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New Telescope Control Program Installed at 1.5-m...(1Dec92)
Telescope
(from CTIO, NOAO Newsletter No. 32, 1 December 1992)

In mid-September the new telescope control program (TCP) was brought
into full time service at the 1.5-m telescope.  This system is closely
modeled on the one which has been in use at the 4-m telescope for over
two years and provides very nearly the same functionality. The TCP
software consists of two parts, each running on a different processor.
The program which actually controls the telescope resides on a VME bus
based Heuricon computer, while the menu driven user interface runs on a
separate PC. The TCP software was written by Germn Schumacher, while
the interface electronics were designed and built by various members of
the mountain electronics group, in particular Ramon Galvez and Rolando
Rogers. The project was largely carried out under the supervision of
Bill Weller.

The TCP implements all (or nearly all) the functions one would expect
of a modern telescope control system. The telescope can be slewed to
coordinates specified for any epoch. These may be entered at the
keyboard, taken from one of several on-line catalogs (e.g. the bright
star catalog, lists of CTIO photometric and spectrophotometric
standards), or selected from a user supplied coordinate list (see
below). A "slew stack" is also provided which automatically records the
target coordinates for each slew operation, so that one can return to
an earlier position without re-entering the coordinates. An important
enhancement over the previous software is that the TCP properly takes
into account the position angle of the instrument rotator.  Thus it is
possible to make offsets in the direction parallel or perpendicular to
the spectrograph slit, and one can also request that the hand-paddle
move the telescope along these directions instead of in RA and Dec. The
TCP also resolves pulses from the leaky-guider so that it is now
possible to use the auto-guider with the instrument rotator set to any
position angle. Another useful feature, for instance when working in
globular clusters, is the ability to use positions which are known only
in the form of offsets relative to some reference position. Once any
star in the list has been identified, the location of the reference
point can be made known to the TCP by entering the offset of that star;
there need not be any actual object at the reference position. The
telescope can then be moved to other objects in the list by entering
their offset. All of these functions are also available on the 4-m
telescope, of course.

One difference from the 4-m system is that the offset guide probe (GAM)
at the 1.5-m cannot currently be moved under the control of the TCP
computer. The probe can, however, be moved manually in order to acquire
guide stars. This deficiency will be rectified in a future project.

As far as actual performance is concerned, an RMS pointing accuracy of
10 arcsec over the entire sky can be routinely achieved. Precision
offsets of up to several degrees, relative to a known position, can be
made to an accuracy of better than 1 arcsec, primarily limited by the
ability to center the reference object on the acquisition TV. The
open-loop (unguided) tracking accuracy is +-2 arcsec per hour.

Users may wish to prepare coordinate lists in the form of ASCII text
files in advance of their run. The format of these is the same for both
the 4-m and 1.5-m TCPs. The entry for each object consists of a label,
three numbers for the RA (hours, minutes and seconds), three numbers
for DEC (degree, minutes and seconds), the epoch in years, proper
motion in RA and DEC (both in arcsec per year) and finally an arbitrary
comment. Each entry is one line of text, containing a maximum of 80
characters, in free format, each of the above fields being delimited by
spaces.  For example:

       6-CMi 7 29 09.4 12 01 52 1988.5 0.0 0.0 Sp. = K2 III

The label field must contain printable characters only, with no commas,
semicolons, spaces or tabs. The number of entries is in principle very
large, however, speed of access suggests that no more than about 1000
objects be recorded in a single file. The TCP computer itself can read
both 5.25 inch and 3.5 inch DOS format floppy disks (either regular or
high density).  Alternatively, coordinate lists can be imported
directly from the Sun computer at each telescope using PC-NFS. In this
case the lists could be brought to Chile on magnetic tape, in UNIX tar
or IRAF card-image format, or could be transferred electronically using
E-mail or FTP.

Steve Heathcote, German Schumacher

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