Download S3.3 Study of Physical Characteristics of High Apogee Space Debris

Study of Physical Characteristics of High Apogee Space Debris
Yongna Mao, Yijun Tang, Jianfeng Wang, Xiaojun Jiang
(National Astronomical Observatories, Beijing, 100012, China)
Abstract – Data acquisition and analysis methods of medium to high apogee space
debris (MHASD)’s optical characteristics are discussed in this paper.
Key words: Space Debris; High Apogee; Optical Characteristics
1. INTRODUCTION
MHASD (orbital altitude higher than 20,000km) are too distant for radar tracking and
high resolution optical imaging [1]. Non-imaging optical observation is most suitable
for determining their physical characteristics, such as shape, size, AMR, attitude, and
outer-layer material. The physical characteristics of MHASD can be obtained by
using time series photometry, simultaneous multi-color photometry, spectroscopy, and
photopolarimetry [2].
Our study involves time-series photometry, simultaneous multi-color photometry, and
low resolution spectroscopy. The observations were carried out at Xinglong
Observatory, National Astronomical Observatories of China (NAOC). Xinglong
Observatory lies 165km to the northeast of Beijing. The observing conditions are
excellent where it offers 220-240 spectroscopic nights and 100-120 photometric
nights per year.
2. OBSERVATIONS AND DATA REDUCTION
Observations - Sufficient data were acquired by using time-series photometry,
simultaneous multi-color photometry, and low-resolution spectroscopy respectively.
Time-series photometry of MHASD in the visual band is one of the effective
techniques for studying MHASD physical characteristics. Our data were acquired by
using the 85cm f/4 and 50cm f/8 telescopes and two 1k*1k scientific grade CCDs.
Figure 1 shows one of the raw images we observed and the reduced curves of the
time-series photometry. The variability consists of two parts, the faster variability is
caused by specular reflection while the slower one is caused by diffuse reflection. The
light curves can help us obtain shape and status information of MHASD.
Figure 1 – raw image and reduced light curve of high apogee space debris
Simultaneous multi-color photometry acts as one of the most powerful tools in cross
identifications [2, 5]. Filter selection is most important [2], a suitable filter-set can
bring us reliable conclusions. We observed the same target by using three telescopes
in three bands (Johnson system B, V, R) simultaneously. The color index distributions
of different targets are shown in Figure 2.
Figure 2 – Illustration of the color index difference between targets
MHASD’s spectra are associated with their outer-layer material. Compared with the
photometric data, low-resolution spectroscopy, carries more information about the
materials of the debris. A raw 2-dimensional spectrum taken by using the 2.16m
reflector telescope and Cassgrain spectrograph at Xinglong Observatory is shown in
Figure 3.
Figure 3 – spectrum of a space debris with 1nm resolution
Data reduction – Automatic reduction is designed based on standard IRAF (Image
Reduction and Analysis Facility) procedures and special features of MHASD,
including zero correction, flatfield correction, aperture photometry, and so on. For
flux calibration, we observe Landolt stars under photometric conditions and use field
stars in non-photometric conditions. Besides the routine astronomical CCD reduction,
the data were also carefully reduced with distance correction, solar declination
correction, flux calibration, and phase-angle correction. Considering the stretched
field stars observed, a method called MGC (mean-geometrical-centering), is used to
compute the center of stretched star images [6]. The flux of the stretched stars can be
computed as well.
3. PRELIMINARY RESULTS
Utilizing the reduced photometric data based on phase-angle variations, we developed
analysis methods for space debris’ technical status, attitude stabilizing mode, shape,
optical cross section area, as well as spin period and attitude variation. Figure 4
illustrates three targets under three-axis stabilization, spin stabilization, and free
rolling, respectively. Note that in figure 5 the light curve of COSMOS 1989 is well
modeled, but this simple model only suits regular targets. We studied cubic and
cylinderic models as well. We obtained optical cross section (OCS) from calibrated
data to study optical characteristics and size of space debris.
Figure 4 - Illustrates the technical status and attitude stabilizing mode
Figure 5 – Fitting of COSMOS 1989 light curve
Simultaneous multi-color photometric data on more than 30 GEO debris in Johnson B
V R filters were collected. Through the data analysis, we found color information
could do a job in space debris classifications. In the near future, high accuracy data
will be collected by our simultaneous 3-channels CCD photometer, which engages
three colors and simultaneity.
Some spectra of high apogee space debris observed were used for color definition and
outer-layer material determination. The data are under analysis.
REFERENCES
[1] Thomas Schildknecht. Optical surveys for space debris. Astron Astrophys Rev
(2007)14:41-111.
[2] TANG Yi-jun, JIANG Xiao-jun, WEI Jian-yan. Review of optical observations of
high apogee space debris. Journal of Astronautics, Vol.29 No.4.
[3] TANG Yi-jun, JIANG Xiao-jun, WANG Jian-feng. 3-axis stabilization GEO
satellites diffuse reflection optical. ACTA PHOTONICA SINICA, accepted.
[4] Sanchez D J, Gregory S A. Photometric measurements of deep space satellites [J].
Proceedings of SPIE 2000, 4091:164-182
[5] Tamara E P, Stephen A G, Kim L. Electro-optical signatures comparisons of
geosynchronous satellites[J]. Proceedings of SPIE 2002, 4847:332-336
[6] Mao. Y. et al. Centering of stretched star images of man-made satellite
observations. Annals of Shanghai Obs, 25,51,2004