The operational support and service for observatories aim at the provision, the preservation and the increase of the availability and performance of the entire structural, mechanical, drive and control systems of telescopes and the related infrastructure. The operational support and service levels range from the basic service with inspections, preventive maintenance, remote diagnostics and spare parts supply over the availability service with telephone hotline, online and on-site support, condition monitoring and spare parts logistics to the extended service with operations and site and facility management. For the level of improvements and lifecycle management support they consist of expert assessments and studies, refurbishments and upgrades including the related engineering and project management activities.
The performance of single dish radio antennas or telescopes is depending on the surface accuracy of the reflectors in the
beam path and the focus/pointing errors induced by deviations/misalignment of the reflectors from a desired direction.
For multiple dish VLBI arrays an additional mechanical effect, the path length stability, is a further source of performance
degradation. For application at higher frequencies environmental influences as wind and temperature have to be
considered additionally to the usually required manufacturing and alignment accuracies. Active measurement ("metrology")
of the antenna deformations and their compensation by "active optics" (AO) respectively "flexible body compensation"
(FBC) are established methods. For the path length errors AO or FBC are up to now not established methods. The
paper describes how to handle the path length errors and the related metrology analogues to the established methods used
for surface and focus/pointing error corrections.
The first European ALMA production antenna is in the final stage of manufacturing and pre-assembly. Precommissioning
of parts of this antenna will start soon. The series production is partly ongoing or in the final stage of
preparation. Design features of the European ALMA antennas w.r.t. to manufacturing, assembly and integration in
Europe and on site, the status of the manufacturing works and
pre-commissioning are presented. An outlook to the next
steps of the realization of the antennas is given.
The optical performance and pointing accuracy of the 1.5 m solar telescope GREGOR depend on the passive and active temperature control design features. Stringent thermal requirements are given in the technical specification for the passive thermal control of telescope structure and the main mirror air cooling system under operational conditions. The telescope structure has to be kept within a range of -0.5K through +0.2K against the ambient temperature. The main mirror temperature has to be kept up to a temperature difference of less than 2K under the ambient temperature with an accuracy of ±0.1K. The temperature difference across the main mirror surface has to be smaller than ±0.1K. Another thermal requirement asks for a main mirror safety cover to prevent the wandering of focused sunlight over the telescope structure in case of control system malfunction or power loss. Features of the chosen passive thermal concept for the telescope structure and the active main mirror air cooling system as well as the primary mirror safety cover system are presented together with the finite element analyses results and tests performed in order to find and verify the chosen design.
Presently the ground-based High Energy Stereoscopic System (H.E.S.S.) with 12 m Cherenkov telescopes is used for very high energy gamma ray astronomy. With these telescopes the Cherenkov light which is generated when cosmic gamma rays are absorbed by the atmosphere is collected by the mirror dishes of these optical telescopes and recorded by digital cameras for further examination. This existing H.E.S.S. Phase I system in Namibia erected and operated by the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany, uses four 12 m telescopes arranged in the corners of a 120 m square for best sensitivity. The next step in order to increase the exploitation of the gamma rays in the atmosphere is to use bigger Cherenkov telescopes with a lower threshold and improved sensitivity. In this paper the results of a feasibility study on the design of Large Cherenkov Telescopes with diameters of up to 30 m are presented. The feasibility investigations done by MAN Technologie in Mainz, Germany had to take into account the required mechanical performance, costs, and local fabrication and erection capabilities of the countries in which the telescopes should be erected.
The optical and thermal design of the 1.5 m solar telescope GREGOR is presented. The three first main mirrors of GREGOR will be made from Cesic, a silicon carbide material. One major constraint of large solar telescopes is the thermal load of the structure and the mirrors. The mirrors are heated by the solar radiation and introduce potentially harmful mirror seeing. GREGOR will use an active mirror cooling system and an open telescope structure to reduce these negative effects. A thermal analysis shows that the equilibrium temperature of the Cesic Mirror without active cooling is 6° above ambient temperature. Additional cooling will reduce the temperature difference of the optical surface and ambient air to below 0.1° K. With tempered airflow (about 2.5 m3/s per square meter mirror surface) the temperature gradient on the surface of the face sheet is less than 0.1°K. The telescope will have an open structure and a complete retractable dome to support mirror and structure cooling by wind.
The operational wind speed for the 1.5 m solar telescope GREGOR which will be erected in 2004 on the Spanish island of Tenerife is specified at 20 m/s. At this wind speed the seeing conditions at the telescope site are good for observations of the solar physics and the effects of internal seeing will be minimized by the wind blowing through the largely open telescope structure. The requirements for an absolute pointing accuracy of 1 arcsec rms and for a relative pointing error of 0.25 arcsec rms have to include the wind load influences. In this paper the numerical analyses of the structural response under static and dynamic wind loads and their impact on the telescope design are presented. For the analyses a response spectrum method using a finite element program system and a time history simulation including the servo system were utilized. For the analyses and simulations detailed finite element models of the telescope were used. The dynamic wind loads on the structure were calculated using a wind turbulence spectral density function and simulated wind speed time histories including site-specific wind characteristics. A pointing model taking into account the displacements of the telescope's mirrors with respect to the adjusted configuration was included in the investigations.