For the last two and a half years the Department of Physics and Astronomy at Louisiana State University has been engaged in a collaborative effort with the Recreation and Park Commission for the Parish of East Baton Rouge and the Baton Rouge Astronomical Society to develop a observatory that can be used for astronomy education from primary school; through graduate studies as well as for recreation and public outreach. The observatory includes a 2,300 square feet facility, a 20-inch diameter Ritchey-Chretien telescope, a black-thinned CCD camera, a computer control system and an internet T1 link. The on site public outreach and education program has been fully active since Fall, 1997 and we are currently in the process of developing a platform- independent system for remotely controlling the observatory over the internet. The initial version of the Java/World Wide Web based software is currently functioning and provides interactive control of the observatory via any Java compatible web browser. The main principles of the remote control system are presented in this paper, along with a discussion of the education and outreach goals of the observatory, details of the facility and hardware, initial measurements of system performance, and a discussion of our future development plans.

A candidate Blind Pointer system for the Stratospheric Observatory for Infrared Astronomy telescope was developed and tested on a telescope aborad the Kuiper Airborne Observatory (KAO). Once an operator inputs the celestial target's coordinates, the Blind Pointer can steer an aircraft and point an airborne telescope to within the focal plane's field-of-view without optical feedback. The Blind Pointer converts the desired stellar object's Right Ascension and Declination into an aircraft heading and telescope pointing-error signals. The Blind Pointer utilizes a global positioning system receiver integrated with an inertial navigation system controlled by a PC-clone computer. This candidate Blind Pointer offers significant advantages over the present system aboard the KAO: fewer components, greater observation efficiencies, increased accuracy, and simpler design. A patent has been filed for the Blind Pointer. Although the Blind Pointer was developed for airborne telescopes, other applications can exploit this technology. This paper describes the Blind Pointer prototype and flight test results from local and New Zealand deployment flights.

The Gemini World Coordinate Systems (WCS) facilities support various types of astrometric coordinates as well as instrument-specific quantities such as wavelengths or times. The astrometric facilities are based on the principle that, for sky-imaging applications, users are concerned only with (i) positions in the focal plane and (ii) celestial coordinates. All intermediate calculations, for example involving the position of the tip/tilt secondary mirror, the orientation of the instrument rotator, the selection of focal station, differential refraction and atmospheric dispersion, and field rotation effects caused by misalignments in the telescope mount, are encapsulated in the WCS transformation. We have implemented a library of C functions which support Gemini astrometric world coordinates. Most of them can be run off-line, and are applicable to other telescopes. More general WCS problems, involving data coordinates as well as astrometry, are treated by breaking the telescope, instrument and detector into a set of 'agents' each of which manages its own local transformations. The individual transformations can then be combined to provide the end-to-end transformations needed by data display and analysis facilities.

Second generation star trackers work by taking wide-angle optical pictures of star fields, correlating the image against a star catalogue in ROM, centroiding many stars to derive an accurate position and orientation. This paper describes a miniature instrument, fast and lightweight, including database and search engine. It can be attached to any telescope to deliver an accurate absolute attitude reference via a serial line. It is independent of encoders or control system, and works whenever it can see the sky. Position update rates in the range of 1 to 5 Hz enable closed-loop operations. The paper describes the instrument operational principles, and its application as an attitude reference unit for a telescope. Actual data obtained at the University of Hawaii's 0.6-m telescope are presented, and their utility for correcting mechanical alignment discussed. The system has great potential as a positioner and guider for (i) remotely operated optical telescopes, (ii) IR telescopes operating in dark clouds, and (iii) radio telescopes. Other application recommendations and the performance estimates are given.

To achieve the highest accuracy boresight pointing performance the Hubble Space Telescope uses attitude feedback from the Fine Guidance Sensors (FGS). There are three FGS's on board HST. During normal operations, one sensor monitors spacecraft pitch and yaw, another monitors roll and the third is the redundant unit. Each FGS senses wavefront tilt interferometrically and converts that tilt into spacecraft pointing error. The presence of spherical aberration affects the signal from the instrument causing a reduction in acquisition and tracking performance on targets whose magnitudes are fainter than 14. This paper documents the efforts to optimize uplinkable, FGS parameters in order to increase the probability of target acquisition that is better than 98 percent over the entire field of view. To this end, the paper describes the Monte Carlo simulator used in deriving the optimized values for the FGS acquisition and discusses methods for testing the new parameters prior to on-orbit verification. It reports on improvements predicted by the acquisition simulator and evaluates on orbit performance with the optimized values. In addition, the paper discusses the commissioning of FGS 1R, installed during the February 1997 servicing mission, with regard to operational options predicted by the simulator. It also reports on how well the new FGS, with its on board alignment capability, is working with the new acquisition parameters determined by the simulator.

SOFIA, the successor of NASA's Kuiper Airborne Observatory KAO, is at present under development as a joint program of NASA and the German Space Agency DLR. SOFIA consists of a 2.5 m class IR telescope operated in a Boeing 747SP airplane at altitudes above 41,000 ft. The environment conditions of the telescope during operations in the open port of the aircraft are very harsh and not comparable with those of earthbound telescopes or space telescopes. The narrowness of the port, the disturbances by aircraft vibrations, aero- acoustic loads and wind, the low air pressure and temperatures, the airworthiness regulations, and the specified pointing accuracy of 0.2 arcsec are challenges for the telescope design, which need peculiar decisions. The SOFIA telescope concept takes up some essential features of the KAO telescope, but also acknowledges the technological progress and the increased mirror size. The optimal use of modern design and analysis methods- 'end-to-end- simulations', which combine the behavior of the optical, the structural, mechanical, and the control system and subdue it to the disturbances in the aircraft environment. The paper presents the principles design features of the proposed pointing control system for SOFIA and the latest result of the pointing simulations.

The main functions of the control system for the very large telescope (VLT) secondary mirror unit are to control the focusing, centering and tilt/chopping movement of the secondary mirror. The most challenging feature of the VLT M2 unit is to tilt the mirror with very high precision and dynamic requirements in chopping and field stabilization mode. During chopping the mirror is tilted up to 10 times per second with a maximum chopping step of 120 arcsec about an arbitrary axis. In the field stabilization mode the mirror has to follow any angular reference signal up to 10 Hz bandwidth with a very high precision. This paper gives an overview on the VLT M2 unit control system with emphasis on the development and realization of chopping control The finally achieved performance and the gained experience are presented.

A prototype telescope for the optical very large array (OVLA) project is under construction at the Observatoire de Haute-Provence (OHP), France. The OVLA will b a long- baseline optical interferometer of 27 mobile 1.5m- telescopes. In 2000, the functioning of the OVLA prototype will be tested outdoors alongsite the two other telescopes of the GI2T to form a 3-telescope interferometer. Firstly, we briefly present the design of this telescope highlighting its unusual characteristics, which include a spherical mount and a thin active primary mirror. We had to study a specific control system for driving mount and for the active mirror cell. Hardware and software design of these two systems are also presented, as well as some test results. Lastly, we propose a complete electronic architecture for the fully equipped OVLA prototype telescope. The telescope system is partitioned into elementary distinct subsystems each controlled by a small embedded calculator linked to each other by an addressable serial bus. With this kind of architecture, the telescope is fully autonomous. Thus the future installation of the OVLA prototype telescope at the GI2T site should be easier, as well as the installation of a large interferometer such as OVLA where 27 telescopes are expected.

Remote observing with Caltech's millimeter wave array at the Owens Valley Radio Observatory (OVRO) is being extended to use the graphical capabilities commonly available on computers today. To allow the instrument to be clearly presented to the user, a rich interface has been developed that combines the use of color highlights, graphical representation of data, and audio. Java and internet protocols are used to extend this interface across the Web to provide remote access. Compression techniques are used to enable use over low bandwidth links. This paper presents the design goals, implementation details, and current status of this effort with emphasis on the monitoring of the array.

As part of the upgrades to our observatory control software, we have developed a replacement for the astrometric kernel and the servoing system at the James Clerk Maxwell Telescope. The new PTCS astrometric kernel operates within the DRAMA tasking system. An EPICS servo controls the antenna drives. The THI, a DRAMA task, translates demands from the kernel and sends them to the servo, and then feeds back to the kernel the current drive encoder positions and the expected time of arrival at source position. The TEL DRAMA task at the top level interfaces between the existing observation control software and the telescope-independent PTCS task. This new system is replacing components of an existing observatory a Vax platform and sent demands via GPIB to a servo on a VME platform. The new PTCS and the TKI software run on a Unix machine and communicate via the DRAMA message system to the upper layer observatory system and via Channel Access to the EPICS servo running VxWorks on the VME platform. In this paper we will review the main features of the new telescope control system, and report on progress with implementation.

The James Clerk Maxwell Telescope is escaping from its dependence on VAX/VMS legacy software by incrementally upgrading its control system using platform-independent tools. The first stage of the upgrade includes a GUI, written in Java and modeled on project planning software, for defining complex observing recipes. Another GUI serves as an editor for observation definition files describing the details of an individual observation. The recipe designer also serves as an observation subsystem controller, executing observing scripts containing combinations of low- level and high-level commands, using the parameters from the observation definition file. The next stage of the upgrade includes a Java-based queue manager. The DRAMA system developed at the Anglo Australian Observatory provides a convenient bridge between the existing VAX/VMS-based instrument tasks and the new controller and queue manager.

The Keck Telescope Control System is organized as a set of independent hardware subsystems, a pointing subsystem, and a high-level TCS subsystem. The pointing subsystem handles real-time coordination of telescope, mount, enclosure, rotators and guiders. The TCS subsystem knows which low- level subsystems are required for a given instrument, and manages the parallel initialization, shutdown, status monitoring and fault recovery of the overall system. The TCS subsystem also provides a user interface which presents the system as a table, with an Overall row and a row per subsystem; each row has status and error message fields, and a set of standard controls. This user interface serves as the single point of access to the telescope control system for the observing assistant and the engineer: all the other observing and engineering tools can be launched from it. This paper describes the above paradigm, with special attention being given to the user interface. Potential use of the same model for other applications is discussed.

In this paper we present a control system design framework that supports advanced automation. The essential features include a hierarchical structure with independent subsystems, standardized command and status interfaces, high-level commands based on the operations model, and transformation of the operator's requests into subsystem demands. Described is an infrastructure consistent with this framework for applications based on the Experimental Physics and Industrial Control System toolkit. The design of the CFHT Telescope Control System Version Four (TCS IV) is presented as an example. TCS IV utilizes the concept of parallel virtual telescopes to regulate the flow of commands to the underlying subsystems. Each virtual telescope and each subsystem is characterized by a well-defined public interface. The virtual telescopes support movement of the associated beams within the mean or catalog coordinate systems. Parallel astrometric stacks implement the mean to observed coordinate transformations.

The Liverpool Telescope will be a fully robotic 2m telescope situated in La Palma and managed from Liverpool John Moores University. The telescope observatory control system is responsible for operating the telescope in a fully automated fashion, with observations selected from a database. After a brief introduction to object-oriented techniques this paper presents a class model for observatory control system database and discusses the choice of programming language and database management system. Finally, we present a brief description of the automatic code generation tool we have developed to allow fast and reliable implementation of the object model and discuss our overall experience of using object-oriented techniques to implement an observatory control system.

The Gran Telescopio Canarias (GTC) project office is in charge of the construction of an optical/IR 10-meter class telescope at the Observatorio del Roque de los Muchachos, in Canary Islands. The conceptual design phase has been completed in summer 1997, and the design of the control system has already started its initial phases. Recently, the complexity of the control system for large telescopes has increased. More and more functions are computer controlled. Distributed computer systems are an effective architecture for these telescope control systems, but distributed semantics are more difficult to deal with. This gives complex architectures that are hard to develop and maintain. Additionally, technological change is continuous in computing, as the periodic reports of control system upgrade programs show. To keep these architectures in step with change is not an easy task. In the GTC control system these issues are being taken into account from the beginning of the project. This paper is focused no how recent advances in distributed computing can help to deal with these problems.

A large prime-focus robotic star tracking device has been designed and constructed and is now undergoing commissioning atop the 9.2-meter Hobby-Eberly Telescope at McDonald Observatory in West Texas. The novel, cost-effective tracker represents a major departure in the way very large astronomical telescopes are controlled in pointing, tracking, and guiding. The tracker development and design implementation included detailed structural analysis, the application of minimum constraint kinematic design to a large gantry-type motion control system, and the unique application of a large precision hexapod to solve the dynamic tilting and focus motion problems. Challenging fabrication, test, and on-telescope assembly problems were overcome. Performance data of the completed device demonstrate that the tracker design and implementation efforts were successful.

During the design phase of the Green Bank Telescope (GBT), various means of providing an accurate surface on a large aperture paraboloid, were considered. Automated jacks supporting the primary reflector were selected as the appropriate technology since they promised greater performance and potentially lower costs than a homologous or carbon fiber design, and had certain advantages over an active secondary. The design of the active surface has presented many challenges. Since the actuators are mounted on a tipping structure, it was required that they support a significant side-load. Such devices were not readily available commercially so they had to be developed. Additional actuator requirements include low backlash, repeatable positioning, and an operational life of at least 230 years. Similarly, no control system capable of controlling the 2209 actuators was commercially available. Again a prime requirement was reliability. Maintaining was also a very important consideration. The system architecture is tree-like. An active surface 'master-computer' controls interaction with the telescope control system, and controls ancillary equipment such as power supplies and temperature monitors. Two slave computers interface with the master- computer, and each closes approximately 1100 position loops. For simplicity, the servo is an 'on/off' type, yet achieves a positioning resolution of 25 microns. Each slave computer interfaces with 4 VME I/O cards, which in turn communicate with 140 control modules. The control modules read out the positions of the actuators every 0.1 sec and control the actuators' DC motors. Initial control of the active surface will be based on an elevation dependant structural model. Later, the model will be improved by holographic observations.Surface accuracy will be improved further by using laser ranging system which will actively measure the surface figure. Several tests have been conducted to assure that the system will perform as desired when installed on the telescope. These include actuator life tests, motor life test, position transducer accuracy test, as well as positioning accuracy tests.

The adaptive optics system design for the W. M. Keck Telescope incorporates over twenty tracking and movable stages on the optical bench. This paper presents a commercial solution for controlling and positioning these stages. It describes the hardware system and the EPICS software interface used to communicate with the off the shelf hardware controllers. It touches on the positional accuracy and repeatability requirements and the selection of hardware to meet those requirements. It examines the cost and packaging issues and tradeoffs between developing custom hardware and software versus commercially available equipment. A method of synchronizing the stages to absolute time for telescope tracking is also presented.

The performance of on Alt-Az telescope depend strongly on its operating conditions. During tracking Alt-Az telescopes generally move slow but in some cases the dynamic range is large. Anyway the position errors must always be as close as possible to zero. A fixed structure controller cannot optimize the telescope performance in terms of error amount in the whole requested dynamic range. On the contrary a digital controller has the ability to modify its structure and its parameter values during operations, according to the instantaneous error values, system status, system actual sped and system characterization. This paper analyzes the problem of stability using such a variable structure controller in a case study.

We have previously described a system that derives the pointing coordinates of an equatorial telescope by measuring the angular position of a dual-axis tilt-table whose frame is rigidly attached to the telescope's primary mirror cell. In that system, two precision tilt-sensors aligned orthogonally and mounted in the plane of the table are used as nulling devices to close an active servo loop which holds the table level as the telescope moves. Rotary encoders measure the angle by which each tilt-table axis rotates, and a mathematical transform converts those encoder readings into telescope hour angle and declination. Recent work has indicated the feasibility of several simplifications to that system. First, by use of suitable low friction bearings on the tilt-table axes, along with non-contacting encoders, the active servo loop is no longer needed to level the tilt- table. Rather, a simple suspended weight keeps the platform almost level, with the residual small tilt error measured by the precision tilt sensors.Second, by suitable orientation of the weight and the tilt sensors relative to the telescope polar axis, the system can measure telescope hour angel and declination directly, eliminating the need for the complex mathematical transform. Experimental result using these ideas are presented.

The Green Bank Telescope (GBT) is designed to be a flexible instrument, accommodating many different types of front ends, back ends, and observing styles. In order to support this flexibility, a system architecture was developed according to the principles of modularity. The system is a loosely coupled group of cooperating computers, tied together to form a complete system. The hardware design of the GBT Control System will be presented. The computer architecture, network architecture, and system synchronization and timing methods will be addressed. Progress towards implementation will be described, and the lessons learned as a result of implementing the system will be covered.

The Green Bank Telescope (GBT) is under construction in Green Bank, West Virginia. The GBT is expected to be operational in mid 1999. Networking the GBT will require innovative application of network technologies. Distribution of data from the originating source to large groups of consumers can be accomplished in at least two ways. The first is to 'unicast' or communicate individually with each consumer on the net. The second is to 'multicast' to a group of consumers. Multicasting is a technology which seems to have merit for distribution of information, but it is inherently unreliable. In some cases, such as observational data, packets must be delivered reliably, while in other cases such as informational displays, reliable delivery is not essential. This paper introduces the basic concepts of multicasting, and also discusses the design approaches of reliable multicast protocols.

While the new, very large optical/IR telescopes setal most of the astronomical limelight, the relevance of smaller telescopes till remain undiminished as far as scientific output is concerned. Mature technology an reduced competition for observing time allow these telescopes and their backed instruments to be fine tuned for specific scientific programs. In order to maximize returns, it is essential to reduce time overheads in pointing and acquisition and ensure that the telescopes spend most of the time observing the targets. A sensitive and accurate auto- guidance system is another necessity. We have developed an acquisition and guidance system, which is flexible enough to be used with a wide variety of instruments at the different existing and planned telescopes in India. An implementation of this system, as part of an imaging polarimeter, has been working successfully for quite some time now. When used with a 1.2 m, f/13 telescope, this system is capable of acquiring the target within a few arcseconds and tracking, with subarcsecond accuracy, on stars as faint as V equals 15, available anywhere in a scan area of 0.05 square degrees, within about 15 arcminutes of the target.

The 1.8 meter Spacewatch telescope and its building on Kitt Peak were dedicated on June 7, 1997 for the purpose of finding previously unknown asteroids and comets. Drift- scanning large areas of sky with a CCD will be done at rates up to 10 times that of the sidereal rate over angles up to 60 degrees of arc along great circles at various orientations. The primary mirror and cell around which the telescope are from the multi-mirror telescope on Mt. Hopkins in Arizona. The telescope's friction drive system allows backlash-free control of its altitude-over-azimuth mount. The mount features bearings of small radii and plenty of motor torque to compensate for wind buffeting. Both incremental and absolute encoders will be used; the absolute encoders will update the position derived from incremental encoders to compensate for the microslipping that is an unavoidable consequence of a friction drive. The control system features commercially produced servo controller cards that are programmed from a user interface program running in a PC under DOS. Realtime operation of the drive is controlled by the interface cards, leaving the PC free to run the display of the position readout and accept keyboard input for the observer without interfering with the drive. It is believed that this design offers the greatest flexibility and accuracy of our search programs.

The 2.5mts telescope designed for the Sloan Digital Sky Survey is a mechancial structure that presents five degree- of-freedom. Azimuth, altitude and the instrument rotator axis are fitted with servo controls. The low frequency dynamic are dominated by the bearing friction. Several mathematical models have been presented in the literature to include its effect into the dynamic model of mechanical structures. The model employed in this paper includes consideration of the Striebeck effect, dynamic behavior at very low velocities and the pre-sliding at near zero- velocity. Result of the parameter estimation of the friction model of the three principle axes are presented as well as the behavior of the structure when different torque stimuli are applied. The mathematical model used to include the friction phenomena into the telescope dynamic model is simple. It does a good job of describing the friction over a wide range of velocities but particularly at or below sidereal rate. It is a straight forward process to determine the parameters and, in simulations, does not require large amounts of computer time.

Scheduled among the deep space communications activities of the 70-m antennas of the NASA Deep Space Network (DSN) are diverse astronomical observing programs with different requirements. For example, the US Space VLBI Project puts great emphasis on reliability for a few well-defined types of observations, for which the software is essentially frozen for the duration of the Project. On the other hand, Solar System Radar research and observations of regions of star formation need ongoing development, sometimes in real- time, of data acquisition and monitor and control software. This paper describes the methodology by which we can allow each user or project a high degree of customization. To do this we rely on a mixture of public domain software and locally developed software. The scheme allows the software configuration in the Radio Astronomy Controller to be switched to an observer's or project's specific configuration within seconds, including specific releases of public domain software. At the core of the Radio Astronomy Controller is a server that controls the R and D equipment. The behavior of this server is largely determined by Tcl scripts, which are customized for the observer or project. An observer working interactively can use a customized Tk client to direct the server via TCP, as well as DSN operational equipment via another server which communicates with DSN controllers. A project or user may alternatively run a client which is specialized for unattended operations.

Two remote presence observations on Dec. 25, 1995 and Mar. 7, 1997 were achieved at the 1-m telescope of Yunnan Observatory. In this paper, the observations are introduced in detail. The technical methods in the remote presence observation are also discussed under the current circumstances of hardware and software in China. The brilliant prospects of the observational method are shown as well.

A class of large satellite communication antennas built in the mid-1970's comprise a potential set of large antennas available for use by radio astronomers upon upgrade. With the advent of low noise technology these facilities have been superseded in the communications industry by smaller, more manageable facilities. Although many have sat idle and decaying over the intervening years, these facilities remain a potential resource for research and education. A pair of such dishes has been acquired by Georgia Tech and one of the 30 meter antennas has been completely mechanically and electrically stripped and new mechanical, control, RF, and electrical systems installed. The antenna is now driven by four continuous-speed vector-controlled three-phase AC induction motors with variable frequency vector motor drives. Sixteen bit resolution optical absolute position encoders on each axis provide telescope pointing data. Sixteen bit resolution optical absolute position encoders on each axis provide telescope pointing data. A programmable logic controller provides interlock monitoring and control. The antenna is controllable both manually via a portable remote control unit and via a Pentium PC running control software on a real-time UNIX-based platform. The manual unit allows limited control at two user-selectable speeds while computer control allows full tracking capability with accuracies of better than 0.3 arcminutes. The facility can be remotely controlled via the internet, although currently only a dedicated line is used. The antenna has been refitted with an ultra-broadband feed system capable of operating from 1-7 GHz.

The GTC project is in charge of the construction of an optical/IR 10-meter class telescope at the Observatorio del Roque de los Muchachos in Canary Islands. The GTC control system (GCS) will be responsible for the management and operation of the telescope, including its instrumentation. Its conceptual design has been completed in summer 1997. The continuous and rapid development of hardware, software and communications technology has permitted a greater complexity in control systems. In their turn, the development of active and adaptive optics, the new methods of optimizing available observing time and the continuous development programs to maintain telescope competitiveness present new challenges in the design of control systems. During its life-cycles, the GCS will be subject to continuous changes brought about by different factors, such as the advent of new technologies, the evolution of the requirements, the development of new instruments and fault correction. These factors must be taken on board with the minimum possible impact, not only on the project but also on the availability of the GTC once it enters into operation. This will only be possible through the selection and planning of an adequate technological framework that enables these changes to be assimilated throughout the life-cycle of the telescope. In this presentation the fundamental aspects of this framework along the current status of the control system design are outlined.

A framework for the construction of network services for observation planning and execution is presented. The framework is implemented using portable public domain software packages, and its components present a simple, self-descriptive application programming interface. Typical components are functionally independent units which can provide services to local/remote clients either via direct connections, or via a WWW gateway. A remote user or software-agent can query a component in order to discover the command set supported.

Up to now receiver control software was a time consuming development usually written by receiver engineers who had mainly the hardware in mind. We are presenting a low-cost and very flexible system which uses a minimal interface to the real hardware, and which makes it easy to adapt to new receivers. Our system uses Tcl/Tk as a graphical user interface (GUI), SpecTcl as a GUI builder, Pgplot as plotting software, a simple query language (SQL) database for information storage and retrieval, Ethernet socket to socket communication and SCPI as a command control language. The complete system is in principal platform independent but for cost saving reasons we are using it actually on a PC486 running Linux 2.0.30, which is a copylefted Unix. The only hardware dependent part are the digital input/output boards, analog to digital and digital to analog convertors. In the case of the Linux PC we are using a device driver development kit to integrate the boards fully into the kernel of the operating system, which indeed makes them look like an ordinary device. The advantage of this system is firstly the low price and secondly the clear separation between the different software components which are available for many operating systems. If it is not possible, due to CPU performance limitations, to run all the software in a single machine,the SQL-database or the graphical user interface could be installed on separate computers.

The axes control of a modern telescope such as TNG requires a large amount of software in order to manage the complex control hardware. The low level software is always the most difficult to develop and test since its behavior strictly depends on the physical device, and theoretical solutions often reveal not applicable. Simulation is precious but field tests are in this case absolutely necessary. This paper overviews the main components of the TNG axes control software, refined and tested on the field.

The primary mirror of the Apache Point 3.5 meter telescope rests on an array of small pneumatic actuators distributed over the back plate of the mirror and within its honey comb cells. A control system constantly adjusts the pressure in the actuators so as to synthesize a perfectly rigid mounting, thus maintaining both the figure of the mirror and its orientation with respect to the mirror cell. In its original configuration, the APO 3.5 meter system exhibited a number of anomalous behaviors that detracted from the optical performance of the telescope. Analysis of the design indicated three basic problems: first that the pneumatic servovalves suffered from mechanical nonlinearities and an adverse dependence of their transfer function on operating pressure; second, that the air supply system could not exhaust air from the actuators rapidly enough near the horizon and zenith; and third, that the control system did not adequately account for the inertia of the mirror under dynamic conditions. Consequently, we have designed and installed a new control system which addresses these deficiencies. The new system employs high-bandwidth, flapper-type proportional valves that eliminate the mechanical problems and permit implementation of a high- performance controller. The new controller utilizes the existing hard points for mirror position sensing, but implements a pressure-feedback inner loop and a more sophisticated dynamic model. The air supply system now incorporates a sub-atmospheric return and operates closed- loop to minimize contamination problems. The new system exhibits substantial improvements over its previous performance, with positioning errors in the sub-micron range. The design has been selected for use on the Sloan Digital Sky Survey telescope.

THe paper describes an actively controlled six-axis orthogonal hexapod mount that provides vibration isolation, suppression and steering capabilities for space observational systems. Experimental results for vibration isolation is presented. The results show that though the passive-only isolation reduces disturbance propagation significantly, the combination of active and passive isolation provides the best option. The active stage reduces the propagation over the passive-only case by additional 35 dB in the mid frequency range of 10-100Hz.

The Observatorio Astronomico Nacional, located at Tonantzintla, Puebla, Mexico, has a 1 m equatorial mount telescope of excellent quality. In order to increase its potential for research, teaching and outreach programs, the Astronomy Institute has generated a project for the remote operation of the telescope and acquisition of astronomical data from the university site in Mexico City. The telescope has computerized control, whose programs are recently optimized for remote control handling. The dome was optoelectronic codified in order to have its movements coordinated with the telescope. The Ethernet type fiber optics network is the communication channel for the remote control of the telescope. This will allow to carry out a significant number of projects for the acquisition and processing of astronomical data. The status of the 1 m telescope remote control system is presented.

Improvements to the general dome conditions and the use of near IR detectors at the National Research Council of Canada's 1.8m Plaskett Telescope have stressed the abilities of the existing encoders. An encoding system that could be installed without telescope downtime and with a minimal impact on resources was necessary. These, and other, issues motivated the development of a method of non-contact encoding using a long line-scan CCD, a precision insensitive ruled tape and digital imaging metrology. Based on previously published simulation and experimental result a project to install such a system on the polar axis of the Plaskett Telescope was initiated. In this paper we present the overall design strategy, processing algorithms and initial test result and analysis. We end with recommendations to improve the capabilities of the approach.

The James Clerk Maxwell Telescope on the summit of Mauna Kea in Hawaii is a 15 meter sub-millimeter telescope which operates in the 350 microns to 2 millimeter region. The primary antenna surface consists of 276 panels, each of which is positioned by 3 stepper motors. In order to achieve the highest possible surface accuracy we are embarking upon a project to actively control the position of the panels adjuster system is based on a 6809 micro connected to the control computer by a GPIB interface. This system is slow and inflexible and it would prove difficult to build an active surface control system with it. Part of the upgrade project is to replace the existing micro with a 68060 VME micro. The poster paper will describe how the temperature of the antenna is monitored with the new system, how a Finite Element Analyses package transforms temperature changes into a series of panel adjuster moves, and how these moves are then applied to the surface. The FEA package will run on a high end Sun workstation. A series of DRAMA tasks distributed between the workstation and the Baja 68060 VxWorks Active Surface Control System micro will control the temperature monitoring, FEA and panel adjustment activities. Users can interact with the system via a Tcl/TK based GUI.

This paper describes an electronic logsheet designed to be easily connected to both existing and new instruments for the Lick and Keck Observatories. The primary motivation for such a log is to automate the recording of basic observing parameters in a form that preserves the best characteristics of paper logs: columns that can be readily annotated with text or sketches, and user choice of what data form the log. To these capabilities, Electrolog adds simultaneous viewing/editing by local and/or remote observers, who can share annotations and emendations, if desired. The log can be written out in plain text, in 'pretty-printed' PostScript, as a FITS ASCII table extension, or as a native- format dump. Either the FITS file or the dump format can be read back in by another instance of the logsheet. It is simple to splice the logsheet into existing data-taking programs. It accepts data in a variety of formats, including raw FITS image headers. As a useful side-effect, a dozen- line Tcl script can generate 'retrospective' logs form a set of FITS image files.

The paper presents an application of fuzzy logic controller to regulate the DC motor driver system of astronomical telescope. The mathematical model of such a telescope is highly nonlinear coupled equations. However, the accuracy requirement in telescope system exceed those of other industrial plants. Fuzzy logic controller provides means to deal with nonlinear functions. A fuzzy logic controller (FLC) was designed to enhance the performance of a two-link model of astronomical telescope. The proposed FLC utilizes the position deviation for the desired value, and its rate of change to regulate the armature voltage of the DC motor drive of each link. The final action of FLC is equivalent to PD controller with a variable gain by using an expert look- up table. This work presents the derivation of the mathematical model of 14 inch Celestron telescope and computer simulation of its motion. The FLC contains two groups of fuzzy sets.

The Hubble Space Telescope (HST), the first of NASA's Great Observatories, was launched on April 24, 1990. The HST was designed for a minimum fifteen-year mission with on-orbit servicing by the Space Shuttle System planned at approximately three-year intervals. Major changes to the HST ground system are planned to be in place for the third servicing mission in December 1999. The primary objectives of the ground system reengineering effort, a project called 'vision December 1999. The primary objectives of the ground system re-engineering effort, a project called 'vision 2000 control center systems (CCS)', are to reduce both development and operating costs significantly for the remaining years of HST's lifetime. Development costs will be reduced by providing a modern hardware and software architecture and utilizing commercial of f the shelf (COTS) products wherever possible. Operating costs will be reduced by eliminating redundant legacy systems and processes and by providing an integrated ground system geared toward autonomous operation. Part of CCS is a Space Telescope Engineering Data Store, the design of which is based on current Data Warehouse technology. The purpose of this data store is to provide a common data source of telemetry data for all HST subsystems. This data store will become the engineering data archive and will include a queryable database for the user to analyze HST telemetry. The access to the engineering data in the Data Warehouse is platform- independent from an office environment using commercial standards. Latest internet technology is used to reach the HST engineering community. A WEB-based user interface allows easy access to the data archives. This paper will provide a high level overview of the CCS system and will illustrate some of the CCS telemetry capabilities. Samples of CCS user interface pages will be given. Vision 2000 is an ambitious project, but one that is well under way. It will allow the HST program to realize reduced operations costs for the Third Servicing Mission and beyond.

A difficulty in writing control software for research telescopes is designing sufficient flexibility to handle continually changing requirements. The primary goal of the control software architecture for NRAO's new 100-meter radio telescope in Green Back, West Virginia is flexibility through the construction of a modular software system. Using the principles of modular design: (i) the number of systems implemented to satisfy the required functionality between users and devices was minimized; (ii) each device was implemented as an autonomous unit; (iii) object-oriented design and C++ were used throughout the system. The purpose of this report is to present the software architecture being used to achieve a modularity in the Green Bank Telescope.

Since March 1997, the TNG Telescope is int its Commissioning phase. In this paper, we describe the structure of the control software of TNG and the on-going activity of the software integration team. The Telescope Communication Network has been completely installed, the control software has been set up and the integration phase is currently in progress. The TNG control software has been designed having in mind the needs of a modern telescope control system: it is based on stable and widespread industry standards; its architecture is fully modular and intrinsically open in order to allow future enhancements and/or modifications of its components. Moreover, the code was written paying a particular attention to its portability. All these characteristics make the TNG control system open to future technology evolutions, both hardware and software-wise. The TNG control software provides a coherent environment where the information flow is constantly guided and controlled through its path across the system. Despite the multiplicity and non-homogeneity of the different subsystems, TNG provides the operator a common framework from the raw data gathering, to the real-time applications, up to the operator interface and archiving system. This was made designing and building a set of layers of increasing abstraction that were mapped onto the various physical components. A brief description of the steps followed during the integration of a number of subsystems will be given.

We describe a speckle-based, telescope-position encoder that overcomes the need the ruled scales and gratings. Using the natural surface markings to produce a speckle pattern, the system is noncontacting and simply aligned. Imaging with a CCD and computing displacements with binary correlation, sub-pixel resolution can be achieved by parabolic approximation. Results of test on the 2-meter telescope at San Pedro Martir are presented.

On-shop test erection has been carried out at the Hitachi Zosen factory in Osaka since 1996. The purpose of this on- shop erection is to check and adjust the sizes of parts, to minimize the assembling errors, to test the telescope drive and active support system of the primary mirror, and to review the processes of final assembling. The alt-azimuth Subaru telescope structure weighting 500 ton is supported by six hydrostatic oil-film pads and is driven successfully by direct drive. The additional test for the instrument rotator drives, cable wrappers, and other were also carried out. We report the preliminary results of the control efficiency.

The Galileo National Telescope is a 3.6 meter Alt-Az telescope installed at the Astronomical Observatory of the Roque de Los Muchachos in La Palma, Canary Islands. The Galileo drive and control systems were designed and developed by the Technology Working Group of the Capodimonte Astronomical Observatory, Naples. Apart from a short review of the drive system, the paper describes a novelty in the adaptive preload sub-system.

The TT1 is a 1.54 m Alt-Az telescope designed and built by the Technology Working Group of the Astronomical Observatory of Capodimonte, Naples, Italy. The standardization process is of course one of the fundamental requirements for telescope control system design and development, well considered in the TT1 design. In this paper we present the approach used to identify a control system applicable to medium-size Alt-Az telescope. The TT1 control system architecture is based on a distributed working flow and it is PC-based, i.e. organized in several interconnected standard PCs and standard fast communication protocol. Every PC is based on the 'dedicated processing unit' concept and it makes real time own tasks independently by other units. Also, the extremely reduced communication flow between PCs, and the internal organization based on the preference given to software rather than hardware solutions, makes its control system extremely reliable, easily reconfigurable and upgradable, obsolescence deprived and independent from any hardware choice.

The encoder is the most used angular transducer in position control applications, such as the main axes position control of a telescope. In astronomical applications a very high precision in axes control is required. So a good encoder system design is essential to satisfy the requirements settled by the scientific goals. Today very good encode system are provided by several suppliers, with multiple readouts and error compensation capabilities into increase the reading precision and lessen the errors. Nevertheless during the lifetime of the system some unexpected errors can arise. In this paper some techniques to recognize, analyze and lessen the unavoidable encoder system error are described, with reference to some case studied.

We adopt the hierarchy structure for the telescope control system of the Subaru Telescope. The system is made up of a TSC, three TWSs, three DCMOMs, three MLPs, and many LCUs. All devices are connected through local network each other.

The computing equipment of the 2.5-m Isaac Newton Telescope and the 1.0-m Jacobus Kapteyn Telescope is being upgraded to improve improve observing efficiency and ease of use, and to reduce maintenance and operation costs. These upgrades have been staged over a period of two years to reduce the impact on operations. Elements of this architecture will be used in the forthcoming upgrades to the 4.2-m William Herschel Telescope. The revised systems have allowed the introduction of a major new instrument for the INT: the Wide Field Camera, shortly to be equipped with a mosaic of four 4096 by 2048 EEV CCDs. On the JKT, the new equipment paves the way for remote operation.