FASSBERG, Germany (DLR PR) — After the successful test of the new hybrid rocket engine “AHRES-B” in spring 2019, the German Aerospace Center (DLR) carried out two more successful tests with the significantly larger VISERION variant on June 17 and July 7, 2021. The test preparations and commissioning were carried out by a team from the Spacecraft Department of the Institute for Aerodynamics and Flow Technology at the test bench for hybrid rocket engines at the Trauen site.
The results of the current tests clearly show that the VISERION engine, which was developed in the DLR projects AHRES and ATEK and has now been tested in the DLR cross-sectional project Simulation Based Certification (SimBaCon), is far more efficient than the previous hybrid rocket engines. For the researchers at the Institute for Aerodynamics and Flow Technology, this is a particular reason to be happy, because hybrid rocket engines are not only fundamentally cheaper and safer than conventional rocket engines, VISERION is also significantly more efficient than all of its predecessors. “The current tests have shown that the technological development of hybrid rocket engines is now far enough advanced for practical use, for example for use in sounding rockets,” explains Dr.-Ing Thino Eggers, DLR Institute for Aerodynamics and Flow Technology.
What are hybrid rocket engines?
Hybrid rocket engines are combinations of solid and liquid engines and combine the best properties of both engine types. The liquid oxygen carrier required for combustion – in this case highly concentrated hydrogen peroxide – and the solid fuel HTPB (hydroxyl-terminated polybutadiene) are in different physical states in VISERION and only react with each other at high temperatures and pressures in the combustion chamber. The advantages: There is no risk of explosion during storage and operation. In addition, the materials used are non-toxic and not harmful to the environment.
More compact, lighter and safer
In contrast to other oxidizer- fuel combinations in hybrid engine , the use of hydrogen peroxide as an oxidizer has several significant advantages: Its use enables engines to be significantly more compact than, for example, when using liquid oxygen. The flat course of the specific impulse allows better controllability and the simple ignition by catalysis saves an igniter as an additional component. The significantly lower combustion chamber temperature and the resulting lower structural requirements also reduce the weight of the thermal protection systems. Furthermore, the hydrogen peroxide used here is easier to handle and store, for example in comparison to the liquid oxygen commonly used.
During the test runs at the test facility at the DLR site in Trauen, the catalytically decomposed hydrogen peroxide reached the combustion chamber at around 650 degrees Celsius. The heat released was converted into kinetic energy – into a thrust of around 12,000 Newtons. VISERION used the fuel almost completely over a period of 27 seconds and, similar to AHRES-B, achieved a significantly higher burn rate compared to earlier hybrid rocket engines. The latter is important for the design of an efficient and compact engine and was also implemented at VISERION through an innovative, twisted “fin geometry”.
Pioneer for efficient and flexible sounding rockets
The test bench in Trauen used for the test has numerous modern measuring and control devices and enables the safe test operation of hybrid rocket engines. The infrastructure for the safe, environmentally friendly handling of large quantities of hydrogen peroxide is unique in Germany.
“ The proof of function is an essential milestone on the way to a flightable combustion chamber in lightweight construction with a load-bearing structure made of carbon fiber composite materials (CFRP). The airworthy variant will be further developed under the name VISERION + and can serve as a hybrid upper level for future altitude research experiments,” adds Eggers.
Research on hybrid rocket engines at DLR
The development and support for the manufacture of the VISERION engine was carried out at the DLR Institute for Aerodynamics and Flow Technology in Braunschweig. The financial basis for the construction of VISERION came from the support of the Investment and Development Bank of the State of Lower Saxony (NBank) . Since January 2021, the VISERION activities have also been supported in terms of personnel by the newly established competence center for fast-reacting satellite transport of DLR Security Research, which has a particular interest in alternative, simply structured upper levels for transporting satellites.