The Blanco Environmental Control System Alistair R. Walker November

2 Blanco ECS – Why? During operation, the optics of the telescope should be at or close to thermal equilibrium with the external ambient The immediate surroundings should not disturb this situation Modern facilities - starting with the ESO NTT on La Silla – address this requirement specifically in the design of the telescope and the building Rene Racine showed in the 1980’s that having the primary mirror surface only slightly hotter (0.5C is significant) than ambient caused the formation of a thin, highly turbulent layer of air just above the primary This led to improvements and modifications to many of the existing ~4m telescopes, led by CFHT. All these telescopes are essentially copies of the Palomar 5m design (1930’s…) The CTIO Blanco modifications were done in the 1990’s led by Jack Baldwin The need has not gone away, indeed, with potentially a better performing imager (DECam) at prime focus, it has become even more important But some of our systems are not being used, and as a system, the ECS has been neglected

3 Blanco ECS – Features from New Cooled floor at C and M levels Double-skinned dome with (external) lower air entry and upper air exit Insulation of telescope floors from lower floors Plumbed glycol for air-water heat exchangers, exhausted well away from the dome Chiller tubes in the hammerhead floor (never connected) TiO paint on the dome (but this overcools at night)

4 Blanco ECS – The Upgrades Relocation of offices and people to the new TELOPS building. All heating turned off Control Room relocated to the ground floor, old room gutted Sealing improved in many places, particularly elevator area Vent doors cut into external dome wall to promote flushing Oil cooling for the RA bearing Cool air blown on the primary during the day, air sucked out at night Stirring fan on the floor More! Dome surroundings, chimney cover/fan, etc etc.

5 Blanco ECS – Since 1995 White TiO paint on the dome replaced with Aluminum panels. Primary mirror cover replaced with a design that allows free flow of ambient air Concrete pathways painted white (non slip!) Mirror blower/sucker plenum removed as it was discovered it was being hit by the radial supports Floor stirrer fan no longer used, chimney fans (F/8) not used, some temp sensors have failed, little monitoring of performance and effectiveness, protocols not followed

6 Blanco ECS – Recommendations Modify/Rebuild the primary mirror plenum. (2 mw ME, 2.5 mw MD, 4 mw MF, $2000). Remove mirror washing seal. Revise oil cooling system Improved display interface for the ECS, associate with TCS, weather, rationalize (The weather part is underway, David) Increase the capacity and modernize the glycol cooling hardware (Underway, led by Brooke, stimulus funding) Replace inoperative temperature probes, upgrade control PC, port software (Some of the repairs are underway) Review protocols, motivate staff, monitor performance, tune system. It’s expected we will start using the mirror chiller/sucker, the helicopter fan, etc. Put Mag Chloride dust suppressant on the GONG/Lowell road in OCTOBER each year. Buy particle sensor.

7 Blanco ECS –Longer Term? Consider opening up more vent area Mount extractor fan internally near the roof, exhaust to the outside

8 Blanco ECS – Summary for ACTR PROJECT ONE Resources are being requested for remaking/rebuilding the primary mirror air chiller/sucker The resources being requested are modest: 2 mw ME, 2.5 mw MD, 4 mw MF, $2000) The installation will take place during the next aluminization of the Blanco primary, now likely to be early 2010B (Aug-Sept?) PROJECT TWO (January Meeting) Revise and update the “control and display” part of the Blanco ECS This is replacement of sensors, upgrade computers, re-write some software Related to TCS, outside-the-dome equipment, etc.