The LCOGT 1-meter network will consist of 2 to 3 telescopes in Ash domes, at each of 5 to 6 sites distributed in latitude and longitude, to provide maximally continuous coverage of available optical sources. Each telescope is matched to a Fairchild 4K CCD imager with 26.6 arcmin field of view, full complement of broad and narrow band filters, and off-axis guiders.
Each site will additionally house a single temperature-controlled, cross-dispersed bench spectrograph, providing full wavelength coverage from 380-880 nm at R=30,000, with off-axis fiber feeds from each 1-m telescope.
Telescope scheduling is a continuous process centralized at Santa Barbara (SBA) to optimally allocate assigned targets to available telescopes. Users will not necessarily know in advance which telescope will perform their observations, and scheduling will change to accommodate targets of opportunity. Data will be stored and checked locally, then pipeline processed at SBA to remove instrument signature and produce an initial catalog of source parameters.
The Schott Borofloat mirror blanks are made by Hextek, Tucson AZ, and are being polished by LZOS, Russia. The primary mirrors weigh 75 Kg and the secondaries weigh 5 Kg. They permit a lightweight Optical Tube Assembly (OTA) weighing less than 500 Kg, including a 100 Kg instrument package. They enable rapid thermal equalization for optimal seeing, and a mechanical design and support system that maintains passive collimation at all telescope attitudes.
The mirrors are Aluminum coated with a SiO2 overcoat for long-term durability.
The optical design uses an f/2.5 primary in a quasi-Ritchey-Chretien f/8 system, fully corrected out to 0.8 degrees with a doublet corrector mounted within the primary central hole. The diagram shows the primary mirror with a 340mm central aperture, the 350mm diameter secondary which is centrally mounted from an Invar hub, doublet corrector, fold mirrors for autoguiders and spectrograph fiber-feed, filter plane and field lens for the CCD dewar.
The M2 baffle diameter is 412mm, and the collecting area is 0.65 square meters.
Our 1.0 meter telescope is an F/8 quasi-RC, with an F/2.5 primary . It has an airspaced doublet near the primary mirror and field flattener at the CCD. The main field has a diffraction limited full field of fiew of 0.8 degree. There will be four pickoff mirrors oriented at 90 degree separations around the main field. Three of these arms will be used for autoguiders, as is depicted in the figure above. The fourth spot will be used for a spectrograph feed.
The f/8 telescope scale is 39um/arcsec (25.6 arcsec/mm).
The Science field of view shows (light gray) the footprint of a possible 8K mosaic imager with 10um pixels (0.26 arcsec/pixel) and 35 arcmin Field of View (FoV).
The dark gray square illustrates the 62mm footprint of the currently planned Fairchild, back-illuminated 4K CCD486 with 15um pixels (0.39 arcsec) and 26.6 arcmin FoV.
The off-axis positions for autoguiders (3, each 6x4 arcmin) or spectrograph fiber-feed are illustrated.
The telescope mount is a stiff C-ring forming the RA axis, resting on friction drive rollers and supported on a base which can be adjusted for latitude (typically 20 to 40 degrees). The C-ring outer diameter (2m) is large enough to support the Optical Tube Assembly (OTA), with 500mm of instrument clearance. The complete telescope weighs about 2 tons.We intend to ship them to site in 3 pieces: mount + mirror cell (pinned to prevent bearing damage), truss assembly, optics and instrument package.
The lightweight OTA employs a cast and machined primary mirror cell as the main structural element, with the M1 vertex close to the Declination axis. The OTA is friction driven from the large Declination wheel, and position read from the smaller encoder wheel. The primary baffle is supported by spiders from the primary mirror cell so the mirror cover can close completey under it. The remote collimation and focus M2 drive is supported on a carbon fiber truss and steel spider assembly, which also supports the secondary baffle.
The telescope and OTA design have been optimized with FEA to ensure the mirrors, correctors and focal plane are maintained within optical tolerances at all telescope attitudes.
This Primary Mirror Test cell is used to verify the repeatablity of axial and radial supports for the primary Mirror. Up to 6 radial and 3 axial sensors will be used the determine the repeatability of the support. The Test Cell will be installed into the mount so motion of the test cell will replicate actual motion of the OTA.
The Miror Test Cell will dubble as a jig secure the truss assembly while the epoxy is curing between carbon truss tubes and the truss nodes.
The Mirror Cell (as seen in orange) is a cast steel piece. The axial and radial supports are attached to the mirror cell.
The Pimary Mirror is a Hextek Blank which is being Polished by LZOS. The primary mirror is 1040mm in diameter with a 330mm hole. The clear aperature is 1000mm and 350mm, respectively. To the right is a FEA model of the print though from the 18point support at 50 degs from zenith. Zenith was modeled as perfect.
Each site houses one cross-dispersed, thermally controlled Medium Resolution Echelle Spectrograph (MRES), which can be fed by one or more telescopes.
MRES utilizes a 79 l/mm R2 echelle, 100mm beam and 500mm focal length collimator/camera. A prototype of the spectrograph concept shown here is currently being assembled for testing at the LCOGT built 0.8m Sedgwick Reserve telescope near UCSB.
The output format is designed to project 17 echelle orders on to a 45x25mm (4Kx2K) format, with coverage from 380-900nm, at R=30,000.
Order separation in the red is 38 pixels (24 arcsec), permitting multiple spectra of the same or different sources to be observed simultaneously.
The diagram shows the off-axis pickoff (green) focused on a tilted aperture plate. The telescope f/8 beam is compressed to f/5 to feed a 70um fiber running to the common spectrograph. The fiber subtends 3 arcsec on the sky.
The optical path to an SBIG aperture viewer (on the left) is shown below the aperture plate. The SBIG camera in the foreground is one of the autoguiders. The design also includes a calibration fiber (top) and insertable mirror for white-light or arc illumination.
The "Sinistro" dewar showing the back-illuminated 4K Fairchild CCD486 behind its field-lens and filter wheel mounting flange.The filter wheel will contain BVRI, ugriZY and narrow band filters. The CCD is connected to the camera electronics by a flex circuit (purple). The dewar and control circuitry are being developed at LCOGT to provide fast and slow 4-channel readout modes, with configurable binning and region-of-interest capabilities.
Also shown are the Cryotiger (PolyCold) gas lines (black, the vacuum pressure gauge (right) and ion pump and vacuum pump fittings (behind).
