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- Motor cables:
- The method of connecting the motors
to their cables is fairly flakey and prone to coming loose.
- New incremental encoder:
- The new incremental encoder for
the RA axis doesn't work when slewed at moderate to high rates. The
problem is possibly in the capacitor circuit for generating
the rate and direction outputs.
- Filter changer:
- A robotic filter changer, Auto-Col, is
currently being designed and built. This is a major challenge.
- Lens cover:
- We need to automate the
lens cover, and provide a heating element (a light bulb?) to keep the
lens warm (to stop dewing) after the cover is closed.
- Computer-controlled roof:
- The roof must be under computer
control, with appropriate safety interlocks to prevent damage to the
telescope.
- Lens dewing:
- The lens has often been covered in dew. One
possible solution is a couple of fans blowing air on the lens
continuously. These fans have now been installed, and it waits to
be seen how effective they are.
- Flat-fielding lamp:
- It would be convenient to have a
flat-fielding lamp available so that we can determine the pixel-to-pixel
variations of the CCD without needing twilight frames.
- Lens cleaning:
- The lens probably needs cleaning once every
could of years
(less if we can stop dewing from occuring). The recommended solutions
are lauryl alcohol, isopropyl alcohol, and acetone, with application
using lint-free cotton swabs. The AAO recommend a drop of Kodak
Photoflow as a wetting agent. Please do not attempt this job without
speaking with Michael Ashley first.
- Mirror alignment widgets:
- Balancing the main mirror in
its cell (so that the collimation remains precise regardless of zenith
distance), is a very tedious task, that would be made much easier if
a purpose built jig was constructed.
- Absolute encoder problems:
- The Dec absolute encoder is
not properly held on its shaft, with the result that it occasionally
shifts, which in turn prevents the telescope from finding the
declination knife-edge.
- Roof crane maintenance:
- The roof crane sometimes jams
after long periods of disuse. A slight tap with a hammer on one of its
bearings will get it going again. Perhaps it needs some preventative
maintenance, or regular movement, to keep it running...
- Limit switches:
- The APT's limit switches have been a cause
of many problems.
- The inner and outer limit switch positions need to be checked
carefully and readjusted. In particular, the Dec south outer limit
appears to be in the wrong place.
- Friction disk:
- The friction disk needs checking for damage,
and reoiling. It may be desirable to install wipers to stop debris getting
between the disk and the rollers.
- Roller pressure:
- It would be nice if there was a more accurate
way of determining the pressure applied to the roller, so that it can be
set with confidence at the beginning of each night.
- Sealing the tube:
- The original Baker-Nunn
camera was designed to have a sealed tube, pressurised with dry
nitrogen, to keep dust and condensation out. As soon as
the filter wheel is finished, we should place some bags of silica gel
in the tube (to absorb moisture), seal the tube, and fill it with dry
nitrogen.
- Motorised tilt/rotation:
- There are three
micrometers on the CCD mounting stage that are not automated. Adjusting
them by hand is extremely tedious, so it would be nice to have computer
control of them.
- Accurate collimation:
- There is one distance in the optical
path of the telescope that hasn't been collimated: it is the distance
between the corrector lens and the mirror. We should perform a series
of focus tests for various values of this spacing, and see if we can
get better performance. It may also be possible to change the distance
between the filter and the field-flattener to increase performance.
These ideas could be tested using the computer model of the APT optics.
The collimation tests should wait until the IRAF autofocussing routine
is complete, since we will then be able to obtain quantitative
measurements of the performance.
- Limit switch wiring:
- The limit switch wiring is complex and
hard to debug. It would be preferable to have a panel of LEDs showing
which limit switch was hit, so that faults could be tracked down
more easily.
- General telescope wiring:
- The recent re-wiring of the
telescope has two problems: (1) many of the wires aren't long enough,
so that stretching occurs as the telescope moves around the sky,
and (2) the quality of some of the wire used was not very high (e.g.,
the limit switches are connected with twin-ax cable that can break
internally without any evidence being visible on the plastic
insulation). We need to improve the wiring to the mirror heater so that
the cable can't become jammed as the telescope moves.
- Roof crane wiring:
- The roof crane and roof motors can not
be used simultaneously. It would be nice if they could be.
- Servo amplifiers:
- We need the ability to drive the servo
amplifiers manually, so that we can slew the telescope if the servo
controller fails. The manual control could take the form of a potentiometer
providing an adjustable voltage to the servo input, with a spring-return
switch used to select manual control.
- Spare parts:
- We have spare parts for most of the boards now.
- Electronics spares:
- While we have lots of spare ICs, we have
almost no common components such as resistors, capacitors, diodes,
and transistors.
- Electronics documentation:
- We need to have comprehensive
documentation for the telescope and its electronics available at SSO.
This should include spec sheets for all the integrated circuits.
- New control computer:
- In the medium term we should look
at replacing the Apple II and servo controller with a PC and a
modern servo control card. A possible choice would be the cards
used by the AAO for controlling the 2dF fibre positioner. This would
allow optimal movement between positions.
- UPS:
- An Uninterruptible Power Supply (UPS) is required to
allow the roof to be closed in the event of a power failure.
- Lightning protection:
-
- Noise reduction:
- With all the various computer fans going
in the APT observer's room, it is not particularly pleasant. It would be nice
to reduce this noise somehow.
- Servo-amplifier cooling fan:
- The servo amplifiers need a fan
blowing air over their heatsinks, otherwise they overheat. The existing fan
is a Papst 110V one that I happened to have lying around, driven by a
240-110V transformer. The fan is not well mounted. This situation needs
to be improved.
- Weather information:
- For fully automated operation, we need
to be able to determine what the weather is like, and to close up if
it is cloudy or raining or the humidity is too high. Here are a few
possibilities:
- Simply obtain by computer the dome open/close status of the
2.3m and AAT, and use this to decide whether to open/close the APT.
- Make our own weather station and interface it to a computer.
We already have a rather nice humidity measurer built as a
vacation project by Weijian Lu working with Michael Ashley in 1994.
- Tap into the 2.3m weather station.
- Tap into the AAT weather station.
- Use the CCD camera on the APT--it is fairly obvious when it
is cloudy.
- Precession of coordinates:
- The MCCD program should have the
capability of precessing coordinates, so that the ``equinox'' command actually
does something besides just affecting the FITS headers.
- Pointing corrections:
- To improve the telescope tracking we
could produce a pointing model for the telescope and apply it in
software. One would first have to disentangle all the corrections
built into Paul Payne's Apple code. Currently, the APT polar axis
appears to be misaligned by about 150 arcseconds.
- Tracking rate adjustment:
- The tracking rate is currently
off by about 0.3 seconds of time in 300 seconds.
- Position determination:
-
Automatic position determination from CCD images.
- Precision alignment:
-
Automatic precision alignment of images.
- DARKTIME FITS header:
- The ``DARKTIME'' FITS variable should include
an allowance for the finite readout time of the CCD.
- Exposure countdown:
- Currently, the PC
does not have a display showing how many seconds remain on the current
exposure. This would be a nice addition.
- Gamma-ray bursters:
-
Mt Stromlo is possibly getting a satellite ground station so that it
can receive immediate notification of gamma ray bursters detected by
a satellite. It is possible that an e-mail message could be sent to
the APT from Stromlo within seconds of an alert, and the APT could then
stop whatever it is doing, slew to the coordinate, and take an image.
- Recordable CDs?:
- The AAO has a CD recorder
in Level 1 of the AAT. This can put 600 Mbytes on a CD, for a cost of
something like $35, making it an interesting option for archiving APT
data. We could buy own own recorder for about $6000.
- Slow-scan camera:
- When the APT becomes
fully remote, it will need a slow-scan camera so that the remote observer
can visually inspect the telescope and building to diagnose faults (e.g.,
if the telescope hits a limit switch and won't drive back).
- Absolute encoder problems:
- The absolute encoders are currently
only used to determine which way to move the telescope in order to
reach the zero-point calibration. The software that does this on the Apple
has some bugs, which for certain positions in declination at least, will
result in the telescope going the wrong way to find the limit.
- Peltier cooler:
- The CCD camera is
cooled by a Peltier cooler, and has a temperature sensor that can be
monitored with a voltmeter at the camera control box. It would be worthwhile
to measure the cool-down performance (temperature versus time) for the
cooler so that we can monitor it over time for degradation. The only
information we have so far is from Wright Instrument's measurements, which
show the cooler reaching 200K in 15 minutes from about 25C.
- Remote resetting:
- To allow remote operation
we need to be able to cope with every conceivable hardware/software fault.
At the moment, there are several things that can happen that require
manual intervention before you can continue:
- If the Apple II crashes, it can not be automatically reset.
Probably the easiest way of fixing this is have the power to the Apple II
controlled by a solid-state relay connected to the PC.
- If the servo-controller crashes, it has to be reset by pushing
buttons on the front panel. This could be readily controlled by the PC,
or else an automatic-reset on power-up could be installed.
- If the PC crashes you are also in trouble. The PC power could be
controlled by a solid-state relay, either controlled by the workstation,
or by an heartbeat circuit.
- If the telescope hits a limit, the servo controller goes into
an infinite loop, and it can be very difficult to drive the telescope
off the limit.
- If the workstation crashes, it can be set to automatically reboot
itself. This doesn't always succeed (e.g., filesystems could be
corrupted, and may not be able to be automatically repaired), but there
is no easy way around this.
- PC crashing:
- The PC still hangs up occasionally.
Also, the communication link between the PC and
the workstation sometimes gets caught in an endless loop which can only
be reset by rebooting the PC and re-establishing the APT Link window.
- On-line data processing:
- The DECstation is certainly powerful
enough to allow the APT data to be processed on-line. The software
is almost ready to go, for the supernova search program at least, but
has yet to be installed.
- Automatic focussing routine:
- An IRAF script is almost
finished that will automatically focus the APT.
- Twilight frame routines:
- Changes to MCCD could improve the
ability to automatically acquire twilight frames.
- Performance information:
- The following information should be
provided to observers:
- Magnitude limit in various filters.
- Expected sky background as a function of moon phase.
- Linearity of the CCD.
- Gain calibration.
- Read-noise measurement.
- Reproducibility of flat-fields.
- Dark current as a function of time.
- Precise readout times as a function of readout speed and size of the
area being read out.
Next: Scientific highlights
Up: No Title
Previous: Troubleshooting and known bugs
Michael C. B. Ashley
Wed Jun 5 14:40:19 EST 1996