How does a rocket's gas pedal work?

Ball valves in space technology

The DARE student team at TU Delft is fully engaged in the development of their new rocket, the Stratos IV. The rocket has a hybrid engine that uses both solid and liquid fuel. Teesing has been sponsoring this project for years and is thinking along the DARE team this year too. Among other things, we deliver the "gas pedal" of the rocket. But how does such a rocket engine actually work?

The purpose of reaching space

The DARE team has been around for 18 years. The development started with relatively small rockets, but the newest model is longer (8.3 m), larger and has more thrust. Student teams compete globally to be the first to reach space(100km altitude, the Kármán line). A student team has never been this high. The current project, the Stratos IV, is expected to reach that height in August and even includes payloads for the ESA and Ariane space organizations. This is a list of the last altitude records:

Year	Rocket	Team	Records (km)
2009	Stratos I	Dare, TU Delft	12,5
2015	Stratos Il+	Dare, TU Delft	21,5
2016	Heros 3	University of Stuttgart	32
2017	Fathom ll	University of California	44
2019	Stratos 4	Dare, TU Delft	(August 2019)

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Drawing; A hybrid motor with saccharine

The hybrid rocket motor

Building a solid fuel rocket for such a height is far too dangerous, a liquid too complicated. So they build a hybrid.

A solid fuel engine is not much more than a hollow tube filled with a mixture of fuel and an oxidizer. As soon as you ignite it, the tube burns from the inside and the hot exhaust gases push the rocket up. The solid fuel engines are easy to manufacture and inexpensive, but have the disadvantage that they are not very efficient and therefore unsuitable for reaching high altitudes. Moreover, the fuel is explosive which causes all kinds of regulatory problems. They have another very big disadvantage: they only have 1 setting: full gas. Once they are lit, you will no longer be able to extinguish them.

A liquid fuel engine solves many of those problems, but is technically very complex to make. Liquid oxygen and hydrogen are injected into the engine separately under extremely high pressure. The liquids are cryogenic: only liquid at extremely low temperatures. Yet this is an engine version that is currently being developed by DARE, but before it is ready for use we are a few years later.

Just like the solid fuel engine, the hybrid engine has a hollow tube containing the remarkable fuel saccharin (coffee sweets). To increase the burning temperature, aluminum powder is added to it and the mix is held together by candle wax. However, that fuel is not combustible under normal circumstances. Only when an oxidizer is injected under high pressure combustion can occur, with the advantage that the motor is adjustable by a valve.

This valve is crucial for functioning and for safety. If the electronics in the rocket detect that the rocket deviates from its trajectory, the engine is shut off (flight termination system). In 2014, the failure of this valve was the reason for the failure of the launch of Stratos II. Since then, Teesing has been sponsoring this valve that ensures that 6 kg / s laughing gas can flow into the engine under a pressure of 60 bar and all associated couplings with JIS thread (widely used in space travel). DARE developed the electromechanical actuator of the valve itself because the standard controls are too large. In addition, we also supply the system to fill the nitrous oxide tank just before launch and the system to ignite the rocket. The latter is done with nitrous oxide, gunpowder and steel wool.

Why does Teesing sponsor?

We like to invest in young technical talent. DARE is a fertile soil for good engineers. In addition to DARE, we have also been sponsoring the TU Delft Ecorunner group for many years (a hydrogen-powered vehicle). We want to contribute to the breakthrough of hydrogen technology - something that Teesing believes in and which we promote. That is why we are also a member of the NWBA, the association that deals with the development of hydrogen as a carrier for fuel.

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