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On December 3rd, 2018, NASA\u2019s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) successfully rendezvoused with the Near-Earth Asteroid (NEA) 101955 Bennu. Over the next two years, the mission collected rock and regolith samples from the asteroid\u2019s surface. By September 24th, 2023, the mission\u2019s sample return capsule (SRC) entered Earth\u2019s atmosphere and was collected by NASA scientists. Analysis of these samples is already providing insight into what conditions were like during the early Solar System.<\/p>\n
According to a recent study, the known trajectory and timing of the SRC\u2019s return provided a rare opportunity to record geophysical signals produced by the capsule using a new method. Because it was traveling at hypersonic speeds as it flew through the atmosphere, the SRC\u2019s return produced a sonic boom that impacted the ground. Using distributed acoustic sensing (DAS) interrogators and surface-draped fiber-optic cables, the team carried out the first reported recording of an SRC reentry with distributed fiber-optic sensing technology.<\/p>\n
<\/p>\n The team was led by Dr. Carly M. Donahue and consisted of her colleagues from the Earth and Environmental Sciences Division at the Los Alamos National Laboratory (LANL), as well as the Department of Geosciences at Colorado State University and fiber optic-based distributed sensor developer Silixa LLC. The paper that details their findings, \u201cDetection of a Space Capsule Entering Earth\u2019s Atmosphere with Distributed Acoustic Sensing (DAS),\u201d recently appeared in the journal Seismological Research Letters<\/em>.<\/p>\n Since the end of the Apollo Era, scientists have studied sample return capsules re-entering Earth\u2019s atmosphere. These studies have helped scientists develop safe and effective methods for sample-return missions and provided insight into the atmospheric entry of meteoroids and asteroids. Until now, these studies employed infrasound and seismic sensors to record the resulting geophysical signals. However, Dr. Donahue and her team saw an opportunity since the trajectory and timing of the OSIRIS-REx mission\u2019s SRC were known in advance.<\/p>\n As Dr. Donahue told Universe Today via email, the reentry was a chance for them to test DAS systems with fiber optic cables to record the geophysical effects produced by the sonic boom. \u201cDAS systems interrogating an optical fiber are still relatively rare,\u201d she said. \u201cKnowing 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.\u201d<\/p>\n The team rapidly deployed two DAS interrogators and more than 12 km (7.45 mi) of surface-draped fiber-optic cables. Their network included six collocated seismometer-infrasound sensor pairs, all spread across two sites near the town of Eureka in the Nevada Desert. As Dr. Donahue described:<\/p>\n \u201cOnce 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. \u00a0The other 7 km of fiber was located along a remote dirt road in Newark Valley.\u201d<\/p>\n<\/blockquote>\n \n\n