SOAR Top-level telescope & facility requirements Revised Draft of 10/1/97 1. Baseline configuration The basic design of the SOAR telescope is Ritchey-Chretien at f/16 on an alt-azimuth mount. The principal foci will be at the two Nasmyth locations, requiring three reflections. Both foci will have an instrument rotator and acquisition/guider (A/G) unit. Two different instrument modules will be # provided: one has a goal to accept the space/mass envelope of a single Gemini instrument, the other will have provisions for # mounting up to three less massive instruments in a co-rotating cluster. # The telescope is required to support at least 1500 kg of # instruments at each rotator flange, with a goal of 2200 kg. The telescope will be bilaterally symmetric up to the two instrument rotator flanges, so at some future time the two modules could be mixed or matched to mount e.g. either two Gemini instruments or two co-rotating clusters with up to six smaller instruments. Switching between foci will be accomplished by rotating the tertiary mirror (M3) to index positions to feed the beam to the desired Nasmyth focus. The 3-instrument cluster will allow rapid switching between each instrument while sharing guide and acquisition functions. Each of the two A/G's will be compatible with an upgrade to a CFHT-bonette-style AO feed. The telescope enclosure will co-track the telescope in azimuth during observations. It will be designed to take best advantage of the expected excellent site and to contribute minimal "dome seeing" consistent with the allowance in the error budget. The enclosure will also shelter the telescope from dust and inclement weather. The telescope facility building will house the equipment needed to operate and maintain the telescope, a control room, and instrument storage and preparation areas. 2. Other facility elements 2.1 Provision for Bent Cassegrain Foci [G] As a goal, provision will be made for 3 bent Cass. foci located on the elevation structure. Provisions include a clear light path to the foci, provisions for indexing M3 to feed the telescope beam to the foci, and provisions for mounting instrument rotators at the foci. Rotators, guiders, etc will not be provided. Four reflections may be required to access these foci. Bent. Cass. payload: 300 kg 2.2 Provision for 4-mirror Cassegrain focus [G] As a goal, provision will be made for a 4-mirror, straight-through Cass. focus. Provisions for removing M3 from this beam, a TBD volume in the mirror cell, and provisions for mounting an instrument rotator at this focus will be provided as a project goal. Rotator and guider would not be provided, only a mounting flange. 2.3 Provision for coaxial laser launch telescope The enclosure will be sized and the telescope top end will be designed in such a way that a small coxaxial laser launch telescope may be implemented in the future. Such implementation may require replacing a large portion of the top end. Maximum launch laser tele. length: 0.5 m mass (estimated): 100 kg 3. Safety Working around an observatory inherently involves risks associated with large moving equipment, high platforms and ladders, etc. All parts of the telescope and facility will be designed to promote safety to personnel and to delicate equipment and to conform to safety policies currently in effect at CTIO. 4. Environmental: The telescope will meet all performance specifications throughout the following range of environmental conditions: 4.1 Normal operations: under these, telescope+enclosure are required to produce at most 0.18" FWHM image degradation Temperature: -1 to 20 C dT/dt <1.5 C/hr [value for 80% of time 8pm-6am, Pachon 88-92] RH 0 to 95% non condensing steady wind <10 m/s [80% of operating time] peak gusts <15 m/s 4.2 Marginal operating conditions: goal will be to maintain same tracking & pointing performance as in previous section. Temperature -10 to 25 C dT/dt <2.5 C/hr [90% of time 8pm-6am, Pachon 88-92] steady wind <20 m/s [45 mph] peak gusts <25 m/s dome shut >20 m/s steady (dust control) 4.3 Non-operating survival conditions: Temperature -25 to 30 C occasional exposure to condensing conditions wind gusts to 150 mph (67 m/s) lightning strikes rain, hail, snow earthquake to 0.4g, 3mm amplitude [based on Magellan spec, ESO spec is 0.34g] 5. Image budget: 5.1 Core d50 encircled energy: The image size budget sets the goals for the telescope in the absence of atmospheric effects and instrument degradation, and pre-allocates limits to the sources of image degradation to guide the design of the telescope and enclosure. Image sizes are specified in arcseconds FWHM. Depending on the shape of the point spread function, these units may or may not be easily converted to a measure of enclosed energy. Assuming a Gaussian profile, an image 1.00 arcsecond FWHM has a 1.18 arcsecond rms diameter (63% enclosed energy) and concentrates 80% of its energy in 1.52 arcseconds. The required image size budget, averaged over a 15-arcmin diameter field is 0.18 arcseconds FWHM contribution from the telescope and enclosure, including the effect of aperture and azimuthally averaged spider diffraction. The diffraction is evaluated at a wavelength of one micron. The field is flattened and corrected with a 2-3 element refractive corrector whose residual optical aberrations throughout the waveband 340 to 1000 nm are included as a term in the 0.18 arcsecond budget. This goal is chosen to degrade the top quartile seeing FWHM of the site by no more than 40% The contribution to image size from seeing is not included in this table, but grows as (cos z)^-3/5 where z is the zenith distance. The total image budgets for the telescope and enclosure are allowed to increase from the zenith according to the same law, thereby keeping the relative contributions the same. 5.2 Scattered light requirement: Optics will be finished to the highest degree of smoothness on relevant angular scales that is cost effective. In addition, the optics will be maintained at a high level of cleanliness and provided with stray light rejection baffles. (see sections 16 and 19.3). 6. Telescope Requirements 6.1 Axis motion: Azimuth: +/- 270 deg Zenith angle, observing: 0.4 < z < 75 deg (i.e. within 15 deg of horizon) Zenith angle, hard stops: -2 and 90 deg Zenith angle, shock absorbers: 0 and 88 deg 6.2 Zenith blind spot: 0.8 deg diameter max. Program interruption at transit:3.2 minutes max 6.3 Slewing: Maximum slew rate: 3 deg/sec. Slew ramp: 1 deg/sec^2 Time for track to track: 100 sec. max, <360 deg azimuth rotation. 6.4 Pointing accuracy: Blind, all sky <2 arcsec rms <0.5 arcsec rms [G] Offsets < 1 degree: <0.2 arcsec rms Offsets within 15' guider fov: <0.1 arcsec rms Blind pointing accuracy in general requires approximately 10 minutes overhead at the start of each night. This procedure may need to be repeated after reconfiguring the telescope to access the bent or 4-mirror Cass port use. 6.5 Track rates: Maximum track rate: 0.5 deg/sec. Track ramp: 0.1 deg/sec^2 max. Settling time between slew and track: 30 sec max. 6.6 Tracking accuracy: Open loop (blind): <0.1 arcsec rms image jitter (after the drift is removed) Open loop drift: <0.1 arcsec per minute # <0.1 arcsec per 10 minutes [G] Closed Loop (Guided): <0.1 arcsec. rms image motion for 1 hour. # Drift due to telescope/guider # flexure: <0.05 arcsec image motion # over 1 hour 7. Specification of foci 7.1 Nasmyth and bent Cass foci: Focal ratio: f/16 Plate scale: 3.22 arcsec/mm Nominal field of view: 15 arcminutes unvignetted Linear field: 279 mm diameter Field radius of curvature: ? meter Central 7' can be used with 1.924 m curvature compatible with Gemini Distance to exit pupil: TBD 7.2 Four mirror Cassegrain focus [G] Focal ratio: TBD Nominal field of view: TBD 8. Instrument rotators 8.1 Nasmyth instrument rotators Availability: Provided on both Nasmyth foci Weight capacity: 2800 kg with CG 2000 mm from flange Rotation range: 360 deg Rotation rate: -5 deg/sec. to +5 deg/sec. Ramp rate: -1 deg/sec^2 to +1 deg/sec^2 Accuracy (open loop): <0.02 arcsec at edge of 15'-diameter field on sky 8.2 Cassegrain instrument rotator Weight capacity: 400 kg with CG 800 mm from flange Rotation range: 360 deg Rotation rate: -5 deg/sec. to +5 deg/sec. Ramp rate: -1 deg/sec^2 to +1 deg/sec^2 Accuracy (open loop): <0.1 arcsec at edge of 3' diameter field on sky 9. Instrument interface modules (A/G units) 9.1 Nasmyth instrument cluster: Mounting surface: A/G unit flange # Back focus distance: 200 +/- 0.6 mm nominal # One Instrument weight: 500 kg, 730 kg max [G] Cantilever: CG at 1000 mm from flange (max) Instrument envelope: a rhomboid, crudely 1.5 m L. x 0.6 m D 9.2 Gemini compatible Nasmyth: Mounting surfaces: A/G unit flanges Back focus distance: 300 mm +/- 0.6 mm nominal # Instrument weight: 1500 kg min, 2200 kg max [G] Cantilever: CG 1000 mm from flange Instrument envelope: 3 m L. x 2.0 m D ``Gemini shape" [G] GIRS + its electronics is requirement Imbalance about axis: TBD 9.3 4-mirror Cassegrain port: [G] Mounting surface: TBD Back focus distance: TBD Instrument weight: 200 kg max. Cantilever: 500 mm from flange Instrument envelope: 1.0 m L x .6 m D [TBD] 9.4 Bent Cassegrain port [G] Mounting surface: TBD # Back focus distance: TBD Instrument weight: TBD Cantilever: 500 mm from flange Instrument envelope: TBD 10. Instrument utilities Requirements for power, data LAN, gasses, vacuum, waste heat extraction, and cabling at the various scientific instrument locations. 10.1 At the Gemini-compatible Nasmyth module: 10.1.1 Gases & coolant: Helium for cryocoolers: TBD liters/minute at a pressure of TBD. Return line at TBD pressure. Purity 99.999%. 100 psi clean compressed air Coolant: TBD liters/min at TBD pressure. Return line at TBD pressure 10.1.2 Power: Dirty power: 220V/3Ph, 50 Hz, TBD Amps Clean power: 110VAC, 50 Hz, 20 Amps # Max instrument power # dissipation: TBD 10.1.3 Signal lines: Video LAN: TBD, US HDTV compatible Data LAN: TBD Control LAN: 100+ MB/s fibernet Time LAN: TBD, GPS receiver Synchro Bus TBD Event Bus: TBD Interlock System: TBD 10.2 At the 3-instrument module: A goal is to provide all of the Gemini utilities as well as dry N2. The required gasses and coolant are: 10.2.1 Gasses and coolant: Dry filtered N2: 10 cfh at 5 psi. Coolant (piping only): 2 lines, 0.38" ID Connection to a waste heat scavenge will be provided. 10.2.2 Power: Dirty power: 220V/3Ph, 50 Hz, TBD Amps # Uninterruptible clean power: 110VAC, 50 Hz, 20 Amps # Max instrument power # dissipation: TBD 10.2.3 Signal lines (from computer room): # Control: Serial, TBD number Data: Optical fiber, number TBD. Coaxial cable, number TBD. # Video acq./guide/wavefront: Serial, TBD number Camera gain: Four twisted pairs. 11. Acquisition & guidance 11.1 Nasmyth AG units Two A/G units are required; one for each Nasmyth port. One is required to support a single large Gemini instrument; the other will support three smaller instruments with provisions to switch the beam between instruments. Both guiders will perform the functions of target aquisition and closed loop guiding, wavefront sensing for active optics control, and active collimation. General requirements for either A/G: Weight: 800 kg 11.1.1 Acquisition/guider: Number: Two probes. Sensor types: TBD (Intensified CCD?), IR sensitivity TBD Field of view: 10 mm (32 arcsec at f/16). Sensitivity: Centroid to 10% of seeing disk at mv=18 @ 1 Hz. Update rate: 0.1 Hz. to 1 Hz. Wavelength selection: TBD, provision for filtered photometric calibration [G] 11.1.2 Wavefront sensor: Faint limit: mv = 16 mv = 20 [G] Integration time: 30 seconds. Program interruption for on-axis correction: <4 minutes including active correction after taking & processing 3 x 30 sec integrations. Update frequency: >30 minutes for on-axis correction but can operate continuously in a differential mode when offset from the field center. 11.1.4 Rapid guider (Tip/tilt guider) Update rate: ~100 HZ [TBD] Faint limit: TBD Sensor type: TBD Sensor wavelength range:TBD 12. Focus monitoring & control A TBD means of sensing & correcting focus errors that are induced by the telescope and enclosure. May best be done w/ on-instrument WFS [G] 13. Field corrector Optical config.: TBD Location: in light path to Nasmyth instrument cluster Field size: 15 arcminute. Design wavelengths: 3400 A - 1.1 micron. Set-up time: 30 seconds. Time to insert: 30 seconds, remote control. Usable with field acquisition and guide cameras, wavefront sensors, ADC 14. Atmospheric dispersion compensator Type: TBD Operating range: 0 to 65 deg zenith distance, 70-75 deg [G] Design wavelengths: 3400 A - 1.1 micron. 15. Tertiary rotator Description: Rotates M3 about the primary optical axis to direct the telescope beam to one of two Nasmyth ports or three auxiliary folded Cass. ports. Number of positions: TBD, 5 [G] Time to beam switch: <1 minute for 180 deg switch. Repeatability: <0.5 arcseconds on sky after motion <0.1 arcseconds " [G] The required telescope blind pointing accuracy may not be attained on the first exposure after M3 rotation. The offsets derived from this exposure will be used to update pointing so that subsequent exposures will meet the pointing spec. 16. Baffles The telescope will be provided with comprehensive baffles and light- absorbing material to eliminate light paths from the focal plane to the night sky or inside of the dome. These will be designed to provide optimal scattered light rejection with minimum obscuration. Obscuration: <4% [G] A goal is employ diaphragm-like baffles in the M3 chimney and elsewhere, which could reduce scattered light when the full telescope field is not in use. 17. M1 cover Description: Seal primary mirror against dust when closed. Protect against blunt impacts of < 20 kg-m/s. Present minimal cross section for wind shake. Allows good air circulation over the primary mirror. 18. Great white spot [G] Description: A screen and illuminating lamps covering the full aperture of the telescope for routine recalibration of the instrumental response over the full field of view. Two banks of flat field lamps will be provided: a high intensity set for quick exposures and a continuum set with color balance filters. 19. Servicing & Maintenance [G] 19.1 Typical time for routine periodic operations: Remove or install primary mirror: <7 hrs Remove or install secondary mirror: <2 hrs Remove or install tertiary mirror: <2 hrs Mount & cable instrument at: <2 hrs Collimate telescope: <7 hrs 19.2 Time to perform servicing and maintenance operations: Service/replace dome truck or drive: <7 hrs Replace shutter drive: <7 hrs Replace telescope encoder & electronics:<7 hrs Replace telescope drive & amplifier: <2 hrs 19.3 Optics cleaning Provisions will be made for regular CO2 or other cleaning of M1 and smaller optics. Manual cleaning is a baseline requirement with automated cleaning as a project goal. A goal is to clean as often as required to ensure that dust scattering does not limit telescope photometric performance. Time to clean telescope optics: 30 mins