On a warm, silent night of August, what seemed to be a tall cabinet with arms laid curiously on the ground holding a metallic object. Although there was almost no wind, some chitchat got carried like a gentle breeze into the control cabin of the Albireo Amateur Propulsion Lab.
Suddenly, distinguishable sounds started to change the ambiance. First, the soft buzz of a fan. Then some tapping on a keyboard followed by the clicking of electronics and turning of valves. A gush of compressed carbon dioxide then filled the propellant tanks and the P-5 rocket engine was just minutes away from firing.
After almost two years of work, all that was left was checking safety protocols and sending an electric signal from a computer far away from the engine. The feed system was checked for leaks, the fire extinguishers were brought close to the testing zone, personal walked away to a safe place and the actions to be executed were read out loud.
A three-second-burn instruction was loaded into the engine’s computer and an assigned person brought closer to an external source of heat to the engine. Once this person went away to a safe place, the click of a button started a ten second countdown. Unfortunately, nothing but smoke came out of the engine. After several attempts, it seemed like the external ignition method was not working. Even though it was clear that the low concentration of the oxidizer would complicate things, it was well known that it could burn with fuel since this was tested two years before and later confirmed with the engine’s injector that year. Lowering the mixing ratio (the amount of oxidizer) and finding an alternative ignition method seemed to be the right thing to do. The problem, however, was there were only twelve days left for testing.
After an intense week of analyzing data and making improvements, the engine was all set for a second attempt. After trying different methods of ignition and mixing ratios, there was still no success. Some tweaks later it seemed like nothing had changed, but on the 14th of August of 2019, a specific combination of conditions resulted in the first successful hot fire of the P-5 making history in Costa Rica and in the region.
For the first time, the computer read a chamber pressure and an upward thrust of almost 100N. Puzzled why the engine worked, the team started to study the feed system and realized that a manual valve in the oxidizer line had been partially closed by accident. This resulted in a fuel-rich mixture that could easily burn with the air outside of the engine, generating enough heat to ignite the atomized mixture in the interior.
The engine was fired several times on that same day and on the 16th of August. With the adopted ignition method, however, it was not possible to start the engine with mixing ratios greater than about 1.2. The team had previously managed to achieve mixing ratios above 4 with only the injector, but even that was far away from the theoretical ratio of 8 which compensated for the low purity of the oxidizer. After analyzing all data, it was concluded that engine was operated to only 20% of its actual power and that as expected, increasing the purity of the oxidizer and finding an alternative ignition method could help the engine reach its intended performance. For a more detailed explanation, you can see this lecture.
As the moon started to bath the testing site with its light, things started to look differently. It was time to leave. Quick footsteps, someone calling from the lab, the squeak of a turning wrench, the click clank of dropping bolts, the thud of drawers, a gush of relieved air; a two-year long project was finally concluded.
The P-5 was AREX’s first milestone and an steppingstone for the things to come. The learning process and research that came with this project was unvaluable: understanding the theory behind liquid rocket engines, designing systems in several varied disciplines, requesting and comparing over 300 quotes to characterize the engine financially, manufacturing and assembling multiple systems, conducting over 120 cold flows, programing a controls interface for the electronics and sensors, handling high pressures and chemicals, doing multiple hot-fires, and starting to pave the way for the development of aerospace projects in a developing country. We hope the P-5 helped inspire people who are passionate about space no matter where they were born or who they are.
Today as we look forward to future propulsion projects that incorporate the learnings from the P-5, we do not stop to challenge the way space is done. Learn about our latest endeavor, Project Polaris an international space collaboration with 99 members representing 17 different countries that work together to develop an innovative rover prototype. To celebrate this two years of the P-5, here is an image gallery with some pictures never shared before!