13,14 July 2005 Feasibilty/Concept Study Mid Term Status Review Telescope Mount Concept Vertex RSI

VertexRSI Project Contacts Program ManagerDavid Finley Director of EngineeringStan Hermann FEA AnalysisDavid Adkins ControlsEd Reese VertexRSI Controls & Structures 1219 Digital Drive Richardson, TX (972) (972) fax format:

VertexRSI Profile VertexRSI’s Control and Structures Division is a supplier of full-motion antennas, telescopes, and other unique control systems and “controlled structure” instruments Relevant Projects Include: Green Bank Telescope Green Bank Telescope Hobby*Eberly Telescope Hobby*Eberly Telescope SOAR SOAR Vista Vista Very Long Baseline Array (VLBA) Very Long Baseline Array (VLBA)

Design Criteria Alt-az mount Azimuth motion+ 270 o Azimuth motion+ 270 o Elevation motion+10 o to +90 o (mechanical travel) Elevation motion+10 o to +90 o (mechanical travel) Velocities and Accelerations Full Performance 0 o To 60 o Elevation Angle Full Performance 0 o To 60 o Elevation Angle Scanning velocities0.2 deg/sec (slow); 1 deg/sec (fast) Scanning velocities0.2 deg/sec (slow); 1 deg/sec (fast) Scanning accelerations0.2 deg/sec 2 (slow); 2 deg/sec 2 (fast) Scanning accelerations0.2 deg/sec 2 (slow); 2 deg/sec 2 (fast) Pointing accuracy Overall2 arc-sec, RMS Overall2 arc-sec, RMS Offset, 1 to 5 deg0.5 arc-sec, RMS Offset, 1 to 5 deg0.5 arc-sec, RMS Offset, < 1 deg0.1 arc-sec, RMS Offset, < 1 deg0.1 arc-sec, RMS Open loop behavior Nonguided image jitter<0.1 arc-sec Nonguided image jitter<0.1 arc-sec Open loop drift0.1 arc-sec in 1 min Open loop drift0.1 arc-sec in 1 min Open loop drift goal0.1 arc-sec in 10 min Open loop drift goal0.1 arc-sec in 10 min

CCAT Mount Overview

Mirror Truss and quadrapod support primary and secondary mirrors, respectively. Reflector Hub Supports Mirror Truss And Elevation Sector Gear Elevation Bearings Support Reflector Assembly Yoke Arms Support Elevation Bearings And Transmit Reflector Loads Into Azimuth Bearing Alidade Rotates In Azimuth, Supported By Hydrostatic Bearing

Reflector Quadrapod Provides Support For Secondary Mirror Quadrapod Legs Supported On Separate Load Path, So Its Loads Do Not Affect The Primary Mirror. Central Hub Supports The Mirror Truss And The Elevation Drive Gear Access In Central Hub For Tertiary Mirror Bent Cassegrain Port In Hub Reflector Assembly Supported On Elevation Bearings

Elevation Drive and Services Reflector Driven By Helical Sector Gear And A Pair Of Motors, Driven Against Each Other To Remove Backlash IGUS Style Cable Wrap Design, Similar to Previous Projects Heidenhain Tape Encoder Tape Mounted On A Ring On The Moving Structure Tape Mounted On A Ring On The Moving Structure Read Heads Stationary, Mounted to the Yoke Read Heads Stationary, Mounted to the Yoke Similar Design to Previous Projects Similar Design to Previous Projects

Alidade The Yoke Arms Provide A Direct Load Path Between The Elevation Bearings And The Azimuth Bearing Pads Elevation Drive Platform Between The Yoke Arms Support The Elevation Drive Motors The Platform Also Ties The Yoke Arms Together To Provide A Greater Stiffness In Sidesway Hexagon In The Base Supports The Yoke Arms And Ties The Bearing Pads Together Azimuth Bearing Pad Elevation Bearing

Alidade Base Hydrostatic Bearing Provides Both Azimuth Rotation And Support For The Entire Mount The Center Of Rotation Is Determined By A Pintle Bearing The Bearing Pads, Drive Motors, And The Pintle Bearing Are Connected By A Series Of Spokes, Minimizing Deflection Between Motion Of The Motors And The Mount. Pintle Bearing Bearing Pads Under Each Hexagon Vertex

Azimuth Drive and Encoder The Drive And Encoding Systems Are Located At The Azimuth Base Level Azimuth Drive Gear Driven System Gear Driven System Stationary Gear Mounted On Inside Of Azimuth Bearing Track Stationary Gear Mounted On Inside Of Azimuth Bearing Track Drive Motors, Gearboxes, And Pinions Located On Moving Structure Drive Motors, Gearboxes, And Pinions Located On Moving Structure Azimuth Encoder Using A Heidenhain Tape Using A Heidenhain Tape The Tape Is Stationary, Mounted On A Ring Supported Off Of The Foundation The Tape Is Stationary, Mounted On A Ring Supported Off Of The Foundation The Read Heads Are Mounted On The Moving Structure The Read Heads Are Mounted On The Moving Structure Azimuth Gear Bearing Track Stationary Tape Ring Read Head

Foundation Interface Azimuth Bearing Mounted On Cylindrical Pier Pintle Bearing Is Supported On A Tower Coming From The Bottom Of The Foundation Azimuth Cable Wrap Located Inside The Pier, Using A Caterpillar Type Design. Pintle Bearing Support Cylindrical Pier

Control System and Dynamics Preliminary Error Budgets Were Derived, Based On: Vendor Specification Sheets Vendor Specification Sheets Field Tests From Similar Systems Field Tests From Similar Systems Preliminary Analysis Preliminary Analysis Derived Budgets Included: Offset Pointing Offset Pointing Tracking Tracking Jitter Jitter Based On This Preliminary Work, The Specification Requirements Appear Achievable Performance Requirements Within Current Technology

Performance Requirements ItemRequirementComment Pointing Accuracy 2 Arcsec RMS Values of 2-4 Arcsec Achievable Offset Pointing 1 o To 5 o 1 o To 5 o < 0.5 Arcsec RMS Reasonable Requirement for this Application Tracking Dynamics 0.25 deg/sec 0.01 deg/sec 2 Achievable Zenith Transit Outage Nominal 8-10 minutes Consistent With Tracking Dynamics Nonguided Image Jitter < 0.1 Arcsec Consistent with Similar Designs. Wind Load Needs More Study Open Loop Drift 0.1 Arcsec/Min Realistic, SOAR meets this requirement

Performance Goals ItemGoalComment Offset Pointing, <1 o <1 o < 0.1 Arcsec RMS Difficult To Analyze And Meet Open Loop Drift 0.1 Arcsec In 10 Min Analysis Suggests This Is Difficult To Meet, Yet Our Experience with SOAR Indicates It May Be Possible

Control System and Dynamics Scan Requirements Are The Subject Of Ongoing Discussions Some Items To Consider In The Following Discussion Specification Terminology Specification Terminology  Scanning Following Accuracy – The Ability To Precisely Follow The Desired Scan Trajectory. The Main Purpose Is Not To Leave Holes In The Scan Pattern.  Scanning Position Reporting Accuracy – The Ability To Know The Precise Pointing Vector While Performing Scanning Dynamics. Performance Is A Function Of The Scanning Pattern Dynamics, Structure, And Control System Performance Is A Function Of The Scanning Pattern Dynamics, Structure, And Control System

Control System and Dynamics Error between commanded and actual position, as reported by the encoder VLBA Type System South Pole Telescope Type

Control System and Dynamics Using Shaped Steps to Reduce Following Error Shaped Steps Can Improve Peak Following Error, But Increase Mount Dynamics And/Or Increase Motion Time Shaped Steps Can Improve Peak Following Error, But Increase Mount Dynamics And/Or Increase Motion Time Peak Error For Example Shown Is About ½ Of Simple Ramp Peak Error For Example Shown Is About ½ Of Simple Ramp VLBA Type System VLBA Type, Shaped Step

Control System and Dynamics Position Reporting Errors Blind Pointing Errors Plus.. Blind Pointing Errors Plus.. Errors Due To Dynamic Deflections Errors Due To Dynamic Deflections Depends Upon As-Built Structure And Dynamic Requirements Some Example Values For Steady State Error Shown In The Table Below For Reference And Science Consideration Probable Structural Values In The 3-7 Hz Range Acceleration =1 o /s 2 2 o /s 2 3 o /s 2 Structural ResonanceSteady State Error, ArcSeconds 2 Hz Hz Hz Hz Hz

Risk Items and Schedule Summary Requirements Achievable Requirements Achievable Continuing Discussion On Scanning Patterns And Dynamics Required Continuing Discussion On Scanning Patterns And Dynamics Required Risk Items Mirror Truss – Space Limitations Pose Challenges To Performance Mirror Truss – Space Limitations Pose Challenges To Performance Scan Pattern Expectations Scan Pattern Expectations Goals For Offset and Open Loop Pointing Goals For Offset and Open Loop Pointing There Are Challenges, But Nothing That Is Impossible There Are Challenges, But Nothing That Is ImpossibleSchedule 29 Jul 05Completion Of Engineering Work 29 Jul 05Completion Of Engineering Work 5 Aug 05Manufacturing Review 5 Aug 05Manufacturing Review 8 Aug 05Start Of Report Writing And Budgetary Pricing 8 Aug 05Start Of Report Writing And Budgetary Pricing 6 Sep 05Work Complete 6 Sep 05Work Complete