Angles and Range: Initial Orbital Determination with the Air Force Space Surveillance Telescope (AFSST)
Abstract : The institution of a robust, comprehensive program of Space Situational Awareness (SSA) necessarily includes observations by ground-based optical and infrared (OIR) telescopes. The Air Force Space Surveillance Telescope (AFSST) has been proposed as a system of telescopes designed to address the ground-based component of comprehensive SSA. A hallmark of our definition of AFSST is that it be composed of inexpensive, replicable telescopes programmed to accomplish multiple surveillance programs, but designed to achieve the difficult design-driving task of accomplishing an uncued search for small objects in Low Earth Orbit (LEO). We discuss the configuration of AFSST and describe one technique by which AFSST simultaneously acquires angle and range data for accurate real-time determination of LEO orbital elements, even upon first detection of the object.
Are curved focal planes necessary for wide-field survey telescopes?
The last decade has seen significant interest in wide field of view (FOV) telescopes for sky survey and space surveillance applications. Prompted by this interest, a multitude of wide-field designs have emerged. While all designs result from optimization of competing constraints, one of the more controversial design choices is whether such telescopes require flat or curved focal planes. For imaging applications, curved focal planes are not an obvious choice. Thirty years ago with mostly analytic design tools, the solution to wide-field image quality appeared to be curved focal planes. Today however, with computer aided optimization, high image quality can be achieved over flat focal surfaces. For most designs, the small gains in performance offered by curved focal planes are more than offset by the complexities and cost of curved CCDs. Modern design techniques incorporating reflective and refractive correctors appear to make a curved focal surface an unnecessary complication. Examination of seven current, wide FOV projects (SDSS, MMT, DCT, LSST, PanStarrs, HyperSuprime and DARPA SST) suggests there is little to be gained from a curved focal plane. The one exception might be the HyperSuprime instrument where performance goals are severely stressing refractive prime-focus corrector capabilities.
Imaging the in-plane magnetization in a Co microstructure by Fourier transform holography.
We report on experiments using Fourier transform holography to image the in-plane magnetization of a magnetic microstructure. Magnetic sensitivity is achieved via the x-ray magnetic circular dichroism effect by recording holograms in transmission at off-normal incidence. The reference beam is defined by a narrow hole milled at an inclined angle into the opaque mask. We present magnetic domain images of an in-plane magnetized cobalt element with a size of 2 μm × 2 μm× 20 nm. The domain pattern shows a multi-vortex state that deviates from the simple Landau ground state.