The All Sky Automated Survey - Prototype Instrument
Prototype Instrument for the All Sky Automated Survey
consists of the specially designed paralactic mount,
and Pictor 416 - CCD camera equipped with 135/1.8 lens.
Mount
It is a horse-shoe design driven in both axes by the stepper motors.
Main characteristics of the drive:
- Outer dimensions: 550 mm x 550 mm x 550 mm
- Horse-shoe diameter 490 mm
- Max. telescope diameter 30 cm (28 cm - default)
- Max. camera wieght ~ 10 kg
- Camera bay: half sphere r ~ 170 mm
- Mechanical pointing accuracy ~ 15 arcsec
- Drive resolution in Hour Angle: 3.4 arcsec
- Drive resolution in Declination: 112.5 arcsec
- Positionning repeatibility: 5% of resolution (no backlash)
- Max slewing rate in H.A.: 5 deg/sec = 180 deg/ 40 sec
- Max slewing rate in Dec.: 150 deg/sec
- Adjustment accuracy of the polar axis: ~ 30 arcsec
- Possible observatory lattitudes:
- (+18 to +54) & (-18 to -54) on horizontal table
- (-70 to +70) on tilted table.

Mount accuracy can be jujged from the following images:
First is direct average of 20 frames, each 30 seconds exposure, separated by
4 mniutes. Time span between first and last image was 1 hour 20 minutes.
Star images are elongated both in RA (improper time constant for the
RA drive step) and DEC (very crude polar axis alignment during these exposures).
Second image is "shift and add" frame (obtained after applying proper
offsets to each image).
Diagram diagram shows offsets (in pixels) necessary to bring all star images
into the same places.
Exposures that we are going to take with this drive will be
probably 3-5 minutes long, so even without further trimming star images should
not be elongated.
Pictor 416 made by MEADE with Kodak KAF-0400 (512 x 768) is used in the prototype.
The only possibility that MEADE provides to control camera
is interactive PictorView (for Windows) program. We have developed independent
library of C routines, enabling us to control camera over the
fast (115 kb) RS-232 interface. We use X Window programs for
interaction with camera via camera server (dedicated program, that talks
to camera over the serial link).
We had to add small fan to keep camera head at temperatures not higher
than ambient +5C.
Sigmatel 135mm f/1.8 is used as our primary lens. It is a fast
lens, providing pixel scale of 13.75 arcsec/pixel. The only major
drawback of the lens is its strange PSF (triangular with two extended
fingers). PSF is better if we observe with standard UBVRI filters.
Software
Our observing system consists of a set of specialized servers and client
programs interacting comunnicating throught the Data Base (simple, remotely
accecible data base system with "get", "put" and "subscribe" functions).
- Servers
- Data Base Server - organizes echchange of information
- Camera Server - talks to the Pictor camera, reads Pictor
messages, gets images and stores them on the disk.
- Telescope Server - talks to the mount motors, converts telescope
positioning commands to the stepper motor control commands.
- Image Server - reads stored FITS-files and sends them to the
requesting clients (e.g. dATAview - image displaying tool).
- Clients
- dATAview - image displaying tool
- Camera - camera control tool
- Telescope - telescope control tool
- Map - Sky_map, air-mass display and user catalogue tool
- Executor - program executing command scripts
- Analyst - data reduction and analysis tool