The KPNO 1.3-m Telescope

A Remotely Controlled Telescope Returns to its Roots

The 1.3 m (50") telescope on Kitt Peak has a rich history, including its role as a prototype for remotely controlled telescopes. Budget constraints forced the closing of this telescope as part of the Kitt Peak National Observatory (KPNO) in 1995, following nearly 30 years of service to KPNO. A request for proposals to operate this telescope was issued to the science community. The RCT consortium, lead by Western Kentucky University, was the successful proposer for operation of the telescope. The telescope returned to limited operations in the Spring of 2004 and has been fully operational since late 2006.

The telescope was originally proposed by the Space Sciences Division at KPNO as the Remote Control Telescope System (RCTS) to be an engineering research platform for the development of remote control protocols for envisioned orbital telescopes. Aden Meinel, during his directorship at Kitt Peak National Observatory, was a key force behind the concept of a remotely controlled facility. Seed money for this project is thought to have come from NASA and/or the Air Force, although this has yet to be documented. The telescope, to be located on Kitt Peak, would be operated from Tucson, using commercial telephone lines for control and data transmission. By the end of 1963, the telescope mount was installed at the downtown office for testing of the communications system and control console. The telescope was moved to its present location in 1965 and the 50-inch metal mirror was installed by the end of that year. By that time, the goal was a fully automated remote-control telescope for ground-based astronomy. This was a conceptual precursor of today's robotic telescopes, somewhat disadvantaged by the computer hardware available at that time. The control electronics occupied five large racks which almost filled the present-day telescope assistant electronics lab.

Dr. S. P. Maran joined the Space Division at Kitt Peak in June 1964 as "astronomer- in-charge, remotely controlled telescope." recalls that, "the design of the system, which besides being ahead of its time, had in retrospect the fatal flaw that almost no significant subsystem used old/proven technology. Even the dome slit was uncharacteristically narrow, since there would be no operator using a finder telescope, and therefore no reason to make the slit significantly wider than the telescope barrel. (I got complaints about that from infrared observers for years after I left KPNO and it was converted to a manually operated IR telescope; they could not both look through the finder and have the main telescope have an unobstructed view.) Add to that philosophy of novelty the fact that the telescope was not only automated but also remotely controlled, and you had planted the seeds of disaster. At least, that's the case if you were planning an operating astronomy facility, rather than an engineering testbed. Generally speaking, other early automated telescopes were controlled from adjacent laboratories so that the developers could easily observe and trouble shoot the test operations. When I came on board the RCT project, the telescope was being put together and we began making test observations and planning a new direction- that it would actually be used for science, not just as a testbed for future space telescopes."

Prior to Maran, the project was then run by its principal engineer, a systems engineer, Mr. Frank E. Stuart. Stuart and another Space Division engineer, Mel Larson, designed the original 50-inch primary. They were not optics people. Frank was a systems engineer and Mel was a mechanical engineer.

The original mirror was spun aluminum.

The Sky & Tel report makes clear why the mirror failed. It tested beautifully in the KPNO optical shop where it was polished. But once it was at ambient temperature on the mountain, it turned out that the shape of the image and thus of the mirror, depended strongly on the temperature. The investigations I then pursued, visiting aerospace companies that did lots of work on these lightweight mirrors for purposes that they could not disclose, revealed that we had rediscovered a well known problem, namely that the bimetallic strip effect involving the nickel coating and the cast aluminum substrate of the primary mirror produced a warping that depended strongly on the reciprocal of the thickness of the edge and on the diameter of the mirror. Although both sides of the primary mirror blank were coated, some of the coating necessarily was polished away on the reflecting side.

By 1969, the telescope was transferred to the Stellar Division, to be operated in manual mode, in part to reduce operating costs. The present observing floor was installed, and the 50-inch became a full-time visitor facility in April of that year. Shortly thereafter, the metal optics were replaced by the present Cer-Vit optics, and the telescope entered the role of optical and infrared photometry, which continued for 25 years. Refinements such as the chopping secondary, observing room (built in part to escape the noise made by the first chopping secondary), TV guiding, and computerization made the operation more comfortable and efficient.

This telescope has played a pivotal role in the development of infrared arrays for astronomical applications, as well as the IR instrumentation (IRIM, CRSP, SQIID, COB) used on the Kitt Peak telescopes. By using the 1.3-m telescope as a test and engineering facility for new, complex instrumentation, the need for significant engineering time when using these instruments on the 2.1-m and 4-m telescopes was virtually eliminated. Finally, the observing record of IRIM (eight years) and SQIID (four years) points out the scientific value of a modest aperture, wide field telescope for infrared surveys and imaging of spatially extended regions.

We thank Dick Joyce and Steve Maran for their substantial contributions to this short history.