All Space All the Time

ANDOYA, Norway (DLR PR) — Reusable carrier systems are exposed to high loads and temperatures when returning to the surface. The German Aerospace Center (DLR) has now successfully tested component structures, measurement methods and evaluation algorithms for the re-entry phase with the flight experiment STORT (key technologies for high-energy return flights from carrier stages). 

In the early morning of June 26, 2022, the three-stage rocket experiment was launched from the Andøya Space launch site in northern Norway. At the apex of the trajectory at an altitude of 38 kilometers, the upper stage reached a flight speed of around 9,000 kilometers per hour, which corresponds to a Mach number of over eight. It then fell into the Atlantic Ocean more than 350 kilometers from the starting point.

“In order to achieve higher flight speeds, we used a DLR sounding rocket with three instead of two rocket stages for the first time,” explains Dorian Hargarten from the DLR Institute of Space Operations and Astronaut Training . “In addition, the third stage with the various scientific payloads flew a particularly flat trajectory at an altitude of 38 kilometers at Mach numbers of up to eight. Here – analogous to the heat development when re-entering the earth’s atmosphere – various high-temperature experiments were carried out at the high heat loads to be investigated.”

Materials that withstand the high thermal loads and dissipate them are crucial for the heat development in the re-entry phase. Robust heat sensors that keep a close eye on the temperature development are also essential. 

“In STORT, the pre-body of the third rocket stage consists of five ceramic segments,” explains the leader of the STORT project, Prof. Ali Gülhan from the DLR Institute of Aerodynamics and Flow Technology . “We have equipped the pre-body with numerous heat flow sensors, thermocouples and pressure sensors every 90 degrees along the four longitudinal lines and are now very excited about the data analysis.”

To carry out the thermal management experiments, the researchers used three fixed canards with ceramic outer shells on the rocket, which were developed by the DLR Institute of Structures. While one canard was actively cooled, the second canard was passively cooled. The third reference canard (without cooling) was also used to study the impact-boundary layer interaction. All three canards showed different structural responses in flight under the same heat load.

A modular and distributed data acquisition system allowed the efficient recording of data from the different experiments. In the previous ATEK project, a standard module made of aluminum alloys was replaced by a hybrid module consisting of a CFRP structure with metal flanges to reduce the weight of the cylindrical payload segments. In the STORT project, the researchers are now testing a significantly lighter module made entirely of CFRP [carbon-fiber-reinforced polymers].

Next to the DLR is the Technical University of Munich involved in the STORT flight experiment by manufacturing the CFRP module. Another international partner is the University of Arizona, which performed simulations for the experiment ‘Impact-Boundary Layer Interaction’ on the canard. The planning and execution of the mission was the responsibility of the Mobile Rocket Base (MORABA) department of the DLR Institute of Space Operations and Astronaut Training. 

The preliminary body was designed and manufactured by the DLR Institute for Construction Methods and Structure Technology. The DLR Institute of Aerodynamics and Flow Technology, which is also responsible for the project management, contributed aerothermal design, active thermal management, instrumentation of the payloads and their modular data acquisition.

The flight experiment, which has now been successfully carried out, is an element of the STORT research project. The project is part of the DLR sub-program focus ‘Reusable space transport systems’. It aims to develop selected technologies and methods with regard to thermomechanical analysis and evaluation of carrier systems. For this purpose, the component structures, measurement methods and evaluation algorithms, which were developed in basic investigations, are adapted for a flight experiment and finally qualified with the flight. In addition to the ground experiments, the flight data provide validation data for physical modelling, numerical simulations and system analysis, thereby enabling a reliable design and evaluation of future carrier systems.

If you had the money, which suborbital spacecraft would you fly on?