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HET & SALT-Type Telescopes

HET & SALT-Type Telescopes. The Hobby-Eberly Telescope. The HET in Texas:. 27-m Mirror Alignment Tower. 26-m Diameter Dome. Tracker Beam. Telescope Structure. 11-m Primary Mirror array. Dome Opening. Control & Service Building. Telescope azimuth rotation bearing.

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HET & SALT-Type Telescopes

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  1. HET & SALT-Type Telescopes

  2. The Hobby-Eberly Telescope The HET in Texas: 27-m Mirror Alignment Tower 26-m Diameter Dome Tracker Beam Telescope Structure 11-m Primary Mirror array Dome Opening Control & Service Building Telescope azimuth rotation bearing Fibre-Coupled Instrument Room 10 metres

  3. 10 metres The Hobby-Eberly Telescope • Primary mirror is 91 identical hexagonal spherical segments of about 1-m each. • Primary mirror is moved only in azimuth, not elevation. • Prime focus payload moves to track the stars. Prime focuspayload 11-m Primary Mirror array

  4. The Arecibo Radio Telescope

  5. The Arecibo Concept: Star moves E to W on sky Centre of curvature at radius of primary mirror Fixed elevation spherical mirror telescope with tracking on focal surface (Arecibo is a radio telescope which first used the idea of tracking objects by moving the prime focus payload rather than the primary mirror). Spherical focal surface: 1/2 of primary mirror radius Tracker follows focus of star. It carries a payload consisting of optics and instruments. Image moves W to E on the focal surface Although pictured looking straight up (i.e. at the zenith), HETis in fact tilted 35º from the zenith. Spherical Primary Mirror

  6. How the telescope tracking works Tracker centred and pupil centred on primary mirror array. Full 9.2 metre collecting area. Tracker off-centre and pupil partially on primary mirror array. At worst extreme, still a 7 metre telescope! Part of pupil off mirror is baffled at exit pupil position

  7. SALT Payload • Prime Focus Payload (~950 kg) mounts on the tracker hexapod: • Prime Focus Imaging Spectrograph (PFIS), now called RSS, the Robert Stobie Spectrograph • SALTICAM acquisition and science camera • Spherical aberration corrector

  8. SALT Payload Details: • Prime Focus Payload (~950 kg) mounts via hexapod to tracker bridge and comprises: • Prime Focus Imaging Spectrograph (PFIS/RSS) • Acquisition camera • Guidance & focus • System • Optical fibre feed • Pupil baffle • Atmospheric dispersion corrector (ADC) • Spherical aberration corrector • Calibration system • 4 instrument foci fed by 45 deg “fold” mirrors

  9. Guide & focus probes Auxilliary instrument Fibre feed Acquisition camera Exit pupil baffle Atmospheric Dispersion Corrector SAC structure

  10. Payload structure (rotating & non-rotating components) made of carbon composite Dummy PFIS/RSS mass Instrument rotator ring Hexapod legs SAC Tracker beam

  11. The END

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