The live engine test on the test bench was a success in terms of student attendance, bringing together more than 150 people

On May 16th, a real bench test of a 260kg thrust rocket engine took place on the basketball courts of the ETSi of the University of Seville, carried out by Álvaro Sáez, a former student of the Aerospace Engineering Degree at the School, together with his father, Jesús Sáez. 

This day included instruction on rocket design and manufacturing,
a brief overview of nozzle theory, a solid propellant characterization experiment, and finally, a final test bench. The test is part of the propulsion system improvement campaign for the NAOS project, which Álvaro and Jesús have been developing since 2015, culminating in the launch of NAOS in May 2021.

The bench test conducted at the Higher Technical School of Engineering is a crucial part of the battery of tests scheduled for the NAOS . This is the most ambitious project undertaken by Coheteros. It is a rocket over 2 meters tall and weighing 7 kg, capable of reaching an apogee of 3 km and being reusable. To achieve this, it features a recovery system consisting of a parachute and an ejection system programmed with an electronic delay. Additionally, it integrates a flight data acquisition system and a tracking and telemetry system that receives the rocket's coordinates at all times via GPS and transmits them to ground receiving stations using LoRa modulation telemetry. Finally, it incorporates a high-resolution onboard camera, also very useful for acquiring data on the trajectory, performance, and stages of the flight.

All these systems are designed, developed, and manufactured from scratch by Coheteros and have been validated with functional tests. Furthermore, the launch platform is structurally designed to withstand the rocket's liftoff loads and ensure a stable flight from launch.

The real-world test bench with an engine like the one carried out at ETSI aims to validate the following design aspects:

• Similarity between the real and theoretical Thrust-Time curve obtained in the simulations. 
• To validate the viability of the new propellant grain inhibition system for the engine. This inhibition system is manufactured using 3D printing in ABS plastic and greatly simplifies the propellant grain manufacturing process, allowing for more frequent batch production.
• Analyze and study the repeatability of the bench tests. A total of four bench tests were performed with the same propellant charge as the one displayed at the school. All of them show very similar thrust-time curves, demonstrating the reliability and confidence in the manufacturing process.
• Characterization of the effect of erosive combustion, a determining factor in the CATOs (Catastrophe At Take Off) suffered in previous tests, with the aim of applying corrective measures to eliminate or mitigate this effect.
• The test has also been crucial in obtaining real data that allows for more accurate predictions of the actions that NAOS will take in its imminent launch. 

However, this demonstration proved useful not only for the designers but also for the multitude of students and aspiring engineers who attended the event. During the exhibition, they were able to verify that the theory and knowledge acquired during their studies were vital to the development of the rocket engine. To this end, several of the theoretical explanations were accompanied by real-world evidence demonstrated live during the event. Nevertheless, they also witnessed how theory often fails to accurately predict reality, highlighting the importance of functional testing for validating designs.

But perhaps the most striking aspect of the meeting was the motivation, attention and interest shown by the students at all times, highlighting the positive atmosphere created throughout.