Rolf Sand

Off-axis telescopes: the future generation of Earth observation telescopes

In 1991 Carl Zeiss started a program to develop powerful telescopes for airborne and spaceborne earth-observation telescopes. This article summarizes some of the main result of this program. To emphasize the importance of these activities a short historical review was added.

HRIS technology development results and their implementation in future hyperspectral imagers

The recent developments within the ESA funded HRIS (high resolution imaging spectrometer) technology program -- aiming at an airborne demonstrator model -- yielded rather successful subsystem developments. HRIS is designed as a true pushbroom hyperspectral imager with comparatively high spatial and spectral resolution, covering the spectral range from 450 to 2350 nm. The main breadboard units, with a space-near design, are essentially: a TMA (three mirro anastigmat, Carl Zeiss) front optics, a dual path spectrometer optics (Officine Galileo) with a novel in-field spectral separation unit, a 2-D SWIR CMT detector array with a dedicated CMOS readout multiplexer (GEC Marconi IR, MATRA MSF for testing), the signal processing electronics (DSS), some calibration elements (DLR + DSS), and the extensive testing of all units. The paper presents the essential results per unit, with possible exception of the front optics (which may not be completed at the conference paper presentation yet), including derived further development efforts. Also, the remaining steps towards an airborne test mission are outlined, together with a brief description of the envisaged high-altitude aircraft. We hope that this paper may also stir some potential users of later airborne HRIS test missions over dedicated target areas. Positive responses would support ESA to pursue the program. The technology units development under the HRIS contract have turned out useful for follow-on instrument developments such as the ESA Explorer mission candidate PRISM (processes research by an imaging space mission). This leads to the conclusion that the achieved development results are a sound basis for future airborne and spaceborne hyperspectral imager developments in Europe. A brief survey of the current PRISM baseline concept is added to the paper.

Design study for high-performance optical communications satellite terminal with high-power laser diode transmitter

The present optical terminal design for a high data rate interorbit communications link with 500 Mbit/sec (or higher) transmission rate is based on high-power laser diode transmitters with 1 W peak power at 800 nm, in conjunction with a direct-detection receiver; two-channel wavelength-division multiplexing, together with the high transmission capability of the off-axis telescope used, contribute to the achievement of the requisite data rates. In order to minimize system mass, the only rotatable device is the telescope.

Investigation of unobscured mirror telescope for telecom purposes

The eccentric three-mirror telescope presently proposed for free space optical communications exhibits diffraction-limited image performance for a relatively large field of view, allowing the design of a simpler coarse-pointing mechanism and a wider range for a fine-pointing mechanism without associated losses of antenna gain. Light baffling in this telescope design is excellent, and allows a reduction of stray light to a minimum; its system parameters are less sensitive than those of two-mirror telescopes, allowing looser tolerances and simplifying structural design.