On April 8, 2024, NASA’s Atmospheric Perturbations around Eclipse Path (APEP) mission deployed three sounding rockets from Wallops Flight Facility in Virginia to investigate how the Moon’s shadow affects Earth’s upper atmosphere. The launches occurred at 2:40 p.m., 3:25 p.m., and 4:28 p.m. Eastern Time, timed to capture conditions before, during, and after the peak of the total solar eclipse. Each rocket reached altitudes between 254 and 256 miles (410 to 413 kilometers), with all instruments—both primary payloads and twelve ejected sub-payloads—successfully gathering data.
The ionosphere, a charged layer extending roughly from 55 to 310 miles (90 to 500 kilometers) above Earth, plays a critical role in radio signal propagation and satellite communications. “It’s an electrified region that reflects and refracts radio signals, and also impacts satellite communications as the signals pass through,” said Aroh Barjatya, principal investigator and professor of engineering physics at Embry-Riddle Aeronautical University. Variations in ionospheric density can disrupt communication systems, making predictive modeling essential for modern infrastructure.
Solar radiation ionizes atmospheric particles during the day, while at night, these particles recombine into neutral atoms. The ionosphere’s behavior is influenced by both terrestrial weather and space weather, creating a dynamic environment that is challenging to forecast. A total solar eclipse produces a rapid, localized sunset as the Moon’s shadow races across the atmosphere, triggering large-scale waves and smaller perturbations. These disturbances can affect different radio frequencies, particularly high-frequency communication channels.
Studying such short-lived changes is difficult with satellites, which may not align with the eclipse path at the right moment. Sounding rockets, capable of reaching altitudes between 30 and 300 miles, fill this observational gap. They operate in a region inaccessible to both balloons and satellites, enabling direct measurements of charged and neutral particle densities, as well as surrounding electric and magnetic fields.
Each APEP rocket carried four secondary instruments, three built by Embry-Riddle and one by Dartmouth College, each roughly the size of a two-liter soda bottle. These sub-payloads replicated the primary measurements, effectively multiplying the data collection capacity. Barjatya noted, “It’s similar to results from fifteen rockets, while only launching three.”
The mission built on results from October 2023, when the same rockets—then launched from White Sands Missile Range during an annular solar eclipse—recorded a sharp drop in charged particle density as the shadow passed overhead. Perturbations capable of affecting radio communications were detected in the second and third launches, but not in the first, which occurred before peak eclipse. The 2024 total eclipse offered an opportunity to compare whether these disturbances began at the same altitude and whether their magnitude and scale were consistent.
Complementary measurements were taken across the United States. Embry-Riddle students deployed high-altitude balloons, while teams from MIT’s Haystack Observatory and the Air Force Research Laboratory operated ground-based radars. Scientists from Embry-Riddle and Johns Hopkins University Applied Physics Laboratory worked to refine ionospheric models using this combined dataset, aiming to improve predictive capabilities for communication reliability.
The APEP rockets’ maximum planned altitude was 260 miles (420 kilometers), positioning them to sample the full vertical extent of the ionosphere’s response to the eclipse. By coordinating rocket launches with balloon and radar observations, researchers assembled a comprehensive picture of atmospheric dynamics during the rare event. The next total solar eclipse over the contiguous United States will not occur until 2044, underscoring the importance of these measurements for advancing both scientific understanding and applied communication technologies.
NASA streamed the launches live via its Wallops YouTube channel and included them in its official eclipse broadcast. Visitors to Wallops Flight Facility were able to witness the launches in person between 1 p.m. and 4 p.m., adding a public engagement dimension to a mission rooted in precision engineering and atmospheric science.