Thanks to stable measurement results: ETH students conquer the edge of the troposphere

In 2020/21, a team of over 50 dedicated students from ETH Zurich, in the association Academic Space Initiative Switzerland (ARIS), realized the 4th research rocket generation to participate in the European Rocketery Challenge (EuRoC) in Portugal. The students had set themselves the goal of winning in the highest category "Rocket with self-developed propulsion and flight altitude 10,000 meters". The functionality of the self-developed hybrid propulsion system was proven by the successful EuRoC launch. The new monitoring system for measuring the load on the research rocket's aerostructure was also decisive for this. 

Reliable measurement results for real occurring loads

The structure of such a rocket is subjected to considerable loads in flight, which can only be partially determined in simulations. For example, influencing factors such as the wind or the shock load when the parachute opens cannot be determined exactly in analyses. However, reliable data for all load-relevant factors are required to realize an aerostructure of the rocket that provides the maximum strength with minimum weight necessary to achieve the goals of the mission. In order to verify and, if necessary, correct the determined loads in flight, a monitoring system for real bending moments and axial forces is required. 

With 4 kilograms at 10,000 m altitude

After the ARIS teams had determined the forces acting on the rocket in flight purely analytically in the past by means of simplified assumptions in simulations, their own monitoring system was used for the first time in the PICCARD mission. Here, the ETH Zurich students relied on strain gauges from Hottinger Brüel & Kjær (HBK), which provide reliable measurement results even under extreme conditions. Accordingly, a complete system was integrated into the rocket. The strain gauges from HBK installed in the system provide essential knowledge about occurring bending moments and axial forces during every phase of the flight. The bending moments and axial forces recorded during the test flight as part of the structural stress analysis subsequently enabled a corresponding weight-optimized design of all load-bearing structural components. The prerequisites for a successful participation in the Spaceport America Cup 2022 in New Mexico could thus be created. Here, the team wants to transport a payload of four kilograms to an altitude of 10,000 meters and bring the research rocket with all its parts safely back to earth.

Ease of integration as a criterion

The fact that strain gages from HBK were chosen for the right measurement technology was on the one hand the result of past positive experience coupled with the international reputation of the company. Another plus point was the ease of integration of the HBK strain gages, which delivered on the promise of "plug and measure" made by the measurement technology experts. 

Source and further information: www.hbkworld.com