“Pi of the Sky” robotic telescope
“Pi of the Sky” robotic telescopeM. Cwiok a , K. Malek b , L. Mankiewicz c , J. Mrowca-Ciulacz d , K. Nawrocki d ,M. Sokolowski d , G. Wrochna da Institute of Experimental Physics, Warsaw University;b Cardinal Wyszynski University;c Center for Theoretical Physics PAS, Warsaw;d Soltan Institute for Nuclear Studies, Warsaw;ABSTRACTEffective search for gamma ray bursts optical counterparts and other fast astrophysical phenomena requiresrobotic telescopes. Such telescopes have to be able to realise programmed survey schedule and to react tovarious kind of alerts. Robotic telescope used in the prototype phase of the “Pi of the Sky” project is described.Design of the full size detector is briefly presented.Keywords: sky survey, afterglows, optical flashes, robotic telescope, automatic telecsope1. INTRODUCTIONGamma ray bursts (GRB) have been discovered in 1969 . Their optical afterglows have been observed for thefirst time only in 1997. It was a breakthough in the GRB studies, because it enables ground based observationsand made possible to perform spectral analysis and measure the distance. Farther research with methodstraditionaly used in astronomy turned out to be very difficult. Although in principle one could observe 2-3GRB’s per day, no one knows where the next will happen and where to turn a telescope. Typical field od view ofa professional telescope is much less than 1 square degree, therefore the probability to spot a GRB related opticalflash by chance is negligible.Alternatively, one can observe continuously large part of the sky with wide angle cameras. This approach wasundertaken by “Pi of the Sky” project. The original plan was to cover π steradians by 16 cameras with lenses offocal length f=50mm and aperture d=36mm. Recently, it was decided to increase the focal length to f=85mm andthe aperture to d=71mm in order to enable observing fainter objects. The expence for that is smaller field of view– about 2 steradian instead of π refered to in the project name. A prototype with 2 cameras of f=50mm has beenbuild. It operates since a year at Las Campanas Observatory. Important part of the system is a robotic mount,which has to combine capabilities of fast move towords a target and precise tracking afterwards.2. THE ROBOTIC MOUNTThe design of the “Pi of the Sky” mount is based on a classical parallactic mount concept. This solution enablespointing to any field in the sky with two drives. The first drive rotates the apparatus around the axis parallel tothe Earth axis. It can point the cameras to any given value of the right ascention (RA) - an equivalent of alongitude on the celestial sphere. The second drive moves the apparatus around perpendicular axis pointing thecameras to a given declination (Dec). In order to observe a given field continuously, the mount has to follow theapparent move of the celestial sphere, compensating the Earth rotation. It requires slow and precise, smoothmovement. In principle, only the right ascention drive is involved. If the mount axis, however, is not ideallyparallel to the Eart axis a correction performed by the declination drive is needed. Moving towords a target hasthe opposite requirements. It needs to be fast and high precision is not very important.We have chosen to use the same drive for the two kinds of movements. It has been designed as combination offriction gear and belt gear. The RA gear has 4 levels. The first three levels are made as belt gears. The last levelis realized by friction gear. The Dec gear has one step of belt gear less. Stepper motor with a step of 1.8° (200steps for full rotation) are used. Kinematics transfer for the RA gear is equal 4434.54. It is 1.461 arcsec for onestep of the motor. In declination, the kinematics transfer is equal 518.4, equivalent to 12.5 arcsec for one step ofthe motor.