As thousands of satellites and pieces of space debris move through low Earth orbit (LEO), the region around Earth is becoming increasingly crowded. At altitudes of several hundred kilometers, the upper atmosphere still creates enough atmospheric drag to slow satellites and alter their orbits. Accurately measuring thermospheric density at these heights is therefore essential for predicting satellite movement, improving orbital tracking, and reducing the risk of collisions.
More than 99 percent of the upper atmosphere is made up of electrically neutral gases in the thermosphere. The term thermospheric density refers to the density of this neutral atmospheric region approximately 100 to 1,000 kilometers above Earth’s surface. By comparison, the ionosphere contains less than 1 percent of the atmosphere. Because ionized gases affect the way radio waves travel, the ionosphere is relatively easy to observe. Measuring atmospheric conditions in the thermosphere is far more challenging.
A New Way to Observe the Thermosphere
More accurate measurements of thermospheric density could advance upper-atmosphere research and provide valuable data for satellite operators and space engineers. Motivated by both scientific and practical needs, researchers at Kyoto University have developed a new technique for mapping this difficult-to-observe region.
“This is an interdisciplinary study between space science and space engineering,” says corresponding author Mamoru Yamamoto. “Reading papers from both fields of research made me realize that a deeper dialogue between researchers in both fields is needed.”
The researchers used publicly available orbital data from Starlink satellites and applied tomography, a technology commonly associated with medical imaging, to study Earth’s upper atmosphere. By analyzing the gradual orbital decay caused by atmospheric drag, the team estimated thermospheric density around approximately 1,200 Starlink satellites traveling at an altitude of about 482 kilometers.
Building a 2D Map of Atmospheric Density
Using these measurements, the researchers created a two-dimensional latitude-and-longitude map showing thermospheric density at an altitude of approximately 500 kilometers. According to the research team, this is the first tomographic analysis of its kind for the thermosphere.
The resulting density pattern showed strong agreement with observations from the European Space Agency’s Swarm satellite mission, which measures changes in atmospheric density along its orbit.
This study builds on earlier research by the same team. In that work, scientists used publicly available orbital data known as two-line element or TLE data from Starlink satellites to estimate how thermospheric density changes over time and with altitude. The new analysis adds another dimension by revealing how atmospheric density varies horizontally across latitude and longitude, providing a clearer view of the thermosphere’s geographic structure.
Making Crowded Orbital Paths Safer
This discovery could provide important practical benefits as the number of satellites and other objects in Earth orbit continues to increase. More accurate thermospheric density data can improve satellite orbit predictions, support collision avoidance, and reduce the risk of impacts between spacecraft and space debris.
The technology could eventually enable near-real-time monitoring of atmospheric density around individual satellites. Such observations may improve space weather forecasting and contribute to safer, more reliable satellite operations in the future.
Source: www.sciencedaily.com