Telescope Control System Users Guide

Created: 01/01/92 by TG
Updated: 07/28/16 by EF


This document describes the TCS program, which controls 1.2m telescope from the flwo48 Linux PC. The system provides controls via a Graphical User Interface (GUI labeled ntcs, see below). The system also runs a command window labeled Telshell, which allows the observer to enter telescope and instrument commands and to run observing scripts.

Table Of Contents


This document covers the program TCS, the Telescope Control System currently in use on the FLWO 1.2m (48") telescope. This program is updated from time to time; please check here for new features.

The purpose of TCS is to control the PC-TCS from the host flwo48, a Linux PC, and move the 1.2m telescope. It manages catalogs and places information from the telescope and catalogs into the data FITS headers. It also controls the topbox filter wheel, telescope focus, and through the guide PC, the autoguider system.


Power for the guider acquisition TV should always be on. You will find the switch mounted on the mirror cell north electronics plate. Make sure the guide PC is up and running. If you need to reboot the guide PC, type "Ctrl-Alt-Del" simultaneously on its keyboard. The message "You can start Realtime system" will appear on the guide PC monitor after various motors are homed in the topbox (a few minutes).

The only way users should start TCS is by starting the Realtime system. TCS is an integral part of the Realtime system. It is started by typing gokep (for Keplercam). If you attempt to start TCS otherwise, bad things will happen!

After you have typed gokep to start up the full system, 3 windows will appear:

These windows all interact. This document will only cover the TCS window. If you have not read the Keplercam primer, you should do so for information on the use and abuse of the other 3 windows. Our discussion from this point assumes you have read this document, and will NOT cover the basics of the other parts.


The TCS window contains an information area that updates every few seconds; it accepts no input. The information displayed includes the state of the telescope, topbox and guider: current and requested coordinates, airmass, HA, ST, Dome azimuth, slew, focus, filter, and guide FWHM, history of commands (GHIST) and peak value (GMax). It displays the status of the dome slit and mirror covers (SLITCOV, either one Shut or Open). Near its bottom, right it displays the current sky temperature (currently from the MEarth Boltwood and our new Aurora units) which shows red (green) for cloudy (clear). It also displays the state of the instrument: file being written, object type (e.g., BIAS), CCD status, integration time, time left for the current exposure, size, program and channel. The last 3 items (see Keplercam) can be modified from scripts. If exposures are made manually after a script finishes, there is no absolute guarantee that it restored fully these 3 items. Observers should monitor these values before attempting observations after using a script.
The TCS window also shows a series of buttons. To select any button place the cursor on the button and depress the left mouse button. The Buttons, starting at top left, have the following functions:

At the bottom of the window are buttons for each filter used with the current instrument. There are 8 buttons for the ccd. If you click on one of these buttons, the filter you select is placed in front of the detector.

The section below the filter buttons controls the autoguider, which is covered at the end of this document.


Some of these buttons when selected cause a window with further choices to appear. This section explores these windows, and their usage. In most cases these windows were designed to pop-up, be used, and disappear. For these windows, other windows will not work until the current pop-up has been dismissed.


When you click on NEW COORDS the above window appears for selection of the next telescope position desired, either manually or via catalog management commands. The single white line can be used to display the last coordinates entered from this menu by using the up-arrow key.

If you wish to manually type in coordinates, simply put the cursor anywhere inside the white line, and type coordinates, for example :

   12:12:12 32:00:01 1950.0 or
   12 12 12 32 00 01 1950.0

Spaces are used to separate the fields RA, DEC, and EPOCH, spaces or colons may be used as internal field separators. A control-K entered on this line deletes from the cursor to the end of the line, and the delete key deletes the character prior to the cursor. The epoch field is optional, but Ra and Dec MUST BOTH be entered!

This white line also allows the management of catalogs. When typing into the white line, three catalog commands are recognized:


Please note that a catalog MUST be loaded before you can retrieve objects. After manually entering coordinates, or selecting an entry from a catalog, click on the "OK" button to transmit coordinates to the PC. In a few seconds, the "Slew Enabled" message will appear on the PC. at this point you can click on the "Slew Enabled" button, and the telescope will slew to the coordinates. See the catalog section below for specification of catalog layout, location, names, etc...

Under this area is a window which displays the loaded catalog, and you may select an object from this window by right clicking on that line.

When you click the Load Cat button this window appears:

You can change the entry under Filter and then click the Filter button to change directories; selecting any listed catalog file loads that catalog.


When you click on the Rates Menu button, this window appears :


Filters must only be loaded by staff. Please make arrangements in advance if your schedule requires a weekend arrival at Mt. Hopkins. It may be neccesary to ship your filters ahead. Filters are normally changed Monday-Friday between 9:15AM and 4:15PM. Note which slot in the wheel each filter is inserted into, as that information will have to be entered by staff into a file used to label the filter button upon startup.


To move to a particular filter, simply click the left mouse button on the appropriate pad. The longest time required to change a filter is ~15 seconds (4 positions). The filter currently on axis is displayed in the TCS window filter position. If you open the west door to the topbox, the filter two before the on-axis filter should be visible. So, if you select the first filter, filter 3 should show thru the open door. If this does not happen, exit the Realtime System, and then restart the Realtime system. If UPS power is lost during a run, exit the Realtime System AND reset the guider, cycle the power to the controllers, and restart Realtime System.


When you click on the Focus Move button, this window appears :
The focusing mechanism is part of the hexapod, which receives commands from flwo48 (a Linux PC) via the TCS window to move the secondary mirror in or out. Lower numbers mean the secondary moves toward the primary. The units are mm. The default size of 0.025 units corresponds to the smallest significant change in the secondary position when binned by two with the ccd. The size of the movement can be changed with the Focus Set button. The current focus position is displayed in the main TCS info window.

NOTE: You may also change focus from the Telshell.

After focusing the telescope, check the on-axis focus for the guide camera. The default on-axis value may need to be changed. Note that on-axis is the only way you should change the guider focus. The guide PC automatically adjusts the focus values appropriate for each guider segment.


When you click on the Misc Menu button, this window appears :

The first two buttons home all stepper motors except the drive motors. Home Tel Focus homes the motors controlled from flwo48 , Home Guider homes the topbox pickoff motors.

The Remote TCS toggle button controls the storage of the guide camera grabbed image file, /Realtime/FLWO48.EXPORT/outfile.fits.gz on flwo48. This file may be useful for remote observing if you need a quick check of your field; it is refreshed every ~10 seconds when you are NOT guiding. In Cambridge, mounts this directory via NFS at /data/flwo48/FLWO48.EXPORT. Other machines have mounted it in the past, but only tdc is a sure thing.
To view the file, use the following procedure. First, make sure that the remote observer at the 1.5m has turned on the guide camera and turned up the gain on the guide camera. Then, follow the rest of the remote observing instructions here.

Set PC Clock resets the Harvey TCS clock when pressed. Do this if you have to reboot the mount PC for some reason.


When you click on the Offset Menu button, this window appears :
"Load New Offset File" prompts for a file of offset positions. To apply catalog offsets, select "Send Next Cat Off". For manual offsets, use the small window to type in the offsets, and then select "Send Manual Off". The telescope will then move (no slew enabling needed). The slew enable button duplicates the slew enable button in the main window (not needed here). See section below on Offset Catalogs for more information.
(1) offsets are in arcsec;
(2) offsets are CUMULATIVE;
(3) there is a new, preferred method to center your observations on a given amplifier, using the TCS command "Amp Center" as described below.


When you click on the Tele tasks button, this window appears :
If you click on Set TelePos, you are presented with a small widget containing the last coordinates to which the telescope was slewed. Clicking on "OK" in this widget will reset the telescope coordinates to the values shown therein.

When you click on the Amp Center button, this window appears :

The top entry is only a display that shows the current amp center (also shown in the Tele Tasks window). This label is updated only after you cancel out of the menu and bring it back up (similarly for the Tele Tasks menu). Clicking on AmpX where X=1,2,3,4 centers the pointing on amp X. Center puts the pointing at the center of the chip. You can also enter arbitrary moves in arcsec in the white window, and then click on "Manual Amp Move" to apply them. Close the window by clicking on Cancel. If the telescope is tracking, this command moves the telescope to amp X immediately after you click on AmpX. AmpX centering is persistent under slews, unlike offsets, which disappear after a slew. However, it disappears if you exit the system.

NOTE: you may also change amp centering from the Telshell.

The CosDec button toggles correction of RA guide pulses for zenith distance. This will help autoguiding, so leave it ON.

The Track button toggles tracking On/Off.

Dome On/Off controls the dome tracking the telescope.

Home Dome will turn off Dome Tracking and home dome

Dome to Az allows you to enter a new Azimuth for Dome. Turn Dome off before setting, then back on after setting.

Stow Tele sends the coords to stow the telescope.

Ref Tele (working again) places the telescope at two sensors and sets the telescope position to the zenith. It is the same as the "tele ref" telshell command.


The rest of the main window contains the info window, which show the current values of telscope position, time, focus setting, etc. This window updates about every two seconds :


Catalogs are of two types, object catalogs, and offset catalogs. All catalogs must be stored in the directory /Realtime/lib/catalogs.


Object catalogs have the following format:
!P.I.: Falco
!Program: Lenses
SDSS1004  10:04:34.8  +41:12:40   2000.0   0.00 0.00
SDSS1029  10:29:13.35 +26:23:31.8 2000.0   0.00 0.00
The first two lines specify the P.I. and Program for the catalog. If these lines are in the file, the information therein will be placed in the headers of all objects selected from this catalog. Subsequent lines have 4 fields (6 if proper motion is needed). The first field is the object name, the second field is RA, the third field is DEC, and the fourth is the epoch. Two additional, optional fields are for proper motion (PM) in RA and DEC in that order. The DEC PM is in arcsec/century and RA PM in (sec of time)/century. To convert the change in RA to arcsec per century, multiply by 15*cos(DEC). After the 4 or 6 fields, never pad with spaces.

Object names must have fewer than 20 characters (fewer is better). Valid object names comprise letters, numbers and characters from the set "+-_." ONLY. Object names must not contain blanks, since the parser uses blanks as delimiters.

If you use a catalog, the name of your object will be part of the exposure.
For example, if you load the catalog above and select the first entry, SDSS1004, typing "total 10" at the command window will produce a 10-second exposure and store it in a file "NNNN.SDSS1004.fits" (NNNN is the file sequence number). You can override the object name by giving the "object" command thus: "object MYNAME; total 10", which will produce a 10-second exposure and store it in a file "NNNN.MYNAME.fits." The name will also be stored in the FITS header, assigned to keyword OBJECT.

Observers are able to write in the catalog directory; please do not clobber existing catalogs!


Offset catalogs have the following format, illustrated from the file /Realtime/lib/catalogs/
          24 0
          24 0
          24 0
          24 0
          24 0
The first field is R.A. offset value in arc seconds, the second is DEC. in arc seconds. Both fields may have values between -500 and 500. The last line in the file is LINK, which is optional. If LINK occurs as the last line in the file, tcs will cycle through this file forever, restarting with the first line after te last line. If LINK does not occur, tcs will tell you to reload a new offset catalog after the last line.


The autoguider is a Linux-based system. Note that the autoguider works best when the TV background is low. Thus, if the sky background is high (e.g., when observing near the moon), turn the TV gain down to minimize this background.

The TV image is grabbed via a frame grabber in the guide PC. The pixel size is about 0.3 arcsec along both the EW and NS directions. The format of 640x480 pixels gives a full field of about 192x144 arcsec (3.2x2.4 arcmin, EW x NS).

The video processor window has clickable "buttons" that allow flipping of each axis for your viewing convenience. See the 1.2m video processor instructions for an overview of its capabilities.

The TCS window provides the user with an interface to that guider. Near the bottom of the TCS window is a box like this

At the top of the box is a label that shows the detector status, (Blocked. Clear or Guiding) and the current segment for the pickoff mirror. This is followed by several command buttons.

The Acquire button will pull down a window like this:

The button labeled Move to Next Segment will cause the pickoff mirror to move to the next segment in the horseshoe, shown here.
Move to the next segment until a guide star is visible on the guide camera monitor.

The button labeled Begin Guide can be pressed once a guide star is in the guide monitor. Avoid stars too close to the edges of the monitor. When Begin Guide is pressed, the guide PC grabs a frame from the guide camera and ships it to TCS, which will then create an Xwindow with the grabbed image. You should then place the flwo48 cursor on the guide star in that Xwindow, and press the left mouse button. Guiding will now begin. If your star disappears (perhaps because of clouds), click inside the window and then Stop Guide. Avoid killing the window, which may hang TCS. After a minute or so, the guider will be stable, and you can begin an exposure. While guiding, pressing any of the guider buttons will stop guiding, but it is best to press the Stop Guide button to stop. During guiding the two graphs at the bottom are periodically updated with guide-star centroiding profiles (E-W and N-S) from the guide PC. (Information printed on the guide monitor is only for debugging.) Adjust the gain lower if the profiles become flat-topped.

The Guide Focus box allows changing the focus value for the current segment only. The guide PC adjusts the guider focus as you change segments, based only on the value set on-axis. Therefore, if you change the focus value for an off-axis segment, that value will be ignored as you move to a different segment. Note that, although guide stars may appear astigmatic as you change segments, the guider is happy. You need not attempt to circularize elongated guide star images!

The Move To Seg # box and movement to a known segment number.

The Button labeled AutoAq will move the pickof mirror to Segment 1, and grab a frame. It will check this frame for a star, and if found, it will begin guiding on it. If no star occurs in Segment 1, it will step thru all 69 segments searching for a star. The Stop Guide button will stop this process.

The button labeled GstarAq finds a guide star using the Hubble guide star catalog (GSC). GstarAq depends on the command "tele chipcen" (left over from 4shooter days), which is aliased to "chipcen" for Keplercam. If you are centered on the center on the array, issue the command "chipcen 0". If you are centered, e.g., on amp 3, issue the command "chipcen 3". This will pass on the offset information to the GstarAq routine. NOTE: when you use "ampcen" to center on a given amp, the corresponding "chipcen" is issued automatically, so you need not fret over it. This routine will search the GSC for guide stars brighter than 13.0 mag in the horseshoe, move the pickoff mirror to a segment containing a star nearest the current segment, grab a frame and display it on the screen, just like Acquire. If GstarAq finds no stars, it does nothing. Left click on the star in this frame to begin guiding. If no star is visible, click anyway, and then immediately hit the red Stop Guide button. Avoid killing the window, which may hang TCS. The most likely reason for absent stars is that the pointing is off (a 30 arcsec pointing error will do it). Another may be bad seeing or cirrus, if the only stars available are nearly as faint as the 13 mag limit. The status window labeled "Kep.err" (which opens by default in the lower-left corner of the monitor where you typed gokep) shows the list of all stars it found. Near the bottom of this window, you should be able to find (you may need to scroll) something like this:

/home/falco/guide/doguide 11 12:27:02.0 +31:29:41.1 3 0 0 > /tmp/autofind
  8  11.91  47.2     3    90   291
  7  11.31  32.8     4   146   179
  3  10.52  39.3     8   175    85
  1  12.82  46.0    10   249    20
 24   9.45   5.7    13   269   240
The first column is the segment number, the second one the V magnitude of the star. If you are unhappy with the star that GstarAq selected, you can pick any other from that list, move to its segment, and start guiding as described above.

The Button labeled On/Off Axis toggles the pickof mirror between Segment 0 (On-Axis) and Segment 1.

The Stop button, mentioned above, is used to stop guiding. It won't hurt if pressed when not guiding.

Under the Stop Guide button is a slider widget, which is the gain control for the guide camera, meant for remote observing. It starts with Rgain at Off (or On but a low gain at 40). The slider is less reponsive than the knob; only use it remotely. You must first click the Rgain button, which will toggle gain on, then you may use the slider to control gain. If you turn the gain too high it can freeze the autoguider; make sure to raise the gain slowly.

Next to the gain control is a hand paddle interface, primarily for use remotely. This is a digital hand paddle, not analog, meaning that pressing down the N button and releasing it will produce a 1 second pulse at the current guide rate in the North direction. If the rate is set at .5 seconds, two clicks should approximate one arc second.