Ukrainian startup conducts new tests for engine of 'self-devouring' rocket

Olga Ozhogina is a Ukrainian space reporter, journalist and photojournalist. She contributed this article to Space.com's Expert Voices: Op-Ed & Insights via the press center at Promin Aerospace, a Ukrainian rocket startup. 

Ukrainian rocket company Promin Aerospace, which is currently developing an ultralight, autophagic launch vehicle, has conducted a new series of studies on its unique engine. The startup's initial tests showed the feasibility of the technical concept. With each new experiment, engineers are improving the design by testing different variations of the engine assembly.

The concept of the rocket is based on autophagic, or "self-devouring," technology, which was initially proposed by Promin Aerospace's chief technical officer Vitaliy Yemets.

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In an autophagic rocket, the hull would be used as solid rocket fuel, in addition to other propellants carried on board. For this purpose, the hull material must be both strong enough and have sufficient combustibility. During the rocket's flight, the body is consumed, allowing for a reduction in mass as it travels and leaving no debris once the flight is completed. This advance would enable more efficient and environmentally friendly launches.

Over two months, three experiments were conducted with different variations of the engine and nozzle design, which allowed Promin Aerospace to identify and investigate challenges, as well as to improve the overall performance of the assembly. As the engine technology is unique, all tests had to be designed by the engineering team from scratch, while detecting and eliminating defects.

Thanks to these initial three tests, it was possible to improve the fuel supply system and test new fuel components, which proved their safety and efficiency. All necessary parameters were measured and recorded.

The fourth experiment: a fuel feeding system

For the fourth experiment, the engineering team used the same oxidizing agent that was used in the third experiment, as well as a bell-shaped nozzle, to keep the variables consistent in the new test. Additionally, engineers used a polymer fuel rod and a gas-oxygen mix for a starter. They utilized multiple temperature probes to monitor the temperature in numerous engine areas and pressure gauges in both the combustion chamber and the pneumatic cylinder.

Following previous experiments, the propellant rod was fed into the gasifier while recording the firing parameters with multiple sensors. The starting fuel and fuel assembly feeding systems were shown to work reliably; no issues with achieving combustion were recorded, and the experiment's starting component provided a higher pressure in comparison to previous experiments.

As the starting fuel was supplied, a pressure of 4 atmospheres (atm) was recorded in the combustion chamber. The fuel supply pressure remained stable between 9 and 9.5 atm, and the starting fuel was turned off at 203 seconds (3 minutes and 23 seconds).

The measured feed rate was 10 millimeters per second (mm/s), demonstrating adequate performance, and the pressure reached a maximum of 12 atm. This experiment remained stable for 252.95 seconds (4 minutes and 12.95 seconds) at a rate of 10 mm/s and 12 atm.

The experiment ran for approximately 280 seconds (4 minutes and 40 seconds). At 252.95 seconds, a flare exited the feed path, followed by a popping sound and termination of the assembly's movement. No damage was caused to the engine or the mount truss, and the experiment results show that everything performed well, although some minor changes must occur. For the next test, the assembly inlet seal was improved

Overall, the system worked reliably and provided sufficient pressure in the combustion chamber. Combustion of components in the operating mode provided a higher pressure than starting fuel. So far, all experiments have allowed the further development of an efficient and safe concept. 

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The fifth experiment

For our fifth experiment, the engineering team utilized another type of fuel and oxidizer but retained the use of the bell-shaped nozzle. The test was conducted similarly to the previous ones, with the starting mix being supplied under a pressure of 4 atm and turned off at 204 seconds (3 minutes and 24 seconds), with the new primary fuel supplied under a pressure of 9 atm.

The pressure within the combustion chamber dropped after the starter fuel was turned off but increased gradually to 10 atm, and by 248 seconds (4 minutes and 8 seconds), the engine's temperature had reached operational level. At 252 seconds (4 min and 12 seconds), the pressure went off the scale, and the fuel assembly stopped. After investigation, the engineers determined that the increase in pressure was caused by a block in the nozzle, as the gasifier's casing was torn off.

Despite this, the engineers found that the chosen starting fuel assembly worked reliably. The pressure in the combustion chamber was correlated with the feed rate of the working components with a delay in the reaction time.

The sixth experiment: the new fuel rod component

The sixth experiment was conducted with the starting mix being supplied under a pressure of 4 atm and was turned off at 188 seconds (3 minutes and 8 seconds). It used a new primary fuel, which was supplied under a pressure of 25 atm. The pressure within the combustion chamber remained at 8.5 atm until approximately 300 seconds (5 minutes) when a flare ignited at the fuel assembly supply unit at the bottom of the combustion chamber.

At this moment, the combustion chamber began to overheat, and the steel turned white. According to both the sensors and heat color charts, it reached a temperature of about 1,830 degrees Fahrenheit (around 1,000 degrees Celsius). The feed rate of this fuel assembly was uneven, with a maximum value of 14 mm/s. The experiment lasted 350 seconds (5 minutes and 50 seconds).

Overall, the experiment passed with pressure within limits and without uncontrolled explosions, proving the reliability of this variant of the construction.

"The use of the new polymer as the main fuel component was efficient and safe, as there was no critical increase in pressure. So we will consider this variant. After that test, the assembly inlet seal will be tightened more to prevent an overheating of the combustion chamber," Yemets said.

The next experiment will be dedicated to testing the new oxidizer. It is expected to increase the efficiency of combustion.

After making final tests, Promin Aerospace plans to conduct the first test launch of its suborbital rocket, followed by its first commercial mission in early 2023. In the future, the company also plans to conduct orbital launches.

Promin Aerospace was established by Vitaliy Yemets and Misha Rudominski in 2021. That same year, the company closed its first investment round and proved the capabilities of autophagic technology, which could reduce launch costs and space debris.

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