Dennis Duneman

Wide field performance of a phased array telescope

A phased array telescope is an array of optical telescopes whose images are coherently combined so as to achieve the resolution of a single but much larger telescope. Phased array telescopes deliver the resolution of very large telescopes without the difficulties and expenses associated with very large optics. To achieve this resolution, a wide field of view (FOV) phased array imaging system must accurately control phase and must superimpose the images from all telescopes to within a fraction of a resolution element over the whole FOV simultaneously. We built a test bed called the Multipurpose Multiple Telescope Testbed (MMTT). It consists of four 20-cm-aperture telescopes phased together with a ± 15-arcmin FOV. It has no mount and is designed for laboratory use only. We present a brief description of the MMTT and then describe performance tests and results. The phasing and image superpositioning accuracy of the array were measured using star tests. Several of the resulting point spread functions were recorded simultaneously at three different field angles to determine the wide FOV performance of this phased array. These images were analyzed and compared to theoretical predictions.

Wide field-of-view phased array telescope

The Multipurpose Multiple Telescope Testbed is described, and initial tests are discussed. After the optical quality of individual telescopes was established with interferometric tests, the cophasing and image superpositioning accuracy of the array were measured using star tests. Point spread functions were calculated with a physical optics code. Preliminary star tests using two of the four telescopes are presented and compared with the predicted pattern. It is concluded that the preliminary results obtained lend credence to the given method of controlling lateral pupil geometry and to previous calculations of optical aberration and optical alignment tolerances.

Hyperspectral observations of space objects

In this paper we present (1) the optical system design and operational overview, (2) laboratory evaluation spectra, and (3) a sample of the first observational data taken with HYSAT. The hyperspectral sensor systems which are being developed and whose utility is being pioneered by the Phillips Laboratory are applicable to several important SOI (space object identification), military, and civil applications including (1) spectral signature simulations, satellite model validation, and satellite database observations and (3) simultaneous spatial/spectral observations of booster plumes for strategic and surrogate tactical missile signature identification. The sensor system is also applicable to a wide range of other applications, including astronomy, camouflage discrimination, smoke chemical analysis, environmental/agricultural resource sensing, terrain analysis, and ground surveillance. Only SOI applications will be discussed here.

Laboratory experiment using phase diversity to extract higher order Zernike coefficients

A theoretical description of Phase Diversity is done in some detail to lay the foundations for the experimental effort. The Phase Diversity algorithm is formulated in the context of nonlinear programming where a metric is developed and then minimized. This development will show how the Zernike coefficients can be solved for directly using nonlinear optimization techniques. Computer simulations are used to validate the algorithms and techniques. The results of the computer simulations are shown. Once the confidence of the algorithms and techniques are established in the computer simulations, they are used on actual laboratory data. Detailed discussion of the laboratory implementation will be described and the laboratory results will be shown.