At 10:30 Central European Time (CET) on 8 November 2016, the HEROS3 (Hybrid Experimental Rocket Stuttgart) research rocket was successfully launched from the Esrange Space Centre in Sweden to great enthusiasm from the students. Reaching an altitude of 30 kilometres, it set a new European altitude record for student rockets. The former record was set last year by a student rocket from the University of Delft, which reached a maximum altitude of 21 kilometres. The HEROS2 experimental rocket was launched on 31 October, but no flight data could be transmitted due to a technical problem with the electronics. The HyEnD student team from the University of Stuttgart designed, built and launched the HEROS rockets themselves as part of the STERN programme on Facebook (Student Experimental Rockets) programme set up by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
HEROS2 and HEROS3 – success through improved technology
"We are particularly pleased with the successful launch of HEROS3 and the fact that the extensive preparations and improvements made to the HEROS rocket were all worth it," said Konstantin Tomilin from the HyEnD team. The hybrid engine, designed by the team from Stuttgart, accelerated the rocket, which was roughly eight metres long and weighed 160 kilograms upon launch, to almost three times the speed of sound. The fuel combination consisted of nitrous oxide and wax. With the aid of the on-board telemetry system, both the most important flight data and the current position of the rocket were transmitted to the ground during the flight. After the landing using the main parachute, the rocket was recovered by helicopter, transported back to Esrange Space Centre and handed over to the team.
Now, further investigations of the engine and the rocket structure, as well as the on board data memory will be conducted. "The first STERN flight campaign in October 2015 already showed how difficult it is to successfully fly such a complex system. Back then, there were technical problems with the HEROS1 rocket engine, which meant it only reached an altitude of two kilometres," and added: "Last year, the students performed detailed fault analyses and engine tests and made improvements to the rocket – they enhanced the thermal insulation of the combustion chamber and incorporated additional temperature and pressure sensors to the rocket, among other measures." The drogue parachute was replaced by a powerful supersonic parachute, which decelerates the rocket before it drops to the ground using the main parachute. Prior to launch, HEROS2 and HEROS3 were completely enclosed in a styrofoam box for protection against the low exterior temperatures. Temperature-controlled heaters were also installed on the ground. It took the Stuttgart engineers approximately eight months to analyse errors, make changes to the design and build the two identical rockets.
"In the meantime, the flight data acquired shows that the launch functioned," says Paula Kysela, one of the HyEnD team members responsible for the electronic system. After failing to get telemetry data during the launch of HEROS2, there was concern about whether HEROS3 would even launch. The team worked hard for five days straight to find the error and a solution." The analysis report suggests that the probable cause of failure was a grounding problem between the launching system and the rocket," explains Karsten Lappöhn. "As a result, when the engine ignited, the on board computer and telemetry system shut down, thus preventing data from being transmitted to the ground."
In the third STERN campaign, the students underwent all the processes that would be encountered in a real space mission: they examined the remaining rocket parts, evaluated all the data available and carried out engine tests to simulate the launch and find ways to improve the rocket.
The STERN programme
The aim of the student programme is to give the participants the experience of a 'real' aerospace project during the course of their studies. At the launch in Esrange, the same safety regulations of professional high-altitude research rockets apply. The students design, build and launch their own rocket, carry out all the tests and run through five reviews within three years. All critical systems are inspected during a review. These include, for example, the engine, tank and radio system. The STERN students were supported by experts from the DLR Mobile Rocket Base (Mobile Raketenbasis (MORABA) des DLR) and by the Institute of Space Propulsion at the DLR site in Lampoldshausen. The minimum technical requirements are that the rocket should have a recovery system, reach an altitude of at least three kilometres and be capable of achieving the speed of sound. A telemetry unit is also required as a payload, which sends important data, such as acceleration, altitude and speed, to Earth during the flight. The participants can decide whether to develop the engine themselves or use a commercial rocket engine. Knowledge transfer between the teams is also important for engineering expertise and technical understanding. The programme is planned and implemented by the DLR Space Administration and is financed by the German Federal Ministry for Economic Affairs and Energy (BMWi).