No. 85 – September 1996 Chilean Senate Ratifies Agreement with ESO Riccardo Giacconi, Director General of ESO On 5 September 1996, the Senate within up to 10 per cent of observing government in direct negotiation with of the Republic of Chile (Second time on all present and future ESO the private claimants. Chamber of the Parliament) approved telescopes in Chile. They also will As part of this Agreement ESO will the Interpretative, Supplementary and have membership on all ESO scien- continue and increase its contributions Modifying Agreement to the Conven- tific and technical committees. Chile- to the development of Chilean astrono- tion of 1963, which regulates the rela- an and European scientific communi- my and the educational and cultural tions between the European Southern ties will henceforth share the impor- development of local communities. Observatory and its host country, the tant scientific discoveries which will ESO is indebted to the Government of Republic of Chile. be made with the VLT facility at Cerro Chile and especially to the Minister of Following formal approval by the Paranal. Foreign Relations, Don José Miguel ESO Council, it is expected that in- By this Agreement the ESO regula- Insulza, and all those who have struments of ratification could be ex- tions for local Chilean staff will be worked towards this Agreement and its changed before the end of this year. modified to incorporate the principles ratification by the Chilean Parliament. The completion of this process is a of Chilean legislation regarding collec- I wish also to recognise the contri- reason for great mutual satisfaction tive bargaining and freedom of associ- bution of all those at ESO who played as the new Agreement consolidates ation. This new regulation will be draft- a role in bringing this about. The ESO the already existing good relationship ed in consultation with a representa- negotiating committee included both between ESO and the Government of tive of the Chilean Government as well previous and present Presidents of Chile, and heralds a new era of co- as local staff representatives. the ESO Council, Professor Franco operation with benefits for both par- Concerning ESO’s juridical immu- Pacini and Dr. Peter Creola, as well as ties. nity on all of the territory of Chile, the many members of the Council. We are The ratification of this Agreement is Government of Chile has indicated to particularly indebted to Mr. Daniel Hof- of particular value for ESO, now en- ESO that these immunities are clearly stadt who has played a continued and gaged at Cerro Paranal in the con- stipulated in the 1963 Convention and significant role in the improvement of struction of the largest telescope of that it is applicable to all properties the Chile-ESO relations. the world, because it signifies a pillar and possessions of the Organisation, Together with all our partners in Eu- of stability for the future activities of wherever they are located in Chile. rope and Chile, ESO can continue en- this Organisation in Chile and thus for Those properties, according to the thusiastically in this new and exciting the development and operation of the Convention, should only be used by scientific adventure of building the VLT observatory into the next century. the Organisation in Chile for scientific Very Large Telescope. All humanity The European astronomical commu- and official purposes. The Acuerdo without regard of national boundaries, nity now has full security that it can reconfirms these immunities and their will benefit from the wealth of new continue to pursue its front-line scien- validity for both, Paranal and La Silla knowledge in the origin and evolution tific investigations in Chile. Observatories. The issue of owner- of the physical universe in which we At the same time the Chilean as- ship of the Paranal site had been set- live, which this powerful new observa- tronomers will have privileged access tled earlier in the year by the Chilean tory will bring about. 1 T E L E S C O P E S A N D I N S T R U M E N T A T I O N The M1 Cell-M3 Tower of the VLT Design Overview and Manufacturing Progress S. STANGHELLINI, ESO Introduction possible when using standard profiles. such that, after manually pre-assem- This possibility is extensively exploited bling the beams, it is possible to weld The primary mirror cell and the prima- in the M1 cell design to generate the them in an automatic mode along the ry support system of the VLT have to ful- variable section profiles used in the 12 seam without any fillet material. A mini- fil stringent requirements. The thin me- radial rafters, and the complicated struc- mum amount of heat is introduced into niscus blank demands a high-precision tures on which the mirror supports are the metal, and the residual stresses are support system and good structural stiff- mounted. The various faces of the struc- low, which is advantageous for the di- ness. Despite its moderate thickness, tural beams and boxes are cut out from mensional stability. the weight of the primary mirror exceeds selected metal sheets in the desired In summary, the laser technology re- 23 tons. To be compatible with the over- shape by a computer guided infrared la- sults in the following advantages for the all VLT telescope design, which has ser beam. The precision of the cuts is design and the construction: been optimised to give a high first eigen- frequency of the tube, the design of the M1 cell must be a light but stiff structure. In addition, the primary mirror support system has to be able to cope with the inevitable deflection associated with the large dimensions. Preliminary studies showed that a space frame of approxi- mately 10 tons weight, together with an appropriate hydraulic support system, would be suitable to support the primary mirror of the VLT. The M1 cell forms part of the sub- assembly called M1 Cell-M3 Tower, and comprises, in addition to the primary cell and tertiary mirror supporting tower, the safety and handling support system of the primary mirror, the cooling system for the primary mirror, and the complete control electronics. In April 1993, following preliminary feasibility studies, ESO awarded com- petitive design and development con- tracts to two European consortia, leading to a complete design of the M1 Cell-M3 Tower, and to a reduced scale mock-up of the M1 support system with actual size prototypes. The design of the French consortium composed of GIAT Industries – Branche Gitech, and SFIM Industries was finally selected by ESO, and a con- tract for the construction of this unit was awarded to the same consortium in Feb- ruary 1995. The major characteristics are described here, together with the summary of the manufacturing status. M1 Cell Design and Construction The design of the M1 cell is based on the possibilities offered by laser cutting and welding technology of which GIAT Industries is a leader in Europe. The technology allows the manufacture of very complicated structures starting from thin metal sheets. It is possible to obtain large beams with very thin walls and internal reinforcements which is not Figure1: GIAT laser welding shop with preassembled parts of the cell. 2 Figures 2a and 2b: The M1 cell. • absence of complex structural • the laser cutting and welding proc- to the telescope at the edge to three an- nodes requiring complicated cuts and ess, being computer controlled, is more nular belts (rings) at the centre. Two of welding, economical for building four units of the these belts are used for the M3 tower • optimum utilisation of the steel with M1 cells than standard construction and its rotating stage, and the third for the use of thin sheets and tapered sec- methods. (See Fig.1.) the Cassegrain instrumentation. All the tions, The M1 cell resembles a truncated assemblies have internal reinforce- • excellent dimensional stability, cone with the upper surface having a ments to stiffen the thin walls. The top • larger internal space for the instal- diameter of approximately 10 m, and a surface of the M1 cell is made of 7 con- lation of equipment and better access thickness of 2.8 m. There are twelve ta- centric rings which have been manufac- than in a conventional space frame pered radial rafters, each of which ex- tured using laser technology and are structure, tends from one of the attachment points used for mounting the axial and lateral Figure 3a: Topology of axial support hydraulic circuits. Figure 3b: Passive axial support prototype. 3 supports. The most external ring is used as base for the lateral M1 supports, while the 6 internal rings, resembling ladders, are used for the M1 axial sup- ports, and for the safety and handling system supports. The thickness of the plates used in the ladders and their cross sections are variable, increasing from the centre to the periphery. (See Figs. 2a and 2b.) The axial supports are positioned in the cut-outs of the ladders by interfaces allowing the fine adjustment of the sup- port position. The position of the cross beams connecting the rafters and con- tributing to the general stiffness of the M1 cell has been optimised, as far as possible, to leave free space for the various pieces of electromechanical equipment. These include the electron- ic cabinets of the M1 Cell-M3 Tower and the Cassegrain instrumentation, and the various hydraulic components of the M1 hydraulic support system. It is worth mentioning here that the final mass of the M1 cell is approximately 10.5 tons, while its first elastic mode, once fully loaded and mounted onto the telescope exceeds 14 Hz.