N24

Normal, interactive usage of the N24 telescope

Please read this document carefully before using the N24 telescope!

Setting up an observing session: what do you need

You need before using the telescope:

• An access device: a smartphone, tablet, laptop, or computer.
• The control device: this is currently a wireless numeric keyboard pad.

Setting up an observing session: how to start

• Log in to the control computer using your favorite SSH client. The login parameters and credentials are the following as of this writing (2019-05-09):

• Control computer: 193.6.22.135
• Login username: csakb
• Password: *password* (please ask)

A few, but highly relevant notes:

• Please ensure that you are accessing over a stable network! The telescope is a real, big hardware. No, nothing serious can happen (see below), just annoying when the connection is broken.
• Take care of your phone or tablet: if these devices are prone to change wireless APs and/or switching between GSM and Wi-Fi network interfaces, sudden shutdown of the control panel is likely. The telescope is a real, big hardware: don't risk the smooth operations with weird operating system settings.
• The control panel is optimized for a bit wide screens, which might not be the default on smartphones. The interactive panel works fine in an adaptive manner (namely, you may change the screen/font size and the landscape/portrait orientation any time), so just use two-finger zoom in or zoom out on your touchscreen to change the font size. This type of alternation works likely on most of the smartphone/table SSH clients.
• The recommended SSH client for smartphones/tablets is the suite named Termius. It is free, small, fast, easy-to-configure, etc. You may use another clients for your own convenience. The control system exploits only a limited subset of features of these programs, we are not aware about any not-recommended SSH clients for this project -- but some of the SSH clients may break the connection by default if the smartphone/tablet became inactive. All of the systems are tested using Termius: that's why it is the recommended smartphone/tablet software.

• Test the wireless numeric keyboard pad (thereafter, numpad): press the Num Lock a few times in order to ensure that the radio link is fine, the battery is not flat, etc.
• Test the telescope by typing the command n24 test. If everything is fine, all of the subsystems must show green Ok (meaning "it's okay") or cyan (some additional Info that might be useful).
• If some of the subsystems are not okay (i.e. you see red Err! messages), restart the telescope:
  • Type the command n24 telescope off, wait a minute (literally a minute), then type the command n24 telescope on.
  • Wait another minute (literally a minute) then test the telescope subsystems again. One minute is needed by the embedded computer (172.24.24.33) to boot properly. However, the n24 test can be issued just a few seconds after turning on the telescope - then all of the subsystems need to show an "Ok" state, except for the embedded computer and the TAU+DEC accelerometer.
  • If error conditions are still present, there might be some more serious underlying hardware-level issue.
  • Turn on the telescope motors by issuing n24 motor on.

If all of the above steps are fine, you can use the telescope now. This list seems to be long, but with some experience, the telescope can be set up within literally a few tens of seconds or a half of a minute.

Observing

• The interactive observing session can be started by issuing the command n24 interactive.
• This command pops up a screen which shows the traditional J2000 RA and DEC positions of the telescope with prominent numbers. If your screen is wide, you see big red numbers. If you use a smartphone with narrow screen, then zoom out and/or increase the font size by two-finger swipe.
• If the sidereal tracking is off (this is the default for a still telescope in its home position), the numbers are red.
• You can start sidereal tracking by pressing Num Lock. In this case, the RA and DEC numbers are changed to yellow.
• You can stop sidereal tracking by pressing Num Lock again. The RA and DEC values should change back to red.
• You can slew the telescope if sidereal tracking is off.
• Use the numpad arrow keys (<- 4, 6 -> and ^ 8, 2 v) to move the into the intended position. You can smoothly monitor the current J2000 RA and DEC coordinates.
• Start sidereal tracking when on target.
• Once the sidereal tracking is on:
  • use the numpad arrow keys to fine-tune the position; and
  • use the + and - buttons to change the speed of the fine-positiong -- the default is 2x sidereal speed (corrected for spherical curvature at higher declinations), the available speeds are 0.5x, 1x, 2x, 4x and 8x sidereal rate.
• In order control the dome, there are some options:
  • Use the buttons on the dome wall to move the dome slit to its appropriate position.
  • Alternatively, use the numpad to move the dome automatically:
    • the combination 5+Enter synchronizes with the main tube,
    • the combination 3+Enter synchronizes with the 30 cm telescope, and
    • the combination 1+Enter synchronizes with the Konkoly telescope.

Note that this synchronization is done only once, there is no option for the dome slit door to automatically follow the telescope(s). This is mainly due to safety reasons. If the dome movement is unintentional, press the backspace key to stop the dome. Note also that this combination of 5, 3, 1 plus Enter should be done relatively quickly, i.e. within 2 seconds. Otherwise, the combination is "lost".

The dome slit door is wide enough for allowing the telescope(s) to stare for half of an hour or even an hour without any adjustment in the dome azimuth. However, all of the three telescope are unable to stare simultaneously, and it is even not so likely for two tubes.

• Before targeting to the next object of interest, switch off the sidereal tracking to allow the fast positioning again.

Feedbacks. There are some feedbacks when the telescope is in motion:

• You see yellow numbers if the sidereal tracking is on. Otherwise, it is red.
• If the telescope is moving fast, the red dome flashlights turn on.
• If unsure, listen to the motors.
• Follow the RA/DEC coordinate numbers on the display of your smartphone/tablet/laptop/computer.
• If the telescope reaches its limitations (e.g. the horizon), both the sidereal tracking and the coarse/fast movement will stop and the position display will blink (blue-red). Use the counter-directions to move the telescope into its normal motion domain.
• If the sidereal tracking is on, you see nearly constant RA and DEC positions. The emphasis is on nearly: while the RA coordinate can jump +/- 1 or +/- 2 occasionally in the least significant figure (i.e. 0.1 or 0.2 seconds of time), the DEC coordinate can slowly drift after a few (tens of) minutes. The former one is due to the finite encoder resolution which is available on this hundred-years-old telescope while the DEC drift is due to the corrections to refraction, J2000 misalignment(s) caused by precession and pointing uncertainties. So, all of these are normal. On a longer timescale, the RA position can also drift (due to the same reasons like in the case of DEC), but this +/- 1 or +/- 2 jumps are more prominent even after a few tens of seconds.
• If the sidereal tracking is off, you see a nearly constant DEC while RA is increasing just slightly (+0.3%) faster than the wall time. Here, nearly is just because the precession and this +0.3% is due to the fact that Earth makes a full rotation in 23 hours 56 minutes and 04 seconds.

Before gaining sufficiently long experience with this telescope, please watch all of these aforementioned feedback possibilities frequently.

Shutting down

• Turn off the sidereal tracking (by pressing Num Lock).
• Use the numpad arrow keys (<- 4, 6 -> and ^ 8, 2 v) to move the telescope to its home position. Use the dome wall buttons to move the dome into its home position.
  • The home position of the telescope is when the telescope points towards the zenith and it is on the west pier side.
  • The home position of the dome when the slit door is right above the terrace door.
• Ensure that the sidereal tracking is off.
• Shut down the interactive session by typing or pressing or tapping Ctrl+C. Or, just simply, close the SSH session on your device.

Troubleshooting

Here we list some of the most known bugs, bug-alike symptoms or typical non-trivial cases:

• If someone has logged out improperly from the control computer (even long time ago) and another and/or same person would like to use the telescope again, the system might respond with the message n24: interactive mode is used by someone else. If and only if you are in the dome area and 100% percent sure that this is the case, then issue the command n24 unlock. Please note this unexpected locking could only occur when the previous user shut down the system in an unexpected manner. Take care to avoid such situations.
• The terminal connection can indeed be broken easily if the conditions mentioned at the beginning of this document meet (about unstable networks, weird operating systems prone to switch between wireless APs and/or GSM networks in a heuristic manner, etc). We try to do our best to have a stable wireless environment, but we cannot support all of the personal smartphones, tablets and laptops at the same time.
• After a longer blackout or shutdown state, one of the telescope bus controllers (a device called bus master) can likely be dumb. This is a known bug which is very hard to reproduce. However, this is an unlikely case, since the default state of the telescope is always a turned on state. In this case, turn off and on the telescope by issuing the n24 telescope off and n24 telescope on commands with some relax time about a minute between the two commands and before testing the telescope again by n24 test. See also the Setting up an observing session section above.
• If you don't know what's going on, make a screenshot, run the n24 test and make a screenshot of the output.
• In any case, if the SSH session is off and the interactive session is closed, all telescope subsystems are automatically go in an idle state after a few seconds. However, note that keep-alive time of the sidereal tracking is a bit longer (around ~15 seconds). Before leaving the place, be sure that all systems are idle.
• Be cautious: the telescope motors (both fast slewing and tracking) are not as quiet, but visitors (or just a few people chatting) can talk down the motors. Think also about dome acoustics.

Unexpected motions

In case of a highly unexpected behavior, please follow the directions above:

• Shut down the interactive control panel by pressing Ctrl+C. The telescope must stop smoothly within a second. The full ramp-down time is around 10 seconds. The clock drive also stops within less than 20 second (~8 seconds on average).
• Otherwise, if the system is still within motion, issue the command n24 stop. It issues a smooth ramp-down instantly, when the full stop should occur also within 10 seconds. The clock drive doing the sidereal tracking also stops instantly.
• Press the emergency switch if there is still some unexpected motion. This is a hard stop. The angular momentum of the telescope is then absorbed by the springs designed for energy absorption. This will yield a swing-like motion for a few seconds. This is normal, however, use the emergency switch just in the very last case (if the first two options do not work). There are no known records for such a case.

Questions & Answers

• Q: It is hard to see the numpad at night. What can we do?

A: Well, it is a nice question. If there is some professional wireless numpad which is available on the market which also has glowing keys, we can upgrade. Don't hesitate to link a nice model!

• Q: Where should I leave the numpad after observations?

A: until further notice, please bring back to some warm place, outside the dome -- where both the observers and the technical staff can find it easily. This is mainly because of two reasons:

• first, if the numpad is inside the dome, the permanent radio link could flat the battery quite quickly;
• second, it is cold in the dome except for summer and cold weather could flat the battery quite quickly.

Just a note: that's why it is important to check the numpad before usage!

• Q: Why Ctrl+C? It is a bit unfamiliar.

A: Ctrl+C is a common way of shutting down processes on many systems. This might be changed in the future at some level, but note that Ctrl+C is the thing which is always there. Like the main switch at the entrance door. Or some emergency switch within a software. Just check the availability of Ctrl+C in your smartphone/tablet. It is easy to access, the recommended Termius program also shows the Ctrl by defult.

• Q: All seems fine, I tested everything twice, internet connection is perfect, but the telescope is not moving.

A: Surely, you have done it, but test n24 motor if the motors are turned on. However, the main cause is likely that someone (a fellow observer, guest, you, the previous observer, etc.) pressed the emergency switch.

• Q: It is hard to fine-tune the DEC direction while I look into the eyepiece. Sometimes it is very hard. What should I do?

A: This is an old telescope and it is a nearly-centenarian telescope with all of its own, original parts. At that time, only the clockwork was made precisely (using electronic motors), but there was no need for an electronic fine control in the declination. Therefore, the drive system in the latter direction show some backlash, which, when combined with the slow focal ratio (f/25, and therefore the high magnification), can highly be prominent. Find your target always from one direction. If you check the printed RA/DEC coordinates while controlling the telescope with the numpad, you can also detect this backlash. This backlash is now around a minute of arc, so using an 50-mm eyepiece with the 24-inch main Cassegrain tube, the backlash is still smaller than the field-of-view. However, higher magnification is still possible: you can either rely on the J2000 numbers or swap eyepieces afterwards.

• Q: Why do I need a smartphone/tablet/computer and this numpad at the same time?

A: This is big telescope, indeed. Observatory-class. By using the smartphone/tablet/laptop, you gain access to the system while using the numpad, you can control the system in a smooth, interactive way. All observatory-class telescopes work in the same way if you need full control and interactive use at the same time. Think about the RCC telescope and its auxiliary interfaces. Or, if you want to manually control the Schmidt telescope, you even have to be at the dome and press the big buttons on the big control panel -- which is not even wireless and cannot be put in your pocket.

• Q: I routinely use my EQ5 + 8-inch Newtonian, how should I be familiar with this telescope?

A: Think about the usage of the SSH client, this procedure with the log-in, running the test diagnostics scripts etc. as a related analogue of bringing your tripod with the clock-drive and the scope to the garden. Think about the numpad as the EQ5 hand controller. See also these access and control things above.

• Q: I routinely use the RCC telscope at Piszkesteto, how should I be familiar with this telescope?

A: Think about this n24 ... commands as a purely shell-based interface instead of the CCDSH commands. Think about the numpad as the rccpanel utility used to fine-tune the telescope. See also these access and control things above.

• Q: Well, CCDSH. Is there any chance to have a CCDSH interface for this telescope?

A: Yes, this is the plan. While a CCDSH-alike environment is suitable for automated control and remote observing, this telescope and the current control system mainly optimized for public outreach activities. If you do a public lecture at the Schmidt telescope, you do indeed press the big buttons on the big control panel and won't use CCDSH at all. This is the same. However, the RA/DEC coordinates presented by this system are surely professional coordinates: these refer to the J2000 epoch and consider all of the instrumental and intrinsic effects behind the scenes (bending of the telescope axes under their own weight, precession, nutation, whatsoever, sidereal time, leap seconds, ...). Therefore, targeting any object on the sky is very fast within the pointing accuracy (which is around ten-twenty seconds of arc) just after gaining a little practice.