KECK OBSERVATORY AND THE LRIS INSTRUMENT

  The W. M. Keck Observatory , located on the summit of Mauna Kea on the Big Island of Hawaii, consists of twin 10-meter telescopes intended for astronomical observations at optical and infrared wavelengths. Both telescopes employ a revolutionary design, in which each 10-meter mirror consists of 36 2-meter hexagonal segments which are aligned to act as a single large mirror (see Figure 8; [6]). These are the largest astronomical telescopes in the world for use at these wavelengths. The first Keck Telescope has been in routine operation since 1993, and has successfully demonstrated the viability of the multiple-segment mirror design. The second Keck Telescope became operational in October of 1996 and is currently dedicated almost entirely to optical observations.

 

Figure 8: a. The domes of the twin 10-meter Keck Telescopes on Mauna Kea, Hawaii. b. The back of the primary mirror on the Keck I telescope, illustrating the network of 36 hexagonal segments which make up the mirror. The infrared camera is mounted at the forward Cassegrain focus of the telescope (i.e., in the central hole of the mirror).  

Throughout the design process of the hardware and software for the Keck Telescopes, the possibility of implementing remote observing, particularly from Waimea, the location of the Keck headquarters in Hawaii, was kept in mind (see Figure 9). The instruments, their motors, and the detectors are operated through workstations that are located in the control room of the Keck Telescope dome. It is not necessary during normal night-time operation to go out to the instrument on the telescope to make any adjustments or changes.

We have concerned ourselves exclusively with enabling remote observing on the Keck II telescope with the Low Resolution Imaging Spectrograph [7] (LRIS; see Figure 10). This is the primary optical instrument at the observatory, and the only instrument capable of obtaining direct images at optical wavelengths. It is used on Keck II almost every night of the year. Although our efforts have concentrated on remote observing with LRIS, we note that all of the instrument interfaces have been engineered in a similar fashion, so our results could be easily extended to other instruments on Keck I or II.

 

Figure 9: The Keck II telescope control rooms: a. in the telescope building itself, on the summit of Mauna Kea, and b. in the Keck headquarters building in Waimea, at an altitude of only 2000 feet. The two rooms provide the astronomer with identical control environments for the telescope and its instruments.  

 

Figure 10: Instruments for the Keck telescope: a. the Near-Infrared Camera (NIRC) in a stowed configuration, and b. the Low Resolution Imaging Spectrograph (LRIS), installed for operation at the Cassegrain focus of the telescope.  

Figure 11 illustrates the organization of the telescope and instrument control hardware at the Keck Observatory. The majority of the complications associated with remote control of the instrument have stemmed from security issues and the desire to not impact normal (i.e., non-remote) observations with the telescope. For example, concerns about the effect of a such a high-speed network, especially in various failure modes, on other computer and network systems at Keck, as we approached this project with our initial inexperience, forced us to isolate remote operations more thoroughly by duplicating the instrument control computer. This machine provides boot information for the instrument motor and CCD detector VME crates, as well as the interface between the user and the control systems. The remote portion of the observing system, the workstation at Caltech, is integrated into the system merely as a remote display, using the X Window System protocols. Although this is perhaps not the most efficient method of providing remote operations, it is certainly the most straightforward, especially in a relatively new and frequently changing facility such as Keck.

 

Figure 11: A schematic of the LRIS instrument control system at Keck Observatory. Note that there are two separate instrument control computers: one for standard on-site observations, and another for remote observations over the high-speed network.