A brief introduction to the TCS
This document is intended to provide a bare-bones outline of the more important
features of the NOT Telescope Control System, and a simple prescription for
moving between targets; it is no substitute for a full manual or actual,
There is also an annotated list of TCS
commands and a table listing the contents of the application keypad command tree.
The User Interface : display,
keyboard, mouse, autoguider displays
Moving to a new object : Select your object, Move the telescope, Start the autoguider.
The User Interface - General
The TCS is controlled from the VT510 terminal to the left of the instrument
control workstation in the telescope control room. To preserve the phosphor
of this display, its brightness is usually turned down during the day.
This display is divided up into three sections. A screen dump is here.
At the top are five rows of status information. These vary dynamically
and provide an up-to-the-moment summary of the system status.
At the bottom are two rows describing the currently available commands
using the application-keypad keys. Note that they are numbered from 0
to 7. Striking these keys on the application keypad will execute the command
displayed, or enter another menu of application-key commands grouped under
the title displayed.
Between these two sections is a larger area where such things as catalogue
contents, status pages, help information and command results may be displayed.
The keyboard prompt lies at the bottom of this region, just above the
application keypad menu.
Almost all user input to the TCS is delivered via the keyboard. Commands
may be typed in longhand at the command prompt (there are numerous abbreviations
and shortcuts, there is no command-line recall) using the main keyboard,
or accessed via the application keypad. You can get help on an incomplete
command line by hitting the application keypad key labelled HELP.
The cursor keys move the telescope
by a preset distance in the cardinal directions and therefore substitute
for the traditional handpaddle. Do not try and use these keys for command-line
recall (there isn't any, and it is annoying to have to repoint the telescope
after making this mistake).
The application keypad keys are used to navigate
the command menu. You cannot type numbers into the command line with
these keys! Use the row above the main keyboard instead.
It helps to visualise the layout of command accessible with the keypad
as a tree, with MAIN at the top. Hitting the key labelled MAIN
returns to the top of the keypad command tree. Any of the keypad keys
0 through 7 will then put you into a new menu of commands or menus. Note
that titles of further menus of commands are CAPITALISED, but actual commands
which cause telescope actions are in lower case.
A command key may execute a telescope operation immediately or prompt for
confirmation or further parameters.
If you descend to a menu of commands in which you expect to find a
certain command (according to the title of that menu) but it is not there,
look out for an OTHERS menu as this may well contain what you are
Commands and submenus may be available via different routes through
the keypad menu tree. Thus it is something of a tangled tree, but the layout
is generally pretty intuitive to follow after a bit of practice.
The TCS mouse is used solely to select sky and star regions for the
autoguider. It will move the pointer around on the rightmost of the two
autoguider monitors above the terminal.
There are two autoguider display screens, mounted above the TCS control
terminal. The one on the left is a simple grey-scale display of whatever
the guide camera is seeing. The one on the right provides pointer control
for selecting the guide star and sky region.
Moving to a new object
The following describes the basic steps necessary in order to move
from one object to another after observations have begun (or after the
startup sequence has been completed).
Select an object in the catalogue
Hit MAIN, then 3 / CATALOGUE. This will provide you
with a list of catalogue operations. Note that there is a second menu
of catalogue commands under 0 / OTHERS.
- Load your catalogue
- Select your object
First you need to load your object catalogue, assuming one exists.
If the last catalogue you loaded was the one that you want to use now,
you do not have to load it again. This catalogue may not be visible in
the TCS display as it may have been overprinted with other command output.
You can restore the catalogue display with the keypad keys 5 / Select
Next and 6 / Select Previous which move the selection bar up
and down the object list, printing each row on the display as it goes.
To load a new catalogue, hit 3 / Load Catalogue. You will be
prompted for a catalogue name. If you submitted your catalogue via the
web form, then you will need to specify its location on the other computer
by preceding its name with "/catalog/".
Now highlight (select) your object in the catalogue list using the 5
/ Select Next and 6 / Select Previous keypad keys.
Move the telescope
Before you can move to the new object, you must turn off the autoguider
if you have been using this. Do this is via the command line with the
- Stop the autoguider
- Move to the object
With the object in your catalogue highlighted on the TCS display, as
described above, hit 4 / Preset to this.
The telescope status will change from "TRACKING" to "SLEWING" and you
will feel the dome move as the telescope moves to your new object. Also,
the rotator will rotate to its new position and the guide camera filter wheel
will move to the closed position.
Start the autoguide
Note: The autoguider camera is intensified and can be damaged
by too much light, so please be careful.
- Change the autoguider filter
- Select the sky region
- Select the star region
- Start autoguiding
Once the telescope status changes from "SLEWING" to "TRACKING" again,
your object will be within the field of view of the instrument. Before
beginning your observations, you will need to start the autoguider.
During the pointing, the TCS was busy looking up the nearest suitable
guidestar to your field and setting the guide probe accordingly. Therefore,
once you are on target, there will also be a guide star within the field
of view of the autoguider. All you have to do is point at that star and
start the autoguider.
The guide star may not be visible, for a number of reasons, including
in order of decreasing likelihood:
This document is not intended to address any but the most basic concerns,
so solutions to the less obvious difficulties will be found elsewhere.
Nevertheless, in the current version, the TCS always moves the TV filter
wheel to the "CLOSED" position when it slews the telescope, therefore you
will always have to move to a transmitting (ND , red, blue, yellow filters,
or just "OPEN") position before you will see the guide star. Use the command
"tv-filter" to change filters on the TV camera.
- The guide camera (TV) filter is closed or too opaque
- The TV is out of focus
- The TV is turned off
- The guide star is too faint
- There is no suitable guide star
- The mirror cover is closed
- It is cloudy
- The dome is closed
Using the mouse, move the pointer to a region in the TV field of view
which is well away from your chosen guide star. Click the left button on
the mouse. This will select the sky region for the autoguider.
Using the mouse, put the pointer on the guide star. Click the middle
button. This will move the guider box onto the guide star.
Start the autoguider. This is most easily done using the command line
command "ag-on", but you can also use the keypad sequence 7 / AUTOGUIDER,
0 / Start Guiding
When the autoguider is running, it will report the detected counts
in the status region at the top of the TCS display next to "Autoguider".
It is possible to guide with counts as low as ~1.0, but that's pushing
the limits of the system. If counts are too high, the TCS will complain
and automatically put in a filter to reduce the intensity of light falling
on the TV.
You should now be ready to begin observations.