Time-resolved Photometric Observations of Satellites: Calibration Spheres and Orbital Debris
- Paper number
IAC-06-B6.1.11
- Author
Dr. Doyle Hall, Boeing, United States
- Coauthor
Mr. John Africano, United States
- Coauthor
Dr. Paul Kervin, United States
- Year
2006
- Abstract
We have developed a program to obtain calibrated time-resolved photometry of rapidly moving targets using the AMOS 3.6 m AEOS telescope on Haleakala, Maui. The observations employ the AEOS VISIM instrument using the Bessel I-band filter (740-880 nm). Data acquisition consists of obtaining observations of one or more Earth-orbiting objects intermixed with several photometric standard calibration stars. Data acquisition rates vary from 0.1 to 2.1 Hz, depending on the target brightness. An integrated reduction tool processes the data in an automated fashion yielding several data products, including nightly instrumental calibration parameters as well as animations of the moving target photometry. The calibrated photometry provides the means to estimate optical cross sections and rough characteristic sizes of satellites and debris. The presence of periodicity in the time-resolved measurements constrains satellite rotation states. Observations of spherical calibration satellites provide measurements of their optical reflectivities and a means to evaluate any departures from spherical surface uniformity that may result from on-orbit processes such as space weathering and/or collisions with small particles. Observations of liquid metallic sodium/potassium (NaK) droplets leaked from RORSAT satellite reactors confirm that these debris have spherical or very nearly spherical shapes and reflect light in a predominantly specular fashion. Combining the photometric data with recent radar-derived size estimates indicates that the absolute reflectivity of the NaK droplets in the 740-880 nm spectral band is 0.86 +/- 0.03, making these among the most reflective artificial satellites orbiting the Earth. Combining the measured diameters and Space Surveillance Network orbital history data provides a means of estimating the object masses, indicating that the largest NaK droplets have masses of roughly 70 to 100 grams.
- Abstract document