Using Track82

Track82 is the only way to activate tracking and change track rates on the 2.1m telescope. The console controls the mirror cover, curtains, platforms, dome, slit, focus, and lights, and has a joystick for moving the telescope axes. Track82 has many other useful features and functions, including a virtual console, a "GO" system for declination that works with cosmo/point, and important safety features that help reduce the risk of accident and mishap.

Starting Track82

Track82 runs on a computer whose monitor, keyboard, and mouse are available in the control room and duplicated in the dome.

Login to your account and issue the command startx to open the X Windows graphical interface. Right-click on the desktop and left-click on the Terminal menu item. In the terminal window enter the command track82 or, if this does not work, /usr/local/bin/track82. You can use this terminal window to issue cosmo/point commands, essential for finding your object, as the 2.1m does not yet have modern automation.

Normal operation is denoted by green lights for PMAC and COMMAND. See Safety and Troubleshooting for information about red status lights.

Setting the track rate

Enter the absolute polar track rate into the text box marked "Enter Rate", using the main Return key when you are finished. While entering a value the box will turn yellow. Illegal values are erased upon Return and replaced with the current track rate. Click 'On' to turn on tracking.

Declination tracking works the same way, but there is no cold start sequence. The declination has considerable backlash, and the control system partly compensates for this defect by turning the shaft the amount specified on the backlash slider upon reversal of direction.

You can use the cursor arrow keys to nudge track rates in 0.001 arcsecond/second increments - no need to hit Return. This can be used as an alternate method to guiding, but requires some skill to avoid overcompensating and guiding on the immediate error.

Moving the telescope

A note on mechanical versus celestial coordinates. When the telescope is on the east side of the axis at 0 hours HA and 0 degrees declination, we call this configuration "tube east." In this case the mechanical sense of motion indicated on the console matches celestial coordinates, so that moving south on the console moves the telescope celestially south. If you don't ever cross the celestial north pole - 90 degrees declination - that's all you need to know. However, if you move the tube to 90 declination - the north pole - and then continue over, you are now in "tube west" configuration, and HA and RA flip 12 hours. In this configuration the mechanical sense for declination is reversed from celestial, so that moving the telescope south from the console will move it back toward the north pole. In other words, the mechanical sense of motion is fixed for tube east. An example: when the telescope is in its usual north service position for Argos, you move the console joystick south to move the tube back toward zenith, even though it's true you are moving celestially north, until you reach the north pole, where continued motion moves it both mechanically and celestially south.

The celestial sense - tube east or tube west - is indicated in Track82, but not the console.

If you are uncomfortable with the console joystick, its response time, or a hand-paddle malfunctions, or you wish to use an alternate button-direction layout, then use the virtual console on Track82 . You may have to use the virtual console if your assistant is using a hand-paddle, say to move the platforms, while you move the telescope (the VC does this) because the console and hand-paddle cannot both have control. Press the buttons on the screen using the mouse, or use the numeric keypad arrows. If you move the mouse off the button it will pop up. Using the keypad arrows you can move both axes, just like the old days when the buttons were on  the console. The arrangement of the buttons can be set to Earth, Sky, and Slit to match your preferences. This also affects the cursor arrow buttons that change track rates. To use Slew, you must click the 'Slew' button while holding down on the F1 key, and then swear an oath that you are in the dome and watching the telescope.

We now have a GO system in declination, thanks to the new single motor servo control on this axis. Click on the GO button in the Declination box, and you will get a text edit box with the declination from your last cosmo/point command, which you may change. Press the foot pedal deadman switch, and click OK. You must keep the pedal down during the entire move. To abort, lift the pedal, or command a N/S motion from the console or handpaddle. You can move the telescope in HA while it is moving automatically in declination. The GO system dead-reckons the destination, so it can be off by a minute of arc, depending on the mechanical action. During GO the declination pre-load motor is off. When you release the foot pedal it turns on, assuming you are tracking in RA.

In tube east, be careful when approaching 90 degrees declination using GO. The telescope might stop just past the north pole, ending in tube west. GO declinations are celestial, not mechanical! An example: suppose you stop at 80 degrees tube west, i.e. you passed the north pole by 10 degrees. If you now GO to 60 degrees, the tube will head for the railing at north service.

In declination you can tap the joystick or reverse direction without hurting the system. But you can do really dumb and damaging things in HA. Except in Guide, you must not toggle E-W: let the motors come to a full stop before changing directions. Use the proper speed: if you are tapping Slew you need to shift down to Search or Set. Get familiar with the telescope arrangement and review the meaning of celestial coordinates to avoid going the wrong way half the time.

The console and monitor cart can be positioned about anywhere on the west platform, with the cart on the right side of the console. Turn the console and monitor so that you can simultaneously see the tube, position data, and controls.

Safety

Track82 provides basic safety features, but even so you can hit something at just about any HA and DEC. Watch the dome and its accessories (bridge, pulpits, catwalk, etc), north pier and its junction box, and platforms. Never assume the bridge is lowered, pulpits retracted, and platforms are down. If you hit something you must stop immediately and call a member of observing support who can come up to the dome and assess the situation. Track82 logs every commanded motion of the telescope and its position.

Track82 provides some safety against collisions. These conditions are color-coded in the zenith distance (ZD) box. In the following, "lower curtain" refers to the top of the lower curtain in its full-down position, with the tube centered in the dome slit.

Refer to my Safety map in our library. It's also under the glass on the console.

1.  ORANGE: About 4 degrees from the lower curtain slew shuts off. The curtain, which is approximately the 70 degree zenith contour shifted 1 hour to the west and 3 degrees to the south, is mathematically extended past the ends of curtain to the north pier, thus providing a sensible transition to rule 4 below.
   
2. ORANGE: Closer than 10 degrees to the north pier slew shuts off. Exercise extreme caution near 90 degrees declination where the junction box on the back side of the pier can be hit by a counterweight.
3. RED: All motion stops when the tube is within 5 degrees of the pier. As with Rule 2 above, you must assiduously watch pier accessories like the junction box, whose existence post-dates the collision data I used, and whose positions remain to be mapped.
   
4. RED: All motion stops at zenith distance 85 degrees or the lower curtain, whichever comes first.
   
5. GREEN: Zenith distance less than 50 degrees is generally safe except in a narrow zone near the north pier, which is protected by rules 2 and 3.
   
6. YELLOW: If none of the conditions above are met, the telescope is near a boundary, and safety is Advisory.

If you run past a slew limit (ORANGE), you can search out. If you search, set, guide, or track into an absolute limit (RED), you should call Observing Support for help. Power cycling the console without Track82 running will leave the telescope with no safety, but if you got into this much trouble you need to call Observing Support.

Argos users have special precautions to avoid the bridge and pulpits. Zenith distances more the 50 degrees require careful positioning of the dome slit with the telescope tube. As a service to Argos users, the tube can be brought down to north service with a slew limit of 85 degrees zenith distance if HA is within 15 seconds of the meridian, and Search can proceed to ZD 89.

Once Track82 is started, the PMAC requires that the network connection be maintained.
If that connection is lost, the PMAC shuts down the telescope in 15 seconds.
Shutdown will also occur if Track82 loses telescope position data from prometheus.
Normal operation resumes when the network connection or position data are restored.