This work presents a new technological concept for large aperture, lightweight, telescopes using thin deployable active mirrors, currently under a feasibility study for spaceborne Lidars. <p> </p>The study is mainly addressed to a DIAL (Differential Absorption Lidar) at 935.5 nm for the measurement of water vapour profile in atmosphere, to be part of a typical small ESA Earth Observation satellite to be launched with ROCKOT vehicle. A detailed telescope optical design will be presented, including the results of angular and spatial resolution, effective optical aperture and radiometric transmission, optical alignment tolerances, stray-light and baffling. Also the results of a complete thermo-mechanical model will be shown, discussing temporal and thermal stability, deployment technology and performances, overall mass budget, technological and operational risk and system complexity.
New technologies are proposed for large aperture and wide Field of View (FOV) space telescopes dedicated to detection of Ultra High Energy Cosmic Rays and Neutrinos flux, through observation of fluorescence traces in atmosphere and diffused Cerenkov signals. <p> </p>The presented advanced detection system is a spaceborne LEO telescope, with better performance than ground-based observatories, detecting up to 10<sup>3</sup> - 10<sup>4</sup> events/year. Different design approaches are implemented, all with very large FOV and focal surface detectors with sufficient segmentation and time resolution to allow precise reconstructions of the arrival direction. In particular, two Schmidt cameras are suggested as an appropriate solution to match most of the optical and technical requirements: large FOV, low f/#, reduction of stray light, optionally flat focal surface, already proven low-cost construction technologies. Finally, a preliminary proposal of a wideFOV retrofocus catadioptric telescope is explained.
The final optical design for a space-borne light detection and ranging (lidar) mission is presented, in response to the European Space Agency "Advanced lidar concepts" proposal for use of a differential absorption lidar system to measure water vapor distribution in atmosphere at 935.5 nm. The telescope adopts a double afocal concept (i.e., four reflections with two mirrors) using a lightweight and large aperture primary mirror. It is derived from a feasibility study that compares several different optical configurations, taking into account parameters such as cost, dimensions, complexity, and technological feasibility. The final telescope optical design is described in detail, highlighting a trade-off with other solutions and its optical tolerances.
This paper describes an innovative approach for a new generation of large aperture, deployable telescopes for advanced
space LIDAR applications, using the thin active mirror technology. The overall telescope design is presented with a
special attention to the optical performances analysis. The mechanical layout with details of the deployment and baffling
technique is shown; the complete satellite thermo-elastic analysis mapping the primary mirror deformation due to the
thermal loads is presented; the control system architecture is explained and the optical design including the angular and
spatial resolution, effective optical aperture and radiometric transmission, optical alignment tolerances, straylight and
baffling is deeply discussed. Finally an overview of different mission profiles that this technology can satisfy is
presented; the imaging performances can be achieved using the shown technology tuning the surface control to higher
This paper describes the design, manufacturing and test of a ground demonstrator of an innovative technology able to
realize lightweight active controlled space-borne telescope mirror. This analysis is particularly devoted to applications
for a large aperture space telescope for advanced LIDAR, but it can be used for any lightweight mirror. For a space-borne
telescope the mirror weight is a fundamental parameter to be minimized (less than 15 Kg/m2), while maximizing
the optical performances (optical quality better than &lgr;/3). In order to guarantee these results, the best selected solution is
a thin glass primary mirror coupled to a stiff CFRP (Carbon Fiber Reinforced Plastic) panel with a surface active control
system. A preliminary design of this lightweight structure highlighted the critical areas that were deeply analyzed by the
ground demonstrator: the 1 mm thick mirror survivability on launch and the actuator functional performances with low
power consumption. To preserve the mirror glass the Electrostatic Locking technique was developed and is here
described. The active optics technique, already widely used for ground based telescopes, consists of a metrology system
(wave front sensor, WFS), a control algorithm and a system of actuators to slightly deform the primary mirror and/or
displace the secondary, in a closed-loop control system that applies the computed corrections to the mirror's optical
errors via actuators. These actuators types are properly designed and tested in order to guarantee satisfactory
performances in terms of stroke, force and power consumption. The realized and tested ground demonstrator is a square
CFRP structure with a flat mirror on the upper face and an active actuator beneath it. The test campaign demonstrated the
technology feasibility and robustness, supporting the next step toward the large and flat surface with several actuators.
This feasibility study compares several optical configurations for an orbiting high-resolution (<1 m) panchromatic push-broom camera. This is an optical subsystem of the CIA (Camera Iperspettrale Avanzata, Advanced Hyperspectral Camera) project, promoted by the Italian Space Agency (ASI), aimed at high-resolution imaging for applications in Earth observation, mainly for environmental control, geology (especially volcanoes), and coastal and inland water monitoring. The study includes optics and radiometric analyses, used to select a fan of candidate optical configurations, including all the solutions suitable for the specific task, namely, Ritchey-Chretien with and without relay, Korsch, and Schmidt-Cassegrain on axis, off axis, and with relay. The result of a trade-off analysis, considering not only optical performance but also other aspects such as cost, volume, complexity, and technological criticality, shows that the Korsch configuration is currently the best compromise, and it is potentially able to satisfy all project requirements. However, the other configurations have advantages that may be considered in the whole-mission assessment.
High energy cosmic rays and neutrinos may be detected by observing the fluorescence showers induced after interaction with Earth's atmosphere. A high energy cosmic rays observatory would benefit from being lifted into space as a larger portion of atmosphere will be observable. Such a system should have a better performance than existing and future ground based observatories, detecting up to 10<sup>3</sup> - 10<sup>4</sup> events per year. However, only a system with large field of view, and large collecting aperture can achieve the requested high sensitivity and acceptable event statistics. Several optical designs for the optics of a cosmic ray space observatory have been proposed so far. Amongst them, the Schmidt telescope, one of the best known reflectors, well matches both those characteristics, and appears as an appropriate solution to solve the problem.
The Extreme Universe Space Observatory-EUSO-is devoted to the exploration from space of the highest energy processes present and accessible in the Universe. The results will extend the knowledge of the extremes of the physical world and address unresolved issued in a number of fields such as fundamental physics, cosmology and astrophysics. Several kind of detectors have been so far proposed for EUSO, all of them requiring some sort of ancillary optics to collect the light from the image produced by the main optics on the focal surface, for an efficient coupling to the detectors. Optical adapters must be selected taking in account several inputs: feasibility, cost, mass budget. Two main options are here investigated: imaging optics (by means of small lenses) and non imaging optics (by means of compound parabolic concentrators). The first kind of focal plane optics is easy and feasible, but it does not guarantee a high concentration ratio. Non imaging optics present much higher efficiency with a concentration close to the theoretical limit, but it also pose new technological diffculties and challenges. This work aims to clarify how this focal plane optics can be made, their limits in terms of concentration of radiation according to the laws of geometrical and physical optics and finally to identify the possible solution to this problem, including available technologies to be used for the construction.
An optical system consisting of a reflecting mirror with a Schmidt corrector plate is presented as a possible design of a space-based observatory for high energy (up to 10<sup>20</sup> eV) cosmic rays, by monitoring the fluorescence showers induced after interaction by cosmic rays with the Earth atmosphere. An instrument of that kind is currently into the evaluation phase as an external payload for the International Space Station. The basic requirements demand a system with large field of view, up to ±30°, and large collecting aperture, ≥2 m diameter, to achieve a sufficient sensitivity and event statistics. Among several possible optical systems for this purpose, the Schmidt camera is the simplest, matching most of the optical technical requirements, with some problem for the obscuration due to the focal plane at such extreme field of view. This paper presents ray-tracing simulations for different designs of large aperture (> 2m) Schmidt cameras with FOV from 40° to 50°, with F/# ≈ 0.7 and ground resolution from 1 to 2 km from a LEO. Better performances are achieved with an aspheric mirror, but performances using of a spherical mirror are acceptable with some compromise in resolution. The overall geometrical transmission ranges from 40% to 78%, according to the selected geometry and FOV. Possible technologies for the construction of the main mirror and all other components, including supporting mechanics will be also discussed.
UVSTAR, UV Spectrograph Telescope for Astronomical Research operates in the 500-1200 angstrom waveband; it has capability for long slit spectral imaging of extended cosmic sources. UVSTAR has recently flown as a Hitchhiker-M payload on the STS 85 mission of the SHuttle Discovery. UVSTAR is a joint collaboration between the University of Arizona and the University of Trieste. The instrument consists of a movable platform and an optical system The platform provides fine pointing within +/- 3 degrees from the nominal view direction, which is near the shuttle +Y axis, i.e. perpendicular to the long axis of the Shuttle and in the plane of the wings. The optical system has two channels, each formed of a telescope and Rowland concave-grating spectrograph with intensified CCD detector. The first channel, FUV, operates in the 850-1250 angstrom spectral range, the second, EUV, has covered the 500-900 angstrom region. UVSTAR includes capabilities for independent target acquisition and tracking. Here we report FUV observations, obtained in August 1997, of the sdO star BD +28 degrees 4211 which is a secondary flux standard and of the central star of the planetary nebula NGC 246, a hot degenerate star which shows strong OVI lines in the optical region. The UVSTAR spectrum of NGC 246 displays remarkable P Cygni profiles indicating a very fast stellar wind.