10:45 AM - 12:15 PM
[PEM12-P01] Observation trials using the Pirka Telescope to elucidate the physical characteristics of LEO debris
Keywords:Space debris, Low earth orbit, Optical telescope
Space debris is man-made objects in orbit around the Earth, and the number of such objects is increasing every year. In 2009, the collision between the U.S. communications satellite Iridium and a Russian satellite that was no longer in operation generated more than 2,300 pieces of debris. There are concerns that the debris may fall to the earth or collide with the ISS, which could cause extensive damage. It is essential to accurately understand the size, materials, and kinematics of the debris, and to predict changes in its trajectory. The Japan Aerospace Exploration Agency (JAXA) is engaged in Space Situational Awareness (SSA) activities to accurately determine the orbits of debris in order to protect humans, satellites, and astronauts from debris threats. Observation of space debris is one of the SSA activities, and this research aims to contribute to SSA. Vananti et al. [2017] performed spectroscopic observations with an optical telescope to determine the surface materials of debris in geostationary orbit and compared them with the reflectance spectra of actual satellite components. Yanagisawa and Kurosaki[2012] estimated the shape and kinematics of debris in low earth orbit based only on the time variation of reflectance. However, the surface materials of debris in low orbit have not been identified. Therefore, the final goal of this study is to identify the surface materials of low-orbit debris. As a preliminary step, this paper attempts to investigate the time variation of reflected luminosity by conducting optical observations of low-orbit debris using a large aperture ground telescope.
In this study, optical observations of low-orbit debris were conducted using the 1.6-m Pirka telescope owned by Hokkaido University. Observations were conducted for four nights on October 26, 27, November 24, and 26, 2022, and a total of 22 pieces of low-orbit debris and artificial satellites were imaged. Compared to observations of debris on stars, planets, or geostationary orbits, low earth orbit debris moves at high speed within the field of view, requiring only a few minutes to a dozen minutes per observation, and also requiring high-precision tracking. If the tracking is successful, a point image should appear in the image, but no point image was found in most of the images obtained.
For the images in which a point image was found, we verified whether the point image was actually the tracked debris or not. The visual diameter of the point image in the frame was calculated, and the size of the debris at the actual orbital altitude was estimated to be much smaller than the existing data. In addition, since similar point images could not be confirmed at the same location before and after the consecutive frames, it was found that these point images were not the target of observation, but were likely to be cosmic rays or shot noise.
In addition, curved light trails were frequently observed in the acquired frames. Some of the curves showed clear luminosity changes, and these light trails were considered to be debris or satellites reflecting sunlight rather than stars with no luminosity change in a short period of time.
On the other hand, for the curves with no significant changes in luminosity, there is a possibility that they are not only stars but also satellites or debris with stable attitude.
In addition, from the observer's point of view, the rotation of the dome of the Pirka telescope could not keep up with the speed at which the low-orbit debris was moving in the celestial sphere, resulting in numerous dome tracking control errors, and as a result, sufficient observation and analysis could not be performed. The present study clarified that there is a limit to the observation of low-orbit debris using the Pirka telescope. In the future, we intend to focus on debris in geostationary orbit and estimate their surface materials using laboratory experiments and the Pirka telescope.
In this study, optical observations of low-orbit debris were conducted using the 1.6-m Pirka telescope owned by Hokkaido University. Observations were conducted for four nights on October 26, 27, November 24, and 26, 2022, and a total of 22 pieces of low-orbit debris and artificial satellites were imaged. Compared to observations of debris on stars, planets, or geostationary orbits, low earth orbit debris moves at high speed within the field of view, requiring only a few minutes to a dozen minutes per observation, and also requiring high-precision tracking. If the tracking is successful, a point image should appear in the image, but no point image was found in most of the images obtained.
For the images in which a point image was found, we verified whether the point image was actually the tracked debris or not. The visual diameter of the point image in the frame was calculated, and the size of the debris at the actual orbital altitude was estimated to be much smaller than the existing data. In addition, since similar point images could not be confirmed at the same location before and after the consecutive frames, it was found that these point images were not the target of observation, but were likely to be cosmic rays or shot noise.
In addition, curved light trails were frequently observed in the acquired frames. Some of the curves showed clear luminosity changes, and these light trails were considered to be debris or satellites reflecting sunlight rather than stars with no luminosity change in a short period of time.
On the other hand, for the curves with no significant changes in luminosity, there is a possibility that they are not only stars but also satellites or debris with stable attitude.
In addition, from the observer's point of view, the rotation of the dome of the Pirka telescope could not keep up with the speed at which the low-orbit debris was moving in the celestial sphere, resulting in numerous dome tracking control errors, and as a result, sufficient observation and analysis could not be performed. The present study clarified that there is a limit to the observation of low-orbit debris using the Pirka telescope. In the future, we intend to focus on debris in geostationary orbit and estimate their surface materials using laboratory experiments and the Pirka telescope.