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The 4-m: Past, Present, and Future (1Dec93)
(from KPNO, NOAO Newsletter No. 36, 1 December 1993)

During the past year Kitt Peak has embarked on its largest, riskiest,
and perhaps most heroic effort in years: a major renovation of the 4-m
telescope.  This follows the six-month closure of the 2.1-m during the
fall 1989 semester for similar work; fortunately, what was learned as a
result of that upgrade gave us both insight and courage to make a major
upgrade of the Kitt Peak flagship.  Before reporting on the present
status and future plans, it may be useful to place this renovation in
historical context.

In the late 1960s AURA was involved in the design and construction of
two, nearly- identical, large telescopes, one to be located in the
northern hemisphere, and one in the south. (Sound familiar?) In the
January-March 1972 Quarterly Report, the project manager for the Kitt
Peak "150-inch telescope," David Crawford, summarized the history as
follows: In March 1961 the AURA Board of Directors asked the KPNO staff
to begin a design study for a large optical telescope. The telescope
was to have a prime focus field of view that must be "large," the focal
ratios at prime and Cass should be about f/2.8 and f/9, and the
telescope should be as versatile as possible without compromising
efficiency. The telescope was to have a minimum lifetime of 50 years,
and was to be designed for high reliability. First-light was announced
the following year, 27 February 1973.

Twenty years later (and nearly thirty years after some of the system
was designed) we are continuing to fulfill the promise of a highly
versatile, efficient, and reliable telescope of large aperture--the
largest telescope in the northern hemisphere available to anyone in the
astronomical community based purely (or as pure as we can make it) on
the basis of scientific merit. The 4-m currently supports a complement
of ten major instruments, many of them state-of-the-art: Hydra, the
multi-object fiber positioner; the R-C and Echelle spectrographs
operated with large-format CCDs; the prime-focus, large-format CCD
camera with its scanning table for imaging objects at a tiny fraction
of the night-time sky level; the high-throughput, low-dispersion
Cryogenic Camera; four IR instruments based upon the explosion in IR
arrays: (the IR Cryogenic Spectrometer, the Cryogenic Optical Bench,
the Simultaneous Quad Infrared Imaging Device, and the IR Imager); as
well as the Fourier Transform Spectrometer (FTS).

As those of you who applied for 4-m time this semester are only too
aware, there was roughly five weeks less observing time available than
is normally the case, due to a prolonged shutdown that extended to 5
October. This shutdown was scheduled in order to complete the first
year of a three-year project to replace the old electronics and
software with modern systems. The motivation for this major renovation
is two-fold: (1) improve the reliability of operation by using systems
that are easier to maintain and diagnose, and (2) improve observing
efficiency (faster slews, more accurate tracking and pointing). In
addition, major efforts are taking place during this same time period
to improve the dome-seeing. (See the article in this Newsletter on
image quality improvements.)

This summer saw the replacement of the servo system (the electronics
via which the telescope motors run), the encoders, and the computer
system that operates the telescope. There was the usual crop of last
minute problems, but thanks to everyone's hard work and cooperation,
the 4-m re-opened exactly as planned. On 5 October the first visiting
observer, Hans Rix, was obtaining data just like any other night on the
4-m, except for the large number of slightly nervous people standing by
"just in case." In the subsequent weeks there has been almost no time
lost due to the new systems, and we are in the process of completing
"Phase I" of the renovation. Efforts are in progress to track down the
remaining nagging problems, the most serious of which is a problem with
the incremental encoders on the dec axis that is the primary culprit in
limiting the absolute pointing accuracy (all-sky) to 10-15 arcsec.
(This is nevertheless as good as we had previously achieved in practice
with the 4-m.) By the time you read this we hope to have this problem
solved, as well as other items rectified.

Despite the incremental encoder problem, our tests have shown that the
4-m now offsets better than I would have ever believed to be possible:
a number of open-loop (unguided) offsets up to 30 arcmin in length were
done at various rotator angles and declinations and in each case the
new object was centered on the slit to within the accuracy of the
relative coordinates (0.2 arcsec). Tracking also appears to be much
improved over the old system. Software control of the leaky guider now
permits guiding from the slit-viewing TVs on the Echelle and R-C
Spectrographs, reducing setup times for many programs.

During 1994 the upgrade to the telescope control system will continue
in order to include support for the atmospheric dispersion corrector
(Risley prisms), provide computer verification that everything is "set"
and ready to observe (read-back of mirror cover positions and
instrument configuration), improved searching algorithms of coordinate
data bases ("What Landolt standards of a specified color are currently
available between an airmass of 1.5 and 1.8?"), and the like.

However, the major work planned for the coming year is upgrading the
instrument motor controllers. The reliability of these has decreased
with time to the point that we are seldom surprised if there is at
least some failure during an instrument block. Replacing the motor
drivers is a daunting challenge: there are 45 motors that control the
4-m instruments and guiders. This is not a project that will bring
about "new science" (such as, say, putting a tip-tilt fast guider in
the PF CCD imager), but it does permit good science to continue to be
done with a minimum of down-time. In addition, replacing the motor
controllers and I/O control multiplexer will allow us to do away with
CAMAC, reducing heat-sources in and around the telescope.

In addition, major steps are underway to improve the thermal
environment: the oil cooling system is in place and will be switched on
later this semester.  We also plan to improve the ventilation of the
dome, following CTIO's lead. MDM, located just down the road from the
4-m, often obtains subarcsec seeing, and we hope to be achieving this
in the near future as well.

While there were literally dozens of people involved in the success of
the 4-m project, the following must be singled out for special note.
The project scientist for the renovation was George Jacoby; Bruce
Bohannan was the project manager. Tony Abraham managed the Kitt Peak
engineering effort. D'Anne Thompson was Project Engineer for the
software effort, and Scott Bulau was the Project Engineer for the new
servo hardware. Bob Marshall managed the mountain programming group
that worked with D'Anne: Kim Gillies, Shelby Gott, Lee Groves, and Jeff
Lewis. Larry Daggert managed the ETS resources. Engineers and
technicians who contributed in a major way to this project included
Khairy Abdel-Gawad, Tom Bajerski, Ed Bell, Bob Bode, Kurt Cramer, Allen
Gerzoff, John Hoey, Patti Jackson, Rene Muhlberg, Kevin Price, Tom
Roussey, Dave Stultz, and Vern Russell. Bill Ditsler made a major
upgrade to the acquisition and guiding TV systems. Jim DeVeny, Bill
Schoening, and Daryl Willmarth were instrumental in the check-out
phase, with staff astronomers Taft Armandroff, George Jacoby, and Phil
Massey participating in the final moments.

In addition to new servo hardware, there is also new stereo hardware:
observers may want to bring their favorite CDs and cassette tapes with
them.

Phil Massey

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