Researcher
研究者名
Yamamoto, Mamoru
Overview
Kyoto, Japan — The space around Earth is becoming increasingly crowded, with thousands of satellites and pieces of debris now sharing low Earth orbit. Even above this region — at altitudes of several hundred kilometers — the extremely thin upper atmosphere can slow satellites down, making accurate information on atmospheric density essential for predicting satellite motion and preventing collisions.
The upper atmosphere is composed of more than 99 percent electrically neutral atmosphere called the thermosphere, and thermospheric density is the term used to describe neutral atmospheric density at heights from 100 to 1,000 kilometers above the Earth’s surface. While the ionized gas of the ionosphere makes up less than 1 percent of the atmosphere, the effect of the ionized gas on radio wave propagation renders the ionosphere relatively easy to observe, while thermospheric observations pose a considerable challenge.
Nonetheless, developing observation methods for thermospheric density is essential both to further advancing the science of the upper atmosphere and for applications in space engineering. These needs inspired a team of researchers at Kyoto University to develop a new method of visualizing this elusive environment.
“This is a multidisciplinary study between space science and space engineering,” says corresponding author Mamoru Yamamoto. “Reading papers from both research fields, we realized that deeper dialogue between researchers from both fields is necessary.”
The team used publicly available orbital data from Starlink satellites to apply tomography, a common technique in medical imaging, to the Earth’s upper atmosphere. By measuring atmospheric drag, or the decay of satellite orbits, the researchers were able to estimate the thermospheric density surrounding roughly 1,200 satellites at an altitude of 482 kilometers.
This approach allowed the team to construct a two-dimensional latitude-longitude snapshot of the thermospheric density at an altitude of about 500 kilometers. The result is the first tomographic analysis of its kind, and one that demonstrates high consistency with the European Space Agency’s SWARM observations, which measure density variations along satellite trajectories.
This new study builds on the team’s previous work in which they estimated the time-altitude distribution of thermospheric density using general orbital information known as Two-Line Element — or TLE — data from Starlink satellites. In contrast, this new analysis extends their previous research horizontally, revealing the latitude-longitude structure of the thermosphere.
The studies from the research team hold significant social impact, as they provide information that can help mitigate the risk of collisions between satellites or between satellites and space debris. The methods used may also eventually be able to support near-real-time monitoring of atmospheric density around satellites, strengthening space-weather forecasting and helping to make future space operations safer and more reliable.
