ESA’s Hera asteroid mission has completed acoustic tests confirming that the spacecraft can withstand the sound produced when launched into orbit. The tests were carried out at the ESTEC Test Center in the Netherlands within the framework of the Agency’s Large European Acoustic Complex. It is Europe’s largest and most powerful sound system and is equipped with quad noise horns capable of producing over 154 decibels of extreme noise.

Diego Escorial Olmos, Hera Systems Engineer, comments: “The launch will be the busiest day in the life of Hera, so we have worked hard to simulate this during the mechanical testing phase, first vibrating the spacecraft on the ESTEC Test Center shaker tables and now blasting as much as possible.” with a noise profile from our launch supplier to be accurate.”

The LEAF chamber is 11m wide, 9m deep and 16.4m high, with one of its walls encased in a series of massive sound pipes. Nitrogen from horns can create noise in excess of 154 decibels, like standing next to multiple jet planes taking off at the same time.

For safety reasons, LEAF can only be operated with the doors closed. Noise is safely contained by reinforced concrete walls coated with epoxy that reflect noise to create an even sound field within the room. The chamber itself relies on rubber bearings to isolate it from the environment, preventing damage to the rest of the testing center or nearby observers.

Hera was powered up for the test sessions and placed in launch configuration with its solar wings folded around its fuselage and its fuel tanks filled with helium, nitrogen, and water. Before testing, more than 130 accelerometers were installed to measure the forces acting on it and then signaled with a microphone to record ambient noise levels to ensure the tests reached their intended scope.

ESA structural engineer Simon Went, who supported the design of the Hera spacecraft and many of its payloads, comments: “Although this acoustic test had been extensively simulated in advance, it was still an unnerving moment when the LEAF camera’s giant doors closed and the audio signals were then activated. Each test session lasts only a minute, but it still felt like a very long time as we waited to find out whether Hera’s structure and components could withstand the sound waves blasting her.”

ESA Mechanical Systems and Structures Engineer Cliff Ashcroft, who led the development of Hera’s central tube ‘backbone’, adds: ‘In fact, the highest, most destructive sound pressure level is felt early in the launch phase, at or near lift-off. – vibrations reflected from the pad and are disabled when the local object bombards the detached launcher. This is a sort of final acoustic “tap on the shoulder” as the launch vehicle and spacecraft move away from Earth.

Hera is Europe’s contribution to the international experiment in planetary protection. After the DART mission collided with the asteroid Dimorphos last year—changing its orbit and sending a cloud of debris thousands of kilometers into space—Hera will return to Dimorphos to take a closer look at the crater left by DART. The mission will also measure the mass and structure of Dimorphos, as well as the larger asteroid Didymos, which Dimorphos orbits.

Hera is scheduled to launch in October 2024 to rendezvous with the Didymos and Dimorphos asteroid systems about two years later.

“The successful completion of Hera’s mechanical testing phase enables us to meet this deadline thanks to the joint commitment of the ESA Hera team, prime contractor OHB and the European Testing Services, which manages the ESA Test Centre,” said Paolo Martino, Mission Engineering Team Leader. .

“By the end of this year, the spacecraft will undergo various functional tests and undergo preparations for the next major testing milestone, long-term operation in the vacuum of space and extreme temperatures in the thermovacuum chamber, scheduled for early next year, followed by a pair of missions that Hera will deploy near Dimorphos.” It will test inter-satellite communications that will support its communication with CubeSat.’