OSIRIS-REx's Sample Return from Asteroid Bennu

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On December 3rd, 2018, NASA's Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer (OSIRIS-REx) successfully rendezvoused with the Near-Earth Asteroid (NEA) 101955 Bennu. This mission aims to collect a sample of rock and regolith from the asteroid's surface, providing valuable insights into the early solar system's conditions.

Successful Sample Collection and Mission Objectives

Over the next two years after entering orbit around Bennu, the OSIRIS-REx team conducted a series of flybys, scientific observations, and survey mapping of the asteroid. The principal goal of this mission is to bring a sample back to Earth for analysis. The Sample Return Capsule (SRC) is set to enter Earth's atmosphere and be retrieved by NASA scientists on September 24th, 2023. Analysis of these samples is anticipated to yield groundbreaking information about the history and formation processes of the solar system.

Significance of the Attempt

Sample return missions are critical as they provide direct evidence and physical materials for planetary research. According to NASA, and similar to previous missions like the Apollo or the Stardust missions, studying returned samples offers unprecedented insight that remote observations cannot provide.

Innovative Data Collection Method: Distributed Acoustic Sensing (DAS)

A recent study published concerning the OSIRIS-REx mission detailed how the team utilized a novel method for detecting the geophysical signals produced by the capsule during its re-entry into Earth's atmosphere. The SRC traveled at hypersonic speeds, generating a sonic boom upon re-entry. The implications of this study extend beyond just the OSIRIS-REx mission; they could significantly alter how future space missions will be analyzed.

Study Team and Collaboration

The study was led by Dr. Carly M. Donahue and composed of researchers from the Earth and Environmental Sciences Division at the Los Alamos National Laboratory (LANL), along with colleagues from the Department of Geosciences at Colorado State University and the fiber optic-based sensing technology developer Silixa LLC. Their paper, "Detection of a Space Capsule Entering Earth’s Atmosphere with Distributed Acoustic Sensing (DAS),” published recently in the journal Seismological Research Letters, outlines their key findings.

The Technical Approach: Utilizing DAS Technology

Traditional methodologies for studying atmospheric entry have predominantly relied upon infrasound and seismic sensors to capture geophysical signals. However, with the precise trajectory and timing of the OSIRIS-REx SRC return known in advance, it became possible for Dr. Donahue's team to explore the use of more innovative technologies. This was a unique opportunity to employ Distributed Acoustic Sensing (DAS) technologies for measuring and recording the sonic boom's signature.

“DAS systems interrogating an optical fiber are still relatively rare,” said Dr. Donahue. “Knowing ahead of time the precise trajectory gave us the scarce opportunity to situate multiple DAS interrogators near the point of highest heating and capture the sonic boom as it impacted the ground.”

The Implementation of DAS: Network Setup

The team swiftly established a comprehensive network involving two distributed acoustic sensing interrogators and over 12 kilometers (approximately 7.5 miles) of surface-draped fiber-optic cables. This network included six collocated pairs of seismometer and infrasound sensors, spread across two designated sites near the town of Eureka in the Nevada Desert.

To illustrate the geographic setup, here is a table summarizing the network configuration:

Operational Efficiency

During the preparation process, Dr. Donahue noted:

“Once the team got the hang of rolling out the 4 spools of optical fiber that each weighed over 100 kgs, installing and retrieving the fiber took less time than setting up the six co-located seismic and infrasound stations. Approximately 5 km of the optical fiber was located at the local Eureka airport, along with many other teams deploying sensors such as infrasound, seismic, and GPS. The other 7 km of fiber was located along a remote dirt road in Newark Valley.”

Data Analysis and Outcomes

Leveraging the robust network they created, the team obtained an exceptional profile of the sonic boom impact as it struck the terrain. The DAS observations yielded a rich data set characterized by a sharp impulsive arrival followed by an extended coda. This data demonstrated features similar to those previously recorded using traditional seismic and infrasound methods.

Importantly, while traditional sensors capture sonic booms at a singular point, the high-density DAS array revealed how the signature of the wavefront altered as it interacted with the diverse and irregular landscape of Nevada. This newfound ability to discern how a sonic boom transforms over distance could signal a paradigm shift in the way atmospheric entry events are analyzed.

Future Implications for Meteor Detection

Dr. Donahue emphasized the potential future applications:

“By having an extremely dense array of sensors, DAS has the possibility of better characterizing the trajectory and size of a meteor. The topology (e.g., hills) of the ground is known to influence the wavefront recorded at the earth's surface. By deploying a dense line of sensors across varied elevations, these effects could be accurately accounted for to produce a more precise trajectory characterization of a meteor.”

The Next Phase of OSIRIS-REx

Upon accomplishing its primary sample collection mission, the OSIRIS-REx spacecraft has been retrofitted for continuation of its operations under a new name: OSIRIS-APEX (Apophis Explorer). In 2029, the spacecraft plans to rendezvous with another Near-Earth Asteroid: 99942 Apophis. This mission aims to gather additional samples to expand our understanding of the solar system further.

Challenges Ahead

While the results thus far are promising, the phases ahead will involve extensive planning and precise execution to ensure the scientific success of the OSIRIS-APEX objectives. The challenges will encompass navigation, sample integrity, and data collection during the spacecraft's approach.

Conclusion

In conclusion, the OSIRIS-REx mission has not only contributed valuable samples from asteroid Bennu but has also pioneered new methods for studying atmospheric entry phenomena through innovative technologies such as DAS. This first of its kind re-entry detection could redefine current practices in planetary science and meteor tracking, promising advancements in these critical areas of research.

For More Information

To explore in-depth details and the cutting-edge findings of the OSIRIS-REx mission, please refer to the following sources:

• NASA OSIRIS-REx Mission Overview
• Geoscience Journal: Detection of a Space Capsule Entering Earth’s Atmosphere
• LANL Earth and Environmental Sciences Division

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