Starting the APT system

Important warnings

• Under no circumstances stand on the telescope when the RA locking pin is removed. The telescope may suddenly slip in RA (as it has for several observers over the last few years), resulting in the possibility of severe personal injury.
• Make sure the telescope is at zero hour angle before moving the roof, else severe damage to the telescope and/or roof will occur. A microswitch should prevent the roof moving unless the telescope is at zero hour angle. If the telescope isn't at zero hour angle, it can be moved there by loosening the bolt on the RA friction drive and then pushing it by hand.
• Keep the lens free of dew at all times! It helps to leave the fans at the top of the telescope on while observing. The lens is made from water soluble glass and can be irreparably damaged by repeated exposure to moisture. Humidity levels above 90% will quickly lead to dewing, well before other telescopes on the mountain are affected. If the lens gets wet, please use the hair dryer to dry it (but be extremely careful not to overheat the glass--you should hold the dryer about 0.5 metres or further from the lens, and move it rapidly to ensure that no point on the glass is heated too much). Do not attempt to clean the lens. Note that in some observing conditions, if the lens gets damp and the fans evaporate the water, the lens will cool further, thereby attracting more condensation, and so on until ice forms.

Starting the mechanical systems

• Turn off the electric blanket lens heater if it is installed, and remove it from the lens. The mirror heater should be left on, with its variac set to 110V. Check that the heater power cables won't get caught when the telescope moves. The purpose of the mirror heater is to increase the life of the mirror coating by reducing the amount of condensation.
• Turn on the fans at the top of the telescope. They help keep the lens free of dew, usually (see the warning in the previous section).
• Check that the two roof chains are off and the lens cover is on (so that the lens won't get damaged if something drops onto it when the roof is opened). The telescope should be held vertical by the RA locking pin. There is a microswitch on the mounting which prevents the roof from moving if the telescope is not at zero hour angle. Before opening the roof, ensure that the fluoro lights are off so as not to interfere with other observers on the mountain.
• Open the roof (the button is in the control room: turn on the roof power, press and hold the OPEN button until the roof stops of its own accord, keep an eye on the telescope to ensure that the roof doesn't hit it). If the roof doesn't move, check that the microswitch on the mounting has been activated.
• Turn off the roof power (in the control room). The reason for doing this is that large mains spikes occur when the telescope goes through zero hour-angle (and activates the roof microswitch). These spikes can crash the PC.
• Remove the lens cover, taking great care not to slip: the ladder is not very stable. It is OK to stand on the telescope if the RA locking pin is in place. While you are up there, make sure that the CCD electronics box is on, and that the several cables going into the CCD electronics box are securely plugged in (the mains cable sometimes pulls out). Put the lens cover behind the work bench, so that it isn't blown around by wind gusts.
• Stow the ladder out of the way, so that the telescope won't hit it. It is best to fold the ladder up and put it on the floor.
• Make sure that the RA and Dec servo amplifiers are off (so that the telescope won't slew when first turned on). The servos are in the control room.
• Take out the pin from the RA lock while keeping hold of the telescope. Check that the telescope is balanced in RA by gently pushing it and ensuring that it moves freely both to the east and west (if you don't do this, the APT may swing out of control and damage itself or you). Insert the pin into the telescope base, this activates a microswitch which enables the telescope to move. The hole into which the pin is inserted is on the north-west side of the mounting, about 0.5m from the ground.
• Tighten the bolt on the RA friction disc, by tightening (using your fingers without a wrench) as much as possible while keeping the large rectangular ``washer'' under the bolt head roughly aligned with the depression in the steel plate. Then use the tool to turn the bolt about 1.5 turn, so that the two black arrows marked there are aligned. Now try moving the telescope in RA by pushing down fairly hard, but not too hard, on the yellow ring, if it moves very easily it is possible that you need to tighten the bolt by one whole turn. If it moves with some difficulty, tighten the bolt 1/8 turn and try again. If the bolt is not tight enough you will find that the telescope doesn't slew and track accurately. If the bolt is too tight it will irreparably damage the friction disk. Do not try to push the telescope too strongly against the friction, since it is not good for it to slip.

Starting the electronics and control computers

• Make sure that the RA and Dec servo amplifiers are switched off at their front panels (so that the telescope doesn't move when the rack is switched on).
• If this is the first night of a run, it is likely that you will need to reinstall 5 cables in the servo controller (this is the sub-rack with the LED readouts in the rack in the control room). The cables are normally removed to avoid lightning damage to the servo controller. Open the left front panel by loosening the two captive knurled bolts, and replace the following cables (they are all polarised so they only fit in one way; ensure the box is off before proceeding):
  • On the Dec (leftmost) board: insert ``DIL''.
  • On the servo interface (middle) board: insert ``P2'', ``P5'', and ``KE''.
  • On the RA (rightmost) board: insert ``RIL''.
• In the control room, switch on the electronics rack. The CCD will take at least 30 minutes to cool and stabilise. For a multi-night observing run it is usual to leave the CCD on at all times.
• Check that the servo controller is on (i.e., the two LED position readouts are on), and the anti-backlash supply is on (this is the power supply at the back of the rack, which is used to pre-tension the DEC worm gear so that the DEC drive is backlash-free--the power supply should be showing about 2 A of current).
• Turn on the Apple IIe computer (the switch is at the back left of the computer; the monitor may need to be turned on too). It should boot up and display the message ``APT Bootstrap loader''. If not, ensure that the APT IEEE BOOT DISK is in the floppy drive (earlier versions of the control program that booted without the IEEE interface no longer work due to upgrades to the position encoders). There are several copies of the APT IEEE BOOT DISK disk available in the APT control room. Note that the Apple computer is more powerful than the Interdata 70 used to control the AAT.
• Press the two red reset buttons on the servo unit. The servo display should change from FFFFFF to AAAAAA for RA and Dec (note: you should press the reset buttons even if the displays are already showing AAAAAA). If the displays do not show AAAAAA after the buttons have been pressed it is possible that the telescope has activated a limit switch. See later in this document for how to recover from this condition.
• Switch on the PC and wait for it to boot. Follow the instructions on the PC screen (at the time of writing, all you have to do is press a carriage return to select option 1 from the startup menu, and then select option ``[A]'' in the subsequent menu by hitting the ``A'' key). The PC will boot the Apple, the Apple will then boot the servo controller, and the PC will then start the MCCD program (which is used to control the telescope and CCD). If these events don't occur, see the troubleshooting section below.
• The servo displays should have changed to 800000 800000 (this happens in the following sequence: RA goes to 000000, RA goes to 800000, Dec goes to 000000, Dec goes to 800000). If not, see the troubleshooting section below.
• Switch on the RA and Dec servo amplifiers to start the telescope tracking. The RA readout should begin counting down rapidly from 800000 (the fourth digit from the left decrements in hexadecimal roughly once per second), and the telescope will now be tracking. The Dec readout should remain constant at 800000 (it may change by plus or minus a few due to the motor rotating slightly when power was applied).
• Switch on the APT Focus Controller (near the PC). It is best not to switch off the PC when the focus controller is on, since this can send spurious pulses to the controller which will slightly change the focus setting.

Preparing to observe

• Login to the DECstation (see the next item if the system monitor isn't working; see ``Turning on and booting the workstation'' if the workstation is off). 0=0 If you don't have an account, you should get one (e-mail mcba@newt.phys.unsw.edu.au); in emergencies you can use the account called ``apt'', with password written on the back of the workstation. Your account should have certain important files set up in it, for details see the file /usr/users/mcba/apt/README (which you can examine by typing ``less ~ mcba/apt/README''). If you don't have the most up-to-date version of these files, then the following description will not work.

  0=0

• If the DECstation monitor is not working, it is necessary to login via the Xterminal. Unfortunately, the Xterminal has an intermittent fault which causes it to crash several times a night. To use the Xterminal, turn it on, this should start a boot sequence which will eventually lead to an invitation to login to mistral.

  5to kill are the apt_comm_process, and any emacs or saoimage processes; try 5not to kill the most recent process or two, since that will log you out).

• Type ``apt_start'' in a DECterm window (you can make one of these by using the left mouse button to pull down ``Applications'' in the Session Manager window, and release the button on DECterm). Here is an explanation of what ``apt_start'' does:
  • Sets the current working directory to ``/data0'', which is where your image files will be written. You should first clean out this area if you are starting a new run.
  • Opens a window called ``APT link'' which shows the communications between the workstation and the PC. When you read out the CCD, this display shows the number of bytes being read back. You can also type ``MCCD'' commands into this window, without prefixing them with the word ``apt'' (although this is awkward since what you type is overwritten by the byte display). Typing commands into the ``APT link'' window is almost identical to using the PC keyboard.
  • Opens a window called ``APT console'' which you can use to enter MCCD commands. You must prefix such commands with the word ``apt'' (which runs a program to send the command to the ``APT link'' window, and hence to the PC), If you need to send quotes, parentheses, or similar special characters you must enclose the command in back-ticks (single quotes) so that the UNIX shell doesn't alter the command before it gets to the PC. The advantage with using ``APT console'' for sending commands rather than ``APT link'' (or typing them on the PC, which is another possibility), is that the UNIX shell's history mechanism and command-line editing is available. You can also embed APT commands in UNIX scripts and in IRAF procedures.
  • Opens a window called ``APT PC screen'' which, after communication is established, will duplicate what is on the PC screen. Note that this screen is for output only, and anything you type in it is ignored.
  • Starts up ``saoimage'' ready for you to examine images.
  • Starts the ``emacs'' editor on the filename ``/data0/log.txt'', in which you can enter a log of the observing session. If this file exists from a previous observing run, you may wish to delete it first, or edit a different file.

  Note that if any of these windows are already running before you type ``apt_start'', you should exit all of the windows first (use ``apt_kill'' to remove the ``APT link'' and ``APT PC screen'' windows; CNTRL-D or ``logout'' in the ``APT console'' window; click on ``etc'' then ``exit'' in the ``saoimage'' window; and use CNTRL-X, followed by ``c'' in the ``emacs'' window, or use the mouse and drag down the ``File'' menu and choose ``Exit'').

  If you accidently delete one of the windows, you can get it back by following these instructions (rather than typing ``apt_start'' again):

  • APT link: type ``apt_start_link''.
  • APT console: type ``apt_start_console''.
  • APT PC screen: type ``apt_start_pc_screen''.
  • SAOimage: type ``apt_start_saoimage''.
  • emacs: type ``apt_start_emacs''.

• Wait for communication to be established with the PC. This can take up to a minute, and is indicated in the ``APT link'' window by a message similar to:

  waiting to open connection with the PC computer....
  connection received on port 2028 from IP number 151 203 92 15
  use CNTRL-C to exit, or "quit" to close and reopen the link

• In the ``APT console'' window type ``apt comm SETTIME'' (must be capitalised ast shown) followed by the return key. This establishes communication with the ``APT PC screen'' window and sets the PC and Apple times from the workstation time. The workstation time is in turn set by a program called ``ntp'' (Network Time Protocol), which queries special server computers on the Internet, and should give an accuracy of 20ms or so. Check that the Apple is now displaying the correct time.
• In the ``APT console'' window, type ``apt calaxes'' followed by return. The telescope will now calibrate the RA and Dec axes simultaneously. Keep an eye on the RA display; it will be rapidly changing, both up and down; at one instant it will suddenly reset to 800000 and then begin counting down at the sidereal rate; This instant is when the RA axis is calibrated, and you should write down the sidereal time to the nearest 10 seconds or so. If you want to calibrate the axes independently, you can use the ``calra'' and ``caldec'' commands. Note that the calibration must be done in the sequence: time, RA, Dec. If it isn't, the Apple will not respond the ``caltel'' command. Important note: I just realised that this may be the reason for the Apple refusing to calibrate sometimes after ``calaxes''! It may be best to do a ``calra'' followed by ``caldec'', until this issue is resolved...
• If the RA display is not counting down at the sidereal tracking rate from 800000 and the DEC display isn't reading 800000, then see the troubleshooting section.
• In the ``APT console'' window, type ``apt coord hh mm ss -1 24 00 caltel'' followed by return, where ``hh mm ss'' is one minute greater than the sidereal time at which the RA axis was calibrated (the number ``-1 24 00'' is a fixed constant, given by the position of the Dec knife edge). The Apple's ``Next Coordinate'' display will be updated within a second, and the ``Current Coordinate'' display will follow a few seconds later.
• You should now be ready to observe. To check the pointing, it is worth going to a very bright (e.g., mag 3) star and doing a one-second full-frame observation (``apt coord hh mm ss dd mm ss slew time 1 sra 1 1 800 1200 speed hi exp readout speed lo''). Note the use of the ``speed'' command to allow the exposure to be readout quickly (in 6 seconds). If the star isn't in the centre of the CCD, follow the directions below in the section ``Calibrating the telescope position''.

Reminder: To observe geostationary satellites or when taking twilight sky flats, turn off the RA servo amplifier for the required period of observations, and then just turn it back on when finished. The APT will slew to catch up with the demand position and resume tracking. Calibration will not be lost.