The Zadko Observatory

The Zadko Telescope is situated in the state of Western Australia at longitude 115 deg 42’ 49’’ E, latitude 31 deg 21’ 24’’ S at an altitude of 50 m above sea level.

The Zadko Telescope was first installed in a 6.7 metre Sirius fibreglass dome in June 2008.  Due to the robotic nature of the telescope which makes hundreds of movements during each night, the demands placed on the dome to continually track the telescope movements caused it to be in constant need of maintenance and repair and eventual failure.

In 2011 it was decided to replace the dome with a purpose built rolling roof observatory. Observatory manager, John Moore, led the design and construction of the new observatory, including the PLC controlled roof, electrics and control room.  Two constant temperature climate controlled rooms were included under the same roof.  One of these is the main operations control room and the other is a service room.  The service room also mirrors the operations room to allow for future conversion into a second control room when further telescopes are added to the facility.

The observatory is a large steel structure that was prefabricated off-site and construction was completed in six monthe.  The curved corrugated COLORBOND® steel zinc-alume roof was installed without gutters to prevent leaf litter buildup and consequent fire hazard.

The walls and ceiling panels of the Operations, Service and main Telescope rooms are 100mm thick EPS core insulated panels which assist in maintaining reasonably constant temperatures throughout the year.  Both the Operations and Service rooms have split system air-conditioning units installed for constant temperature control.

The main control for the automatic operation of the roll-on roll-off roof is provided by a Burgess PLC system which was designed and installed by the French Zadko collaborators from l’Observatoire de Haute Provence. This system includes electrical and mechanical interfaces for temperature, humidity and wind sensors, a flat field lamp, emergency stops, limit switches and a main control panel.

The telescope is protected from sudden adverse weather events by a suite of weather sensors located on an external mast. Cloud, rain, humidity, wind and temperature sensors interface with the Burgess PLC control unit which opens and closes the rolling roof. This may happen several times per night in variable weather conditions. The approximate time to open or close the roof is two minutes.

The main drive for the roof movement is two 3-phase 0.75 kW brake flange motors connected to in-line helical gear boxes (46:1 ratio) installed on either side of the observatory and connecting to a geared rack on the roof. The motors are powered through a variable speed drive controller located in the Burgess PLC cabinet. All critical power for the drive and computer control is provided by a Socomec 7 kVA Uninterruptible Power Supply (UPS), which insures roof operation (particularly closure) and computer control in the event of an external power failure.

Telescope

The telescope and mount were built by DFM Engineering (USA). The telescope is a one metre f/4 focal ratio hybrid Ritchey-Chretien design. The main mirror has a diameter of 1.007 metres and a focal length of 4.0386 metres. The focal plane is 467.9 mm below the surface of the primary mirror.

Mount

The telescope is supported on an equatorial fork mount. This mount is sited on a vibration isolated concrete pier. Mechanical vibrations from the rest of the observatory concrete pad do not exceed one arcsecond and are damped out within one second. The mount has a slew speed of three degrees per second.

Camera

Camera info here

Control

Control of the telescope, camera and mount is performed by robotic software developed at l’Observatoire de Haute Provence. This also controls acquisition, downloading, processing and dissemination of the camera images

Calibration

A flat field screen is suspended from the rolling roof at a distance and angle to achieve optimum results for camera calibration. An illumination lamp for the screen is mounted at the top of the telescope optical tube assembly.

System Sensitivity

The system can achieve 21st magnitude (R band) for a single 180 second exposure. Typical sensitivity for a 2 to 3 minute exposure is 20th magnitude (R band) for a source 60 degrees from the Moon. Unfiltered images are calibrated against stars in the USNO-B catalog. The Andor IKON-L sensor has a peak quantum efficiency of 95% at a wavelength of 570 nm.

Climate

The weather conditions on site are conducive to optical astronomy with hot dry summers and clear viewing skies. The annual average cloud cover is 48%.  Seaonal cloud cover is 12% (Jan-Mar), 54% (Apr-Jun), 75% (Jul-Sep) and 50% (Oct-Dec).  Rain occurs on an average of 103 days of the year with the majority of the rainfall occurring between May and September.

Note: The above cloud cover statistics were derived from a multi-decadel study from the 1940s – 1980s and may have changed due to variable climate factors.

Dark Skies

On a moonless night the sky brightness overhead is typically 21.4 magnitudes per arc second squared.

Seeing

The average seeing measurement of the full width at half maximum from images typically varies between 2.0 to 3.5 arcseconds at zenith and 3.5 to 6.0 arcseconds at an elevation of 45 degrees.