The Near Earth Object Survey TELescope is an astronomical survey and early-warning system for detecting near-Earth objects sized 40 m and above a few weeks before they impact Earth. NEOSTEL is an ESA funded project, starting with an initial prototype currently under construction at OHB in Milan. The telescope is of a new "fly-eye" design inspired by the wide field of vision from a fly's eye. The design combines a single objective reflector with multiple sets of optics and CCDs, giving a very wide field of view. When complete it will have one of the widest fields of view of any telescope and be able to survey the majority of the visible sky in a single night. If the initial prototype is successful, three more telescopes are planned, in complementary positions around the globe close to the equator. In terms of light gathering power, the size of the primary mirror is not directly comparable to more conventional telescopes because of the novel design, but is equivalent to a conventional 1-metre telescope and should have a limiting magnitude of around 21. The project is part of the NEO Segment of ESA's Space Situational Awareness Programme. The telescope itself should be complete by end of 2019, and installation on Mount Mufara, Sicily should be complete in 2020, having been agreed with the Italian Space Agency in October 2018. Development of the telescope was reported as on track in Feb 2019.
Optics
The fly eye aspect of the telescope refers to the use of compound optics, as opposed to the single set of optics used in a conventional telescope. Classically, telescopes were designed around a single human observer looking through an eye piece. As technology has developed astrographs have been used where either a photographic plate or CCD records the image, which a human observer can then view. With the human eye no longer directly observing the image there is no longer a restriction on a single viewing point. Further, as asteroid detection technology has developed, software has become fully automated and no longer requires a human observer to view the majority of images at all. Light enters the NEOSTEL telescope through the aperture and is reflected off the primary mirror onto a beam splitter, which is a hexadecagonal pyramid in shape. The split beam then passes into 16 separate aspheric lenses and on to 16 corresponding CCD image sensors. NEOSTEL uses the 16 CCD cameras to view 45 square degrees of light entering the telescope aperture. The resolution is 1.5 arc seconds per pixel across the whole field of view.
