1. HEGRA HESS I HESS II 10m 2 108m 2 600m 2 Personal view Stimulate a discussion

2. HEGRA

3. Air shower experiment > 6 different detector types (particles and gammas) Imaging air Cherenkov telescopes seemed finally to be the most promising detectors Partly combined Very good for evaluation of different techniques From first telescope (6m 2, 19pixel) Stereoscopic system with 5 identical telescopes (10m 2, 271pixel)

4. HEGRA HESS

5. HESS I Dedicated experiment on γ-ray-astronomy in the energy range of TeV Wide field of view Southern hemisphere Stereoscopy with 4 identical telescopes

7. HEGRA => HESS I Local crew Constant maintenance and fast repair Well prepared campaigns Clear and precise specifications Good balance in performance of telescope components Optimum on performance for money Precise specifications save a lot of money Dedicated site under our control (including all the infrastructure) Large site => flexibility No interference with other experiments in the region Political problems successfully solved for Namibia Better monitoring of internal conditions (bending, pointing…) and external conditions (weather…)

8. Professional help on engineering Experience in industry with antennas up to ~60m Ø dishes with better precision than is needed for Cherenkov telescopes Why reinvent the wheel, even if it might be fun Available and reliable technology = focus on physics 1.Concrete foundation 2.Steel work (cut and welds) 3.Mechanical engineering (bearings, drives, safety) Minimize need for human intervention A stiff and robust dish Simple maintenance, little adjustment work How well do engineers understand their design?

9. Our approach to HESS I (and now HESS II) Design studies (realization of our wishes, feasibility, cost estimate, steps in size which costs) Engineers prepare tender on a structure (mount + concentrator) bmechanical engineering Engineers help in the approval of technical components and their assembly Tracking Design of mirrors and adjustment mechanics + quality control + installation + adjustment Collaboration Industry Responsibility on the realisation stays with the collaboration

10. HESS I HESS II

12. HESS I => HESS II Improvements in some details Different company for engineering Tracking and safety concept by industry (only an adaptation of a standard industry product) No principle change in the approach Drive system (biased, tooth wheels in elevation) Mirror adjustment (closer to dish) The current design was chosen from two studies

13. HESS I Schlaich Bergermann & Partner Solar dish technology Improve by x10 HESS II MT-Aerospace (former MAN technology) Radio telescopes technology Relax by x10 DRIVES! (biased, gear box)

14. Structure (mount, concentrator) Mechanical engineering Mirrors Mirror adjustments Steel Bearings Drives Stiff dish, adjust rarely Aluminium as reflecting material Coating?? thickness of aluminium, quartz? Cleaning?? quartz coating is fragile Aging?? (~3%/a, dependent on the manufacturer) HESS I has friction drive HESS II has tooth wheels Standard items (Precisely defined Well controlled by engineers Fabrication with local companies)

15. Conclusions Dedicated large site Local crew Engineering for engineers Rely on available technology Be ready for new technology Do physics

17. Assembly of first telescope

19. Die H.E.S.S. Teleskope (2003)