Portable In-Field Acoustic Sensor Array

Project Objective

The Portable In‑Field Acoustic Sensor Array project is focused on the development of the Real‑Time Display 2 (RTD2) Sentinel, a portable, standalone, time‑synchronized acoustic‑intensity measurement system designed to autonomously operate for long‑duration periods and capture data essential for reducing uncertainty in Space Launch System (SLS) liftoff acoustic environments.

Project Description

The Portable In-Field Acoustic Sensor Array project is focused on developing the RTD2 Sentinel, a portable, standalone, time‑synchronized, long‑duration acoustic‑intensity measurement system that enables NASA to collect high‑quality acoustic data in environments where traditional instrumentation cannot be deployed. Built entirely in house, the RTD2 Sentinel integrates Inter‑Range Instrumentation Group time code, Format B (IRIG‑B)-synchronized timing via Global Positioning System (GPS), low‑frequency acoustic‑intensity sensing and a robust active/passive thermal‑management system into a compact, battery‑powered package capable of operating autonomously for a week or more without external power or network connections. This capability allows teams to deploy multiple synchronized sensor arrays around a launch pad or test site and capture detailed acoustic information during critical events.

The project was initiated in response to findings from Artemis I, where post‑flight analysis revealed larger‑than‑expected uncertainties in models predicting duct overpressure (DOP) and low‑frequency liftoff acoustics. These low‑frequency pressure events are especially important because the Space Launch System (SLS) is highly sensitive to them, and accurate predictions are essential for ensuring the safety of the vehicle, crew, and ground systems. To address these gaps, the RTD2 Sentinel systems are being developed to support the deployment of a linear array of ten systems within the Launch Complex 39B (LC‑39B) pad perimeter, positioned outside the plume region but close enough to capture the low‑frequency acoustic source characteristics and signatures that play a role in structural loading and internal vehicle acoustics.

Each RTD2 Sentinel unit consists of a four‑sensor acoustic‑intensity subarray, a standalone data acquisition unit, a GPS‑synchronized IRIG‑B timecode generator, an active and passive thermal‑management system, and a long‑life battery system. These arrays measure not only the amplitude of acoustic pressure but also the direction of wave propagation, enabling the determination of the location, strength, and efficiency of acoustic sources during liftoff. This includes characterizing the complex interactions between engine plumes, the flame trench, and surrounding structures. In addition to acoustic‑intensity measurements, the system architecture is intentionally designed to be flexible and modular, allowing teams to integrate other types of sensors, up to four per system, for measurements such as pressures, strain gauges, accelerometers, or mixed configurations, expanding its usefulness beyond acoustics alone.

The goal of the project is to generate the high‑fidelity datasets needed to improve physics‑based acoustic models, refine prediction tools, and reduce uncertainty in liftoff environments for SLS and future launch systems. These data will directly support updates to liftoff acoustic models, provide validation for Exploration Ground System (EGS) acoustic requirements, and help characterize transient phenomena such as igniter shock and ignition overpressure events. 

Beyond SLS, the RTD2 Sentinel technology is designed for broad applicability across NASA programs. Its portability, autonomy, and modular sensor architecture make it suitable for engine and motor development testing; lunar and Martian habitat testing; far‑field community acoustics; and any scenario requiring synchronized, remote, long‑duration measurements. The project includes the procurement and integration of multiple system components, data acquisition hardware, GPS‑synchronized timing modules, pressure transducers, sensor stands, batteries, thermal‑management hardware, and protective enclosures.

Project Results and Conclusions

The RTD2 Sentinel systems were successfully fielded for the Artemis II campaign, marking the first operational deployment of the newly developed long‑duration, standalone acoustic‑intensity arrays within the LC‑39B Pad perimeter. All units were installed, and the team completed full pre‑launch functional checkouts and configuration verification. Following Artemis II liftoff, the project will analyze the collected low‑frequency acoustic and overpressure data to assess system performance; validate the measurement approach; and begin refining SLS ignition overpressure, duct overpressure, and liftoff acoustic models based on the new dataset.

The RTD2 Sentinel systems are expected to significantly enhance NASA’s ability to characterize and model the complex acoustic environments associated with an SLS launch. By providing long‑duration, time‑synchronized measurements from multiple locations within the pad perimeter, the system will supply higher‑fidelity data for validating predictive models and improving vehicle acoustic design margins. These measurements also enable corroboration of existing datasets and support integration into numerical acoustic inverse modeling frameworks, improving the accuracy of reconstructed source fields and propagation behavior. The modular sensor architecture further allows mission‑specific configurations, enabling teams to capture pressure, vibration, strain, and other key parameters alongside acoustic intensity. Together, these capabilities will reduce uncertainty in liftoff acoustics, support safer and more efficient operations, and inform future upgrades.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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