John L. Africano

Photometric signature inversion

We explore the problem of reconstructing a 3-d model of a convex object from unresolved time-series photometric measurements (i.e., lightcurves). The problem is broken into three steps. First, the lightcurves are used to recover the albedo-area density of the object as a function of the surface normal. The ill-posedness of this inversion is considered and a suitable regularization scheme proposed. Second, the albedo and area contributions are separated using either transits or additional measurements at different wavelengths. Finally, the Minkowski problem is solved to produce the 3-dimensional shape corresponding to the area density.

Time-Resolved I-Band Photometry of Calibration Spheres and NaK Droplets

Wehave developed a program to obtain photometry of Earth-orbiting satellites using the U.S. Air Force advanced electrooptical system 3.6m telescope’s Visible Imager instrument, which acquires time-series charge-coupled device images at typical rates of 0.1 to 2.1 Hz. Observations of 12 spherical satellites provide measurements of I-band albedos (i.e., reflectances) and evaluation of surface nonuniformities. Best-fit specular diffuse albedo models enable brightness predictions and a means to grade the quality of the spheres as photometric calibration reference objects. CalSphere-4A appears to be the highest quality calibrator of the 12, with the best-fitmodel reproducing 90% of the measurements to within 0:03 stellar magnitudes. This four-decade-old sphere reflects in a predominantly diffuse fashion and has a total albedo of 67% that is somewhat lower than expected for fresh white paint, effects likely due to space weathering. The aluminum Lincoln Calibration Sphere-1 shows predominantly specular reflection (albedos 59%) but with 0:3 magnitude deviations between data and model that recur every 30–90 s, likely due to one or more surface irregularities. Three other predominantly specular aluminum spheres display less frequent but larger amplitude deviations. Observations indicate that sodium/potassium droplets leaked from Soviet radar ocean reconnaissance satellite reactors are highly reflective specular spheres that can also serve as optical calibrators.

A Geosynchronous Orbit Search Strategy

Since more than 10 years there is evidence that small-size space debris is accumulating in the geosynchronous orbit (GEO), probably as the result of breakups. Two break-ups have been reported in GEO. The 1978 break-up of an EKRAN 2 satellite, SSN 10365, was identified in 1992, and in 1992 a Titan 3C Transtage, SSN 3432, break-up produced at least twenty observable pieces. Subsequently several nations performed optical surveys of the GEO region in the form of independent observation campaigns. Such surveys suffer from the fact that the field of view of optical telescopes is small compared with the total area covered by the GEO ring. As a consequence only a small volume of the orbital element-magnitude-space is covered by each individual survey. Results from these surveys are thus affected by observational biases and therefore difficult to compare. This paper describes the development of a common search strategy to overcome these limitations. The strategy optimizes the sampling for objects in orbits similar to the orbits of the known GEO population but does not exclude the detection of objects with other orbital planes. A properly designed common search strategy clearly eases the comparison of results from different groups and the extrapolation from the sparse (biased) samples to the entire GEO environment.

Phoenix Telescope at AMOS: return of the Baker-Nunn camera

The number of objects orbiting the Earth has been increasing dramatically since the launch of Sputnik in the late 1950s. Thousands of orbiting objects, active satellites or debris, need to be tracked to ensure the accuracy of their orbital elements. To meet the growing needs for space surveillance and orbital debris tracking, the Air Force Maui Optical and Supercomputing Site (AMOS) on Maui, Hawaii is bringing back one of the original Baker-Nunn cameras as the Phoenix Telescope to contribute to these efforts. The Phoenix Telescope retains the wide-field attribute of the original system, while the addition of enhanced optics allows the use of a 4k × 4k pixels back-illuminated CCD array as the imaging camera to provide a field-of-view of 6.8 degrees square (9.6 degrees diagonal). An integrated software suite automates the majority of the operational functions, and allows the system to process in-frame multiple-object acquisitions. The wide-field capability of the Phoenix Telescope is not only an effective tool in the space surveillance effort, but it also has a very high potential value for efforts in searching for and tracking Near-Earth objects (NEO). The large sky coverage provided by the Phoenix Telescope also has the potential to be used in searching for supernova and other astronomical phenomena. An overview of the Phoenix system and results obtained since first-light are presented.

Optical observations of the orbital debris environment

The Air Force Phillips Laboratory (PL) is tasked by Air Force Space Command to characterize the orbital debris environment. Part of this task is to search for and detect debris using the optical facilities at the PL Air Force Maui Optical Station (AMOS), which is located at the Maui Space Surveillance Site (MSSS). The goals of the program are discussed, with emphasis on the detection program. This includes telescopes and sensors available, how they are used, and handoffs from one sensor to another. Results of this correlation, as well as conclusions on the orbital debris environment, are presented.

Characterization of the near-Earth Asteroid 2002 NY40

Abstract : In August 2002, the near-Earth asteroid 2002 NY40, made its closest approach to the Earth. This provided an opportunity to study a near-Earth asteroid with a variety of instruments. Several of the telescopes at the Maui Space Surveillance System were trained at the asteroid and collected adaptive optics images, photometry and spectroscopy. Analysis of the imagery reveals the asteroid is triangular shaped with significant self-shadowing. The photometry reveals a 20-hour period and the spectroscopy shows that the asteroid is a Q-type.

Automated detection of orbital debris in digital video data from a telescope

Abstract As part of a program to measure, monitor, and predict the orbital debris environment the Orbital Debris Program Office of the NASA Johnson Space Center (JSC) collects video data through a 3-m zenith-staring liquid mirror telescope located in New Mexico. This paper presents methods and results from a PC-based digital video processing system that automates the detection and measurement of orbital debris and meteors in these videotapes. Results using the automated system were compared to those from two trained observers in reviewing 40 h of video. These results demonstrate that the computer-automated system outperforms the combined results from two trained observers, achieving a 17 percent improvement in the detection rate of orbital debris per tape and a three-fold improvement in the detection rate of meteors.