Universal Iterative Hybrid Rocket

The Universal Iterative Hybrid Rocket (UNITY) project is the current focus of the AG Experimental Rockets. In close cooperation, our SGs are working on a hybrid rocket with exchangeable payload and mobile launch capabilities and equipped with a single-stage parachute system. At the core of the project is the iterative development process, in which a very simple initial version of a system is developed, which can be quickly accessed and modified to find more sophisticated solutions in the following iterations. During the project, the Phoebe solid fuel rocket will be developed in addition to the Hyperion hybrid rocket. Thus, modular subsystems which are compatible with both rockets, such as the parachute and electronics segments, are to be tested in flight without the complicating elements of the hybrid engine. In parallel, the hybrid engine is developed and tested on the ground. With extensive digital documentation and reviews, we aim to provide a professional framework for the project. The development is divided into three subsystems.

Hybrid drive

The hybrid drive used for Hyperion is developed by the SG Engines.

Hybrid drives use a solid fuel and liquid oxidizer. This approach allows combining some of the positive properties of solid propulsion and liquid propulsion systems. Hybrid drives are generally simpler to construct than liquid drives, but can achieve a similarly high level of efficiency depending on the fuel combination and, in contrast to solid drives, can be throttled and are significantly safer.

The developed hybrid engine HYDRA 5 uses a solid fuel HTPB (hydroxyl-terminated polybutadiene) in combination with the liquid oxidizer nitrous oxide (laughing gas). The finished engine should produce a thrust of up to 1500 N and have a total impulse of 12.5 kNs.

The complete hybrid drive consists of the oxidizer tank, main valve, and combustion chamber. In order to build the lightest possible engine, the combustion chamber shell is made of carbon fibre reinforced plastic (CFRP). Hard paper is used as structure and insulation inside the combustion chamber. A combustion chamber made of steel is used for engine tests on the ground at the DLR site in Trauen, this enables the engine to be changed quickly and thus enables multiple tests to be carried out in a row.

After an initial burn test of the new engine at DLR in Trauen, work is currently underway on the second iteration of the engine, which is scheduled to be tested in spring 2023.

Hydra 5.1 engine test in Trauen, 20.10.2022

Electronic systems

The electrical systems inside and outside the experimental rocket are designed by SG Electronics. In line with the UNITY project, key requirements are universal applicability, modularity, and easy iteration. This concept is particularly reflected in the stacked structure of the latest electronics.

Tasks such as supplying power, on-board flight data calculation, or the sending of telemetry data are not performed by a single but by several dedicated boards. The stack consists of standardized circuit boards that can be plugged together in any configuration. The communication of the boards and the provision of infrastructure takes place via the ERIG bus (ERBus). This represents the heart of the rocket, distributing power and data throughout the rocket and allowing for the easy addition of new components. The specified pinout is minimal, leaving room for expansion and special payloads.

The power supply unit (PSU) stabilizes the input voltage of the redundant batteries and offers the option of switching off all of the rocket's electronics via a switchable relay. This enables the entire on-board electronics to be switched off via an umbilical. At certain launch sites this is a safety requirement.

The Rocket System Stalker (RSS) provides the ability to monitor signals and events on the ERBus. These are sent wirelessly to a ground station together with the data from some sensors.

Previous ERIG rockets have flown with commercially available flight computers, which has repeatedly led to limitations in reading data and adding functions.

To improve this, the UNITY project is developing its own flight computer ICARUS (Interconnected Avionics for Recovery of Unmanned Systems). The system is intended to make in-flight real-time tracking of rockets or other unmanned aerial vehicles as well as recovery faster and more precise. In addition, with the development of our own flight computer, we gain access to all data generated during the flight.

During the first iteration, three subsystems are the main focus. First, the flight computer itself, which ensures a successful recovery of the rocket. A second communications module is to send telemetry to a ground station. The third module allows the rocket to determine its position using GPS. In the long term, further modules with sensors for redundancy, a module for starting the engine, and an interface for an experimental payload will be developed.

Rocket structure and recovery system

Development and construction of the rocket structure and the recovery system is the responsibility of the SG Rocket Systems.

The structure of the rocket consists of individual segments. These consist of laminated carbon or fibreglass tubes with connecting rings glued into the ends, all these parts are manufactured in the ERIG workrooms. The connecting rings are used to attach the individual segments together using screws. The entire rocket consists of between five to seven such segments of different lengths.

At the top is the nosecone. Its aerodynamic shape ensures the lowest possible air resistance. Below the nosecone is the payload segment, followed by the electronics segment. When the electronics detect the highest point of the trajectory, it sends the command to deploy the parachute to the recovery segment below. The recovery system consists of two identical independent release mechanisms, which are located above and below the parachute capsule, and a lateral ejection flap. The parachute is ejected by elastic rubber rings tensioned with servo motors. This provides redundancy and thus protects against mechanical failure of one of the trigger mechanisms or failure of apogee detection. The second mechanism is triggered after a specified time a few seconds after apogee, calculated pre-launch.

The bottom segment of the rocket is the propulsion segment with its two configurations. On the one hand there is the hybrid variant, which is divided into a tank segment, valve segment, and engine. On the other hand, the solid variant, which can accommodate different sizes of solid rocket motors. On the outside of the drive segment, interchangeable stabilizers can be found, which, depending on the chosen configuration, ensure the optimal stability of the rocket.

Phoebe solid fuel rocket assembly and integration before launch