan on purchasing. This will help initiate an earlier flight, record general statistic such as altitude, velocity, apogee and more and provide for means to base my own designs upon. By using a purchased flight computer for the first flight, I can be assured of a lower chance of failure for important data collection that will benefit me in the future. After static testing tomorrow, I will begin working on a homing device of sorts over spring break to use for rocket recovery. This will be of my own work.

March 29, 2013:

After a few days delayed by poor weather and schedule problems, the new B-200 motor finally was able to be tested. Compared to the previous A-100 motor, the B-200 seemed far more than double in size. Weighing over a half pound, I could already tell that the result of the static fire would be impressive, whether in a good way or bad. Prior to testing, we also decided to experiment with capacitors as a new method of ignition: using the quick discharge of high voltage to create a spark. This seemed to be possible and so we opted to use this method with the pyrotechnic igniter. However, the pyro igniter was accidentally left at home, and rather than waste more time to retrieve it, we used a long piece of fuse instead. The result was frightening. Standing behind a sort of bunker, we heard the pressure build up, and watched it release as the entire nozzle blew off into the sky. Standing in shock, we watched as material fell from the sky, a good hundred feet up. Upon further inspection, the retaining cap had also ripped the screws through the casing, and cracked the test stand in half as well. Despite hours of searching, the nozzle was gone. Although the result was dismal in terms of hours of work, we know now for certain that the B-200 nozzle is more than sufficient to handle the weight of the actual rocket.

The stand after the static fire The cracked stand Fuel projectiles