1. focal plane & Fiber positioning robot system for LoRCA 1.Schmidt optics data sheet (approach). 2.Focal plate. 3.Positioner pre-design, Focus mechanism. 4.Auto guiding telescopes, Auto guiding CCDs on focal plane. 5.Field view camera. 6.Trade-Off Studies. Interfaces By Justo Sanchez Instituto de Astrofísica de Andalucía (CSIC) Granada, Spain Marc Dubbeldam Centre for Advanced Instrumentation Durham University, UK

2. Schmidt optics data sheet (aproach). The Schmidt telescope at Calar Alto Observatory, was installed there in 1980by the Max Plank Institut für Astronomie¨, Heidelberg; originally it had been operational at the Hamburg Observatory since 1955. Look at the adapted piece to adapt the different latitudes

3. Schmidt optics data sheet (approach). Corrector Schmidt (Firs lens): It is 80cm diameter lens in UBK/ Schott glass. UBK7 is like the standard BK7, but red extended to 300nm to the UV (BK7 goes to 350nm). The infrared cut it is at 1500nm for booth glasses. Then transmissions are guaranteed from 300nm to 1500nm The distance from corrector (Ø80cm) to primary mirror (Ø120cm) is “deduced” knowing the FOV=8⁰, and compatible with: FOV=8⁰ or 33,5cm Focal =F3 or aperture angle of ≈19⁰ Distance primary to focal plane =240cm Radius of curvature primary =480cm Radius of curvature focal plate=240cm

4. Schmidt optics data sheet (approach). The second optical element is a concave spherical mirror: 120cm diameter, the primitive radius of curvature of this sphere is 480cm. BUT has not a central hole. The reflectance layer is made in aluminum with good transmissions from 350nm to 1500nm.

5. Focal plate The nominal Focal plane is a spherical circular casquette (Sphere radius 240cm) of 33,5 cm diameter. That’s means the light rays arrive perpendicular to this casquette, and the actuator need to be perpendicular to the sphere surface. In the past the Schmidt was used with square photographic plates of 24cm side, then the glass photo plate must be curved, inside a cassette that replicate the nominal sphere curvature. The focus mechanism has three part: A. a moving part (containing the cassette), width ≈9cm B. a fixed part that contains the motors to focus, width ≈8cm C. a baffle structure that support the two previous parts and it is attached to the spider plate, width ≈9cm 1: cassette width ≈ 28cm 2: cassette height ≈ 4.5 cm 3: distance from focal plane to fixed part of focus mechanism ≈ 9cm 4: focal plane approximately. 5: distance from moving part of the foc. mech. to the baffle structure ≈ 8cm In the fixed part of the focus mechanism, we can see that there is a “distances measure indicator”. For visual adjustment.

6. Focal plate The baffle structure is square, made in plastic or hard paper (6), we can only “speculate” that serves to protect the internal rails that permits the fine movement of focus mechanism. This structure is attached to the spider plate (7) Is essential to gain space in the back focal plane, to accommodate the actuators and fibers. We need to remove, and redesign : ---the moving and the fixed parts of the focus mechanism…… gain ≈ 17cm ?? ---the moving, the fixed and the baffle parts………………….…….gain ≈ 26cm ?? The spider it is formed by 4 metal plate in the tube of the telescope that are “apparently” soldered to a spider plate (7) that “we think serve to support the three parts of the focus mechanism” spider plate

7. Focal plate The 33.5cm diameter curved focal plane permit to place different numbers of actuators depending of the actuator diameter and package used. A simulation is done to give us some idea Number of actuators in Schmidt telescope, assuming our actuatorsand the AVS NEW V1 and V2 SIDEBigBossDESIAVS NEW V1AVS NEW V2 patrol area (mm) Diameter33,7213,85612,00817,7816,62 pich (center-center) (mm)29,21210,415,414,4 focal plane side (mm) **300 actuators / side *10,2725,0028,8519,4820,83 nº actuators (X/Y array) *105,55625,00832,10379,49434,03 nº actuators (hexag.packa.) *101,57601,41800,69365,17417,64 In V2 the motors are joined and the central fiber is displaced Like DESI *of course decimal are not realistic situation. **to acomodate the focal mechanism SIDE BigBoss DESI AVS-NEW V1 X_Y package Hexagonal package For X-Y package the FOV is the 96%, due to dead area between actuators. For hexagonal package, the Field Of View (FOV) to position the fiber is the 100% (no dead area between actuators).

8. The proposed actuator must be short, to permit to curve and to twist the fibers in relaxed curvature radius. Because we need to remove and redesign the focus mechanism, we propose not reduce the maximum FOV of 335 cm, and re-design a new at the back focal plate. The auto-center / auto-guiding CCDs might be inside of the maximum FOV. A pseudo-hexapod with three moving points can resolve focus and tip-tilt defocus on the focal plate (proposed by Marc Dubbeldam, Centre for Advanced Instrumentation, Durham University, UK) Positioner pre-design, Focus mechanism

9. The Schmidt The telescope provide two guiding cameras in two auxiliary north-west and south-east of the main tube, with these the RMS auto-guider error is 0.56 arcsec for RA and DECLINATION and star <=11 magnitudes. This error can be considered 1/10 of the minimum fiber diameter, assuming all the other errors (actuator repeatability, position error of the object in sky, and systemic error) are smaller than 0.56 arcsec or 6.5μ Because the telescope scale it is 86.2”/mm or 11.6μ/” the minimum fiber diameter correspond to 5.6 arcsec or 65 μ Auto-guiding telescopes South east auto-guiding telescope Auto-guiding CCDs on focal plane Also we need some auto-center and auto-guiding CCDs inside the focal plate, the idea is to have the maximum of bright stars on some/all of these CCDs working at same time: 1-To focus the focal plane, that depend of temperature, RA and DEC of telescope, etc 2- To measure the plate scale, that depend of the same parameter. 3- To measure the small residual rotation angle of the north- south axis telescope respect to Sky N_S. 4- To measure and control of the Absolute atmospheric refraction, that depend of paratactic angle, atmosphere, etc 5- Auto-guide with more precision that the auto-guiding telescopes Focal plane with 4 CCDs (inside) would be enough?? in positions North, South, East, West. (Front view of projected SKY, up to north telescope)

10. To assure the final position of each fiber in front of the object we need a Fiber view Camera placed (if it possible) in the central position of the 1,2m mirror (but no hole), the fibers are illuminated by the spectrograph, and the FVC take a image of those fibers and too of the other fixed fibers in the plate called fiducial fibers number??. The software make calculi of difference to the perfect position and send movements to the actuators in some iteration, just to be sure the positions of the fibers are inside the required error. Problems: The primary mirror has not a central hole. Field View Camera (FVC) Solutions: we plant several, briefly (sure more) : 1 To put the FVC in a spider centered at the spherical primary mirror level→ means a few vigneting for the external part of the FOV lateral, 2 To put a curve mirror in a spider centered at the spherical primary mirror level and to reimage in a FVC placed in the center of the focal plane → means: a few vigneting for the external part of the FOV lateral, is a symmetrical solution, NOT CENTRAL IFU available 3 To put a curve mirror in a spider centered at the spherical primary mirror level, but tilted to reimaging in a FVC placed in the exterior area of the focal plate → means: a few vigneting for the external part of the FOV lateral, image of focal plate not to the same scale, non- symmetrical solution (software compensation), PERMIT CENTRAL IFU 4 To place the FVC at the level of the corrector lens, but looking to the primary mirror. This is possible because the natural aperture of the fibers (NA=0.22 → F2.27 → aperture angle of 25.2⁰) this is more or less similar to the F3 of the telescope, of course the fibers are retro- iluminated by the spectrograph side. → means: some vigneting, image of focal plate not to the same scale (software compensation), this is a non-symmetrical solution, PERMIT CENTRAL IFU Continued next slide

11. Continued previous slide The idea is to mount a small mirror at 45⁰ in the internal part of the corrector lens, that receive the light of the focal plate fibers (actuators + fiducial fibers) and illuminate a perpendicular to axis telescope camera, with a F4.5?? to see all the primary mirror.?? Field View Camera (FVC) Corrector lens, from inside telescope 6 The ideal solution it is to be sure the actuators can work in open loop inside the pointing absolute requirement (6.5μ!!!), which means certify in the lab that each XY send to a “repetitive actuator” is corrected by each pointing correction matrix, that know the particular offset for each actuator for a specific XY. TOO MUCH WORK IN THE LABORATORY. IF FINALLY WE ARRIVE TO HAVE A ABSOLUT REPETITIVE ACTUATOR STABLE IN TIME, TEMPERATURE, GRAVITY, FIBRES FORCES, AND MORE PARAMETERS. 5 mount a circular retractable structure, that move the FVC just in front of the Focal plate, the fiducially can compensate the possible repositioning error of the camera, by software. (proposed by Marc Dubbeldam, Centre for Advanced Instrumentation, Durham University, UK)

12. Trade-Off Studies Multiplex - observing efficiency vs. cost. Actuator control - open loop vs. closed loop:- – Open loop using stepper motors: can the required accuracy be achieved? – Closed loop using servo motors: requires encoders (costly?) or focal plane viewing camera. Viewing camera cannot achieve required resolution in single exposure - scanning mechanism required. Fibres have to be back-illuminated. Reference points (fiducial fibres?) required in focal plane. Acquisition and guiding:- – Telescope has auxiliary guide scopes. ! FLEXURE ! – Auxiliary cameras in focal plane: how many needed to provide sky coverage? Active focal plane (tip/tilt, focus) required?

13. Trade-Off Studies (cont’d) Mechanical interface with telescope:- – Interface with existing spider: Severe space restrictions (depth) necessitate new pick-off design and may lead to more expensive, sub-optimal focal plane design. “Messy” interface: mounting provisions may be in awkward locations, fibres and electrical harness needs to be routed in-situ, etc. Restricted working space inside optical tube would make installation extremely challenging. – Replace existing spider with new support structure: Flexibility w.r.t. accommodating existing pick-off design. Nice “clean” interface: fibres and harness can be pre-routed with connectors in convenient locations. However: – ! Implementation requires removal of primary mirror ! – ! New structure needs to be lifted into optical tube - access required through hinged corrector assembly ! – ! Work to be carried out at approx. 6 m height above floor - Health and Safety ! !!! Need mechanical drawings for Schmidt optical tube assembly !!!

14. Interfaces Optical:- – Telescope focal plane: convex, spherical surface, 2400 mm radius, 8 deg. (Ø 335 mm) corrected Field of View; Stability, distortion, atmospheric refraction / dispersion, etc. – Acquisition and guide cameras; Field of View, optimum location, etc. – Fibre output. Break-out panel with connectors on side wall of telescope. Mechanical:- – Interface with telescope: need drawings for Schmidt optical tube assembly. Electrical:- – Actuators; – Acquisition and guide cameras; – Tip/tilt & focus mechanism. Software – Focal plane configuration; – Acquisition and guiding; – Focal plane control (tip-tilt & focus). ! Need to define interfaces as soon as possible !