5  Telescope Control System

Telescope is on commercial power not on UPS. If there is a power glitch telescope power will be turned off.

5.1) Introduction

5.2) The TCS PC

5.3) The Telescope Control Console

5.4) Manually Restoring Coordinates Using the Tilt Meters

5.5) Telescope Hand Paddle

5.6) The Dome

5.6.1) Introduction

5.6.2) Dome controller

5.6.3) Back-up procedure for closing a disabled dome

5.6.4) Obtaining dome flat fields with the white screen.

5.7) Moving The Telescope Away From the Horizon

5.8) Time Synchronization

5.9) What to do When Things Don't Work

5.1  Introduction

This chapter describes how to operate the telescope and the display console. The telescope can only be moved by manually pressing push buttons at the telescope or hand paddles. We are currently looking at the feasibility of upgrading the system to work under computer control. Figure 5-1 shows the basic building blocks in the control system.

The observer spends most of the time in the observing room where the telescope and its finder-guider-filterwheel known as the Multiple Instrument System (MIS; Chapter 6) are controlled using two computers. The first computer, a Pentium PC that runs the Telescope Control System (TCS), controls the telescope pointing. The second, a Sparc5 workstation called kilauea provides the user interface to the TCS and MIS mirrors and spectral lamps, and also the CCD data acquisition and image processing (Chapter 4).

A telescope hand-paddle in the observing room enables setting and guiding the telescope, and changing the focus. To slew the telescope the observer must go into the dome and operate the slew buttons on the telescope console. It is easily possible to slew the telescope into the northern pier when observing in the north-west part of the sky. Thus, it is also possible to let the telescope track into the pier and observers should be wary of this, especially when working at high northern declinations.

5.2  The Telescope Control System PC

The Telescope Control System (TCS) program, which displays the current position of the telescope, is controlled by a Pentium PC computer. The current TCS was developed by Robb Lovell, Bob Barr, and John Thorstensen in 1997. Eventually, we hope to have a new TCS that will automatically control all the functions of the telescope. The TCS computer is left on at all times (in the computer room), but its monitor may be turned off or the brightness turned down (both controls are inconveniently located at the front of the monitor). The TCS monitor is the one just to the right of the kilauea monitor on the observer's table.

Figure 5-1: Control System Overview

Figure 5-2: Generic xtcs Window

The XTCS program running on mcgraw supplies the xtcs window to set all of the TCS quantities, i.e., set RA, DEC, Epoch and Dome encoder (Figure 5-2).

To change the display epoch of the telescope coordinates press TCS Epoch in the xtcs window, type the epoch into the Display Epoch pop-up window, and press carriage return.

To reset the telescope encoders, center a bright star of known coordinates in the CCD or spectrograph slit then complete the RA, Dec, and Epoch fields in the xtcs window. Click the mouse on Set encoders in the Setup pop-up menu, and the display will automatically be updated. The RA, Dec, and Epoch fields on the TCS Monitor will be flushed and updated.

Warning: The TCS can be somewhat flaky when updating its quantities. In particular, you must enter an epoch with one decimal place, e.g., 2000.0, and always press carriage return separately in each field that you change. As a last step, check the TCS monitor to be sure that the quantities have changed as you intended. If not, don't move the telescope, but enter the numbers again until you get it right.

The current dome home position is 51 degrees. To reset the dome azimuth, go out into the dome and read the current position, as indicated by the red marker located under the slit, and enter it into the Dome encoder field found in the Setup pop-up menu. Pressing carriage return will update the dome encoder and TCS monitor display. The position of the dome slit with respect to the telescope is displayed as rectangle on the TCS monitor. (Figure 5-3 shows the same monitor atop the telescope console). Rotate the dome using the hand paddle to keep the * symbol centered in the window. When the dome is approaching 180^o out of phase the * symbol flashes at the top of the window. Also a dome azimuth error is displayed just under the current Dome Azimuth on the TCS monitor. The * symbol turns into a O when the dome is occulting. It's a good idea to check the actual dome azimuth a couple of times per night, as the usefulness of the video display depends on the dome encoder having been set correctly. Occasionally the dome encoder can accumulate an error.

5.3  The Telescope Control Console

The Telescope Control Console (Figure 5-3) is located in the north-east corner of the dome. It is on casters and can be moved. However, the telescope counterweight can crash into the console if you move it from the standard position.

The telescope positions are displayed on the TCS monitor that is perched precariously on the top of the console, next to the pencil sharpener. That display is the same as the TCS monitor in the control room. The two built-in monitors are vestigial, as are the other readouts on the console. A pull-out draw to rest finding charts and papers lies just below the main panel of switches. The sidereal amplifier is housed at the bottom of the cabinet. Be careful not to accidentally kick the toggle switch off with your feet.

The Telescope Control Console is kept in the dome to enable the operator to maintain visual contact with the telescope while slewing, because it is possible to crash the telescope into the northern pier when moving to the west at high declinations. It is also possible to let the telescope go below the horizon. Novice observers, and even experienced but sleepy observers, can misinterpret the numbers on the TCS monitor, or zone out. The only reliable way to prevent a serious accident is to watch the telescope during the slew motion. Remember that the telescope coasts as much as 10 degrees after releasing the slew buttons.

Figure 5-3: 1.3m Telescope Control Console

A number of the console features are obsolete. The only current functions are:

POWER:

Turn the key to apply power to the drive chassis (it is normally left at the ON position).

START:

Starts the telescope console if the key has been turned to ON.

EMERGENCY STOP:

Removes power from the motor drive chassis and all the hand paddles. Use it to stop a run-away telescope at any time.

TRACKING MODE SELECTOR:

Set this rotary switch to 60 Hz unless you plan on trailing objects. (The sidereal rate oscillator is broken, but the 60 Hz drive is a close approximation.) Turn it off at the end of the night.

N, S, E, W:

Basic directional buttons. When used alone they move the telescope at guide speed. The telescope can also be moved at guide speed (1.33 arcseconds/second) using a hand paddle in the observing room.

SLEW:

Hold down the slew button then press the N or S and E or W button(s) to move the telescope at high speed (2.5 degrees/second). The telescope coasts along for 6 to 10 degrees after releasing the slew buttons. The quickest way to perform long slews is to hold down the slew button with your left hand and the direction button(s) with your right hand. About 15 degrees before reaching your object release the directional button(s) and then control the speed by giving 1 to 2 second bursts on the same directional button(s) as the motors slow down. You cannot reverse direction until the telescope has come to a complete stop in that axis. The slew facility is only available at the console. When you are within 2 degrees of the object it is more efficient to use the set speed than to try short jabs of the slew buttons.

SET:

Hold down the set button and then the direction button(s) to move the telescope at medium speed (100 arcseconds/second). The telescope can also be moved at set speed using the hand paddle in the observing room.

7^o SLEW:

Used to slew the telescope to the horizon. Must be used in conjunction with the LIMIT OVERRIDE button.

FOCUS:

We recommend changing the focus using the hand paddle in the observing room. The focus numbers on the telescope console and observing room display are not synchronized.

The telescope has to be re-focussed as the temperature of the telescope truss structure changes. The focus decreases by approximately 2 units per ^oF drop.

DOME LEFT-RIGHT:

You can rotate the dome from the console, the dome control box, or any of the hand paddles. The telescope is looking out of the dome slit when the * symbol appears in the box window of the telemonitor video. Keep the * symbol centered; there is no automatic dome control.

PLATFORM UP-DOWN:

The platform can be raised for engineering purposes. A siren sounds when the platform is raised because the instrumentation can crash into the floor. Do not raise the platform to open the mirror petals. Use the stepping stool provided for this purpose.

CONSOLE LIGHT:

Remember to turn the light off when integrating!

MIRROR COVERS:

The mirror covers are opened and closed manually. Use the small stepping stool which is stored in the corner of the platform to gain access to the crank which is located at the south-west or north-west corner of the mirror cell.

5.4  Manually Restoring Coordinates Using the Tilt Meters

If the TCS loses its positions you must manually restore the coordinates using the tilt meters. Go into the dome, turn the tracking mode selector off, and slew the telescope to the zenith. Back in the observing zoom use the hand paddle with set motion to bring the tilt meters to zero. The tilt meters are located in the computer room Right middle rack. Check that the RA field in the XTCS window is set for the current sidereal time plus about 30 seconds, the Dec is at 31^o 57' 00", and the epoch is the current date. Then press SET ENCODERS in the XTCS setup pop-up menu. Go back out into the dome, turn the tracking mode selector back on, and point at a bright star. (Obsolete: If necessary use the piggy-back refractor to acquire the star). Center the star in the slit or CCD, enter its coordinates and epoch in the XTCS window, and press SET ENCODERS in the XTCS setup pop-up menu.

5.5  Telescope Hand Paddle

Various paddles are connected to the telescope, but under normal circumstances you will only use the one located in the observing room. It allows guide and set motions, focus, and dome rotation. It is easily possible to crash the telescope into the northern pier, especially when working at high declinations. That is why there is no slew button available in the observing room.

5.6  The Dome

5.6.1  Introduction

The observatory dome is a single skin aluminum hemisphere 9.1 m (30 ft) in diameter, manufactured by Ash Domes. The outside surface is painted with titanium oxide and slightly over-cools by radiation at night. A DROP-OUT shutter allows the telescope access down to the horizon although this is limited in practice by the English cross-axis mounting design. The dome is operated manually but has a computer readout to allow manual centering of the slit from the observing room.

Figure 5-4: Dome Controller

5.6.2  Dome controller

The dome can only be opened and closed from the control panel located inside the dome (Figure 5-4), and only when it is at the home position of 51^o.

To open the dome:

• Ensure that the mirror covers and dark hatch are closed.
• Press the main shutter open button. There is no need to keep your finger on the button. It will automatically stop when fully open.
• Press the DROP-OUT open button. It is locked out until the main shutter opens by a few degrees. You must keep your finger on the button. When fully open the sound will change.

Special attention must be paid to ice build up during the winter months. Do not attempt to open the shutter doors if they are iced over. Try turning the icy area towards the sun.

To close the dome:

• Close the mirror covers and dark hatch.
• Turn the dome to the home position (51^o) and ensure that the contactor boxes are centered.
• Close the DROP-OUT shutter (keep finger on button).
• Close the MAIN shutter (it will stop automatically).

5.6.3  Back-up procedure for closing a disabled dome

The dome shutter doors can only be operated when the contactor box is at the home position of 51^o, and making positive contact with the feet attached to the dome. If it seems that the contactor box is not supplying power, realign it exactly. In the unlikely event that the contactor box still fails to supply power, it will be impossible to open or close the dome from the dome control panel.

To open or close the dome when the contactor box fails:

• Rotate the dome to the home position (51^o).
• Climb the ladder and retrieve the power cord from the motor unit near the bottom of the shutter.
• Plug the power cord into the Auxiliary Shutter Power Source (Figure 5-5).
• Open or close the shutters by climbing the ladder and using the AUXILIARY SHUTTER CONTROLS (Figure 5-6) located near the motor.
• Disconnect and STOW THE POWER CORD.

Figure 5-5: Auxiliary Shutter Power Source

Figure 5-6: Auxiliary Shutter Controls

5.6.4  Obtaining dome flat fields with the white screen

The dome is equipped with a round white screen for obtaining flat fields and a lamp with a dimmer switch that illuminates it. The lamp and dimmer are mounted on the south end of the telescope pier.

• Make sure the dome is at the home position, 51^o
• Open the mirror covers and MIS hatch.
• Move the telescope to H.A. +01^h 19^m, and DEC. -12^o
• Make sure the tracking is off.
• Turn on the flat lamp and turn off all the other lights in the dome. Flats work best with minimum of extraneous light.
• Adjust the dimmer to get about 25,000 counts per pixel with times not less than 5 seconds. (Shorter exposure times may result in uneven illumination of the CCD by the shutter).
• Remember to stow the telescope and close the mirror covers and MIS hatch when you are finished.

5.7  Moving the Telescope Away from the Horizon

It is possible to crash the telescope into the northern pier when observing at high northern declinations. It is also possible to let the telescope go below the horizon.

If the telescope is inadvertently left to track to the horizon you must use the 7^o SLEW and SLEW OVERRIDE buttons together with the correct direction button to get the telescope back to near the zenith. (Make sure you have the direction correct, or you will continue to turn the telescope upside down!).

5.8  Time Synchronization

We synchronize all of our computers' clocks to the GPS time servers at Kitt Peak, with alternative servers designated should one of them be down. The network time protocol (NPT) program runs on all of MDM's computers. So their time should be correct to within about 1 second.

5.9  What to do When Things Don't Work

If you can't seem to fix a problem yourself, please call Bob or Steven until 10:00 pm. Their phones numbers are on the cork board in the control room.