SCC Architecture Presentation - Thirty Meter Telescope

TMT Primary Mirror Control System (M1CS) 

Segment Controller and Cables (SCC) 

Concept Description 

C. Shelton, C. Lindensmith, M. Colavita 

2010 February 16 

TMT.CTR.PRE.10.016.REL01 

TMT Confidential

Note 

This presentation is intended to provide additional 

reference background information only. The SCC 

Architectural Concept Document, 

TMT.CTR.10.010.DRF01, shall take precedence over 

any information provided in this presentation 

TMT Confidential 

2

Introduction 

The intent of this presentation is to provide background 

material to potential ti suppliers of the M1CS Segment 

Controller and Cables (SCC). 

Background material 

– Thirty Meter Telescope overview 

– The primary mirror (M1) and its control system (M1CS). 

– Segment Control and Cabling (SCC) 


3

Thirty Meter Telescope 

Astronomy’s Next-generation Observatory 

TMT.PMO.PRE.08.012.REL01 4 4 

TMT Confidential

TMT Overview 

The Thirty Meter Telescope will give astronomers the clearest and 

deepest picture of the Universe 

This telescope will push the frontier of technology, fully integrating 

the latest innovations in precision control, segmented mirror design, 

and adaptive optics to correct for the blurring effects of Earth’s 

atmosphere. 

When combined with the unprecedented light-collecting area of the 

primary mirror, TMT will be the most capable and sophisticated 

telescope ever constructed. 


5 5

Telescope Optics 

M1 System 

M2 System 

M3 System 


6

The TMT Primary Mirror (M1) 

Person 

The core technology of TMT is its 492-segment, 30-meter diameter 

primary mirror. 

There are 492 mirror segments mounted to the mirror cell 

Each segment has 3 actuators, 6 edge sensors (2 per intersegment 

edge), and 21 warping harnesses (WHs). 7 

TMT Confidential

Telescope & M1 Cell 


8

Group of Segments From Above 


9

Group of Segments From Below 


10

TMT M1CS Components 

Segment 1.4 m 

Segment Support 

Assembly 

Sensor Preamp 

prototype 

t 

Actuators 

3 per segment 

Sensor Control Bd. 

prototype 

Drive half 


Sense half 

11

M1 Control System 

Man in Mirror Cell 

TMT Confidential 12

M1CS Functions 

M1CS maintains the shape of the segmented M1 

mirror. 

M1CS minimizes global M1 distortions caused by: 

– Tilting the telescope (gravity sag) 

– Temperature 

– Wind 

– Vibration 

– Fabrication and installation errors 

M1CS has 

– Edge sensors and actuators to correctly position segments 

relative to each other, and 

– Warping harnesses, to correctly shape individual segments. 


13

Edge Sensors and Actuators 

Edge sensors and actuators move the 492 mirror segments 

relative to each other. 

The edge sensors report displacement, tilt, and the gap between 

adjacent segments. The actuators move each segment in piston, tip, 

and tilt. 

The edge sensors are to have noise better than 5nm noise, drift 

better than 1nm/C and 1/nm week, to be linear over a 300 um range, 

and to be monotonic over a 5 mm range. 

The actuators each have a voice coil and a precision linear encoder 

operating in a local closed loop, at 5000 Hz update rate. Each 

actuator has a stepper motor that offloads the voice coil. 

The control laws connecting the 2772 sensors to the 1496 actuators 

are implemented in “Node Boxes” and in the “Global Loop 

Controller” 

. 

The update rate for positioning the segments is 20 Hz. 


14

Warping Harnesses 

Warping harnesses (WHs) bend each segment to its optically 

perfect shape. 

There are 21 WHs per segment, each with a stepper motor and a 

strain gauge 

There are 3 temperature t sensors per each segment 

Control of these is split across 3 WH Boxes, each handling 7 

stepper/strain gauge pairs and a temperature sensor. 

The strain gauges just report applied force back to software. There 

is no local closed-loop control of the motor. 

WHs are adjusted no more than 10x per night, possibly much less 

frequent. The WHs are only powered up during these adjustments. 

t 

Only one motor / strain gauge pair is powered up and addressed at a 

time, per WH Box. This means both the motor and strain gauge 

connections can be analog multiplexed to a single driver per WH 

Box. 

15 

TMT Confidential

M1 Control System 

SCC Hierarchy 

The Global Loop Controller (GLC), in a environmentally controlled 

computer room, connects to a Power and Signal Unit (PSU) on the 

telescope 

The PSU connects to six Sector Hubs 

Each Sector Hub connects to 14 Node Boxes. There are 84 Node 

Boxes. 

Each Node Box connects to 5 or 6 segments. There are 492 

segments. 

Each segment has 3 actuators. There are 1476 actuators. 

Each segment has 6 drive-half and 6 sense-half edge sensors. 

There are 2772 edge sensors pairs (drive plus sense). 

Each segment has 21 WHs. There are 13,284 WHs 

Each segment has 3 temperature sensors. There are1476 

temperature sensors. 

There are 82 spare segments each with sensors, WHs, temperature 


sensors, and cabling. 

16

SCC Components 

and dRequired dQuantities 

Table 1. Quantities of SCC components. 

Total for 

telescope 

Total 

including 

7th sector 

Total with 

spares 

A1. Power and signal unit 1 1 1 

A2. Power and signal cabling 1 1 1 

B1. Sector hub 6 6 6 

B2. Sector hub cabling 6 6 6 

C1. Node box 84 84 88 

C2. Node cabling 84 84 88 

D1. Segment lower box 492 492 517 

D2. Segment actuator box 1476 1476 1550 

D3. Segment lower cabling 492 492 517 

D10. Segment upper box 492 574 603 

D11. Segment warping harness box 1476 1722 1808 

D12. Segment sensor preamp 2772 3234 3396 

D13. Segment upper cabling 492 574 603 

The SCC does not include segment actuators, edge sensors, 

WH motors TMT or Confidential strain gauges 

17

Cabling and Connectors Quantity 

Number and type 

of conductors, 

per cable 

Source 

Destination 

sh hielded twisted pair 

u nshielded twisted pair 

d iscrete wires 

co oax 

Overall shield 

C onnectors per cable 

le ength(m) 

Moving Frame Mounted - must be 

vacuum compatible 

Seg Upper Box Seg Sensor Drive 2 2 0.80 * 3,234 4 12,936 10,349 6,468 

Seg Sensor Preamp Seg Upper Box 2 2 1 2 0.80 * 3,234 7 22,638 18,110 6,468 

WH motor WH Box 4 1 1 0.25 21 12,054 Wires are part of motor 5 60,270 15,068 12,054 

WH strain gauge WH Box 4 1 1 0.40 21 12,054 Wires are soldered to strain gauge 5 60,270 24,108 12,054 

Temp Sensors WH Box 1 1 0.40 3 1,722 Wires are soldered to temp sensor 3 5,166 2,066 1,722 

WH Box Seg Upper Box 4 1 2 0.50 3 1,722 9 15,498 7,749 3,444 

Qty per segment 

Total 

Qty 

Notes 

onductors per cable 

C 

ubtotal Conductors 

S 

opper Length (m) 

C 

ubtotal Connectors 

S 

Fixed Frame Mounted Shielded Cat5e or Cat6 cable with RJ45 IP65 connectors is acceptable for these 

Seg Upper Box Seg Lower Box 4 1 2 0.4 1 

This cable is demated/mated at the 

Segment Upper Box end during 

492 segment exchange 9 4,428 1,771 984 

Segment Actuator Seg Lower Box 4 1 2 0.6 3 1,476 9 13,284 7,970 2,952 

Cell Floor Mounted Shielded Cat5e or Cat6 cable with RJ45 IP65 connectors is acceptable for these 

Seg Lower Box Node Box 4 1 2 5.5 1 492 Length is 3-7m, average is shown 9 4,428 24,354 984 

Node Box Sector Hub 8 2 4 6 84 Length is 2-10m, average is shown 18 1,512 9,072 336 

Sector Hub Power & Sig Unit 8 3 2 4 90 6 Length is 80-100m, average is shown 21 126 11,340 24 

Number of segments 492 Number of Conductors 200,556 

Number of spare segments 82 

Total Copper Length (m) 

Number of Node Boxes 84 

(SCC Provided) 92,782 

Total Connectors 

Number of Edge Sensors 2,772 coax = coaxial cable 

(SCC Provided) 23,382 

Total Cables 36,570 * Most Segments have 6 Edge Sensors - some have fewer 

Cables procured through SCC 


Cables procured elsewhere 

18

Location of Sector Hubs 

and dPower and dSignal lUnit 

One of six Sector Hubs 

on back of mirror cell 

One of six Sector Hubs 

on back of mirror cell 

YM1 

SECTOR-B 

SECTOR-A 

SECTOR-C 

1 

2 

3 

4 

5 

15 21 55 

45 66 

36 56 

29 47 68 

37 57 

28 46 67 

10 22 38 58 77 

6 16 30 48 69 

11 23 39 59 78 

7 

8 

17 

18 

31 

32 

49 

50 

70 

71 

12 24 40 60 79 

13 25 41 61 80 

9 19 33 51 72 

14 26 42 62 81 

20 34 52 73 

27 43 63 82 

35 53 74 

44 64 

54 75 

65 

76 

SECTOR-F 

XM1 

SECTOR-D 

SECTOR-E 

Ø30m 

Power and 

Signal Unit(1x) 

View from Sky 


19

Node Box Locations 

Node boxes (84x) 

TMT Confidential 20

Segment-to-Node-Box to Mapping 

The primary mirror is comprised of 6 

identical sectors. One sector is 

shown. 

Each sector has 82 mirror 

segments, for 492 total segments. 

Each sector has 14 Node Boxes, for 

84 total Node Boxes. 

In each sector— 

12 Node Boxes control 6 segments 

2 Node Boxes control 5 segments. 

A possible mapping of segments to 

Node Boxes is shown by the color 

coding. 

The Node Boxes are shown as red 

squares. 21 

TMT Confidential

Block Diagram of SCC components 

on the Primary Segment Assembly 

Actuators 

Warping harnesses & temp sensors 

C2 

D2.1 

Actuator 

Board 

D2.2 

Actuator 

Board 

D1 

Lower Box 

D2.3 

Actuator 

Board 

D11.1 

WH Box 

D13 

Upper cabling 

D11.2 

WH Box 

D10 

U pper Box 

D11.3 

WH Box 

… 

Edge- 

Sensor 

drive 

blocks 

1…6 

D3 

Lower cabling 

D12.1 

Sensor 

Preamp 

… 

D12.6 

Sensor 

Preamp 

CD. Segment module 

Edge-Sensor sense blocks 1…6 

Design of D10 Upper Box and Sensor TMT Confidential Preamp D12.1-6 provided by TMT 

22

Primary Segment Assembly 

Mirror Segment 

Mirror Segment 

Axial Support Rod 

Diaphragm 

3 ea Whiffletree Guide Flexure 

Warping 

Harness 

Actuators, 

21 ea 

Moving Frame 

Fixed Frame 

Tower 

Mirror Cell 

Cell floor is 6 ft below 


Edge sensor 

Drive/Sense 

Pair 

3 ea Actuators 

23

Location of SCC Components 

on Pi Primary Segment tAssembly 

Sensor Drive Side 

Sensor Sense Side 

Sensor Preamp/ADC 

Edge sensor 

Drive/Sense Pair 

Warping 

Harness 

Actuator 

Board (3) 

Actuator 

Warping Harness Box (3) 

Segment Upper Box 


Segment Lower Box 

To Node Box 

24

Warping Harness Box Location 

Warping 

Harness 

Boxes 


25

Detail of Warping Harness 

Strain Gauge 

Stepper Motor 


26

Location of Edge Sensors 

Segment 

Edge Sensor 

6 ea. Drive 

Central Diaphragm 

(bonded to segment) 

Drive 

Sense 

Drive 

Sense 

6 ea Sense 

Axial flexure 

assemblies 

Sense 

27 ea. bonded to 

segment 

Drive 

Drive 

Sense 

Sense 

Drive 

Sense 

Drive 

Alignment Arrow 

Points to center of M1 


27

Vacuum Compatibility 

The mirror segments are aluminized (coated) in a vacuum, first on 

installation then every two years. 

All components on the segment and moving frame must be vacuum 

compatible. These are 

– Segment Sensor Preamp Assembly 

– Warping Harness Boxes each with a Warping Harness Board 

– Segment Upper Boxes each with an Segment Upper Board 

– Temperature Sensors, with wires and connectors 

– Cables 

Segment Sensor Preamp Assembly to Segment Upper Box 

Segment Sensor Drive Block to Segment Upper Box 

Warping Harness Box to Segment Upper Box (3x492). 

The Segment Upper Box to Segment Lower Box cable disconnects 

at tthe Segment tUpper Box end dfor this coating procedure. 


28

Segment Installation / Removal 

Lifting Talon 

Segment 

Upper Box 

Stays with 

Segment 

Assembly 

Segment 

Lower Box 

Stays in Place 

in Mirror Cell 

Segment Lifting Jack 


29

Primary Segment Assembly 

Test Bed 

Segment 

Upper Box 

goes here 

Actuator 


30

SCC Architecture Presentation - Thirty Meter Telescope

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