GRAS and the space industry

The extreme noise and acoustic energy unleashed by a rocket launch has the potential to cause damage and disruption, even at distance. To keep the crew and space vehicle itself safe, and to protect payloads and the surrounding environment, several acoustic studies and experiments need to be carried out before and during launch.
GRAS supplies the measurement microphones for studies carried out by universities, space vehicle operators, and space agencies worldwide. Our microphones are used by space agencies like NASA, JAXA, and ESA, as well as private sector players like MSI-DFAT and Siemens.

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Wind Tunnel Test

A rocket travels at speeds of up to 24.500 mp/h, struggling against gravity before leaving Earth’s atmosphere. The unsteady aerodynamics and sheer force of aeroacoustic powers at play at such speeds pose at serious risk, not only to the integrity of the space vehicle, but also to its payload. To ensure a smooth(ish) ride, engineers use wind tunnel tests to enhance the design and stability of their rockets.

The GRAS 48LA UTP Microphone, High Pressure is often used in such test scenarios to document effects of changes in the design with high accuracy and repeatability. It is an Ultra-thin Precision (UTP) high-pressure surface microphone for aeroacoustic testing. The microphone is only 1 mm (0.04 inches) in height and, therefore, ideal for measurements in boundary layers and turbulence.

Payload Monitoring

All space rockets are built to protect the payloads they carry within certain well specified limits. This also includes limits for noise, or acoustic energy. Simply put, the space vehicle operator guarantees its customers that the noise inside its cargo bays and payload fairings will not exceed certain levels during launch. And to document this, the space vehicle is equipped with measurement microphones, that act both as a safety precaution and as documentation.

The GRAS 47BX line of acoustic sensors combines the high precision and reliability of GRAS measurement microphones with the need for fitting sensors into very confined spaces and narrow structures. With an installation height of less than 10 mm, GRAS flush-mount microphones can be integrated into virtually any design without sacrificing acoustic properties.

DFAT/DFAN testing

Direct Field Acoustic Testing (DFAT®), also sometimes referred to as Direct Field Acoustic Noise (DFAN) testing, is a crucial process for ensuring that satellites and other payloads can withstand the extreme acoustic energies experienced during a rocket launch. GRAS Sound & Vibration works closely with MSI-DFAT and Siemen’s, the world’s leading providers of DFAT/DFAN tests, who have selected GRAS microphones for their test setups.

DFAT/DFAN testing involves surrounding the test object with loudspeakers designed with the specific purpose of generating extremely high sound pressure levels over the entire frequency range of interest (20-10000Hz) to replicate the intense sound field of a launch. The goal is to validate the object’s integrity to an acoustic field that can reach an overall sound pressure level (OASPL) of up to 150dB!

To monitor the sound field during DFAT/DFAN testing, and to document compliance with the test regime, microphones are placed between the loudspeakers and the test object to receive the full blast of acoustic energy. The microphones need to be highly accurate at extreme sound pressure levels. They need to be small, to minimize interference with the test environment. And they need to be sturdy, to survive repeated tests while delivering reliable measurements every time. The GRAS 46BD ¼” CCP Pressure Standard Microphone Set meets the specifications for such powerful and crucial tests.

Launch Testing

To assess the impact of a rocket launch on the surrounding environment, scientists and space agencies conduct tests and measurements of the sound power of rocket launches. These tests are becoming increasingly important as rocket sizes grow with mankind’s ambition to return to the moon and to venture even further out.

To precisely measure the sound power of a rocket launch, a number of measurement stations are set up around the launch site, up to almost 2 kilometers from the rocket. After the launch, the space vehicle's trajectory is then used with the measured acoustic data to calculate the space vehicle’s radiated sound power.

The GRAS 46BG microphone is rapidly becoming the go-to microphone for these measurements due to the very high noise levels.

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