The Hera Asteroid Mission Detects Intriguing Sound Phenomena

ESA’s Hera asteroid mission has successfully completed acoustic testing, proving that the spacecraft can withstand the intense noise generated during lift-off. This testing took place at the Large European Acoustic Facility in the Netherlands, which is equipped with a powerful sound system capable of producing over 154 decibels of extreme noise.

Diego Escorial Olmos, Hera system engineer, explains the importance of simulating the launch process to ensure the spacecraft’s safety. The testing involved vibrating the spacecraft on shaker tables and then subjecting it to the noise profile sourced from the launch provider. The LEAF chamber, where the testing took place, is 11 meters wide, 9 meters deep, and 16.4 meters high. It is equipped with enormous sound horns that can generate a range of noise up to 154 decibels.

To ensure safety, LEAF can only operate once its doors are closed. The chamber’s steel-reinforced concrete walls contain the noise and are coated with epoxy resin to reflect noise and create a uniform sound field within the chamber. The chamber itself is isolated from its surroundings to prevent damage to the rest of the Test Centre and nearby human observers.

Hera was prepared for the test sessions by filling its fuel tanks with helium, nitrogen, and water and configuring it for launch with folded solar wings. More than 130 accelerometers were installed on the spacecraft to measure the forces exerted on it during testing, and microphones were placed around it to record the surrounding noise levels.

Simon Whent, an ESA structures engineer involved in designing Hera’s structure and payloads, describes the nerve-wracking moment when the LEAF chamber doors closed and the horns were activated. The tests lasted only a minute, but it felt like a long time as they waited to see if Hera’s structure and components could withstand the intense sound waves.

Cliff Ashcroft, a mechanical systems and structures engineer at ESA, explains that the highest and most damaging levels of acoustic pressure occur during the early launch phase. These vibrations are generated at or close to lift-off and bombard the departing launcher. However, it’s also a kind of final acoustic “pat on the back” as the launcher and spacecraft leave Earth.

Hera is part of an international planetary defense experiment and will return to the Dimorphos asteroid to study the crater left by the DART mission’s impact. The mission will also measure the mass and composition of Dimorphos and the larger Didymos asteroid that it orbits around. Hera is scheduled for launch in October 2024, with a rendezvous with the asteroid system expected two years later.

Paolo Martino, leading the mission engineering team, expresses his satisfaction with the successful completion of Hera’s mechanical test phase. He credits the dedication of ESA’s Hera team, prime contractor OHB, and European Test Services for meeting the deadline. The spacecraft will undergo further functional tests and preparation for sustained operation in space-grade vacuum and extreme temperatures in a thermal vacuum chamber. Inter-satellite link testing will also be conducted to ensure Hera remains connected to the CubeSats it will deploy near Dimorphos.

The completion of acoustic testing marks another milestone in the incredible adventures of the Hera mission. The successful tests demonstrate ESA’s commitment to ensuring the safety and success of this important space exploration endeavor.