1. The Observatory

1.1 Introduction

The Caltech Submillimeter Observatory is a 10.4 meter submillimeter antenna at 13,300 feet on Mauna Kea in Hawaii. The telescope is an alt-az f 0.4 dish, with positions for receivers at both the Cassegrain focus, and in the sidecab, which is effectively a rotating (with zenith) Nasmyth focus. We are able to observe from 0.5 to 88.5 degrees zenith angle, except in certain areas where we are restricted by local obstructions: mountains, JCMT, etc. The telescope is contained within a very compact, rotating dome structure, which has 2 large shutters which open to allow observing.

The classical Mauna Kea night will allow observing from around sunset till sometime after dawn. There are 4 constraining features on this. Firstly, it is not permitted to get sunlight on the dish surface, secondary and its support legs, backing structure, or Teepee This may restrict you a little in getting started, though obviously not much if your sources are in the east. It is possible to observe until ~10 AM in the morning, if one carefully chooses sources in the west, and closes the shutter partially to shield the dish. There are a couple of reasons for keeping the sun off the dish. Being a submillimeter dish it is very sensitive to thermal gradients in the structure. These will probably affect you anyway during the first hour after sunset - we are currently investigating them and hope we may be able to model the effect. Also, the dish surface is more than good enough to focus the suns rays, even at an oblique angle, and this can do a great deal of damage to cables, equipment and people. Secondly, the inversion layer. This needs to fall below the summit for good submillimeter observing, and this usually happens sometime near sunset. Its return over the summit is a little less predictable, but is usually soon after sunrise, though occasionally it is possible to continue observation nearly all day if suitable sources (i.e., far from the sun) can be found.

The third reason is simply one of sleep - single shift operations at these frequencies (and at this altitude) make for tiring observing sessions. The fourth involves the need for our day-crew and engineers to have some access to the telescope for maintenance, though this can be negotiated for special cases.

1.2 Our Cozy Dome

The usable space in the dome of the CSO is a 3 story structure, shaped rather like a horseshoe. The first floor contains a galley, toilet, storage rooms, the Uninterruptable Power Supply, and the mechanical workshop. The base of the stairwell between the Galley and store room also contains the emergency food, water, heating and lighting supplies. The second floor contains a lounge room and bathroom, storage closet, the computer room, Control Room, Electronics Lab, a cryogenics storage area, and access to the antenna alidade platform and sidecab. Much of your time whilst observing will be spent on this floor. The third floor contains a receiver/electronics lab, and another storage room.

The galley contains the important equipment: a microwave oven, hotplates, sink, hot-air popcorn popper, fridge etc. The only other room on this floor you are likely to use is the mechanical workshop, which also contains the main control panels for the Dome Drives and Shutter Drives, which you are unlikely to need except when there is a problem, as these are usually controlled from the Control Room.

On the second floor , the Electronics lab also doubles as the backend room. It contains the Accousto-Optic Spectrometers, their related IF conversion units and the Backend Computer. There are four AOSes - two are 1024 channel, 500 MHz bandwidth units, one 1024 channel, 50 MHz high resolution unit and a 2048 channel 1.5 GHz model. The four can be run simultaneously or in any combination, and the position of the 50 MHz AOS within the 500 MHz bandwidth of the IF can be adjusted. The two 500 MHz AOSes can be overlapped fully or partially, within the 1 GHz bandwidth offered by the heterodyne receivers.

The main room here is, of course, the Control room, and it is quite likely that you may find yourselves rarely leaving it (apart from your frequent trips outside to check the weather!). From here, you have complete control over all aspects of the observatory, apart from receiver tuning. Note that the storage closet (between the lounge and the bathroom) is were we keep most consumable stores such as paper, pads, pens, printer cartridges etc.

Note that the observatory also has an intercom system. It is entirely separate to the phone system, and a special phone in each room is attached to it. This allows you to talk to people in any room, or to page someone by dialing 30. The ordinary phone system has 2 lines, and is available in the galley, control room, computer room, receiver lab, electronics lab and mechanical workshop. It is not an exchange system - just dial 1, then the area code etc.

As you may have noticed, the entire dome structure rotates. This means that we have to have a supply of fresh water contained within the dome, plus a holding tank for waste water (including the sewer). These are each of the order of 400 gallons. Please be sparing in your use of fresh water - it is quite a job to fill the tank, and drain the waste tank. Thank you. This rotation also means that your vehicle may not be where you think you left relative to the doors - this is not an affect of the altitude.

Each room is fitted with 2 heating systems - a fan/heater unit, plus radiant panels in the ceilings. These should always be turned off in any room which is not occupied for long periods of time, as electricity up here is very expensive. You will also find 2 water jugs. These are meant as not-so-subtle hints. The altitude has a number of affects on your body which you should be aware of. Firstly, it is (hopefully) extremely dry up here, so you will dehydrate very easily. This is not helped by the body's reaction to low oxygen levels - unfortunately, the kidneys react by preferentially retaining salts and dumping water. Actually, this is part of a process of thickening the blood as a means of increasing the blood oxygen content. Thus, it is recommended that you drink AT LEAST one large glass of water (or equivalent) an hour. If you don't, you'll be sorry - severe headaches are caused by dehydration at least as often as directly by oxygen deprivation. If you are not aware of the various problems with working at high altitude, please ask us for a copy of a report on this.

Please also note that static electricity is a very big problem up here, mainly due to the dry atmosphere. PLEASE be sure to ground yourself before touching any sensitive equipment, particularly receivers. You will also note that the wall plugs come in 2 colors - white and orange. This is because we have 2 separate ground systems, a `dirty' (white) ground and a `clean' (orange) ground. Be careful not to attach any equipment to clean power which may be inherently dirty, or which may provide some shorting path to the dirty ground, such as via the chassis. If in doubt, please ask a staff member.

The Observatory has three components to its power supply. Firstly, as of October 1988 we transferred from local, mountaintop generated power to Hawaiian Electric Company power. This is something of a mixed blessing and hence, we now have a small backup generator (the second component) which can provide power for emergency functions, such as closing the shutter and operation of the CTI compressors for maintaining the receivers. Eventually this probably will be wired so as to allow observing to continue during a protracted power outage, though initially it will only be for emergency use. The third component is the Uninterruptable Power Supply, which is a standard AC/DC battery/AC system which can supply the computers and certain aspects of the receiver chain for short periods.

If the main power is down for a protracted period, it will be necessary to shut down certain equipment to ensure this system can maintain the vital items. See the relevant Emergency procedures manual for more information on this. There are copies of it in the Control Room, the UPS room and with the LPG cylinders for the generator.

1.3 Starting the Control System

When you first arrive in the observatory each evening, you are required to do a `walkabout'. This is to check for anything that has been left in a dangerous position for observing. Large items, such as the crane, and many doors which may foul the dish have interlocks on them to prevent the antenna driving if they are in an unsafe position. However, it is always possible that some piece of equipment may have been left out in such a way that it could hit the dish, or may fall when it is moved. Though all staff will always make sure not to leave anything in a dangerous position, it is naturally the responsibility of the person about to drive the telescope/dome system to ensure that it is safe to do so. A walk around the front of the dish on the first floor (commonly called the apron), followed by a check of the alidade platform, sidecab, and third floor should be sufficient, and only take a few minutes. It can easily be done in a fraction of the time the shutter doors take to open. Newcomers to the observatory will be shown this as part of their introductory tour. Look for things like ladders left against the wall in the sidecab etc - anything that may foul the telescopes movement, particularly in zenith. See the section on Antenna Motion Limits for information on limit and interlock switches.

In the control room, near the phone, there is a box housing several rows of colored lights. This is the Control Panel If any of the red lights are on, you should not try to move the antenna or dome. If you happen to try to move the dome while one of these lights (apart from the Emergency Stop lights) is illuminated, you will probably cause a fault to occur, by driving the antenna into the dome. The computer does know when an Emergency Stop button is pressed. So the basic aim before starting observing is to ensure there are no red or orange LEDs illuminated, and that the three green LEDs for the Dome Drive system are illuminated. When you have this state, you can start to slew the dome/antenna system to your source. If you do hit one of the dome/antenna limits, you will need to follow the procedure in Chapter 6 to enable movement again.

The dome and antenna are normally powered down when observing is not taking place. The following steps will power them up. The observatory is usually left disabled by the use of the Control Room Emergency Stop Button. This is pushed to disable the antenna, dome and shutter. Note that this currently only disables the Azimuth, Zenith angle, dome and shutter motors. It does not disable the chopping or focusing motors of the secondary mirror, nor any other motors relating to the fourth and fifth mirrors, or the chopper wheel. When an Emergency Stop button is pushed, its internal light is extinguished and a red led on the Control Panel is illuminated to indicate which button is pressed, disabling motion. If you find that an Emergency Stop Button has been engaged, you must check with any other persons in the dome before disengaging it. If you engage an Emergency Stop Button for safety reasons (for instance, if you are working on the telescope structure, or on a ladder etc.) you should place a note on the engaged button stating that you should be consulted before the button is disengaged.

The main controls relevant to the general movement of the telescope/dome system are in the Workshop (room 106) on the first floor , though these are not used as much now we have control from the Control Room. The only aspect of the drive system which is occasionally of concern to observers is the dome drive motors, which must be forced against the azimuth rail to drive the dome. Pressurizing the drive hydraulics is performed from the comfort of the Control Room. On the lower left-hand side of the Control Panel you will find two buttons and three lights. Basically, the left-hand button enables the Dome Drive Motors, and the right-hand button disables the drives. If any of the three LEDs is red, or unilluminated, the dome drive is disabled (and physically disengaged). Press the left-hand button: the three LEDs will (within a couple of minutes) turn green. You must NOT try to drive the antenna/dome system in Azimuth from the computer until these three are green. Pressing the right-hand button will reverse this procedure.

Apart from enabling the telescope/dome system, you will also need to open the Shutter. This is also performed from the Control Panel in the Control Room, via the 3 buttons immediately to the right of the Dome Drive Controls. Note that you will have to have released the Emergency Stop button before you can open (or close) the shutter. The left hand button initiates the opening sequence - whilst it is flashing green, the shutter is in the process of opening - when it turns a solid green, it has finished. The percentage open is shown by the LCD display, 0 being closed and 99 being fully open. Do not worry about small deviations from these numbers at the extremes: any hieroglyphics are due to oxygen deprivation. To close the shutter, simply press the Close button - it will stop automatically when it is fully closed. You do NOT need to press the Stop button - this applies to both opening and closing. Again, the same philosophy applies to the LEDs. Note: if you wish to reverse direction (ie change from opening to closing during the actual opening process, or vice versa), you MUST press the Stop button (center of the three) before starting the other cycle.

1.4 Shutting Down the Observatory

When leaving each morning, the observatory should be shut down as follows. The shutter takes a while to close, so you should first start it closing by pressing the Shutter Close button on the Control Panel in the Control Room. The Antenna should be stowed using the STOW command to UIP, or by sending it to an azimuth of between 80 and 100, and a zenith angle of 15 degrees. Note that the STOW command will arbitrarily select an azimuth near were the Sun will rise. This is to prevent us from continually parking in the same place, and therefore minimizes wear on the slip rings. If you are stowing the telescope after sunrise, be sure that you do not slew the telescope through the Sun's azimuth! After the antenna has driven to the correct position and the shutter is closed, the Emergency Stop button in the control room should be pushed in.

If you have been using the SIS receivers, please make sure you have turned off the magnets.

The shutter doors MUST be closed before you leave the observatory.

Be sure the secondary mirror is not chopping.

All of the blower/heater units should be turned off. All lights should be turned off, and the side doors should be locked.

1.5 Antenna Motion Limits

The dome can rotate around and around and never break any wires. It has slip rings. The antenna, however, has a cable wrap, and it cannot rotate forever. The antenna can rotate through 444 degrees, starting at an azimuth of -92 degrees (west) passing through north at az=0 and continuing clockwise to 352 (almost north again). This range allows the tracking of most objects without any interruptions to allow the wrap to unwind. These limiting azimuths are enforced by two levels of limit switches. Upon hitting the first limit switch, motion in the current direction will be disabled, but you can still drive off the limit switch under either computer or hand paddle control. It you somehow hit the second limit switch, all motion of the antenna will be disabled, and you will have to jumper out the limit switch to move. The limit switches are mechanical, and they are hard to position precisely, so the above quoted limit positions may be off by one or two degrees.

The zenith angle motion is limited too, of course. The telescope cannot be sent to a position lower than about 88.5 degrees. It can be sent slightly past the zenith, to about -2 degrees, though in fact we rarely go past 2 degrees. Each of these limits has a pair of limit switches like the azimuth ones. The capability to go to slightly negative zenith angles is not currently used to track celestial objects. In fact, it can be difficult to track objects within about 1.5 degrees of the zenith, as the 'OFF' position used in spectral OO scans is often in azimuth, and you may not be physically able to move the beam on the sky that far.

There are a number of other limit switches and interlocks in the observatory. These are mainly to prevent various objects from fouling the antenna. They all have indicators on the Control Panel in the Control Room. The large overhead crane has a limit switch to stop the antenna moving if the crane is not in its fully stowed position, which is up against the side of the dome. The portable hydraulics lift for accessing the secondary must also be stowed next to the Galley door . The TeePee door and the door on the rear of the sidecab must also be closed, as they can interfere with the antenna at certain zenith angles. Also, the railing next to the front door to the sidecab must be in its 'rearward' position i.e., it must be in the pair of holes nearest the sidecab, not the pair about 4 inches further towards the Control Room . There is also an interlock on the hoist to the cryogenics platform.

1.6 Using the Hand Paddles

It is sometimes necessary or convenient to move the antenna or dome manually. There are two `hand paddles' to allow this. These are the only form of manual control of the antenna/dome structure which we have, and their use is very rare. Before explaining the hand paddles it should be noted that normally the antenna and dome cannot be moved independently in azimuth. They can differ in relative position by about two degrees, after that there would be a collision. If the antenna were to push the dome, you would hear an unpleasant noise as the clutch slips. If the dome were to push the antenna, the antenna would be back driven. The antenna shouldn't be back driven except in an emergency. Only CSO staff members should use the dome hand paddle.

The most commonly used hand paddle is the antenna hand paddle . It is located in the TeePee and is normally plugged in to the left side of the Antenna Control Limit Box (the box in the TeePee with the LEDs on the top). To use this hand paddle, first idle the antenna computer (using the UIP's IDLE command). The antenna computer should be idled so that it will not move the dome as you move the antenna. Now proceed to the TeePee and find the hand paddle. You probably should disable both directions (azimuth and zenith angle) using the toggle switches on the hand paddle. If you do not, the motions may slowly drift even if you are not pressing either of the motion push buttons. Now use the toggle switch on top of the box just inside the TeePee door to switch to hand paddle control rather than Computer control. A red light should be illuminated on the hand paddle. Now enable the motion on the axis you wish to drive, and use the push buttons to send a drive voltage.

In some cases it is desirable to drive the antenna in azimuth with the hand paddle, while having computer move the dome to keep the dome and antenna from colliding. To do this, the antenna computer must be running its normal program, and the antenna should not be idle. When the antenna is idle, the dome and antenna motors are turned off by the antenna computer. If the antenna is idle, the best way to get it out of that condition is to enter

UIP> ALTAZ

UIP> TRACK
under UIP. The antenna should be accelerated slowly with the handle paddle, since the dome servo was not designed for this mode of operation. The dome will seem sluggish.

The dome has a hand paddle too, but it is used even less often. It is located inside the dome motor controller box (The big grey box behind the UPS batteries in the in the UPS/Electrical Room , room 108, immediately beneath the Control Room on top of the RFI shielding). It must be plugged into a cable that is normally plugged into a socket located in the upper left hand corner of the box, outside of the RFI shielding. The limit switches on antenna-dome relative position are BYPASSED when this hand paddle is used. This means you can easily run the dome into the antenna and cause the antenna to be back driven.

Both of these hand paddles have a problem. The drive voltages are supplied by internal batteries, which often go dead or fall out of their internal battery holder. If the hand paddle doesn't work, check the batteries.

The only likely circumstance for using the antenna hand paddle is when the dome and antenna get so far out of alignment that they cannot be driven by computer control. This requires you to maneuver the antenna so it is aligned with the dome in an azimuthal sense. To do this, drag the hand paddle from the Teepee to the area next to the workshop where you will find the LVDT limit switches and mechanical buffers which all relate to the dome/antenna azimuth relationship. Look up - you will eventually realize that the mechanism from the antenna between the two sets of limit switches is not centrally located - and it should be. Carefully, enable the azimuth control, slow rate on the hand paddle, and try moving the antenna in one direction. Simply move it so it is as nearly centered as you can get it. Stow the hand paddle, remembering to disable both axes on it, and return control to the computer by toggling the switch inside the Teepee door to the left from Hand Paddle back to Computer Control.

1.7 Focus Control

Computer control of the secondary focus is handled from the UIP command FOCUS, which allows you to send the secondary to a specific position, or to have the secondary follow the preprogrammed focus curve. The focus position is shown on the bottom left corner of the antenna status display. The units displayed, and the units used in the focus command, are millimeters at the secondary encoders, except for the theta (rotation) position, which is displayed in degrees.

There are two modes for having the secondary follow the focus curve. In continuous update mode, the secondary will be moved anytime the antenna computer decides it should be - regardless of whether an integration is taking place. The other mode, stealthy mode, allows the secondary to move only when the antenna is changing positions on the sky. The secondary will remain fixed during an integration. Stealthy mode is the default.

The FOCUS command allows you to specify an offset that will be added to the value from the focus curve.

Since moving the secondary has an effect on pointing, the antenna computer attempts to compensate. Small offsets (TAZO and TZAO shown on page 1 of the antenna status display) are recalculated each time the secondary is moved. If for some reason you wish to disable the pointing adjustments, issues the UIP command
UIP> TOA DON'T_FOCUS_COMP
this is done automatically if you specify optical pointing. To re-enable the adjustments, type
UIP> TOA DO_FOCUS_COMP
It is a game observer who will fiddle with such things however.

The X_POSITION, Y_POSITION and THETA_POSITION commands work just like the FOCUS command described above, but they act upon the X (left-right), Y (up-down), and theta (rotation) motions of the secondary.