PROJECT OF THE 130 cm TELESCOPE
FOR THE SKALNATÉ PLESO OBSERVATORY
Jozef Žižňovský
Stakčín, December 2012
The described system consists of a 1.3m alt-az mounted Cassegrain-Nasmyth
telescope with two Nasmyth focal stations.
Both Nasmyth focal stations are equipped with a field derotator.
It contains a control system and a software communicating with the dome
control unit and a meteostation.
In principle it is a robotic telescope.
Manufacturer and supplier: ASTELCO Systems GmbH, München
Instruments in the foci:
CCD camera for near UV, visual and red spectral region
IR CCD camera for infrared region
Echelle spektrograph
It will be provided in the frame of the European Regional Development Fund
in three steps:
1. Telescope: till the end of 2013
2. Dome computerisation : 2013
3. Focal instruments and infrastructure: Spring 2014
1. TELESCOPE
1.1. Optics
Main mirror M1, free aperture
~ 1 300mm
Main mirror M1, mechanical diameter
~ 1 310mm
Main mirror M1, focal ratio
System focal ratio
Wave front error
Field of View at Nasmyth focus
F/2.8 *
F/8
 /6 at 633nm RMS
> 0.5 deg
Mirror material
Zero Expansion Glass (Zerodur
or Astro Sitall)
Mirror coating
Al (Aluminium) + protection layer
Mirror reflectivity
R > 94%
The primary mirror is a thin low expansion glass meniscus.
Its shape and optical performance therefore has to be actively controlled during
the observations.
The active mirror support system consists of a combination of an 18 point
whiffle-tree support and 9 axial actuators. The actuators are controlled by
a Shack-Hartmann sensor unit as a part of the telescope system, like the
autofocus thermal control.
The Shack-Hartmann unit allows checking the online alignment performance
of M1 and M2 mirrors and helps to regain the collimation of the optics after
recoating.
The primary mirror is fixed radially by a 4 point preloaded spring pad system,
which guarantees the permanent position of M1 during all telescope
movements between zenith and horizon positions as well as at high slewing
rates of the telescope.
The surface accuracy of the optical system will be proven by interferograms
at factory acceptance.
At final acceptance, there will be on-sky tests carried out at the Observatory
with the supplied Shack-Hartmann sensor unit available at the Nasmyth focal
station.
2. Mechanics
2.1 Dimensions
Maximum height (tube in vertical position)*
440 cm**
Minimum height (tubus in horizontal position)*
300 cm**
Optical tube lengths
300 cm**
Maximum radius of movement (horizontal position)
215 cm**
Required concrete foundation diameter
300 cm**
Total weight of the telescope in basic specification
~7t
* Calculated from the lower surface of the telescope basis
** Dimensions after the preliminary design phase
2.2 Telescope structure
The structure of the telescope is a special, super-compact “ASTELCO Design”.
The telescope tube is a welded Serrurier truss design made from steel. This
guarantees a minimal and predictable bending of the tube. All welded parts of
the telescope are annealed to relax tensions. This very stiff and rigid design
reaches high values for the eigenfrequencies of the system and therefore
allows observing at wind speeds up to 15 m/s.
The telescope’s central part connects the upper and lower truss sections and
holds the combined motorized M1/M3 mirror doors. This section connects the
tube assembly by means of two hollow flanges to the fork arms of the mount.
Through these hollow flanges the light path of the telescope is sent to one
of the 2 Nasmyth foci.
A motorized rotating and self-centering M3 unit is provided to reach both
Nasmyth foci by software control. Rapid and precise focus change between the
two Nasmyth foci gets a simple standard task to be able to use two different
instruments at two foci at practically the same time.
The lower Serrurier truss part holds the mirror cell with the M1 primary mirror.
The mirror cell allows easy access for maintenance – for mounting and
dismounting the primary mirror a special ASTELCO tool is supplied.
M2
M3
M1
2.3 Telescope mount and drives
The tube assembly is mounted between both fork arms of the alt-az mount.
The fork arms are connected to the mounting base plate.
On the upper end of the fork arms the bearing housings, the encoders and
the motors are located.
The accuracy of the perpendicularity of axes is < 10 arc sec; residual errors
are corrected by the software.
Slewing speed* 20°/sec
20°/sec
Absolute pointing accuracy
< 5 arcsec RMS
Differential pointing accuracy
< 0.2 arcsec RMS
Tracking accuracy without autoguider
< 0.5 arcsec/10 min
Tracking accuracy with autoguider
< 0.25 arcsec/10 min
Effective encoder resolution
328 increments per arc sec
(0.003 arc sec / increment)
FOCAL INSTRUMENTS
1. CCD camera for near UV to red spectral region
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Quantum efficiency in the interval of 400-760nm: 80%
Sensor size 10k x 10k, class: 1
Pixel size: 8-10 µm
Interface for communication with the computer via fiber optic cable
(1 Gbit)
Dark current maximum: 0.01e‐/pixel/sec
Readout noise: less than 5e- (rms)
16 bit AD converter
Cooling with cryotiger to < -100° C
Example: Spectral Instruments 1110S
http://www.specinst.com/Brochures%20Rev%20A/1100S-camera-broch_RevA.pdf
2. IR CCD camera for near infrared region
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Quantum efficiency in the interval of 900-2 300nm: 70%
Sensor size 2k x 2k, HgCdTe technology, class 1
Pixel size: 15 µm
Dark current maximum: 0.01e- /pixel/sec
Readout noise: less than 20e- (rms)
16 bit AD converter
Cooling with a Stirling engine to 70° K (-203° C)
without the necessity of liquid Nitrogen use
Example: Teledyne Scientific
(Manufacturer and supplier of detectors for
the Hubble Space Telescope and the James Webb Space Telescope)
http://www.teledyne-si.com/infrared_visible_fpas/index.html
3. Spectrograph
Hihg-dispersion échelle spectrograph to the Nasmyth focus:
• R = 40 000 for seeing 3"
• Spectral region: 400-760nm
• CCD camera 2k x 2k
• Calibration lamps for ThAr line spectrum and continuum light
• Interchangeable slits (apertures)
• Software for remote control of the spectrograph and its CCD camera
Manufacturer, contractor: Lasertechnik Berlin
Subcontractor: Hamburger Sternwarte
Thank you for your attention!
Price (incl. VAT):
• Telescope
• Dome automatization
• Spectrograph
• CCD camera
• IR CCD camera
• Coating unit for the 130 cm mirror
• Fiber optic cable from Poprad
• Data storage devices
• Diesel-electric generator
∑
1 030 000 €
53 500 €
480 000 €
340 000 €
590 000 €
280 000 €
124 000 €
36 000 €
15 000 €
2 948 500 €
Sponsored by:
European Regional Development Fund,
100%