Sloan Digital Sky Survey

Sloan Digital Sky Survey Technical Requirements and Performance Specifications for the 2.5-Meter Telescope

Revision History

*Date*	*Revision Description*
10/17/97	Initial document release.

Table of Contents

1.0 Introduction

1.1 Scope............................................................................................................Rev. 8/97

1.2 Change Control...........................................................................................Rev. 10/97

2.0 Environment

2.1 On-site Compressed Air.............................................................................Rev. 8/97

2.2 Enclosure Overhead Door Opening.........................................................Rev. 5/97

2.3 Maximum Operating Wind Speed.............................................................Rev. 8/97

2.4 Normal Operating Wind Speed.................................................................Rev. 8/97

2.5 Operating Temperature Range..................................................................Rev. 7/97

2.6 Lightning Protection...................................................................................tbd

3.0 Telescope Parameters

3.1 Basic Telescope Parameters......................................................................See URL

3.2 Wind Baffle Dimensions............................................................................Rev. 7/97

3.3 Wind Baffle to Enclosure Door Opening Clearances............................Rev. 7/97

3.4 Wind Baffle Drive Friction.........................................................................Rev. 7/97

3.5 Camera Weights..........................................................................................Rev.

4.0 Telescope Axis Controls

4.1 Pointing Precision.......................................................................................Rev. 7/97

4.2 Tracking Precision.......................................................................................Rev. 8/97

4.3 Maximum Tracking Rate.............................................................................Rev. 7/97

4.4 Maximum Tracking Acceleration..............................................................Rev. 7/97

4.5 Absolute Fiducial Transducer Precision.................................................Rev. 7/97

4.6 Normal Operating Range............................................................................Rev. 7/97

4.7 Safe Operating Range

4.7.1 Telescope Azimuth..........................................................................Rev. 7/97

4.7.2 Telescope Altitude...........................................................................Rev. 7/97

4.7.3 Instrument Rotator...........................................................................Rev. 7/97

4.8 Normal Velocity Range...............................................................................Rev. 7/97

4.9 Safe Velocity Limits.....................................................................................Rev. 7/97

4.10 Maximum Acceleration Rate......................................................................Rev. 7/97

4.11 Home Position Accuracy............................................................................Rev. 9/97

4.12 Mechanical Stops on the Instrument Rotator.........................................Rev. 7/97

4.13 Mechanical Stops on the Azimuth Axis..................................................Rev. 7/97

4.14 Locking Pins

4.14.1 Telescope Azimuth........................................................................Rev. 7/97

4.14.2 Telescope Altitude........................................................................Rev. 7/97

4.14.3 Wind Baffle Azimuth.....................................................................Rev. 7/97

4.14.4 Wind Baffle Altitude.....................................................................Rev. 7/97

4.14.5 Instrument Rotator.........................................................................Rev. 7/97

4.15 Mechanical Brakes

4.15.1 Telescope Azimuth.........................................................................Rev. 10/97

4.15.2 Telescope Altitude.........................................................................Rev. 10/97

4.15.3 Wind Baffle Azimuth......................................................................Rev. 7/97

4.15.4 Wind Baffle Altitude......................................................................Rev. 7/97

4.15.5 Instrument Rotator.........................................................................Rev. 7/97

4.16 Wind Baffle-to-Telescope Tracking Precision........................................Rev. 7/97

4.17 Sense Switches on the 15-degree Hard Stop..........................................Rev. 7/97

4.18 Telescope to Wind Baffle Alignment Clamps........................................Rev. 9/97

4.19 Telescope to Wind Baffle Bump Switches..............................................Rev. 7/97

4.20 Small Telescope Motions Within the Enclosure....................................Rev. 7/97

4.21 Telescope Counterweights

4.21.1 Telescope Balance.........................................................................Rev. 7/97

4.21.2 Counterweight Motor-driven Operation....................................Rev. 7/97

4.21.3 Counterweight Manual Operation...............................................Rev. 7/97

4.21.4 Counterweight Position Display..................................................Rev. 7/97

4.21.5 Counterweight Covers...................................................................Rev. 7/97

5.0 Telescope Motion Interlocks

5.1 Azimuth Axis Motion..................................................................................Rev. 7/97

5.2 Altitude Axis Motion..................................................................................Rev. 7/97

5.3 Instrument Rotator Motion........................................................................Rev. 7/97

5.4 Motor Drive Capstan Slip Detection........................................................Rev. 7/97

5.5 Telescope Stop Buttons.............................................................................Rev. 8/97

5.6 Telescope Drive Motors.............................................................................Rev. 8/97

5.7 Wind Baffle Drive Motors..........................................................................Rev. 8/97

5.8 Telescope Brakes.........................................................................................Rev. 8/97

5.9 Interlock System Status Display................................................................Rev. 8/97

6.0 Instument Exchange Controls and Interlocks

6.1 Maximum Instrument Lift Force................................................................Rev. 8/97

6.2 Instrument Lift Automated Control System............................................Rev. 8/97

6.3 Instrument Change Interlocks...................................................................Rev. 8/97

6.4 Instrument Change Indicator Lights........................................................Rev. 8/97

6.5 Low-level Illumination Lamps...................................................................Rev. 8/97

6.6 Observer Intercom System........................................................................Rev. 8/97

6.7 Cartridge Cart Staging Area......................................................................Rev. 8/97

6.8 Camera Doghouse Doors..........................................................................Rev. 8/97

7.0 Optics

To be developed

8.0 Imager

To be developed.

9.0 Spectrograph

To be developed.

10.0 Fiber System

To be developed.

11.0 Telescope Performance Monitor

To be developed.

Appendix A - Glossary of Terms

1.0 Introduction

1.1 SCOPE

This document defines the technical requirements and performance specifications for the major hardware systems associated with the Sloan Digital Sky Survey (SDSS) 2.5-meter telescope. This document also serves as a repository for information on site environmental conditions and telescope construction parameters relevant to the telescope hardware systems.

1.2 CHANGE CONTROL Revisions to this requirements document are approved by the SDSS Telescope Change Control Board (TCCB). Requests for revisions should be submitted to Bill Boroski via e-mail (boroski@fnal.gov) or by fax (630.840.8032). Revision requests will be forwarded to the TCCB for review and consideration. As necessary, the TCCB may solicit the help of technical experts to aid in the evaluation of specific requests. Notification of each revision to the requirements document will be provided to the SDSS organization via e-mail messages sent to sdss-general@astro.princeton.edu. 2.0 Environment

2.1 ON-SITE COMPRESSED AIR

The maximum pressure available from the APO site air compressor is 120 psig (set by the burst disk on the compressor). The site air compressor is set to cycle on when the pressure drops to 80 psig and cycle off when the pressure reaches 110 psig. Air pressure to the site is regulated to 100 psig. Systems connected to the site air compressor should be designed to operate with an air pressure as low as 80 psig.

Reference: Dan Long e-mail (8/14/97).
Revised: 8/14/97

2.2 ENCLOSURE OVERHEAD DOOR OPENING

Design vertical clearance of overhead door: 144" above the finished floor.
As-built vertical clearance of overhead door: 146" above the finished floor

Reference: W. Siegmund e-mail (5/27/97).
Revised:

2.3 MAXIMUM OPERATING WIND SPEED

The telescope enclosure shall be closed by the time the wind speed reaches 60 mph. It should be noted that the site operational wind speed limit is 35 mph (average, not peak) and that the enclosure is designed to withstand wind speeds to 134 mph.

Reference: W. Siegmund.
Revised:

2.4 NORMAL OPERATING WIND SPEED

The telescope will be operated under wind speeds up to 35 mph.

Reference: S. Kent.
Revised:

2.5 OPERATING TEMPERATURE RANGE

The operating temperature range of the telescope is 20 deg. C to -20 deg. C.

Reference: ITF Meeting (7/20/96).
Revised:

2.6 LIGHTNING PROTECTION

(TBD)

Reference:
Revised:

3.0 Telescope Parameters

3.1 BASIC TELESCOPE PARAMETERS

Walter Siegmund has prepared a reference document titled "Basic Telescope Parameters" that summarizes information on various telescope and wind baffle parameters such as mass, center of gravity, moments of inertia, etc. The document also contains the procedure for setting the drive motor preloads for the telescope altitude and azimuth axes. This document can be found at the following URL: http://www.apo.nmsu.edu/Telescopes/SDSS/eng.papers/19970514_BasicTelescopeInfo/19970514.html

Reference: SDSS Tech Note # 19970514
Revised: See URL.

3.2 WIND BAFFLE DIMENSIONS

With the telescope and wind baffle at 0 deg. elevation:
      Maximum height of the wind baffle: 137" above the finished floor
      Maximum height of the wind baffle support: 138" above the finished floor
      Vertical clearance of the wind baffle: 6" above the finished floor

Reference: W. Siegmund e-mail (5/27/97).
Revised: 5/27/97.

3.3 WIND BAFFLE -TO-ENCLOSURE DOOR OPENING CLEARANCES

With the telescope and wind baffle in the stow position, the side-to-side clearance between the wind baffle and the enclosure door opening is 13.1". The door clamps encroach 5" on either side of the door opening at about 84" above the finished floor.

Reference: W. Siegmund e-mail (5/27/97).
Revised: 5/27/97.

3.4 WIND BAFFLE DRIVE FRICTION

The friction for the azimuthal motion of the wind baffle is 9000 ft.-lb. The friction for the altitude motion is 900 ft.-lb. friction..

Reference: SDSS Tech Note # 19950608
Revised:

3.5 CAMERA WEIGHTS

The camera weight exclusive of the optical benches is 673 pounds. The optical benches add another 30 pounds, so the total camera weight is 703 pounds. This is the total weight that is supported on the instrument latches and kinematic mounts.

The saddle fully assembled weighs between 280 and 317 pounds, depending on whether the intermediate LN2 dewars are empty or full. This is the weight on the saddle latches.

Thus, the total weight of the camera/saddle assembly on the telescope is between approximately 980 and 1020 pounds.

The camera operations cart weighs 240 pounds. Thus, the maximum that the instrument lift must handle is the weight of the camera, saddle, and operations cart, which is 703 + 317(full) + 240 = 1260 pounds.

Reference: Jim Gunn e-mails (10/10/97 and 10/15/97).
Revised: 10/16/97

4.0 Telescope Axis Controls

4.1 POINTING PRECISION

The pointing requirement is 3 arcsecs RMS radius error. This is equivalent to 2 arcsec RMS per axis, or +/-5 arcsec per axis.

Reference: Table 2, SDSS Tech Note 19970527, "2.5-m Telescope Pointing Error Budget", by W. Siegmund.
Revised:

4.2 TRACKING PRECISION

4.2.1 For time scales between 1 and 10 minutes, the tracking error shall be less than 165 mas RMS per axis. Basis: Uncorrected tracking errors cause astrometric errors. Given other entries in Table 10.2 of the Black Book, one finds that the uncorrected tracking error can be as large as 258 mas RMS radius error without exceeding the target of 265 mas RMS radius error. Of this, about 50 mas RMS radius error is due to bearing wobble, etc. This leaves 180 mas RMS servo error per axis.

Comment: This tracking error requirement applies to operation of the telescope under worst case wind conditions. Under calm conditions, the maximum tracking error should approach 10 mas RMS per axis. This is consistent with SDSS Tech Note 19970523, "2.5-m Telescope Tracking Error Budget", which gives 10 mas RMS servo error per axis as a goal.

References:

1) Black Book, Table 10.2, "Contributions to Astrometric Errors."
The uncorrected tracking error entry in this table comes in turn from Table 1, SDSS Tech Note 19970527, "2.5-m Telescope Pointing Error Budget."

2) S. Kent, "Astrometric Calibration: III. Requirements on tracking errors", May 29, 1997.

4.2.2     For time scales less than one minute, the tracking error shall be less than 100 mas RMS per axis. Basis: Image broadening due to such motion must be less than the best seeing (about 800 mas FWHM, or 340 mas RMS per axis). 4.2.3     The tracking rate shall be accurate to one part in 4000 averaged over one minute. Basis: Drift of 0.5 pixel in 55 seconds will cause image elongation. Notes: 1.   Time scales:
      Astrometric CCD crossing time - 11 sec
      Photometric CCD crossing time - 55 sec
      Time between standard stars (Tycho catalog) - 6/minute.
      Camera crossing time - 10 min.

4.3 MAXIMUM TRACKING RATE

Azimuth:   45 arcsec/sec (3x sidereal)
Altitude:   15 arcsec/sec (3x sidereal)
Rotator:    45 arcsec/sec (3x sidereal)

Basis: Minimal zone of avoidance near the zenith gives a reasonable limit of 3x sidereal.

Reference: S. Kent, Telescope Controls Requirements Discussion (4/26/97).
Revised:

4.4 MAXIMUM TRACKING ACCELERATION

The maximum acceleration during tracking shall not exceed 0.02 deg/min./min. (maximum)

Comment: This is high. It comes while tracking inside a region near the zenith where we know that we don’t actually track in practice.

Reference: S. Kent (11/8/96).
Revised:

4.5 ABSOLUTE POSITION TRANSDUCER PRECISION

Altitude:   7.2 microns RMS (+/- 18 microns at the transducer radius).
Azimuth:   7.2 microns RMS (+/- 18 microns at the transducer radius).
Rotator:    30 microns RMS (+/- 75 microns at the transducer radius).

Basis: These values are derived from pointing precision requirements. One arcsec corresponds to 6 microns at the magnetic fiducials on the azimuth axis. Also, for the rotator, one pixel of transverse motion across the CCD array's body to trailing edge (462 mm) is allowed. Sources of error that will contribute to transducer precision include tilt error, sensor angle error, noise, and thermal drift.

Reference: Telescope Controls Requirements Discussion (4/26/97).
Revised:

4.6 NORMAL OPERATING RANGE

Azimuth:    Center: 90 degrees, +/- 270 degrees.
Altitude:    Range: 25 - 87 degrees
Rotator:      Center: 90 degrees, +/- 270 degrees.

Comment: The altitude operating range applies to normal tracking and slewing operations. For instrument change, the telescope must be allowed to reach the zenith.

Reference: ITF 7/20/96; S. Kent, "Azimuth Range for 2.5M Telescope and Rotation Range Revisited", 7/9/96.
Revised:

Note: A clearly specified motion and orientation convention for all axes is needed. W. Siegmund will publish a convention (4/26/97).

4.7 SAFE OPERATING RANGE

4.7.1 TELESCOPE AZIMUTH Range: Center: 90 degrees, +/- 285 degrees.

Basis: Should the normal operating range be exceeded, the interlock system will initiate a directional inhibit to prevent further motion outside of the normal range. For a velocity change from 2 deg/sec to 0 deg/sec, the telescope azimuth coasting distance is calculated to be 5 degrees. The safe operating range includes room for the telescope to coast to a stop once a directional inhibit has been applied.

Reference: W. Siegmund, 6/30/97.
Revised:

4.7.2 TELESCOPE ALTITUDE Range: 0.6 to 90.5 degrees.

Basis: The telescope altitude operating range is determined by the position and performance of the upper and lower shock absorbers. Note that actual locations may vary slightly from the design drawings.

	First contact with shock absorber	Shock absorber at full compression.
Lower limits	0.9 deg	0.0 deg.
Upper limits	90.3 deg.	91.2 deg.

Reference: Telescope mechanical drawings E326315 and E326316.
Revised: 4.7.3 INSTRUMENT ROTATOR Range: Center: 90 degrees, +/- 285 degrees.

Basis: Should the normal operating range be exceeded, the interlock system will initiate a directional inhibit to prevent further motion outside of the normal range. For a velocity change from 2 deg/sec to 0 deg/sec, the rotator coasting distance is calculated to be 1 degree. The safe operating range includes room for the rotator to coast to a stop once a directional inhibit has been applied.

Reference: W. Siegmund (6/30/97).
Revised:

4.8 NORMAL VELOCITY RANGE

Azimuth:    0 - 2.8 deg/sec.
Altitude:    0 - 2.8 deg/sec.
Rotator:     0 - 2.8 deg/sec.

Basis: The slew rate is set by requiring the average slew time to be about one minute. The slew rate expected by the TCC will be 2.8 degrees per second. The control system will need to be able to respond to this.

Comment: These velocities apply over the normal operating range of the telescope. Refer to the section on safe velocity limits for limits when the telescope altitude axis is outside of the normal operating range.

Reference: ITF minutes (7/20/96); Notes from control/interlocks requirements review (7/20/96).
Revised:

4.9 SAFE VELOCITY LIMITS

Azimuth:     3.5 deg/sec.
Altitude:     3.5 deg/sec. (over the normal operating range)
                     1.0 deg/sec. (outside of the normal operating range)
Rotator:      3.5 deg/sec.

Basis:
1) Velocity limits of 3.5 deg/sec provide headroom for normal jitter of the control system. These limits may be adjusted later based on operating experience.

2) When the altitude axis is outside of the normal operating range, the telescope is nearing the upper or lower shock absorbers. The maximum velocity near these limits must be lower to avoid hard contact with the shock absorbers in a run-away situation.

Reference: Telescope Requirements Discussion (7/1/97).
Revised:

4.10 MAXIMUM ACCELERATION RATE

Azimuth:   50 deg/sec²
Altitude:   50 deg/sec²
Rotator:     100 deg/sec²

Basis: Derived from limiting acceleration to 3 m/sec² at 3.5 meters, which is the distance from the telescope altitude axis to the secondary mirror. It is noted that 3 m/sec² is the maximum seismic acceleration expected at the site. It is also noted that the maximum acceleration depends on the kinematic mounts for the imager. The axis control system will allow as little as 0.3 degrees/second/second.

Reference: Telescope Requirements Discussion (7/1/97).
Revised:

4.11 HOME POSITION ACCURACY

Azimuth:     +/- 0.2 deg.
Altitude:     +/- 0.05 deg.
Rotator:      +/- 0.1 deg.

Basis: Driven primarily by the precision to which the instrument kinematic mounts and the instrument cart must be aligned during instrument change requirements. The requirement for rotator and altitude axis alignment was derived by assuming a kinematic mount alignment requirement of +/-0.062" at a radius of 20" (radial position of the kinematic mounts on these axes).

Reference: W. Siegmund (6/30/97); Requirements Control Group Phone-Con (9/12/97).
Revised: 9/12/97.

4.12 MECHANICAL STOPS ON THE INSTRUMENT ROTATOR

There shall be no mechanical stop on the instrument rotator.

Reference: ITF (7/20/96).
Revised:

4.13 MECHANICAL STOPS ON THE AZIMUTH AXIS

There shall be no mechanical stop on the telescope azimuth axis.

Comment: Procedures will be used for power out movement of the telescope in azimuth to avoid cable breakage.

Reference: ITF (7/20/96).
Revised:

4.14 LOCKING PINS

4.14.1 TELESCOPE AZIMUTH There shall be no locking pins on the telescope azimuth axis.

Basis: Telescope brakes will be used to hold the telescope in position.

Reference: Telescope requirements discussion (7/1/97).
Revised:

4.14.2 TELESCOPE ALTITUDE There shall be no locking pins on the telescope altitude axis.

Basis: Telescope brakes will be used to hold the telescope in position.

Reference: Telescope requirements discussion (7/1/97).
Revised:

4.14.3 WIND BAFFLE AZIMUTH There shall be no locking pins on the wind baffle azimuth axis.

Basis: Friction in the wind baffle azimuth drives will hold the wind baffle assembly in position.

Reference: Weekly Friday Phonecon (5/30/97).
Revised:

4.14.4 WIND BAFFLE ALTITUDE There shall be no locking pin on the wind baffle altitude axis.

Basis: The brake on the wind baffle altitude drive motor will be used to hold the wind baffle in position.

Reference: ITF (7/20/96).
Revised:

4.14.5 INSTRUMENT ROTATOR There shall be no locking pin on the instrument rotator.

Basis: There is sufficient friction in the rotator bearing to hold a balanced rotator in position. A switch cutting power to the motor will be used to hold the rotator in position during instrument change operations.

Reference: ITF (7/20/96), W. Siegmund e-mail dated 2-May-97.
Revised:

4.15 MECHANICAL BRAKES

4.15.1 TELESCOPE AZIMUTH 4.15.1.1 A mechanical brake shall be installed on the telescope azimuth axis.

4.15.1.2 During brake engagement, the position of the telescope azimuth drive disk cannot move more than 2 arcsec RMS (equivalent to 12 microns RMS, or +/- 31 microns at the drive disk radius).

4.15.1.3 The brake shall have automatic and manual control modes. During automatic operation, the brake shall be controlled by the MCP.

4.15.1.4 Operators shall have the capability to manually release the brake during power-out conditions.

4.15.1.5 During brake engagement, decelleration of the telescope shall not exceed the maximum acceleration rate.

Reference: Telescope Controls Review Discussion (4/26/97); Requirements Control Group
Phone-Con (10/3/97)
Revised: 10/3/97.

4.15.2 TELESCOPE ALTITUDE 4.15.2.1 A mechanical brake shall be installed on the telescope altitude axis. A single brake on one of the drive disks is sufficient.

4.15.2.2 During brake engagement, the position of the telescope altitude drive disk cannot move more than 2 arcsec RMS (equivalent to 12 microns RMS, or ± 31 microns at the drive disk radius).

4.15.2.3 The brake shall have automatic and manual control modes. During automatic operation, the brake shall be controlled by the MCP.

4.15.2.4 Operators shall have the capability to manually release the brake during power-out conditions.

4.15.2.5 During brake engagement, decelleration of the telescope shall not exceed the maximum acceleration rate.

Reference: Telescope Controls Review Discussion (4/26/97). Requirements Control Group
Phone-Con (10/3/97)
Revised: 10/3/97.

4.15.3 WIND BAFFLE AZIMUTH There shall be no brake on the wind baffle azimuth axis.

Basis: There is sufficient friction in the wind baffle azimuth drive motors to hold the wind baffle in position during power-out conditions.

Reference: Telescope Controls Review Discussion (4/26/97).
Revised:

4.15.4 WIND BAFFLE ALTITUDE 4.15.4.1 A mechanical brake shall be installed on the wind baffle altitude axis to hold wind baffle position under maximum operating wind speeds.

4.15.4.2 The brake shall be automatically applied whenever power to the brake is lost.

4.15.4.3 When being applied, the brake shall limit maximum wind baffle deceleration to 100 deg/sec².

4.15.4.4 Operators shall have the capability of overriding the brake. Disabling the brake by removing the drive chain is acceptable.

Basis: A mechanical brake is required as there is insufficient friction in the wind baffle altitude drive motor to hold the wind baffle altitude position during windy, power- out conditions.

Reference: Telescope Controls Review Discussion (4/26/97).
Revised:

4.15.5 INSTRUMENT ROTATOR There shall be no brake on the instrument rotator.

Basis: There is sufficient friction in the rotator axis bearing to hold the rotator in place during power-out conditions.

Reference: W. Siegmund e-mail (5/2/97).
Revised:

4.16 WIND BAFFLE-TO-TELESCOPE TRACKING PRECISION

Azimuth: +/- 1 cm at the end of the wind baffle aperture.
Altitude: +/- 1 cm at the end of the wind baffle aperture.

Basis: Vignetting of the corner astrometric chips.

Comment: 1 cm corresponds to 0.11 degrees.

Reference: Telescope Requirements Discussion (7/1/97).
Revised:

4.17 SENSE SWITCHES ON THE WIND BAFFLE 15-DEGREE STOP

Sense switches shall be installed on the wind baffle 15-degree stop to detect the state of the stop lever.

Reference: ITF (7/20/96).
Revised:

4.18 TELESCOPE-TO-WIND BAFFLE ALIGNMENT CLAMPS (Altitude, Azimuth)

4.18.1 There shall be an alignment clamp between the wind baffle and telescope to maintain the azimuth alignment of the telescope and wind baffle to within 0.017 degrees.

4.18.2 No manual release is required on the alignment clamp.

4.18.3 Compliance shall be built into the alignment clamp assembly to relieve radial run-out stresses should the telescope/wind-baffle assembly need to be moved with the clamp engaged during power-out conditions.

Basis: The cartridge transfer cart spans the gap between the telescope and wind baffle when the foremost cartridge bay is positioned over the instrument lift plate. The instrument cart rails on the telescope and windbaffle must be aligned to within 0.017 degrees in order to ensure proper alignment of the cartridge alignment pins, the cartridge cart plate, and the instrument lift plate.

Reference: Requirements Control Group Phone-Con (9/18/97)
Revised: 9/18/97.

4.19 TELESCOPE-TO-WIND BAFFLE BUMP SWITCHES (Altitude and Azimuth)

4.19.1 A means of determining and recording that a bump has occurred between the telescope and wind baffle shall be provided.

4.19.2 No action shall be taken by the interlocks system as a result of a bump between the wind baffle and telescope.

Comment: Several means may be used to detect bumps, such as bump switches or the wind baffle LVDTs. Data from the LVDTs will be logged to file by the TPM and can be used to analyze bumps. If necessary, a "bump" study could be made to determine if bump switches should be used actively in the interlock system.

Reference: ITF (7/20/96); Telescope Controls Requirements Phone-Con (5/2/97)
Revised:

4.20 SMALL TELESCOPE MOTIONS WITHIN THE ENCLOSURE

Small movements of the telescope within the wind baffle shall be allowed with the enclosure in place. No special monitoring is required by the interlocks system.

Basis: Due to the limited amount of space within the enclosure, there is little benefit in providing systems to allow limited telescope/wind baffle motions while the enclosure is in place.

Reference: Telescope Requirements Discussion (7/1/97); e-mail between M. Klaene and W. Siegmund.
Revised:

4.21 TELESCOPE COUNTERWEIGHTS

4.21.1 TELESCOPE BALANCE 4.21.1.1 The counterweight system shall allow the telescope to be balanced when no instrument is attached.

4.21.1.2 The counterweight system shall include the capability for altitude balance adjustment after instrument mount.

4.21.1.3 Capability for counterweight adjustment during observation shall be included and augmented if needed.

Basis: Provisions for balancing the telescope when no instruments are attached are required for safe operation of the telescope. It is noted that the telescope cannot be balanced without the spectrographs in place. Therefore, if a spectrograph is removed from the telescope, a dummy weight must be installed in its place in order to maintain telescope balance.

Comment: Automatic adjustments to the balance after instrument change would become a requirement only after experience during construction and operation.

Reference: ITF 7/20/96
Revised:

4.21.2 COUNTERWEIGHT MOTOR-DRIVEN OPERATION 4.21.2.1 Under normal operations, positioning of the counterweights to balance the telescope shall be done by the telescope motion control processor (MCP).

4.21.2.2 The MCP shall have the capability to adjust the position of each counterweight independently.

Reference: ITF (7/20/96)
Revised:

4.21.3 COUNTERWEIGHT MANUAL OPERATION The counterweight system shall be designed to allow for manual operation.

Reference: ITF (7/20/96).
Revised:

4.21.4 COUNTERWEIGHT POSITION DISPLAY The position of each counterweight shall be digitally displayed on the front panel of the counterweight control module.

Comment: During manual operation, observation of the weight will be adequate to determine position.

Reference: ITF (7/20/96).
Revised:

4.21.5 COUNTERWEIGHT COVERS Each counterweight shall be enclosed within a steel cover equipped with a window to allow the counterweight position to be observed.

Reference: ITF (7/20/96).
Revised:

5.0 Telescope Motion Interlocks

5.1 AZIMUTH AXIS MOTION

5.1.1 A two-level interlock shall be installed on the azimuth axis to inhibit azimuth rotation beyond the safe operating zone.

5.1.2 The Level-1 limits shall inhibit telescope movement in the direction beyond the limit but allow movement in the direction away from the limit. The Level-1 limits shall be positioned at each end of the normal operating range.

5.1.3 The Level-2 limits shall remove power from the azimuth drive motors, thereby stopping all telescope azimuth motion. The Level-2 limits shall be positioned at each end of the safe operating range.

Reference: ITF (7/20/96).
Revised:

5.2 ALTITUDE AXIS MOTION

5.2.1 A two-level interlock shall be installed on the altitude axis to inhibit altitude rotation beyond the safe operating range.

5.2.2 The Level-1 limit shall inhibit telescope movement in the direction beyond the limit but allow movement in the direction away from the limit.

5.2.3 The Level-2 limits shall remove power from the altitude drive motors, thereby stopping all telescope altitude motion.

5.2.4 The altitude motion limit switches shall be installed at the following locations:

	Lower Limit	Upper Limit
Level-1 Limits	0.8 deg.	90.3 deg.
Level-2 Limits	0.6 deg.	90.5 deg.

Basis: These positions will allow the telescope to reach the stow and instrument change positions without encountering a limit switch. In all cases, the Level-1 limit switches are encountered shortly after the shock absorbers begin to compress. The Level-2 switches are encountered well before the shock absorbers are fully compressed. Reference: ITF 7/20/96; Telescope Requirements Discussion (7/1/97); W. Boroski e-mail (8/13/97).
Revised: 8/13/97.

5.3 INSTRUMENT ROTATOR MOTION

5.3.1 A two-level interlock shall be installed on the instrument rotator axis to inhibit rotator movement beyond the safe operating zone.

5.3.2 The Level-1 limits shall inhibit rotator movement in the direction beyond the limit but allow movement in the direction away from the limit. The Level-1 limits shall be positioned at each end of the normal operating range.

5.3.3 The Level-2 limits shall remove power from the rotator drive motors, thereby stopping all instrument rotator motion. The Level-2 limits shall be positioned at each end of the safe operating range.

Reference: ITF (7/20/96).
Revised:

5.4 MOTOR DRIVE CAPSTAN SLIP DETECTION

5.4.1 A slip-detection system shall be provided on the azimuth, altitude, and rotator axes to detect non-rolling contact between the motor drive capstans and the drive disks.

5.4.2 The interlock system shall shut down the motor drives if capstan-to-drive-disk slippage exceeds the equivalent of 1 degree of capstan rotation.

Basis: Telescope drive motors must be shut down before drive disks are damaged by excessive slippage of the drive capstans on the drive disks.

Reference: Telescope Controls Requirements Discussion (4/26/97).
Revised:

5.5 TELESCOPE STOP BUTTONS

Telescope stop buttons shall be installed near the telescope to disable the motion control system. These buttons shall not be lit during normal telescope operations (telescope on). A button that is active shall be lit as an indication that it is active. Each button shall provide a positive interrupt to the motion control system. Each button shall be clearly marked as a shut-off for the 2.5m telescope drive system.

The following systems shall be disabled:

A. The telescope altitude, azimuth and rotator axes.
B. The wind baffle altitude and azimuth axes. The wind baffle altitude brake shall be enabled. Telescope stop buttons shall be installed at the following locations: A. Three buttons on the observing level, mounted on the observing deck railings. These three switches must be outdoor switches that will provide for telescope drive shutoff when the building is off the telescope. They should be mounted as close to the telescope as possible for quick user access. They should also be mounted in a manner that limits visitor access. Mounting locations shall be as follows: 1) One button on the north rail, 17 degrees east of the enclosure in the closed position. All hardware shall be mounted such to avoid mechanical interference with the telescope enclosure.

2) One button on the south railing, 17 degrees east of the enclosure in the closed position. All hardware shall be mounted such to avoid mechanical interference with telescope enclosure.

3) One button near the center of the west railing.

B. Two buttons on the observing level, mounted on the telescope fork. 1) One button on the east face of the north fork (with respect to the telescope at the stow position).

2) One button on the west face of the south fork (referenced as above).

C. Four buttons on the lower level, mounted on the exterior walls. 1) One on each of the 4 interior walls, spaced evenly around the lower level. D. One button in the control room. 1) One button mounted on the wall in the 2.5-meter telescope control room. Basis: These telescope stop switches are installed to provide personnel safety and equipment protection. They allow an individual to quickly disable motions of the telescope that may be endangering other personnel. They are not intended to be a substitute for lockout protection on service panels.

Comment: If reasonable to install, the APO operations staff would appreciate a controller that will give the status of all the buttons so one can tell which is on/off from the control room or a terminal.

Reference: Mark Klaene and Walt Siegmund; Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

5.6 TELESCOPE DRIVE MOTORS

Power to the telescope drive motors shall be disabled as soon as the telescope brakes are applied.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

5.7 WIND BAFFLE DRIVE MOTORS

Wind baffle drive motors shall be disabled whenever the telescope motors are disabled.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

5.8 TELESCOPE BRAKES

Engagement of the telescope altitude and azimuth brakes shall be inhibited if the telescope is moving.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

5.9 INTERLOCK SYSTEM STATUS DISPLAY

The status of the interlock system shall be displayed in an X-window accessible from any on-site terminal.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

6.0 Instrument Exchange Controls and Interlocks

6.1 MAXIMUM INSTRUMENT LIFT FORCE

The maximum force exerted by the instrument lift shall not exceed 1500 lb.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97

6.2 INSTRUMENT LIFT AUTOMATED CONTROL SYSTEM

6.2.1 The MCP instrument change control script shall be operable through IOP, SOP, and through direct access to the MCP.

6.2.2 The same instrument change system information shall be displayed in the control room and on the operator terminal mounted near the telescope. The video display does not have to be the same in both locations.

6.2.3 Lift control circuitry shall time-out if not refreshed with a motion control request every 10 milliseconds.

6.2.4 The MCP shall report interlock error status to the observer. All error messages should be clear, concise, and unique. APO observers should be included in error message development.

6.2.5 The operator shall have the ability to pause the instrument lift at any time during the lift operation. The operator shall have the ability to continue the lift or to reverse the operation through the use of up/down buttons on the instrument lift control pendant.

6.2.6 The instrument lift control pendant shall have an up button, a down button, and an emergency stop button. The up and down buttons shall be deadman switches. The emergency stop button shall disable power to the instrument lift.

6.2.7 All new instruments shall be ballasted to look like existing instruments, or shall have new counterweight and force/position curves generated.

6.2.8 Each time the telescope brakes are released, the MCP shall read the instrument id switches and verify that the counterweights are positioned properly. If the counterweights are in the correct position for the installed instrument, the telescope brakes can be released. If not, an error message shall be displayed to the operator.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

6.3 INSTRUMENT CHANGE INTERLOCKS

6.3.1 Interlock requirements associated with the corrector lens cat house shall be addressed by the UW group.

6.3.2 The telescope stop buttons shall be used to disable the telescope drive systems during instrument change operations. No key switch is required.

6.3.3 There is no requirement to sense that covers are in place on a cartridge or corrector assembly. Such covers include plug plate covers, slithead covers, and corrector lens covers.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

6.4 INSTRUMENT CHANGE INDICATOR LIGHTS

6.4.1 All instrument change indicator lights shall be visible under full sunlight and tolerable under dim conditions.

6.4.2 There shall be an indicator light (Exchange Position Light) near the cart staging area to indicate that the telescope is in the instrument change position and is safe to approach.

6.4.3 There shall be an indicator light to indicate that the lift plate is in the fully-down position. The light shall be operable only during instrument change operations.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97

6.5 LOW-LEVEL ILLUMINATION LAMPS

6.5.1 Low-level illumination lamps shall be installed to illuminate the area under the telescope for instrument change operations.

6.5.2 The low-level illumination lamp system shall be capable of manual and computer control.

6.5.3 The MCP shall turn on the low-level illumination lamps immediately after the telescope stop switch is pressed for instrument change, and shall turn off the illumination lamps when the stop switch is released.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

6.6 OBSERVER INTERCOM SYSTEM

There shall be an intercom link between the telescope enclosure and the 2.5-m control room. (APO task)

Reference: Instrument Change Operations Review (8/4/97)
Revised: 8/4/97.

6.7 CARTRIDGE CART STAGING AREA

6.7.1 There shall be a marked staging area near the telescope for the cartridge cart. No sensors are required to detect the presence of a cart in this safe zone area. (APO task)

6.7.2 The following switches shall be mounted near the staging area:

1) Telescope stop switch;
2) Exchange Change Position light;
3) Manual switch to turn on low-level illumination lights via relay contacts. Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97.

6.8 CAMERA DOG-HOUSE DOORS

Telescope altitude and azimuth motion shall be inhibited whenever the camera dog-house door is not fully closed.

Basis: The telescope will hit the dog-house door if the door is open.

Reference: Instrument Change Operations Review (8/4/97).
Revised: 8/4/97

7.0 Optics

To be completed. 8.0 Imager To be completed. 9.0 Spectrographs To be completed. 10.0 Fiber System To be completed. 11.0 Telescope Performance Monitor To be completed.

Glossary of Terms and Acronyms

FWHM	Full-width, half-max.
MCP	Motion Control Processor
TCC	Telescope Control Computer
TPM	Telescope Performance Monitor

This document is maintained by William N. Boroski for the Sloan Digital Sky Survey.
Please send questions or comments to: boroski@fnal.gov

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