A team of researchers working on DARPA’s Atmosphere as a Sensor (AtmoSense) program made an unexpected discovery while monitoring Earth’s atmosphere. The team detected unusual disturbances linked to a SpaceX Falcon 9 rocket plummeting through the atmosphere during reentry.
AtmoSense aims to use the atmosphere as a global sensor by measuring acoustic and electromagnetic waves that travel through it. The program, which began in 2020, was originally designed to track ground-based events such as underground explosions that could indicate security threats. However, the latest findings suggest that the technology can also detect disturbances from reentering spacecraft.
While analyzing data from controlled explosions in New Mexico, researchers noticed a significant drop in total electron content in the atmosphere.
“As the team was looking at the data, they saw a huge drop in what’s called total electron content that puzzled them,” said Michael Nayak, program manager of AtmoSense. He compared the effect to blocking water flowing through a hose, leading to a measurable decrease in volume.
Further investigation linked this anomaly to a Falcon 9 reentry on the same day. When the team reviewed data from previous SpaceX missions, they found that the electron drop was consistently present across dozens of launches. “The phenomenon is highly repeatable,” Nayak confirmed.
Advanced detection of atmospheric disturbances
AtmoSense’s ability to detect such disturbances suggests that the atmosphere could be used to monitor a wide range of events beyond just ground-based explosions. DARPA noted that the findings are significant for national security, as they could help track objects reentering Earth’s atmosphere.
Researchers are set to present the latest AtmoSense results during a virtual workshop from April 15 to 17. The findings may pave the way for new techniques to identify atmospheric disturbances caused by both natural and man-made events.
AtmoSense operates in two phases. The first phase focused on developing models to predict wave propagation from large events such as earthquakes and volcanic eruptions. The second phase aimed to improve detection limits by testing the models against smaller-scale events.
In 2024, two field tests in New Mexico were conducted to validate AtmoSense models. These tests involved six controlled detonations, ranging from 1-ton to 10-ton explosions. The data collected closely matched the predicted wave propagation models, proving the system’s accuracy.
Falcon 9 and the future of atmospheric sensing for DARPA and the US
SpaceX’s Falcon 9 has completed over 450 missions, making it one of the most frequently used rockets in spaceflight history. The partially reusable two-stage rocket is designed to launch payloads into orbit and then return to Earth for a controlled landing.
The ability of AtmoSense to detect disturbances from Falcon 9 reentries demonstrates its potential to track atmospheric wave patterns from various events worldwide.
DARPA aims to refine the technology so that it can sense and analyze atmospheric waves created by any significant event on Earth, providing critical data for scientific research and national security.
