I
I

I

I

l.

2.

INTRODUCTION

MCC HISTORY AT TRW

TABLE OF CONTENTS

PAGE

1

8

!

3. DESIGN DEVELOPMENT

3.1 OBJECTIVES AND PROGRESS

13

13

I

I

i

I

I

I

I

I

I

I

I

I

I

I

3.2

3.3

3.4

TASK STATE_NTS

OPTIC INVESTIGATION AND TEST

3.3.1

3.3.2

NAS8-35635 Investigation

Physical Measurements

Measurement of Optical Losses

System Effects

Summary

Electrical Measurements

3.3.1.1

3.3.1.2

3.3.1.3

3.3.1.4

3.3.1.5

Analyses

3.3.2.1

3.3.2.2

3.3.2.3

3.3.2.4

3.3.2.5

3.3.2.6

3.3.2.7

3.3.2.8

14

15

15

15

20

21

24

24

24

24

24

28

33

39

39

46

Specular Reflectance Analysis

Tolerance Analysis

Optical Design

Support Analysis

New Design Optics

Part Physical Measurements

Optical Measurements

Concentration Ratio CheckEnergy Throughput 46

3.3.2.9 Element Performance 46

3.3.2.10 Coatings 46

3.3.2.11 Electrical/Optical Test Results

of the Improved MCC 57

3.3.2.12 Multi-Element String Measurements 61

3.3.2.13 Correction Methods for MCC

Element and String Test Data 68

CELL STACK DESIGN AND INVESTIGATION 75

3.4.1 Solder Investigation 78

3.4.2 Alternate Bonding Methods 78

3.4.2.1 Adhesive Bonding-Top Contacts 78

3.4.2.2 Gold Germanium Eutectic 78

3.4.2.3 Welding 79

3.4.2.4 Stack Subassembly 82

i

I
TABLE OF CONTENTS (CONTINUED)

PAGE

3.5

3.6

•

4.1

3.4.3 Electrically connected Versus Isolated

Cell Stack-Heat Sink

3.4.3.1 Heat Sink Bond

3.4.4 Coverglass

3.4.5 Cover Adhesive

3.4.6 Conic Mirror

3.4.7 Cell and MCC Element Ele_trical

Interconnections

3.4.8 Summary

STRUCTURAL DESIGN OF THE MCC

3.5.1 MCC Primary Mirror

3.5.2 MCC Secondary Mirror

3.5.3 Secondary Mounting

3.5.4 Mirror Manufacturing Methods

3.5.5 MCC Element Bonding Methods

3.5.6 Complete MCC Element Assembly

MCC SUPPORT STRUCTURE

3.6.1 Frame Design

3.6.2 Insert Design

ANALYSIS

THERMAL CONSIDERATIONS

4.1.1 Thermal Performance for Cell Output

4.1.2 Secondary Mirror Temperatures

WEIGHT

PERFORMANCE ANALYSIS

4.3.1 Overall electrical Achievement

4.3.2 Electrical Output Corrected for Known

Defects

4.4 ADVANCED DESIGNS

4.4.1

4.4.2

4.4.3

4.4.4

4.4.5

4.4.6

4.4.7

Material Thickness Change

Material Type Change

Coatings

Advanced Cells

Combined

Manufacturing

Offpoint Performance

ii

82

85

85

85

85

88

93

97

97

97

97

101

101

101

108

108

115

125

125

125

125

127

130

130

130

133

133

133

133

133

134

134

134

i

I

I

I

I

i

i

l

I

I

I

I

I

I

I

I

I
I

!

I

I

I

I

I

I

I

I

i

I

I

I

I

I

I

I

I

TABLE OF CONTENTS (CONTINUED)

5. CONCLUSIONS

6. RECOMMENDED FOLLOW-ON WORK

APPENDICES

A

B

C

TEST AND INSPECTION DATA

ELECTRICAL MANUFACTURING

MECHANICAL MANUFACTURING

iii

PAGE

135

136

138
I

I

I

I

I

l

I

I

l

I

4

4

4

4

4

4

4

P_

I

FIGURE INDEX

Figure 1-1

Figure 1-2

Figure i-3

Figure 1-4

Figure 1-5

Figure 1-6

Figure 1-7

Figure 2-1

Figure 2-2

Figure 2-3

Figure 2-4

Figure 3-1

Figure 3-2

Figure 3-3

Figure 3-4

Figure 3-5

Figure 3-6

Figure 3-7

Figure 3-8

Figure 3-9

Figure 3-10

Figure 3-11

Figure 3-12 Through 3-17

PAGE

Miniature Cassegralnian Concentrator Concept 2

Front of Large Deliverable Panel 3

Back Of Large Panel Showing Flat Cable Harness 3

Front of Small Panel 4

Back of Small Panel Showing Flat Cable Harness 5

15 x 56 Array in Operation 6

Close-up of the Assembly Just After Completion

in the Manufacturing Facility 7

Contract NAS8-34131 Technical Results Summary 9

Contract NAS8-35635 Technical Results Summary i0

MCC Element Evolution 11

Tri-Hex Grid (THG) Panel Evolution 12

Front Side View of Predecessor NAS8-35635 MCC

Element in Tri-Hex Grid 15A

Surface Accuracy Error Measurements for #15

Primary and Secondary 16

Surface Accuracy Error Measurements for #12

Primary and Secondary 17

Element #12 Tolerance Errors 18

Element #15 Tolerance Errors 18

Rounded Areas of the Primary were Found not to

Contribute to Collection Efficiency as Designed 19

NAS8-35635 Mirrors were Relatively Diffuse 22

Distortion can Cause Significant Loss of Output 23

Test Result-70 vs 77% Optical Transmission

Investigation 25

Test Results-Off Axis Performance Investigation 26

Effect of Mirror Finish on Performance 27

Effect of Selected Tolerances 29

on MCC Performance New vs Old

Design

v

t_RBCEDIN( _ _AGE BLANK NOT FILMED
FIGURE INDEX

(CONTINUED}

Figure 3-18

Figure 3-19

Figure 3-20

Multiple Misalignment Test Case vs Two

Measured Assemblies

MCC Element Off-Pointing Performance with

Concentration Ratio as a Parameter

MCC Element Off-Pointing Performance of CODE V

Optimized Designs

Figure 3-22 New Design Showing Ray Trace for Entrance of

Rays with Zero Pointing Error

Figure 3-23

Figure 3-24

Figure 3-25

Figure 3-26

Figure 3-27

Figure 3-28a

Figure 3-28b

Figure 3-29a

Figure 3-29b

Figure 3-30

Figure 3-31

Figure 3-32

Figure 3-33

Figure 3-34

Figure 3-35

PAGE

30

31

32

34

New Design Showing Ray Trace for Entrance from

Three Degrees from the Left 35

New DeslgnShowing Ray Trace for Entrance from

Three Degrees from the Right 35

Energy on Cell vs Tracking Error

Collimated Source 36

Rays Reaching Cell vs Variations of Secondary

Offpoint Collection Angles 37

New vs Hyperbolic Output 38

The New Primary MCC 000 Rev E. 40

Coatings on the Front and Back Provide Precise

Optical and Thermal Properties MCC 000 Sheet 2 41

The New Secondary MCC 010B 42

Equation for the Secondary Mirror Surface 43

The New Cone Provides Tooling Reference Points 44

Tolerance Allowance for Nominal Offpoint

Performance 45

The Specularity of the Uncoated Mirror is a

Factor of Ten Improved Over the Previous Design 47

Specularity of the New Mirror Remains Five Times

Better Than the Previous Design After Coating 48

MCC Off-Point Curves for LIPS III Hardware 49

Coating Sequence for Optic Surfaces

(Primary Sub-assembly Without Spider Shown) 51

vl
FIGURE INDEX

(CONTINUED)

PAGE

Figure 3-36 Front of New Element Shown While Operating,

Spider and Secondary Back are Painted with

SI3GLO 52

Figure 3-37

Figure 3-38

Back of MCC Element Showing Mounting Position,

Solder Bonds for Electrical Interconnection, and

Complete SI3GLO Coating

Method for Finding Specular Reflectance

of Cone

53

55

Figure 3-39 Conic Mirror to Cell Output Ratio as a

Function of Cone Reflectance 56

4

4

4

4

Figure 3-40

Figure 3-41

Figure 3-42

Total Fraction of Light to Reach Cell Which is

First Redirected by the Conic Mirror (Zero and

Typical Tolerance Allowances Shown)

Both Deliverable Panels were Tested Using a

Solar Tracker, Adapted from a Celestron

Telescope Mount

The Operation of the Seven Accepted Secondary

Proof Items Shows Higher Than Desired Variation,

But Still Within Reason in the Projected

Operating Maximum Angle of i.I Degrees

58

59

60

Figure 3-43

Figure 3-44

Reasonable Shaped I-V Curves Result from

Operation of a Six Element String Near

Normal Offpolnt

Some Mismatch Phenomena Are Visible in the

String I-V Performance

62

63

Figure 3-45 Large Mismatch Losses are Easily Visible in a

Number of Severely Offpointed Strings 64

Figure 3-46

Figure 3-47

Figure 3-48

Reverse Bias Test of Element Within String

in Natural Sunlight (No Corrections)

Five Six-Element By One-Element Strings of a

Group Designated "A" Show Some Variation from

Ideal Output After Correction for the

Conic Mirror

Strings of Group "B" Show Less Variation than

Group "A"

65

66

67

Figure 3-49 Offpoint Performance of Two Sub-Arrays

(5 Parallel x 6 Series) Compared to Perfect Optic

Performance (Corrected for Cone Deficiency

R = 70%)

vii

69
Figure 3-50

Figure 3-51

Figure 3-52

Figure 3-53

Figure 3-54

Figure 3-55

Figure 3-56

Figure 3-57

Figure 3-58

Figure 3-59

Figure 3-60

Figure 3-61

Figure 3-62

Figure 3-63

Figure 3-64

Figure 3-65

Figure 3-66

Figure 3-67

Figure 3-68

Figure 3-69

Figure 3-70

Figure 3-71

Figure 3-72

FIGURE INDEX

(CONTINUED)

Temperature vs Resistance Reading for Mounted

Thermistor IM001-XXX

Illustration of Mismatch Caused by Cell

Efficiency Combined with Mirror Offpoint

Small Panel Mismatch Tally and Calculation

Test Result-Assembly Loss (11%) Investigation

Solder Test Investigation Data

Cell Performance Test (100 Sun Flasher Intens.,

Room Temperature) Before & After Weld/Solder

Of Front Cell Contact

Weld Schedules Developed for All Vendors

Cell Performance Before and After Vapor Phase

Soldering of Cell Rear Contact to be BeO

Substrate

Cell Heat Spreader Trade

SK-MCC-063 Insulator, Heat Sink

Cell Cover (Plain) MCC 050

Cell Stack Mechanical Attachments Investigated

Adhesive Trade for Cone to Cover Bond

Cell Top Interconnect

Interconnect to Heat Sink

Interconnect to Heat Sink Weld Test Results

Cell Stack Electrical Interconnection Design

Cell Stack Materials Trade

Assembly with Secondary Mirror Shown

Mechanical Design Options

Picture of Spider to Primary Mounting Position

Showing Mounting Boss

Mirror Material and Manufacturing Trade

Optic Mechanical Attachments Investigated

viii

PAGE

70

72

74

76

77

8O

81

83

84

86

87

89

90

91

92

93

95

96

98

99

100

102

103
APPENDIX A:

Figure A1

Figure A2

Figure A3

FigureA4

Figure A5

Figure A6

Figure A7

Figure A8

Figure A9

Figure AI0

Figure All

Figure AI2

Figure AI3

APPENDIX B:

Figure B1

Figure B2

Figure B3

Figure B4

Figure B5

FIGURE INDEX

APPENDICES

PAGE

Materials Used on Test Plate for Acoustic

Exposure and Thermal Cycling A2

Thermal Cycling Results A2

Acoustic Spectrum A5

Half String Outputs for 15" x 21" Panel

Corrected for Insolation and Temperature A6

Combined Strings Corrected for Insolation

and Temperature A9

Combined and Individual Half String Data

Normalized for Output at ISC and Corrected

for Conic Mirror Reflectance of 0.70 A10

Data for 15 x 56 Panel Corrected for

Temperature and Insolation A12

Data from 15 x 56 Panel Corrected for Conic

Mirror Reflectance of 0.70 AI5

Secondary Proof Mirrors Effect on Offpoint A21

Secondary Proof Normalization and Conversion A22

Coating and Part Defects in Small 15" x 21"

Panel A24

Inspection Results of 15" x 56" Panel A25

Electrical Test notes showing locations of

shorted and open cells A26

Be0 welding tool (left) and conic mirror

course alignment tool B4

Conic mirror to coverglass bonding tool. B6

Cell and Be0 insulator to primary vapor phase

solder tool, and secondary to spide vapor phase

solder tool B9

MCC Vapor Phase Yields BII

MCC Panels - Kitting Plan BI6

x
FIGURE INDEX

(CONTINUED)

PAGE

Figure 3-73 Complete Miniature Cassegrainian

Concentrator Assembly 104

Figure 3-74 Assembly of MCC Element into Panel Showing

Detail of Snap Insert 105

Figure 3-75 Third Generation MCC Hardware from the

NAS8-36159 Contract 106

Figure 3-76 Existing MCC Assembly Process Flow Diagram 107

Figure 3-77a Large Tri Hex Grid 109

Figure 3-77b

Figure 3-77c

Figure 3-78

Figure 3-79

Figure 3-80

Small Tri Hex Grid

Detail Assembly of MCC Elements into

Tri Hex Grid

Hex vs Tri-Hex Trade

THG Fabrication Process Trades

Compaction Methods

ii0

iii

112

113

114

Figure 3-81

Figure 3-82

Figure 3-83

Figure 3-84

Figure 3-85

THG Mechanical Attachments Investigated

Fixed Insert

Sliding Insert

The sliding-to-fixed insert bond

THG Insert Design Requirements

116

117

118

119

121

Figure 3-86

Figure 3-87

Figure 3-88

Insert Materials

Plastic Options for Baseline Insert Design

Push Strength (LBS) for Adhesives for

sliding Insert

122

123

124

I

I

I

Figure 4-1

Figure 4-2

Figure 4-3

Figure 4-4

Figure 6-1

The latest temperature prediction for LEO

MCC Panel Weight Analysis

Weight of Piece Parts and Weight Summary

MCC Element Capability

Recommended Follow-On Development Plan

126

128

129

131

137

ix
I

I

l

I

I

!

,11

,11

,11

,11

4

4

,11

,11

4

,11

,11

,I

Figure B6

Figure B7

APPENDIX C:

Figure Cl

Figure C2

Figure C4

Figure C5

Figure C6

Figure C7

Figure C8

Figure C9

Figure CI0

Figure Cll

Figure C12

Figure C13

Figure C14

Figure C15

Figure C16

Figure C17

Figure C18

FIGURE INDEX

APPENDICES

(Continued)

Harness Fabrication Instructions for. 15 x 21

and 15 x 56 Panels

Schematic (66 optic Panel)

Trapped Rubber Molding Concept

Strip Sampies and Tooling

Cross Strip Sample in Test Fixture

Mini Panel with Tooling

Insert tooling for Tri Hex Grid

Rubber Insert Mold

The Screw Pin Concept allowed easy disassembly

Baseline Insert Assembly Design

THG Process Manufacturing Development

Tooling for the small THG panel

Tri-Hex Grid Specifications

15" x 21" Panels with 15" x 56" Layup Tool

Drawing TOW Through Die

Layup Process

Rubber Inserts Installed in Panel

Straightening Setup

15" x 56" Flatness Results

xi

PAGE

BI7

BI9

C2

C3

C4

C6

C7

C8

C9

CII

C12

C14

C15

C16

C18

C19

C20

C21

C21
ACKNOWLEDGEMENTS

The following personnel contributed to this project in

the capacities shown:

IRA ALLARD

PETER BARRETT

SAUL BASHIN

FRED DENINGER

MANNY GARZA

LARRY GILMAN

JERRY JACOBY

MARK KRUER

JOEL MARKS

GEORGE MESCH

MARK MYERS

DEBBIE TILLER

MANUFACTURING ENGINEERING

DYNAMIC ANALYSIS

PRODUCT DESIGN

MANUFACTURING ENGINEERING

ELECTRICAL TESTING

MECHANICAL DESIGN

OPTICAL DESIGN

PROJECT MANAGER

ELECTRICAL TESTING

MANUFACTURING

MANUFACTURING

SUBCONTRACTS

Special thanks to Mr. Mark Myers and Mr. Fred Deninger

of the manufacturing division for long hours of painstaking

effort beyond the call of duty.

Xll
l

l

I

I

I

I

I

!

I

I

!

I

!

I

I

I

I

I

i

i. INTRODUCTION

This miniature cassegrainian concentrator (MCC) development project is third in

a series of NASA sponsored programs conceived to advance photovoltaic concentrator designs for spaceborne arrays. Achieved during this project were broadened solar acceptance angle, increased optical efficiency, and increased manufacturability of both the optical elements and the support structure. The MCC

was raised to NASA development level 5 (Component of engineering model tested

in relevant environment) through thermal cycle and qualification acoustic

testing. A pilot line quantity (270) of MCC elements were produced, three of

which were submitted for flight on the LIPPS III experimental satellite.

Previously set goals of >28W/kg at the panel levels and >160W/m 2 are projected

to have been achieved by the present hardware and new capability projections

of as much as 87W/kg using ultra lightweight optics and advanced 27.5% silicon

concentrator cells seem feasible, all at a cost of less than $500/W.

Shown in figure 1-1 is the basic operational characteristics of a cassegrainian

type concentrator. The chief advantages are small storage volume, passive

thermal cooling and the capability to fine tune the optical input through

multiple mirror surface shape reflectance control.

Figures 1-2 and 1-3 show the back and front of the large fully operational

35 x 142 cm panel built during this contract. Figures 1-4 and 1-5 show the back

and front of the small fully operational 35 x 53 cm panel built during this

contract. Figure 1-6 shows a close up of the panel in operation. Figure 1-7

is a close up at the completion of assembly in the manufacturing area.
II

=_,.

a,_ o

_,_ c_

r..,o"-_

._="_ =

:';_ _-

im

_ ,,.-

. (_ I=:

im

'-_ E"- '- _"

0 I..

ol
iIIIiIIIiIIIIIIIIII

,OF PO@}{ QU_Z.Z

_J0

r-I
ORIGII',IAL ?AGE I_

Figure I-4. Front of Small Panel.

:,i! iI

i

i

I
I

I

I

I

I

I

i

I

I

I

I

I

i

I

I

I

I

i

I

,_:_IGINAL PAGE IS

OF. POOR QUALITY_

c .

Figure i-5. Back of Small Panel Showing Flat Cable Harness.

5

i
i

l

!

Figure 1-6. 15 x 56 Array in Operation.

ORIGINAL PAGE Ig

OF POOR QUAI,]TY
!

I

I

I

I

I

i

I

i

I

I

I

I

I

i

I

I

I

I

Figure 1-7.

Close-up of the Assembly Just After Completion

in the Manufacuring Facility.

©RIGIN_L PAGE IS

OF,I_)OR QUALITY,
2. MCC HISTORY AT TRW

Figure 2-1 shows the early development of the MCC design

under contract NAS8-34131. Goals of 160 W/m 2 and 28 W/kg were

established as reasonable for the MCC design assuming current

technology capabilities. Feasibility was demonstrated through

construction and test of a nine element module.

Figure 2-2 presents the results of the immediate

predecessor contract fbr MCC development, NAS8-35635.

Significant improvements were made in the pursuit of the goals

established in NAS8-34131.

The evolution into third generation hardware of the element

(Figure 2-3) and the support structure (Figure 2-4) were set as

goals for the present NAS8-36159 contract. All goals have been

met by analysis of test articles.

I

I

I

I

I

I

i

I

i

I

I

I

I

I

i

I

I

I

I
I

I

I I:

i

I -"

I =R

Im

¢J

| _.

=J

I .-m

V_

I

I

I

uJ

z:_ _

___. _ _

._ o

i

Z .d

,_ _ -

o,, _ mu,, Z

_sp_. _,,_, e,- g

.__ 8 ,-o ...E

ff-.R

.=.,,,,

8_

OF £_R QUALITy.

I
J_P

n:

mm

imI

inZ

_50g o

C_

O_ CO

_=

T

iii

°

t8••

10

C_JI

OJ

_,-

_n

o_,.

Lt-
11

I

_._I

(_J

,p-.

00
i;

I-,-

I,iil0 i-- i---

z_

r_X

• "0 © III! z w

u_ 1,1,1

IJJ In

_n, aJ

_=_ z_

z "3_

I

©i

. ,...m!1

00
l

I

I

I

I

I

I

I

I

i

I

I

I

I

I

I

I

I

I

3. DESIGN DEVELOPMENT

3.1 OBJECTIVES AND PROGRESS

The objectives of this contract were to :

ao Improve the miniature Cassegrainian concentrator (MCC)

optic design in terms of total energy throughput and

offpointability

b.

Co

Design a cell stack compatible with the MCC and

capable of low earth orbit operation for five years

Manufacture the complete optic and cell stack and

measure the improvements

d. Further develop the support structure of the MCC panel

e. Manufacture the improved support structure and enough

MCC elements to fully populate two testable panels.

All objectives have been met.

13
3.2 TASK STATEMENTS

The task statements listed here were followed in

performance of this contract. NASA directed modifications to

the tasks following the basic statements.

o Element Optical Design

- Improve normal and off-pointing performance

- Select materials and process based upon performance and

cost

o Cell Stack Development

- Isolated/nonisolated element designs

- Analysis/development test for 30,000 LEO cycle goal

o Panel Development

- Select substrate type (hexagonal/trihex grid)

- Incorporate redesigned element

- Finalize element attachment design

- Test development hardware (elements, substrated,

attachments)

- Design panel wiring for 30,000 LEO cycles,

manufacturability, low cost

- Fabricate 15" x 56" panel (IO active elements)

- Perform development tests in support of LEO goal

o Pre-prototype Panel

- Panel level design update

- Fabricate 15" x 21" panel (100% active elements)

- Deliver for long-term thermal cycling

o NASA Modifications

- Deliver the three elements developed in tasks 1 and 2 to

NRL to support launch of test articles

- Paint the primary and secondary emitting surfaces with

SI3GLO white thermal control coating
!

I

I

I

i

I

I

I

!

I

g

I

I

I

i

I

i

I

3.3 OPTIC INVESTIGATION AND TEST

TWO efforts were initiated to improve the optic design of

the MCC elements as compared to the design produced and tested

under contract NASS-35635 pictured in Figure 3-1.

The first effort was directed at finding reasons why

performance of the design was not significantly in accordance

with predictions. The second effort was directed to finding how

to improve the offpoint performance of the design by changes in

the mirror surface and interrelated geometries.

3.3.1 NAS8-35635 Investiqation

3.3.1.1 Physical Measurements

The size and geometry of the primary mirrors was measured

using a Cordex 3000 by sampling points along the surface in an

absolute coordinate system. Results shown in Figures 3-2 and

3-3 indicate ±.0025 inch error in the figure X coordinates

compared to the theoretical design values. This is equivalent

to a 6' arc error. The cup bottom on which the birdcage

assembly rests was flat to within ±.0005 inch. The cup center

was offset from the primary surface figure center by 2 mils.

The center of the front surface of the solar cell was

offset from the cup center by 3.8 mils. The height of the front

surface of the solar cell from the cup interior surface was 1

mil lower than the designed placement.

The placement of the secondary in the birdcage brought the

tip of the secondary 12.5 mils above the nominal Z direction

design point. The secondary was found to be tilted by .12 °

compared to the XY reference plane of the primary cup. A

Numerex Surface Profilometer measured the surface of the

secondary by dragging a scribe across in various radial

directions. The surface geometry was within a 6' arc error.

When combined with the birdcage offsets, the secondary

absolute position in the XY plane was found to be i0 mils offset

from the primary mirror cup center.

15
!

qh

ml

n r,

i:

II "' ! -a,i _- I _ I "

o

_ _c._

ID0 --

°__ el a,l._ r- II

ORIGINAE PAGE IS

OE POOR QUALITY 4

15A 0'} W

_0o

o.
I

_ o0ooooooo ooo

_0__ _

_ ............

0000000000 0000

O0 00000 0

I0

o

:z:

F--

o0oooooooo ooo

oooooooooo ooo

,oaoliI0oo

,,,iileell

1

_mm

olll

oo

oeloeiIle,

o

o

o

co

eeoeeeel_ee

oeeooeeeeee

___o_ _

eooeeeeoe0e

!

I_1_

oO

I--

Z

GO

0

I.LI

>-

L.I_

O0

>.-

0

GO

>-

0

I.L.

0

o4

0

0

Ood

od

0

oeeeeeeeee0e

ioolimeealo

,ooo*leJleoeoo,

...J

o

F--r_

Xr_-

Lj_r_

÷ -r

16
I

"_, N

I

I

I

I

IN

I °

1.1_

l

W=

t._

i °_-

Z

>- 0

U _

_ Z

_.1 >--

U e_

I

0

I--"

_J

I--

o 0 o _0 o o o o _ % _, °

L'%i ,.--, ,--4 0 0 ,--i ,--0 ,-.-i I 0 ,--4 _ ,-.4

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 _ 0

IX

¢Y

m

O _ ,,-4 _ _ ¢'_ I'_ ,_ _ _ _ ,_- l,_

r'-. Q _ _ _ r-.- _ ,-.J r'-. _ ¢%.j _ c,"> _ao

(_ 0 ,=-4 ,--_ i'.J i-,,"} _ ,c:d- Ll") _ _ 'c:l" t.Z') ii_

_ 0 r,.. CO _ r... ¢,0 0 cr_ r',.. ¢,0 {'_

¢,,.1

! _ t.¢')

, .,.. ,.

,--4 0 0 _" _ 0"_ 0,1 CO _ _ CO

0 0 _ l,_ 0"_ CO _ _ _ O0 _ ,,,-4

r'-.. ,.-4 _ t.")

¢'%.i ,.-,4 _ ,=-4 _ _ _ r.... L"%J ,.-4 L'%i r....

17

I

W

LL.

I
.12°

,6 °

1.8 °

,Oil8

.005

,0125

.024

6'

6'

31,1 °

.0038

SECONDARY TILT

BIRDCAGE TILT

CONE TILT

SECONDARY XY DISPLACEMENT

CONE XY DISPLACEMENT

SECONDARY + Z DISPLACEMENT

CONE + Z DISPLACEMENT

PRIMARY ARC ERROR

SECONDARY ARC ERROR

CONE ARC ERROR (.4)

BIRDCAGE XY DISPLACEMENT (CELL DISPLACED)

FIGURE3-4: ELE]VENT#12 TOLERANCEERRORS

,006

,006

.OlO

,005

,12

0,8

0

,6

6

2

31.l°

SECONDARY XY DISPLACE

SECONDARY X DISPLACE UP

CONE DISPLACE Z UP

CONE DISPLACE XY

SECONDARY TILT

CONE TILT

BIRDCAGE DISPLACE X AXIS

BIRDCAGE TI'LT

MINUTE PRIMARY ARC ERROR

MINUTE SECONDARY ARC ERROR

CONE ARC ERROR

FIGURE3-5: ELEIVENT#15 TOLERANCEERRORS

18

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
IIIIIII

__

I __(,F) bJ IIIIIIII

___._

_;_-

•p t_

_.Ld

II

19

%

t-- 0

01i

(J

ee- 0

s

/

f

•fIr

e- o

01i

(J

ee- o

e-.

o

F--

LIJ

pcz_ zo

(J

F--

I-- ozz

I,

r-_ tJJ z

-'_ (.9

_-_ L_J

=E

>-

,,i (jZ

I_ L_J 0

uJZ0

Z .--I 0 0 !

c_

I.i.I

U-
The cone lower edge was i0 to 20 mils above the cell. This

compares to a design goal of zero Z displacement. The cone XY

plane offset was measured at 5 mils from the cup center The

cone angle designed to be 31.5 °, was measured to be 31.1 °.

The cone as mounted in the birdcage was tilted from the XY plane

by 1.3 ° .

The average measurements above are summarized from Figures

3-4 and 3-5.

3.3.1.2 Measurement of optical Losses

Primary Mirror. It was noted that there was some rounding of

the optic edges.at the inside and outside of the primary (Figure

3-6). To see if this contributed to energy collection losses, a

number of masks were created to successively shadow more and

more portions of the mirror in those positions using the theory

that shadowing of unused portions would produce no change in

output. The optic was set in a solar tracker specially designed

for this application and current output was monitored.

Successive masking of the outer edge was performed until a

noticeable drop in current was seen. The size of the mask inner

diameter was compared to the optic design and was noted to be

approximately 19 mils less in radius than the primary mirror

outer edge. This represented a 4% loss in collection efficiency

from expected.

More masks were placed on the secondary mirror with

successively greater diameters until again a noticeable drop in

output was noted. This radius represented the unusable portion

of the primary mirror near the inner cup edge. The distance,

.298 mils or 33 mils greater than the inner cup radius design,

represented approximately 2% loss in collection efficiency.

The primary mirror was physically distorted by screwing the

edges down in the holding fixture with excessive force to see

the effective change in output. A 2.1% loss in output was noted

at the extreme range of distortion, estimated at i0 to 20 mils

of "squeeze."

20"

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

Conic Mirror. The gap between the cone and the cell represented

an "escape" route for the collected light. To check this the

optic was mounted in a fixture such that the cone could be

varied from 0 to 80 mils from the surface of the cell. The

measured loss was 0.3%/mii of gap for 0 pointing error and with

a 15 mil gap, a 14% loss was experienced at 2° offpoint.

3.3.1.3 System Effects

Mirror Reflectance. The reflectance of each mirror has a direct

effect on energy throughput. In all positions, the primary and

secondary mirrors will redirect the light with some resulting

reflectance loss composed of absorbed light and diffusely

reflected light not reaching the cell. The amount of light

reflected by the cone is a function of offpoint. The AMO

reflectance of silver is generally quoted at 95% energy

throughput. Since the GaAs cell only responds to light with

wavelength between 0.4 and 0.9 micrometer,, the reflectance of

the mirrors in this range is of interest and must be used for

energy throughput calculations as measured by a GaAs device. To

this end, spectral reflectance measurements of primary and

secondary mirror samples were made. Based upon these

measurements, the effective reflectance in the band 0.4 to 0.9

micrometer, was calculated for solar outputs of AMO, AM1, and

AM2. The AMO reflectance averaged 0.965 for the secondary and

0.985 for the primary, and was not significantly different when

calculated for AM1 and AM2 standard suns.

Specular Reflectance. Mirror samples were submitted for overall

scatter measurements. A measurement is shown in Figure 3-7.

The measurement corresponds to roughly 11% loss of usable light

in the MCC optical system.

Misaliqnment Effects. The intention of this test was to get a

feel for the sensitivity of the optics to possible assembly

misalignments. A MCC element was mounted in the solar tracker

and the birdcage containing the cone and secondary were misaligned from the most stable position. Slight movements (5 to

i0 mils) of the birdcage resulted in output changes of up to 10%

(see Figure 3-8).

21
l.-

crJ

fJ1

>- m

(%1

r_mo

u)

u)I

tlJm

Go c

u.

.4J

w-I

o. Em

r.r)

c)

o:

rrX

._I

_J

LU

(.I

O:

.J

Cf)

r-1

•_ ILl •0 "I"

C_ 3[

IOm C:)

UIv

t,"l

r-

__ _= o

c_

f,.,. oco

,frou

o_-

IuS

"

E e-_ o _

e-

•r- °_-. _ xo

00

IIIIIII

I

°1
II

II

a +o,-,z.

_w I,-

I oo:Z:=_

___ Oo _ _z

IIIIIItI

\

:©\ II

23

F-- ZD0

_L

14.

14. 0

(/3

ill

I11

CO

iu

COI

c")

(U

:3

E7)

I,
3.3.1.4 Summary

A summary of the optical testing of the NAS8-35635 design

is shown in Figure 3-9 for on point measurements and Figure 3-10

for offpoint measurements.

The many potential loss mechanisms that were apparent could

easily account for the nine percent onpoint loss (7%/77%).

Offpoint losses for the design could be even worse especially

due to the misalignments inherent in any manufacturing process.

3.3.1.5 Electrical Measurements

Electrical output measurements of the optics studied above

were reported in NAS8-35635 as 9 to 11% loss in output during

onpoint with the expected concentration ratio of 127 not met by

the test measurements of -114. These measurements were

reconfirmed. Offpoint testing was also performed as in Figure

3-8 to reconfirm the data.

3.3.2 Analyses

Two analyses were performed to support the investigation

and testing of the NAS8-35635 MCC.

3.3.2.1 Specular Reflectance Analysis

A computer model of the MCC element was generated and

energy loss due to scatter from the mirror surface was

calculated as a function of overall mirror reflectance and RMS

surface roughness. The results, shown graphically in Figure

3-11, indicate that surface roughness must be tightly controlled

to minimize scatter losses. The NASS-35635 polished to a

"commercial" finish had a finish between 200 angstrom to 1000

angstrom roughness. At 200 angstrom and .98 mirror reflectance,

the loss of energy attributable to scatter alone was 0.19

-[1-(.98) 2 ] = .15 i.e., 15%.

3.3.2.2 Tolerance Analysis

The mirror assembly was analyzed for output using the

IPAGOS optical analysis program as modified for the MCC system

to determine collection efficiency as a function of offpoint.

The Standard curve for perfectly aligned optics is the one shown

for technology development goals. However, since mirrors are

24

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

._ c=.

| _

I _ :g

:,L _:

'g.

| _"

_*

U 0

5-a

I

I -

I

!

O_

_C

5 _

5:

|-

_Z

o

_j',_

I

Od

=_ . _

.._ o _'-

Z_J

_,lk--

I

25

I
26
I

I

R

I o _

.. O-- Z

I Z QNw_ _w Z

_ _ 0

0 L_ _

I __ XoWz L0 z

_o Z_ m w

I _ _o _ =

I _ _ 0 d 0

I ° ....... _

I _

I _ <_

I _ " < +

_O_

I _ __ --

__0_

• 0 _

I { ,,,,,, ,•

I _._1 "_'_-_ _1_ _3_SASOO_HO_HgI_O3_OO_SNn_O_O_

_5_1

I

27

I
not ideal surfaces due to inherent piece part manufacturing

tolerance allowances, and mirror assemblies further suffer from

tolerance allowances, it was decided to investigate the

sensitivity of the optic design to these tolerances.

Each mirror component was considered separately and then as

a typical composite based on measurements of the optics as

assembled from section 3.3.1.1.

I

I

I

I

Each component was analyzed for the effect on energy

collection as a function of translations along three orthogonal

axes, rotations about three orthogonal axes and surface

allowances as called out in the mirror manufacturing

specifications such as the i0 arc minute allowance variation in

the figure of the primary mirror or the 31 ° ± .5 ° cone angle

allowance.

The results are illustrated in Figures 3-12 to 3-17, for

individual components. In some cases, the design is very

sensitive to tolerances which are fairly tight in the design.

When a combination of factors is considered, the resulting

offpoint is illustrated in Figure 3-18. Included in the figure

are the test results from two measured optics. The test

performance is actually better than that predicted since the

prediction assumed all worst case directions for output loss.

3.3.2.3 Optical Desiqn

The design of the conventional Cassegrain system was varied

to determine what improvements in offpointability could be

achieved without significantly decreasing onpointed output.

Results from an IR&D project showed that changing the geometric

concentration ratio from the baseline 163 to lower values

improved offpointability at increasing loss of optical

transmission (Figure 3-19).

If the thickness of the system was allowed to vary,

improvements in offpointability could also be achieved (Figure

3-20 ) but with significant decrease in volumetric packing for

launch.

Some slight improvements could be made by varying the conic

mirror surface, but none would address the inherent problem of

tolerance allowance losses (missing of the mirror entirely).

28

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I W _e_ I" i_

IE e "1 • E Ikl • U.I I-. I _1 w • _ "

I _, ,;, .: _ --N _ O I_ N

vl I# t 1 %

_: J' \1_ "-,, _ 13. ,III I11 _, | ii -"_ Z

eq _ ,..,,,. __ ml Ikl •t \\_-" --_ . ,.,, ,_/ , ---

•: I-_ _, _ _ ...... , I-= II _11, I ..=!

T I I I I I I I I _6 , I I I I I I I I _a

i II II II II II II

• 1113 N0 Agti:li:J Ii:J0tl:Jd 11:13 NO A9klqN:] 1ii:)tl:Jd

I -uo N, I1_ _-;, _--! I --le

I _ .--- ._'_-

-" ,/ 1,

I 11 _i. • i,.,i

_=, ! 71 \ I-I_ il I,\ "--. "-_

- l "_.. ill_-

I _° 1 t',_ \ -1i ! t:\ -.4+-

=. i ",, I .{

"': ii-,', _ I I i I I ] F" ]' '"_' '' I /::

11_3 NO _91d]N:J 1NlOtl:Jd 11:10 NO _9kl:iN] IN:JOti:ld

I o -,

+ I-IX ;

I

'

_14-_i

II/

=-..j,

_ .,I..._"

.i-.._

: "i, -'" '- ,, ,!II

i _..--_ _ "i Ill /i/ ,/ /.=

" I,i I ,'.7"- _...'_.......-_ = i_ i ili / --ill

I -, =i t ,,, )l,'/ ,,""- ----- G"! ,...-..,_ I_ I I",/,,' Ill # _'"!

I li I!1 # I < -

I ol| oil-m__ f d _ I_ I /oil / Jill #

I i I!i =_" I II' I I I .1i II OI I l!i ° i II II " II I 1 II i I iI l O =

I

I

1113 NO _gU3N3 Ii|3U]d 1130 NO _OH]N3 Ii]3U3d

29

i (%) NOISSII_SNVHJ. 3VDIJ.dO .LN31_3"13

31

I

I--

LU

cC

c,o

<C

O

,=_

Z

0

h.-

Z

Z

0

-r"

I--

Z

0

I,.i..I

Z

h--

Z

0

I

0

I--.

Z

..-I

I

u.I
" jL,

z

Z

,=.1

=g

I,i,.I

100.0

90.0

BO. 0

70. O

60.0

50.0

,_0.0

30.0

20.0

10.0

0.0

_ -- z-

- BASELINE DESIGN

0 = CODE V DESIGN l

I_I - CODE V DESIGN 2

i

".................. ii..................i..............i-_._i'\ '...... i..

.................

,, 1

............................•.....................................................T'".i " ".'"".'""''"'.'.

.....................................................................,.-I:-!1...............

i

!

................................................................................I ..... , .,.

" I

| i

0.0 2.0 3.0

!

].0

i

''i ..................

_._|

_.0 5.0

FIGURE 3-20:

OFF-POINTING ANGLE (DEGREES)

MCC Element Off-Pointing Performance of CODE V Optimized Designs

32

r
I

I

I

I

I

I

i

I

i

I

I

I

I

I

I

I

!

i

I

It was decided to dispense with conventional optical design

techniques to achieve offpoint enhancement. Instead, a

technique was conceptualized to use portions of the secondary

mirror to redirect light from the primary during offpoint

conditions toward the cell (Figure 3-21) as well as modify the

surface figure of the portions used during onpointing to also

direct any remaining offpointed light to the cone and thence to

the cell. It was decided to optimize the design for three

degrees of offpoint. The NASS-35635 secondary mirror blockage

diameter of 0.564 inches was retained to allow comparison with

the NAS8-35635 design even though the actual mirror surface was

only 0.50 inches in diameter. After a number of two dimensional

iterations of the optic stack surface figures, the resulting

operation of the stack in two dimensions seemed satisfactory as

shown in Figures 3-22 through 3-24. Except for a very few rays,

all rays entering the optic reach the cell.

3.3.2.4 Support Analysis

A three dimensional computer model was constructed for

IPAGOS analyses. Calculation of the offpoint performance showed

tremendous improvement over the baseline design (Figure 3-25).

The model was analyzed for tolerance effects as was the

baseline and again tremendous improvement was seen. Figures

3-12 through 3-17 show the improved capabilities compared to the

baseline design. The multiple parameter tolerance buildup was

input to the model and again the improvement was great (Figure

3-18).

The secondary mirror was further optimized for output by

consideration of changing the angles of the mirror portion

devoted to redirecting the offpointed rays. Figure 3-26 shows

the effect of varying the inner and outer zones from the

baseline.

The design was checked against an optimal hyperbolic

secondary which used the full 0.564 diameter of the secondary

mirror blockage size for light collection. Cone angle was

varied to check for possible synergistic design effects. Figure

3-27 displays the results of this comparison. The new secondary

is clearly superior in the quantity of light collected.

33
H _(PEf_BO L OlD

OPTI/_IZED FDR_

ON AKI5

C oPIF'ov/vO

P,4,_BoLol_ G E LEmE_,'T

FIGURE 3-21:

I

FIGURE 3-22:

CONCEPT USED TO REDESIGN THE COMPLETE MCC

OPTICAL STACK.

\\\

-- DEIIGN

,-LC

NEW

I I

/

fT,_

05 ' "

SHOWING RAY TRACE FOR ENTRANCE OF

! 0 °

• / /I._

RAYS WITH ZERO POINTING ERROR.

34
!

!

Ii

!

I

I

• I

"_" _11" ".. I "" -- _ -- -- --

_ I , I \

", I "'/-/" \ t;'_, /I

\ i 1l'l I 'iI ,71 "

I

I

I

I

I

I

I

I

!

I

i

/;

//

_/, // J

i f/

_/.\t

i

FIGURE 3-23: NEW DESIGN SHOWING RAY TRACE FOR ENTRANCE FROM

THREE DEGREES FROM THE LEFT.

0 3 (_

1'

_._-_----__._:_- .......... -..... -_.

/

I \ -.\I "-_ "-.

FIGURE 3-24: NEWDESIGN SHOWINGRAY TRACEFOR ENTRANCEFROM

THREE DEGREES FROM THE RIGHT.

35
NW.

_0 NO AOB_N3 1N_O_3d

36

O I!II
I

I

II

, ../ ,iiTT

I IFIdIFIO O=IZI'IVWHON

MJ

I " _ _'_ >1 _ :_"_:_ '_ _" _ _ _ '- °

I

_I _

i ii | _ ILl

"= _

.i z-_ <

_< - z

c_J

I

¢,')

_J

L-_

1

37

I
_3

C3,

|R

i

O

a,,,,.

Z

•,r -1-

!

I

i

-_ |

_|

,4- ,__-

@

i

I

I I i I [ I o

q _ a0 r. © _ 'q" i

1NdlNO 3AIIV'13U

- II Z

38
I

!

!

i

I

I

I

I

I

i

I

I

I

I

i

I

i

I

The cone angle for the new system was optimized at 17 ° .

A 17 ° versus 18 ° cone angle comparison is shown in Figure

3-25.

3.3.2.5 New Desiqn Optics

The new primary is shown in Figure 3-28. The new secondary

is shown in Figure 3-29 and the new cone in Figure 3-30.

3.3.2.6 Part Physical Measurements

New optics were ordered to the design derived in the above

analyses. The first articles were measured for surface figure

and part tolerances. Since the parts were designed with keying

for assembly measurements to these keys were added together for

the various components to create tolerance build up potential

offsets.

As for the NAS8-35635 design, the positioning of the cell

surface and XY placement within the cup, the XYZ positioning of

the secondary mirror considering the tolerances measured, and

the XYZ positioning of the cone considering the tolerances

measured were determined. All part dimensions except for the

secondary figure were found to be within the tolerance

allowances generated for the part manufacturing specifications

(Figure 3-31) from the tolerance analyses. Actual values are

given in Appendix A.

A Jones & Lambson EPIC 30 comparator was used to check for

figure accuracy of the cone, secondary and primary against an

accurate mylar of the drawings in the appropriate magnification

range. A casting of the primary was made from the first article

which was then checked on the comparator at 10 x magnification.

The cone and the secondary were directly checked at 20 x. The

primary and cone were within the required figure tolerance. The

secondaries (ten in a11) deviated from the required figure by

varying amounts. Due to schedule constraints, it was decided to

use seven of them which were believed to be close enough but not

within tolerance, with the intention of checking the effect of

the variations by electrical measurements of a single standard

primary subassembly which included everything except the

secondary and secondary mounting.

39
'_o

o

//

l IF--,_-===_ -

40

I-.-

0

0

-i

Z

I--
IIIIiIilI

Oki_ ;(N_,J__ F<A:]F Tg >-

OF POOR QUALIT_

41

oo

_

z

t_Z

O-O

i,l

t_ O

t_ZZO

i, ,,,

,,, I---

-rl-- "' Z 0 z ,_

I-- m,-

,_ ,,, 0

O0

O_JI

I.I-
o

(23

c27

+1

,.D

N

H

co

._; ,._ --r,o O0 L.,O 0

=D -- O0 0

I-- 0

0 0 + I +1

+1 0 0

l'--- 0 0

__J

LI_ °" ""

-- ("U.

I I

• .° -

_W _

LZW _

W_ _

W Z_

<WW

ZO_ O_

_z _w

_WZ

Ob_ WO

OW_ z_o

xo _ o

i,

r_

0 m0

o

Lr_

o

i

I

I

I

i

I

0

u_

-I

42

Q

• .r,_ ,_,v4', _tq

PE _OR QUM,ITY

Z

C3

C3

W

U3

xw

--O z

._

OW_

_Jw

<_(_)

_-_L_

_--¢y

OC0

nm

Z

H

CD

00

O

o ww

o I.--Z

CPO

+1 W G)

--3

U_ OW

r_ d_I

OU

OL

_--O

LO

O0

I

0J

I

nq o_

O o

O

CO o

w

__J

£_)

o9

X

z

z

o

o

h--

0..

0

Z

0

r_

Z

0

I--"

I

ILl
!

l

I

!

Secondary Reflec%oE - Sheet 2 of MCC-010.8

This reflector is a surface of revolution whose profile

defined in the x, y plane by the following table of points.

origin of the x, y coordinate system is defined in Sheet I of

MCC-OIOB

is

The

x ¥ x ¥ x y

0 0 .099620 .035240 .159421 .068776

.044298 .011870 .101384 .036190 .161206 .069854

• 044366 .011889 .103148 .037144 .162991 .070931

• 046296 .012430 .104908 .038101 .164775 .072008

• 048220 .012990 .106668 .039060 .166561 .073084

• 050139 .013569 .108427 .040021 .168347 .074158

• 052051 .014167 .110185 .040983 .170135 .075229

• 053956 .014785 .111943 .041945 .171924 .076298

• 055858 .015423 .113701 .042908 .173716 .077364

.057752 .016078 .115459 .043870 .175508 .078427

• 059638 .016752 .117216 .044831 .177300 .079491

• 061519 .017443 .118975 .045794 .179092 .080557

• 063394 .018152 .120732 .046756 .180882 .081626

• 065262 .018878 .122490 .047720 .182668 .082701

• 067124 .019620 .124247 .048684 _184450 .083782

.068979 .020379 .126004 .049650 .186227 .084872

.070827 .021153 .127759 .050616 .187998 .085972

• 072669 .021943 .129514 .051584 .189761 .087084

• 074505 .022749 .131268 .052554 .191515 .088210

'.076334 .023569 .133021 .053526 .193259 .089351

• 078156 .024403 .134772 .054500 .194993 .090508

• 079972 .025250 .136522 .055477 .196715 .091681

• 081782 .026110 .138270 .056456 .198431 .092865

.083586 .026982 .140017 .057438 .200141 .094056

• 085385 .027865 .141763 .058423 .201851 .095248

• 087179 .028758 .143506 .059411 .203564 .096436

• 088968 .029661 .145248 .060402 .205279 .097621

• 090752 .030573 .146987 .061398 .206995 .098804

•092533 .031493 .148724 .062397 .208712 .099986

• 094309 .032420 .150484 .063415 .210429 .101168

• 096083 .033355 .152275 .064482 .210445 .101178

• 097854 .034295 .154063 .065552 .282101 .142548

• 155851 .066625

• 157636 .067700

FIGURE 3-29b: EQUATION FOR THE SECONDARY MIRROR SURFACE

43
5

gW < 7_rkJ I

CO 09 cY

'--'_ _ h n

I

(_.) CD ._.J _ -_ L,I

I

W W :2[ -- --

LO m- _- .. CO

N _'_" w_ z I

09 tL _- Z (_9 ]> _-- I

w-

_-- 0_,I ._] I,I .._.J 09 ._['

r,'_"(..) • CDZ

2 I

< W W (.D

:7 .... C_

.. --OJ _-_-- OJ _ I

_] I I _- I I I

CD

__JLJ CU m

I

r_3 .,_ -- " W

I +,,,,I- I < I

I

+ ) N I

-!

•-- P') LO -- _ C_'

_i 0__ " o o o o _ •

_ . oo o o _, I

+, • • " w -Hi F- !

__£}:, C, 0 ,_ rj-)

!

£O0.R <'-:.:'.: :":" .: .:

44 T ?

I
I

!

0 0 o 0 0 o

<_<_

•r- _-

C_C3

O0

0 0 _'_ 0

0 0 0 0

(:_ ° °

I--

Z _ ....I

0 _ "' "'

U t'_ Z m_"

',' Z 0

c_ 0 r.._) ,;,

I.I- I_l I.I- C_

_--- F-- It. b'- U..

Z 0 Z 0

t.,.J Z _ ;i_

e.-

°1-.

E

0 o

• • - - o

A A

._I ILl < --.I I..LI l.J.l

UO < Z _ <'<

X X _ X XC.D I-- _'_ r_ £%.

c_: ._j < --J 0 0 0

:_ _ >._ 0 _-_ _ _ --J N I"-- N_" I_' _ _

>-

>- ,<

< Z

_'- 0 L_

_'_ _ 0

_.. c/) r._.)

tJ- t.I- LZ.

0 0 0

Z Z Z

0 0 0

_Z

0_

_0

_Z

z N

45

e--

o

tf,._

p.-

o

I--

oO

I

S-
3.3.2.7 optical Measurements

The specular reflectance of a primary mirror sample was

measured to be a factor of ten improved over the NAS8-35635

hardware before coating and a factor of five improved after

coating (Figures 3-32 and 3-33). As required, all mirror edges

were sharp and no unusual surface variations were observed.

Testing for poor output portions of the mirror due to surface or

figure variations was therefore not required.

The gap between the cone and the cell was set at 8 ± 1 mils

by the cover and adhesive (see cell stack design).

3.3.2.8 Concentration Ratio Check - Enerqy Throuqhput

Two optics were measured for energy throughput by measuring

current of the cell with and without the secondary in place. A

mask with a hole the size of the cell active area was placed

over the cone to measure 1 sun output without the secondary in

place, then the mask was removed, the secondary was replaced,

and the total MCC element output at concentration was measured.

The measured concentration ratio was 114 and 117 versus an

expected concentration ratio of 134.7. When corrected (section

3.3.2.13) for known deficiencies in the conic mirror (see

Coatings), the CR became 134.4.

3.3.2.9 Element Performance

The offpoint performance of three MCC elements was measured

(Figure 3-34). As expected, the performance was significantly

improved over the NAS8-35635 hardware, though slightly lower

than predictions. The lower offpoint output was subsequently

explained to be due to conic mirror coating deficiency (see

Coatings). At this time, the decision was made to continue with

the design into Phase 4, complete population of the deliverable

panels with MCC elements of the new design.

3.3.2.10 Coatinqs

It was not the intent of the design program to address

coating applications. Only data and design concepts which were

applicable to this design and available from scientific or

engineering literature were incorporated into the design. A

brief summarization follows.

46
ItIIIIIIIII

__

30_8

I 47

¥

0

w

0
H

LO

"_r O

I---

01

II

1.1_

(%1

£.I

fJ

C_

rr

rrH

•.,'4 ...i

U.I

¢J

,._ n-"

O. ",¢ E --I

cOO

01 O3

4-1

r..

[.0

_ tO

01 01

!

0

_1 _1

.o

ClO £.CJO

ZL "¢_

C%IJJ _IiI

I"- I0 .I-,I

I,,,=Im 0"11

-r"_ -J:-

00

v'_0

£::)E ..E ..

I"" I'--

, ! i I 1 I

+i

i"i

f

!I;

t'1

i,I

i

i;;I

°:i

1;

:i

i:!

•i

iii ,_

i•

;1

ii;

+I•i

To

!+

o

tI

i

i ' t It ! I i * + I I i. , !t II i , i t ! It

-+I

+--t

_iI

i,

oo

Ti

0

"'_"I

o _" z_

I

-" |

_.,,,

.CU rr'_ --_" _ ""

"|_-_,_J

o

-I
lIIIiIIIIlIIIIIlIII

0D

4dPJ O0_ r,..

r_ .==i_ --.i ..i

14J i.i=i i=i.i s.iJ w X 0 0PII iI # t0

¢_

/

\

i0

¢n

IIiII

0 ¢_000

oo t'_ ¢£3_ qlP

INdlIlO IVl01:10 IN33_3d

49

I0

000

LU

0

:w

I--

_ =,. E I 0 ! 0

_0

I

0

3_ m

5. wm

S.. Q>t! U

¢,

I.
Optical Coatinqs. The coatings required for this design were

identical to those for contract NASS-35635 hardware. Silicon

oxide of 1700 A was vacuum deposited over 1600 A of silver which

was vacuum deposited on the reflective nickel surface of the

mirrors (Figure 3-35). The SiO coating is projected to be able

to protect the optic from atomic oxygen effects based on

extensive analyses performed by many companies and NASA centers

nation wide. Other coatings such as indium tin oxide are also

acceptable and can be incorporated as they are defined and

tested.

Protective Coatinqs. Only the solar cell interconnect with

silver metallization is subject to environmental attack in this

design. A thin coating of silicone adhesive could be used for

protection. It was not included in the present design.

Thermal Control Coatinqs. An added task to the design was the

incorporation of SI3GLO paint for thermal control of the MCC

element. This silicone based white paint was used to coat the

back (sun facing) surface of the secondary mirror, the sun

facing surface of the spider mount for the secondary mirror

(Figure 3-36) and the back surface of the primary optic (Figure

3-37) .

Standard procedures using solvent wipe of the nickel and

aluminum surfaces prior to a spray paint coating with the Sl3GLO

were found to be sufficient for good adhesion of the paint to

the painted surfaces. To test for adhesion, a MIL SPEC

procedure was followed which consisted of scribing the painted

surface of a sample, applying tape, and pulling the tape from

the sample. No failure occurred. The sample was thermal shock

cycled 100 times from -192 ° to +60°C. The tape test was

performed again and no adhesion failures were observed.

Other Considerations

o Primary and Secondary Mirror Coatinq Quality. The

adhesion of the optical coatings was of varying

quality. The mirror vendor used two vendors as

coating subcontractors but did not maintain

traceability. Subsequent assembly of the primary and

secondary mirrors incorporated the use of a protective

and cleaning polymer which was spread on the surface,

let dry, and removed with tape. When the polymer

coating was pulled off, the surface coating of some

5O

I

I

I

I

1

I

I

I

I

I

I

I

I

I

I

1

I

I

I
IiII!III

51

I

Q

f,. Q

e3_EI

P,

-.i

:hE

"r.

e_

r_

F-'-

e_

i, zz

I'-

I

w
Figure 3-36.

!

Fro_Df New Element Shown While Operating,

Spider and Secondary Back are Painted with S13GLO.

52
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

l

I

I

I

Figure 3-37. Back of MCC Element Showing Mounting Position, Solder

Bonds for Electrical Interconnection, and

Complete S13GLO Coating.

53
o

primaries and secondaries (portions of the SiO and

SiO+Ag) were removed as well. Discussion with the

vendors determined that the coating adhesion should

have been much greater than the adhesion of the

polymer, and that the failures were most likely

attributable to insufficient surface cleaning prior to

coating. The only fix available was to strip and then

re-deposit the coatings. Since the effect of

stripping on the mirror surface was unknown (such as

potentially roughening the polished surface), and the

damage was apparent on only a few optics, it was

decided to leave the coatings as is without testing

the remaining coatings. Temperature shock testing of

a mirror already showing partial coating failure did

not induce any further degradation or removal of the

coatings. Coating failures from thermal cycling or

other stress during NASA testing will not be

considered as design failures since an in-place

acceptance test would find coating manufacturing

problems for any flight optics. The use of the

polymer as an acceptance test is recommended for such

acceptance testing.

Conic Mirror Coatinq Quality. All conic mirrors were

visually inspected for coating defects such as missed

or darkened sections or localized haziness. Coating

quality in terms of absolute reflectance was not

measured. After the measurement of offpoint

performance of a large number of optics showed

significantly high losses at small offpoint angles,

test data was reevaluated to determine the cause.

Data for output of the cell stacks with a cell sized

mask was compared to output of the cone and cell

combination with no secondary mirror (Figure 3-38).

Since all light entering the cone would be absorbed by

the cell, the reflectance of the cone could be backed

out of the measurements as shown in Figure 3-39. Data

for four optics showed that the conic mirror

reflectance only achieved 65 to 70% in the 0.4 to 0.9

micrometers GaAs response range. The reasons for this

were unknown. However, after questioning the coating

vendors, it was found that a "proper" mounting

procedure in the coating chamber to guarantee uniform

coating quality was not used due to schedule and cost

pressures from the electroforming vendor. The

physical reason for the loss whether due to scatter or

absorptance should be investigated. It is known that

the loss is not caused by contamination. A series of

cleaning fluids, acetone followed by freon followed by

isopropyl alcohol, had negligible effect on most conic

optics. Those improvements that were measured only

increased total reflectance of the cone from 0.65 to

0.67 in a limited number of cases.

il

II

I

I

II

II

I

I

i

I

I

I

I

II

il

I

To check the extent of the low conic reflectance, all

180 optics to be mounted in the large deliverable

panel were checked on an X25 solar simulator for total

reflectance as measured by the GaAs cell in the

54
I

I

I

I

i

I

I

I

i

I

i

I

I

I

i

I

I

I

I

SOLAR INPUT

A Eo/vE /n_sK

IN PL4 r.E

\

/

/ 0 FU/.L. SOW O/u

pqlRROI_ ,,_,,_0

CELt..

FIGURE 3-38 METHOD FOR FINDING SPECULAR REFLECTANCE OF CONE.

55
3.3

3.2

3.1

3.0

2.9

2.8

E

2.7

Q

cO

"- 2.6

r_

" 2.5

2.4

2.3

100 95 90

FIGURE 3-39

Data Points

! ! I I I I

85 80 75 70 65 60

REFLECTANCE (%)

Conic mirror to cell output ratio as a function

of cone reflectance.

56

I

I

I

I

i

I

I

I

I

I

I

I

I

I

I

i

I

I
I

I

I

I

i

subject optic using the same methods as outdoor sun

tracking testing. The range of reflectance was

measured to be 59 to 71% with an average of 66% and a

standard deviation of 5%. The ±5 ° illumination

angle from normal as is typical for the X25 due to

geometry of the simulator did not skew the results

since even 5 ° illumination angles for light rays

would still reach the cell.

The effect of the low conic reflectance was checked in

the previous tolerance analyses by looking at the

total light reaching the cell via the cone for all

pointing conditions. Figure 3-40 is a plot of the

percent of light versus pointing angle for the new

design which first bounces from the cone. It was

obvious that the conic mirror was as important as the

primary and secondary mirrors when considering the

total system performance.

Using the average measured cone reflectance it was

possible to recalculate from the test data the

normalized offpoint characteristics of the MCC

elements, substrings, and modules if the conic mirror

had been 97% reflective. The absolute output of the

onpointed and offpointed elements could be similarly

corrected. All plots of output versus offpoint for

the small and large panel strings were corrected

accordingly. The plots showed verygood agreement

with the response as analyzed during the tolerance

analysis. Variations due to other electrical effects

are discussed in section 3.3.2.11.

3.3.2.11 Electrical/Optical Test Results of the Improved MCC

Element

Measurements of individual optic/electrical performances,

performance of strings of a single element in parallel by six

elements in series, and 5 elements in parallel by six in series

were made using the solar tracker and mounting hardware designed

especially for this application (Figure 3-41). All measurements

were corrected to 1 sun AMO exposure using a GaAs standard cell

and were further corrected for temperature based upon readings

from thermistors mounted on the back of two randomly selected

elements.

Output Variation with Multiple Secondary Mirrors. The "proof"

secondaries were tested for variations in offpointability using

a single primary subassembly. Figure 3-42 shows the performance

of each of the seven accepted secondary mirror samples from the

separate electroforming tools as corrected for the cone

reflectance losses discussed in the "Coatings" section. The

variability is fairly significant in terms of expected offpoint

I

57
i(...++.

_ ,,+,-3,

J

_ _ O = = = = = = = + =

IAIOI:I::I ONIIAIO0 ll30 01 AOU3N::I IYlOl 40 NOIIOVI=I-I i

1%) UOUI:IIIAIOINO0

;{ m

N

]! I

'i il

I

58
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

i

ORIGINAL PAGE Ig

D.,E POOR QUALITE

Figure 3-41. Both Deliverable Panels were Tested Using a Solar

Tracker, Adapted from a Ce|estron Telescope Mount.

59
tv')

r",,,

f

×_z

o

z_

0¢

c_

x-_

tl

..... t ........ ]

!i:_:i:__i] ..... t

..... ._ ..... l ........ -_ .................. I .........

60

]

• _ ..... t o. -

..... ;.i..

ORIGINAL PAGE IS

.0_ _OOR QUALITY

" i

.............. ". , A+-_ ..,_ ......... _--

.

_ ;i-:-.:- :.__:-.::]::-::--: ::.:

l ' - ; LT_ i " .

......... .::i{i=7.!. :7 : =:7t ::::::--.- :

/

.... ;:;;.! .,.

•'+ _ "

_1 "" : _ :± _'2 "'-'2 .... ;': .........

.............................. I.IJ
!

!

!

!

i

I

I

I

I

I

I

I

I

I

I

I

I

I

I

performance of a mixture of the secondaries but it is important

to note the relatively flat response each achieves for three

degrees of total offpoint, near the center of the performance

band.

3.3.2.12 Multi-Element Strinq Measurements

Full current voltage (IV) curves were generated for each

six cell in series substring located on the small and large

deliverable panels. Zero degrees through three degrees and in

some cases up to five degrees variation from normal sun were

measured using a NORLAND 3001 data acquisition system with a

fast load, and a concentrator one sun standard traceable to a

balloon GaAs standard. The pertinent data from all measurements

are located in Appendix A.

Offpoint Performance. The optics for the small 35 x 53 cm panel

were chosen from optics with the initial high efficiency

(>20.6%) cells available from ASEC. As expected, some loss due

to matching of efficiency rather than matching of current at a

set voltage was encountered. Essentially, each string is

limited by the lowest MCC element current performance, which is

in turn a combination of absolute cell output after assembly,

mirror tolerance buildup effects on light collection efficiency

and relative pointing of each of the elements. An ideal

measurement of a well matched string is shown in Figure 3-43 for

one substring. Figure 3-44 shows the effect of current limiting

on the IV characteristic of another string. The sudden current

increase near short circuit with a sharper knee indicates

mismatching of output is occurring within the string. Figure

3-45 shows even greater mismatching to occur. A single MCC

element which was found to be significantly low in output in

string 3B was measured for the reverse voltage of the element as

a function of string loading (Figure 3-46). The low output

element ran quite hot in reverse as expected, but did not

degrade after more than three minutes in the condition of

approximately three volts at 300 mA across the cell.

The normalized offpoint performance of each of the strings

of the small deliverable panel as corrected for conic mirror

poor reflectance is shown graphed in Figures 3-47 and 3-48.

61
.5

z_.

×z_

za

v

62 I/

ORIGINAL PAGE IS i

OF. POOR QUALITY
IIII

IIIIII

L'

c=

i ×z_

_8

,,J

x_

L_VB

IIiII

............_ .....- .......
u"

o

z.

=_'__

×r

7-;

Z-

.^

.J

c.,

×-_

IAi

V

i

-_--_ ...... - _-_:--____.__
I

!

I

I

I

i

I

I

I

I

I

I

I

I

I

I

I

I

I

FIGURE 3-46

REVERSE BIAS TEST OF ELEMENT

WITHIN STRING IN NATURAL SUNLIGHT (NO CORRECTIONS)

STRING 3B

String Wltage

String Current

Voltage Element

Mismatch

Excluding #11

7

8

9

10

11

12

A

1.50V

300mA

.816

.868

.890

.844

-2.78

.886

5.5%

CONDITION

B

2.g6v

300mA

.790

.840

.880

.780

-1.23

.900

6%

65

C

4.95V

294mA

.842

.867

.893

.869

-.589

.915

4.2%
t_

r,,,

'It

_D

',:1"

5,3

Z=

o.

u-

.:- .g.

O_

_...a

I

=:-=::_..... ---I------_m----b _, , Ii ! i -q-'-_ ....:-_--_..... q........

z_-z: _-- x .... + .................. , .......

! , ____ ...... _.:a.._--_........{.........

1 _ _ ...................... -- .......... ._,r .,-_ .... _ I _ _,- - _

......... # ...... 4 ....... 7_ ......... _ -- "IZZ---'--- ' .._ ..... _ .................................... "It

- -_-_---- --/_.--Z;7-Z- -- --2_Z---_Z2-'T_I#--- .... -.: ......... a,,_2 :_ --IL C.7: 11-i_: :_ - 7"_i-_:- : __ _ : . :_ " . i -

--z

....... a "- _' -'_---'---?----_- -----_"---_--q--,'---"-I 7 -I .............. _

i

....... _.......... i ........ ' =:_-::::::z _7--__ilc_.__ ..................... P--=-.-_ ::: :--:--;- :-:--- : " :

-__IZ72Z__Z ---------__Z_-._'Z77__- _--'_--_-=_-----"_-----Z'_ -- , ........ 7"...... Z-- Z717__-____ ........ ! _i:. :_:: .... : .i.

.................. .,.......... i. ....._-__ __,,_-...... ____aw._,q_ .... _--_--....... '.... ij-7-_-j_--2.11li_ _..:..:_i::;: -- - |

_:---.--:i--=::-:_=:--- .... _---=./_-_.,--::----_-=---=q--------==.c-= ...... _.......... --t ......... _,........ :...... : - g :_

'_-----=:_'----"----:--::==-O ....... ---7-t=_--_..... i..... ---_......... _ _ ..... : . - _

........'......i ................ '..... :::c7__-_:::___= _::-__.___

....... ------I_xZ--Z_ZIZZ---!i--2_7_7--7_: _-.i - - -

I ......... _----_ t_-_t __--- .... i - _- ! - t_ --

: ======================= T-- -4 .......... # -- q ........ I--_...._ ......::::::::::::::::::::::: _ "_

....... ; ........ _ ............... _ .... ___L_7_7_L_'_:Z- _-i 2--7_.i_ - _.................... CJ __

....... _...... ,..................... _ II________ILIIJIIJT_Z.,IIjZ_I:I__7_ZZ_--ZZ_L_ ....... Z

!::--{:_:-L-_---i::_:i_Z---- _ _................ --4 . -__.____.___ - ...... - +..... - -- >........................... .................. ff........ _+........ _-u

:-7:_-::i--==x= =::=:_ -:_--:_:__.. --_ --= _--:=: _..-_---=t .......<-_-_-_=-_: :-:i..:. _ -

71:_-7_-qi,-- X 7_-7_-Z__:-._---Z--,-_--q----. _........ "..................... 4.......... 4.......... i-:-:::-_:::::.x ::.

..... {......... :P-:i:./::I-.::=_-:-i::::il--:-_-_-_---'--:$:--'-_-_-q-,:-_c:--:V-_z_--c:=g_ -....___............ _ _ ---.

_c_:_-_:._::L_-_7__ _-.T;.......... t ......_..... _---------I-_ --I----T----T--- T ........V ....... .....: " -

-, ........ T ....... _ ........ _. _" .... , --_ ..................... i I _ _."-"

.... L __> .--1 .... , .... Z _._.... i__12_--_72_ KTT. _.___..-_............ M

........... :, : :-___ : --'--::._=- :----r===--_ ....... _.............................................. t _!::::_1

'_ : - :___:::- __ ................................................... _.......... _................

......................... _ .... _ .............. r_---:-.T----'t :..... 1 ..... i --_ .... ! ..... | " - _

..... i ............... r, . ,:........... i......__....... _......... '......; ............ L:-::. _._ Z _ _ _ _

.......z':---:::4--i:-.-_".......t---:--- - i-Z--_--:--:-_.........._:-:z:.: '' ::__::_:_.............

------- ............ _ .................... _ ..... _........................ _ MiZ__±I!i:-Z_'_Z-__',.--: .... - ....

........ + ..... _ ............... -_......... __-7--Z----____ -------JJ-I2 ..........................

....... , ..... _- -1, ,.,_..... _==-_ _ _

.-. j ....... 4........ "' _"-___:_7-----_ ...... _ ................. 7_cii:_-_-_,:_zi:::-.;.__::- '- :- : ::::

Zjj_z___Z._.iZjIIII:+,j.-_IIL-L .l_ l. "- i+------_--- -------L_-- -_--1--_ --.... --4 .... _ ...... i ............. _. ta-

...... i ..... _........ , .... l----, iZ----_- .Z-__I---7-Z ._-ZT-.-IZ.---- _--___'__'ZZ-_J_-Z._J-_ZZ[: -77z .... _ ................

' ---,' = ......... ;- 4 .................... *........................... I ""'

'._:--_---{i_: {i._--i{---!!-._ _--::__---.---7- ---_:=:-'-7-z=.==---':=4:-:-:_-:::f::_}::ii_i:L::i _ _

.................... 4........................................... ; ............... , - ,,_,_

[.__-- : ----Tli-_J:_ I .- _Iz_'- a, z:--l_,_"" ' _-'_ZI2_T--_----_ZT--_=L---_22.-----.,, _ ;__.t _ , ;-----, --4 ................................. ......... ; . gg

, ' ........ _ ..... Z - ................. _ ........................ .....:_:_:--.::/.:--::_--: - .=:=.._ ........÷ .....................................................

:--=---.=_-:--=_=-..z _-,_:---_----=_ ---:_--=-_---:----,=_=4:-==---:-i=----:i::_-- _ _,.,-:-_.

.... _..... 4- r.-, . _.r.,,..._ ........ __.._x.a.__,.......... +.......... +........ _............... , . _ - -- |"

.......... IlZ........ {.... ----_----- . _........................... _ ........ :-==---d ....... _...... ,,-=_-------_-_ _ ............. _- -:...... _....... _ ................... "' "

• I " _ ._ _,. _ _ ..... _ _+ .... _ __xe.............. _ .......... '. ...... 4 ........ _ . I I'-"

---- l-J-J1. - ---i 7----_i,.i±'" --- -_ ....... ,--- _ ............... _ ............ _ ...... _ ......... X

71 .... _l J.-- +- __--___ ,-----'_, ! .......... --:+ ZTj:Z.TI.;-T-.iZ----__'--TIZi:7-_'.i7 " " " _- ___ _

.......... , ............ _ ____--- ................. , , _/_ 0 ....... I......1 --_- ..... L_............. _...................... I ...... _ ....._..... -.-

Z Z --4 ......... _ ............................... ÷................................... " .... , " ' " ..J __i

......... _......... _.......I_---_:_C:-----T:-------_-_---_--........... - :-:I: -:: .... :---_:--:::-_;--: - _2 : "'_

, . _I_....----ZL_-----_q ----._............. _ ........ _ .............. i - ' " >"'

:: :-_Z:__.=--------li:_--_:=_=_--'_-t==_---:::......::::::::::::::::::::::::: ::::::::::::::::::::::::_ - W aa

==:-:-I-=::-=4 - ..... :i--=_. :=--==-_< :: ..... ----v----:k - __-:, _ :-::-!._-:::::: ::::::-:-:.-.:= ::_---:_ .. -::--a

.......... L.... I ....... , --_ - _ -- "--_---_C_'_ ...... I ....... , ! !

.... ! ...... 4 ........... :--:_--::=--_---a- "-----_..... :_-:. :; .t- : .... I--::::: .- . • :-:

....._........1........----*----...... a, • : _I.-----_- .-._- _.... _ ..... -_ _

' " "_ I ...... _ ....... _" -:I_

J1Z-- . Ji :_ J_ 7J Z ZZZ _-J--J_ .-7.'ZZ_:_Z __-_-_-_-_-_-_-_-+ _ _-J-._J-Z1Z ._ZZ .-J2Jy_Z ZZ Z Z11J :1_ J_ _ __ : Z - :: .....

- • _ .................. _ ......... *.... :-.:7:-: :::: :::::::::::::: :::::::::: - : :::- i. :. : :

..Z - _ _ Z_ L-I: _ZZ2L21-- Z2ZLAZ_" _ .....[............... _ - I . ta. -

.......... ......................... ' .....................i ...... i.

............... ............. , ................................ _ ............ : ...... _ ...... I .... -

-4 ..... i"_'iiZ_7_'.Z:'2tZ:'_i _Z-_'IZ " I:Z_'Z.-_IZI.:..7:::_" J:." "i _

......... _..................... __ --_ -=....._ ..... _- . :: .:

.................................. _ ........ , ...! ............. _ .... ......I........ ,........ I....-fizz................... +....,............. :.._:Ni:i: . - .... _ .... t ........ I ........ '. ....... t ..... _,..................... , , . -_', - "
!

I

!

!

!

!

!

!

!

I

i Z_ -

_-7

_z

!

!

|

!

!
I

Paralleling of two sets of substrings into two groups for

measurements with five elements in parallel by six elements in D

J

series was performed. The measured output of the groups were

compared to the expected output based upon the individual i

component substrings within the group. Excellent correlation |

was found (see Figure 3-49).

i

3.3.2.13 Correction Methods for MCC Element and Strinq Test Data i

All test data was corrected for known test conditions and

test item deficiencies.

AMO Sun. The correction to AMO sunlight was simply

accomplished by using test standard composed of a GaAs m

concentrator cell calibrated to a balloon flown GaAs primary

standard. The GaAs test standard was monitored continuously i

during test of the test items.

i

AMOcal. value x test item reading = corrected reading i

Std

Std Testvalu e

a

Temperature. The correction for temperature for panel string i

tests was accomplishedby mounting two thermistors to the back

of randomly selected elements on the panel, and reading the i

resistances on Fluke 8060A calibrated meters. Each resistance

was compared to a resistance versus temperature calibration •

chart (Figure 3-50) to define the base temperature, and then

6°C was added to the readings due to the known temperature

m

difference between the cell and the thermistor mounting position i

including bond thermal resistance.

The current correction factor used was 0.045%/°C. The I

voltage correction factor was -1.6 mV/°C. The factors were

derived from thermal testing of two elements on the panel while i

on the solar tracker. Both factors corresponds closely with

data available from GaAs cell literature. R

W

Vmeas + (T-28)(-1.6 mV/°C) = Vcorrec t

Imeas x [i + (T-28)(.0045)] = Icorrec t H

i

Conic Mirror Reflectance

o Based on Figure 3-40 and assuming typical tolerances

apply to the onpointed MCC element output, the

correction for conic mirror reflectance rho at 0 °

is:

68
I

6g

I
i:

IIIlI

;_ oi

_,__I

-_"I

=!---

7O
I

I

I

0

current

(.41 x rho) + .59

= corrected current

For offpointing measurements, the perfectly aligned

optic reflectance curve was used to correct the

measurements.

I

I

I

I

I

I

I

I

i

I

I

I

I

I

I

I

Data presented for offpoint check was only corrected

using the perfectly aligned optic correction. The

result is that in many cases, the output at offpoint

angles was corrected to be greater than the 0°

offpoint condition.

For onpointed measurement for concentration ratio and

absolute output of the elements, the 41% conic

reflection represents a maximum and will vary between

25 and 41%. Similarly, the reflectance of the cones

vary between 59 and 71% with an average of 66%.

Therefore, the range of correction factors is as

follows:

1

= 1.202 high

(.41 x .59) + .59

1

= i. 078 low

(.25 x .71) + .75

1

= 1.144 average (.36 x .65) + .64

Corrections for groups of elements in strings have a

higher probability of being near the average values.

Mismatch Effects. Cell mismatch for the concentrator design is

complicated by the additional consideration required due to

variability of manufactured element tolerance effects. A high

efficiency cell matched with a less quality optic may be

equivalent to a lower efficiency cell in a high quality optic,

but this would change as a function of offpoint. Conceptually,

this is illustrated in Figure 3-51. Therefore, it can be

expected that if low mismatch losses are desired, extensive

testing and matching of a large population of MCC elements would

be required.

Due to the small population of MCC elements available for

this contract, the variability of the assembly tolerance

effects, and the need for a dedicated grader for MCC element

output which was not available, and the short time available for

assembly and test, elements for the small deliverable panel were

kitted into strings according to cell efficiency measured after

the welding process used for electrical connection of the

contacts.

71
_=_ J.N:IHHrlo J.N =IIN] "I=I =I.LI'I"IOSBV

7Z
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

The MCC elements were mounted in the panel and tested. One

shorted element was subsequently removed and replaced. Offpoint

testing was performed. The panel was later tested for the

output of each element at short circuit and open circuit. The

results of that test, presented in 3-52, show a number of

elements with substandard output at short circuit. The mismatch

which results, especially due to current limiting as seen in the

current voltage (IV) curves of Figures 3-44 and 3-45, directly

reduces the maximum power of the tested string or strings.

As a rough approximation, the short circuit current of each

of the elements in a string can be averaged to get an average

string current which may then be divided into the lowest element

short circuit current in a string to derive an effective

mismatch, all assuming the open circuit voltage of the elements

are very close in value.

Shown in Figure 3-52 are the average current for the six

cell string, the calculation of mismatch for the string, and the

calculation of average mismatch for all the strings, which is

7.7%.

For the larger deliverable panel, all 180 elements as

completed were measured for current at 85% of open circuit

voltage using the x25 solar simulator and matched as best as

possible prior to assembly into the panel. As an additional

complication, the cells from the three cell vendors were kept in

separate strings. It was noted that the MCC elements with

Varian cells were particularly poor in output due to the welding

difficulties encountered (section 3.4.2.3).

73
E

_cp')

_.<

c_}

r_

t4"}

o_

t.,-)

_ooo_o

t4')

__0I

CO

t-e

t.¢')

OQO00_

_0_Ix

tJr)

Cr,

Od

II

t.I.

taJ

LJJ

CO

_,_I _*

r.,.

or,

000000 000000

Z0

...J

-J

_J

s"Z

bO!W

U.

IIIIIIIIIIIIIIIIII

74
I

I

I

I

3.4 CELL STACK DESIGN AND INVESTIGATION

The baseline design for electrical interconnection was

soldering of both the top and the bottom connections as was

performed for the MCC element designed under NAS8-35635. It was

noted under that contract that significant degradation of the

current and voltage was experienced by the cell after

soldering. Measurements were performed under 1 sun AMO.

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

To determine the possible causes, various portions of the

stack assembly process were investigated. Figure 3-53 records

the investigation areas. A plan was developed to test the cells

for gross effects. The bare cells were tested at one sun AMO.

A number of configurations using solder versus no solder were

run through heating cycles as used for the cell stack assembly.

Samples were heated in both vapor phase solder station (VPS) and

a hot plate. In most conditions the samples degraded similarly

to those in contract NAS8-35635. The sample size was large

enough to show that soldering was the degrading mechanism. The

results are shown in Figure 3-54. Average losses were computed

for the various processes by combining data of similar origin.

For example all cells with solder on the front contact were

grouped together, ignoring other factors in the process such as

mounting method. This enabled gross judgements of defect

mechanisms. As a second refinement, successively greater

narrowing of the error band and grouping of the cells within the

band, helped establish that it was the soldering process itself

that was causing the degradation and probably the front contact

solder bond.

Subsequent discussion with the vendors indicated that

unlike silicon, GaAs will be wet by solder. Therefore, in any

environment where the solder cannot be precisely controlled, a

potential for solder flowing over the GaAs and shorting the

junction exists. Both the hot plate and the vapor phase solder

method are not precision controlled for solder placement.

The soldering process (front contacts versus rear contacts)

was investigated by substituting another process for the soldering and checking the results. In parallel with this, the

mechanism of degradation caused by the solder was investigated.

Effort was concentrated to make connection on the front contact.

The options were soldering, welding, and adhesive bonding

75
i; o

'L--

QP co

LUg---

(::)

F--"

LO

F----

O0

1,1

_5

,'-Mv

(/3

6O0

.-J

>--

uJ

(/3

09I

..J

O9

i,I

F---

60

ijj

q_I

i

00 vl

V_4-- ,---

{3_ S.-U

rO

ul ul (]J

rO 4-)

ul {" I_ 0 ..E:

fO {3.

_- rO

En -i_

U0 4-)

ro _- c.o

_.0 (.)

Qj ._

•_-_ t/1 "_ (lJ S.-

(._

I--- Z

i-.-i

E:3

p,..

LId Z0

(.J Z

_J

...J

L_J 0

0 "I

_.. 4-)

_.X

0

::_PI---

4,o

e_

I-- Z

L_

I"-

+l E0003

,d_ ._,-

• _--. r-- Ill_

•,-"UU f,.- (/_

4-) ._ (l_

_0 4-_ -(.-) .,-- 4._

0"1 _J1_ ,---

}--

(.C)

i,i

F-"

c;

_.JLE

_0

"0 _- 4-)

E.P

,--- (U _0

,-'-4.-)01

rO

U (lJ

-_ 4--}

qJ.,- :3 O U UO • J:::: C_

e'- ¢"_, ¢_

U

rO

(_

4-) O0

r--

f..•

•p Gr/

--_p.

0",-- U _J

pM

+1

L/1

"0

"0

_0

4-)

bO _-

_0

C:_'O

tn 4-_

4_ v1

.l-)_.0

ro "_

(.J _.

hLIJ

I-"

¢:3

UJ

C)

i--- Z

C_0

2=

UJ

LIJ

¢U

=E

LIJ

I'-- Z

LIJ

LId

p,- U }"-

p,- ,.,

_- I-- Z

C_

_'..j

U-

,_:UO

}.-.

I, II

V1

--.I .C'_ U I--" _=

t/_ "1-- t/)

76

h'%

Lr_I

h'%

LJJ

LO

LL

IIIIIIIIIIIIII
i ....

°''',o.,o,,.-''''''" oo oo

>_ ..................................... ,_= m m : +_ _l::r_::mm_:mm;m=....

+ -- I .... "'*'*''*''*'*'''***'*"

I _ = _:_...s.c,_._,, ?..=,-?_+_._, 11_i___ _

_ "r _ : " " I II III 11 I I II I II I

m :,..+..+++.+: ..... - ..... :.+..++.s .... +

if+ .... s..s+...=o::o =s ............... +:-.-

I_'_3 . , o , , , . . , , , , . , . . . . . . . , ..... , . , . o , , . . .

•,_ oo o oo oo oooo o o o o

.... 0,....0...,...0,..,, ,... ........ .i _ _ ooooooooooooooooooooooooooooooooo_oo

im iim I1+m el o _ II _1 m. iI i_. N _l.m . i_,11Q II Ii _. _1 m -.

oo1111 oo oollooll ool0o oooo oo oo oo oo oo oooooo

c- .r--

° =++ o_H ____.._ _ ____o_______+J.=.

-IJ +++++,++:+++,-;,++*+,++-++++--++++++-:,_,++- o ,;+.- ,; . _

I+ .... ++ ++++++

o =-_ ,=I_p,=,_._::=::z-.:-=s:p..+s:_:._mr, r._._o_:_mr+_,-:

_,- u.. _ allSo_,oo..Sooo_ooS_oooSo_Soooo._.ooooo .. * *,_ *,_+ ..... _+,_ ",_ '_ -_+_.:'_+_ .... +_+ * .

-I?? 't, 'r'P?'_? , ? ? 'P,,, ,,?'P'P'r 'P_'

t--- • i_ _ i,- i.. o . o il i_ _ i_ i1_ m _1 i_1. i_ o hi m iii 1_1i_ I_ i+,1 ii =..11141+011

III • . .... • ....... . . • • • . ................ I_

-o,,,+o_+..,o-,,,+++ -m +.',---oo+o_.-_. m-,uo_. .,:,,:,._-'_--'u_,-_.t_-'--',_._

, , , ., . _ . ., .. ._'T';.'T';'TT'T"TT,'T,'T'T'T_, -

C,+_'+I | Iiiiii+i+H'i++_::i++ff++ iIL'=I P+L++|gIIP+-'+I

,-- ,'o ._., ,,,,'V,?, ?+_P+"P,'P"i"P?,+ ?,?,,?, ?"P,'_?,,

•r- Q,_ oo o o o ooo o ooooo o oooo o o o o ooo o..='o _o,_GGG G +._ ..._ >,,

i ................ ", ........ "= ...... ".'..'.

'P , ,'P"t........ 't-- 't'+._ '+Y'_'+';;'+'/'_'_'_i'_'_'Y'+'+'+ i l I | I I l

,,, U izs[smosg[g.,, gsS.soS ooo. $,,o s..s,,,,s oos

"+ "<+ "+-'++ "._ .._ • .+ • • .___,+++__,_,.:+ "+<+.'++_; ",_ (I? ? 't, ,?,?,?? '?'I?, ,, ,, 'P, ,, ?

I--4 I ....... • • • ..... • ........ • • • • , .......

• I,--'.4

• II Nm.m -- i,_1_ ,11 o. _ - .4)wi _. + _1_t.. 411, ,1__ _1,11 I.,,10 _1,,S .g ,-_ o o-._ .... IC,, o ,. o ,..o o ,.,. o - ,, +.-,,

dgII II iiii IIiiiiiiiiii ... . iiiiiiiiiiiiiiii . .

.......... m e+ e+ m +w _m _ m e+ mm_ mmmm

I

I

I

I

I

I

I

I

I

I

I

I

. ,.L ._BB

o_ mm . I- ml m II

1'--4

I

77

_.J OJ t,-

I_ -ro _ _"U m

o&+oo _o

o ++_ _,- =.=

==='_ + ++

"_ _ X _ _=' S. I_.

fll l.J _- 1,3 _ II

, : .< , _ g

_ .- 0, <, +-

o _

0

E_

t.- -.J _- -_ e-

= ¢ =

=_ +, o ++ = "; _

U iu

I'i _-" II _ IU

IU 41 _ IU II i,..i

0

DI_IGINAL PAGE IS

L.O

I

_D

*r--
3.4.1 Solder Investigation

It was surmised that the solder was flowing over the top

edges of the GaAs wafer and shorting the exposed junction at the

edge of the cell. As a first attempt to control this perceived

mechanism, a number of cells were sent back to the supplier,

ASEC, and an SiO coating was applied to the sides of the cells.

Assembly of some of these cells in the VPS station yielded

no better results than before. Since the back contact of the

cell was required to make full-intimate contact with the heat

sink, and solder was the best viable material, elimfnation of

the uncontrolled VPS method was not considered practical. After

success with another process (welding) was established, further

process investigation was halted.

3.4.2 Alternate Bondinq Methods

Any method to bond the top contacts had to be able to

survive a vapor phase solder reflow process without debonding or

shorting the cell. The reflow would be used for the bottom

contact and/or the heat sink to primary bond.

3.4.2.1 Adhesive Bonding-Top Contacts

A silver filled adhesive was identified as a potential

alternate to solder. Epoxies, polyimides, and even ceramics

were considered. These processes were to be investigated in

another ongoing program for which the results were made

available. No effort was spent on this contract on these

alternatives. The ceramic adhesive has good promise. The other

adhesives degraded greater than 5% in thermal cycling. Scatter

of the data was high.

3.4.2.2 Gold Germanium Eutectic

A gold germanium eutectic (350°C flow) was also

considered but again results were available from another

program. The bonds could not be made without significant

degradation.

78

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

-I

I

I
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

3.4.2.3 Weldinq

Since it was clear that soldering would not be viable with

cell top contact installation, welding, a method with which TRW

has had considerable development experience on silicon but not

with GaAs was attempted. Initial trials developed good bonds

but shorted the cell. The weld voltage was decreased until a

good bond was retained and average cell maximum power point

degradation was less than 1.2% (Figure 3-55). Testing was

performed with a LAPSS moved to a range corresponding to i00

suns AMO exposure. The weld voltage range to maintain good

electrical and mechanical bonding was more narrow than typically

used ranges for silicon cells.

It was found that the weld schedule for GaAs was very

specific to the cell manufacturer, most likely as a function of

both cell construction and metallization method. For

engineering purposes, an individual weld schedule was developed

for each the ASEC, Spectrolab and Varian cells, without further

investigation into exact weld metallurgy phenomena. The weld

schedule for each vendor is shown in Figure 3-56.

Both the ASEC and Spectrolab cells had silver final

metallization on the front and back contacts. The Varian cells

had gold contacts. Contact metallization material was not

specified for the cells for this application due partly to the

original assumption that the cells would be soldered.

The silver interconnect to silver contact weld achieved the

highest consistent weld strength of greater than 1 kilogram pull

(shear only). An attempt to weld silver interconnects to the

gold contacts was not successful due to the very low (<.05 kg)

pull strength. Therefore, additional unplated interconnects

were plated with gold of the same thickness as the silver

interconnects and welding was again attempted. The resulting

welds were significantly lower in strength (<.4 kg) and good

adhesion was very difficult to attain without significant

degradation of the cells (>10%) as evidenced by the extremely

narrow weld schedule. Backing off of the time and increasing

the voltage, and increasing time with decreased voltage compared

to the baseline weld schedule yielded even worse results.

79
FIGURE 3-55: CELL PERFORMANCE TEST (100 SUN FLASHER INTENS., ROOM

TEMPERATURE) BEFORE & AFTER WELD/SOLDER OF FRONT CELL

CONTACT

GaAs WELD SCHEDULE

CELL VOLTAGE TIME

NO. (V) (MS)

5

70

49

41

83

4

95

"94

*99

"13

"17

*9(

2]

1.

5_

5._

1(

PRESS

(Kg)

.56 100 1

.56

.56

.56

.58

.58

.58

.58

.60

.60

.60

.60

.60

.60

.60

.60

.62

.62

.64

.70

.72 i00 1

ELECTR. BEFORE

PULL

Isc Voc Pop STRENGTH

(MA) (V) (MW) (lb.)

346.7

341.7

338.7

348.0

343.0

341.6

342.9

347.7

335.0

340.0

• 344.2

336.3

332.4

346.9

335.2

338.3

344.2

324.4

339.3

341.6

335.1

ELECTR. AFTER I

PULL

Isc Voc Pop STRENGTH!PA/PB

(MA) (V) (MW) <lb.) i

I

335.3

342.9

347.7

337.5

336.8

342.7

335.9

332.7

333.2

345.4

332.5

329.3

341.3

329.7

335.9

343.9

326.9

338.7

337.0

! 0

i.981

5.01 !1.012

.999

2.8W .984

.986

.999

.966

.993

1.0C .980

1.003

3.2W .989

.991

.984

.984

4.5C .993

.999

3.7W 1.008

3.5W .998

5.5W .987 1

0

DURAT APLIT. PRESS

(DIAL) (DIAL)(Ib)

8 5.5 1

8 5.5 +

345.2

346.4

349.2

373.6 1.08 348.1

344.2

347.9

339.5

335.6

332.9

341.2

(9% Shorted) i i Averag_

341.0 5.01

335.3 5.5S

367.2 1.08 341.3

250.7

314.8

332.1 5.51

342.3

(30% Shorted) Average

0

.984

.960

.983

(.728)

0

0

.938

.998

1.003

.97B

EDGE COATED CELLS/N(_NO)=SHORTED CELLS

80

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I o

i _

| _

I : t _ _ 0

oo _-_ I , Z_"

o 9 o o 8 o o o <j<

<_ _ =,"1

o o o __o

N_. 0 • o

| N o,

u_ _ '

_J

i °

_j _

I _ N x

_J

•-I-- x

U

• • i i i

._ SS07 7931_13373

I

81

I

U7

I

f47

U_
Although the degradation of output of the Spectrolab cells

was slightly greater than the ASEC cells after welding, the

sample size was insufficient to determine if this was

significant. No more cells were available for these

experimental purposes.

All future subcontracts to vendors will require the cell to

be silver metallized since the silver welds were so successful

and there is no compelling reason to retain gold contacts.

3.4.2.4 Stack Subassembly

Pretested welded cells were placed in a VPS fixture to bond

the cell to the heat sink with a one mil solder preform between

the cell and heat sink. The preform was slightly smaller than

the cell. After soldering, the cells were tested. Degradation

averaged only one percent (Figure 3-57). The welded front

contact with VPS rear contact was made baseline.

Thermal shock testing (i00 cycles, liquid nitrogen to

100°C) showed no additional degradation of the substacks.

3.4.3 Electrically Connected Versus Isolated Cell Stack-Heat Sink

The heat sink for the solar cell could be made either

electrically conductive or insulative. The heat sink exists to

isolate the brittle cell from the thermal expansion mismatched

copper nickel mirror. The heat sink is required to have an

expansion coefficient very near to that of the GaAs cell to

minimize stress on the cell.

A molybdenum sink would provide a conductive path to the

MCC mirror. An alumina or beryllia sink would provide

insulation from the mirror.

In light of the goal of low cost and light weight a

comparison was made between advantages and disadvantages as

shown in Figure 3-58.

Clearly, an electrically insulated design is most desirable

since it simplifies control of the electrical power without

compromising the design of the conductive graphite substrate and

mirror mounts.

82

I

I

!

I

i

g

I

I

i

i

i

i

i

i

i

I

i

I
I

'_

I!iII

F- | ooGO

mr GO

r_

0 | = ®

C) CC_

r_

=_

I =otJJ _-

F--

U_ Fmp Z

CO

ii | =U_

=LLI

1.1.1

._J | "'-_ Z _ E _ I °e._ z

LIJ

_J _J

II

¢'_A•

__ O0 CO t_ (,)

U'- r. O0r O0 CO

_ O_____

<_v ..... U U_--.

i.I.i

r,-

U

--v

_I_0

._J --v

CM

--

u).J

(_CZ

CO (2_ r. CO (:n

_0 r._ CO r.. r_. 0 C_ _ C_ C_

c__ _; o__

(,) 0'_ (,)_ (.)

(-,) (,)__ (,)

_0__ CO _0

_0 r. O0r r.

_')_ _.o_

_J

>- Q

._J

.-J

_t z

83

coo

_J

o

-.J

....J (_ z

t---4

I

ii

o

o

e- e-
I.i.I

122

>-0Z

.-I 0

,#

CO

,-4 0

,-I

--J

:::} 13,1°,-- _ °

e-

-.I _1__

0 0"-_

aJ

_..

,,a Q; ._

I-- _-_ _ .,- ,_.

..J_

c_ o; oJ Io

,,,

$

EE

..,J

Z0

"" I--

I'-- I--Z

_ ,,, 0

0 .--I IJ,.

C.)_ IJ.-

_.1_0

r,,"0"

Z0

I'--

ILl Z0

--J

I--

,--.I

ILl

84

c_

O_

I'--

M.,.,I

I.,i.I

r.,

r_

I,--

r."

ILl

r':

I'-

ILl

-r

.--,I

.J I

OO

I,.L.

IiIIIIIIIIIIIiIIIIi
!

!

I

Beryllia was selected over alumina due to its high thermal

conductivity and hence, lower effective operating temperature.

The cost of alumina versus beryllia is not significant once the

cost of metallization and high precision manufacturing are

factored into the total cost.

!

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

The heat sink is shown in Figure 3-59. The two isolated

metallized pads were provided before it was found that no

mechanical attachment of the cone to the heat sink would be

required. The pads will be eliminated in any future

procurement.

3.4.3.1 Heat Sink Bond

The heat sink was bonded to the primary mirror using the

vapor phase solder method. A pre-fluxed preform of 1 mil Sn62

solder was held tightly between the heat sink and the nickel

surface of the mirror in a specially designed tool which was

then lowered into the vapor phase station.

3.4.4 Coverglass

A coverglass (Figure 3-60) was incorporated into the cell

stack to protect the cell from electron, proton, and other

corpuscular radiation. Protection from atomic oxygen is also

provided. The cover material was antireflection coated CMX, a

ceria doped borosilicate glass manufactured by Pilkington, Great

Britain. CMX was chosen over fused silica due to cost, wide use

in other programs, and better thermal expansion match to GaAs,

and to the nickel conic mirror.

3.4.5 Cover Adhesive

The cover adhesive is Dow Corning 93-500 silicone. This

adhesive is standard to the solar array manufacturing industry.

Adhesive bonding was chosen over mechanical capture of the cover

over the cell. The darkening of this adhesive in this

application should be investigated and is recommended for any

future contract.

3.4.6 Conic Mirror

As defined in the Statement of Work for NAS8-36159, the

conic mirror is considered part of the cell stack. A number of

options were considered for mounting of this mirror to the cell

85
LL)

_c2_ t I i

I'

(fJ

t_J

LJ E_:

LLJP_

G-LJ

L,I LLJ F- i--

.-J --J Ca_

CI- :7

'I

._J

.-.J

G_

c'd _.j oJ

Lf'1

ED

LID0

ORIGINAL PAGE I_

oE POoR QUALt'r_

\

\

J

o._

J

x\\\\\\\NI

b.%" .... .'.'q

k'\"x"r'X-'X-_ xd

db G_

-'_ t£3o

I

o_

chx

-- CD

C)V

>- IK

i,i _j

r,n ._

] ....J.. I

Od

t_

C_3

v'3

C_J o •

_J

aD

0'3

0"3

G_

C_

ooo

ooo

ooo

DJ

,jZz

_-- ._j

"_D.J

>-- _,-* ED

._J (.D __J

CD _--._CD

_-z (.D

°°

c.0z

F.--

__1

D._

1"-,3

,,.o

f',o_

qDu_

c.31

cn_ G U3

;ZZ

ozu

oo

4-1

coz

CD

I--4

coz

2g-

_t

_.A

r-c:)

o

go

X _.2 X _ ×

g

b_

u

_m

lgm

cg

?

NN

86_ ' . .............

IIIIIIIIlIII

i.i.i

l,

1IIIf
I

I

i

L_

N

U')

-J

<:_

b-"

ORIGINAL PAGE

OF POOR QUALITY.

o

o

+1

o

c)

o o

o

Od

4.1

O

OJ

87

(_D

I-4

_J

CO

ED

LJ

CO X

-- Od

I I

Z Ln

cO

0

__I i

EL o_

o

0

rY LD

ILl 0 --

> o

O C_) --

(_9 (--)LJ

---] (j

__j u0

Ill

(_9

o

i

i,
stack (Figure 3-61). A cover with metallization could be used

to solder from the cone to the cover. Potential thermal

mismatch stresses, cost of the specialized metallization process

(even for over 100,000 units), and loss of cone to cell optical

centering flexibility, excluded this choice. The cone to heat

sink solder bond was excluded due to added complexity of a new

part and lack of precise positioning control in the soldering

process. Direct soldering of the cone to the glass was

considered. Indium solders wet well to glass but the process

required (brushing with a metallic brush wet with the solder at

elevated temperatures) made this impractical. Adhesives which

were considered are shown in Figure 3-62.

DC93500 was a low strength candidate chosen chiefly for its

low (around -120°C) glassing point, lower than the -80°C

temperature minimum expected in a low earth orbit for the

array. This would yield low glass to nickel strain and

therefore little likelihood of failure under thermal cycling.

DC61104 was chosen for its higher strength, and low temperature

compliance. Lefkoweld epoxy was chosen for its resilience and

availability as well as experience with flight space- craft.

Another epoxy (EA934) was considered as a stronger material, but

it had somewhat less resilience. Of the cone to cover adhesive

bonding methods, the Dymax 628T ultraviolet curing acrylic

adhesive was selected for high processibility, relative low

thermal stress, and high strength. Considerable mechanical and

thermal cycle stress testing was performed to assure the

capability of withstanding a LEO environmental exposure.

3.4.7 Cell and MCC Element Electrical Interconnections

The cell stack electrical interconnect designs were

patterned after similar TRW manufactured interconnects used on

flight hardware. The cell top contact interconnect (Figure

3-63) was a plated kovar material chosen for thermal expansion

match to GaAs. The physical configuration incorporated two

bonding pads at the corners of the cell, and an out of plane

thermal expansion loop.

The interconnect for the back contact (Figure 3-64)was

designed to pick up the gold plating electrical path on the

beryllia heat sink upon which the cell backside was soldered.

!

I

I

I

i

88
!

II!!| --_

_._

CO CU

U __ | e__j !!II i•_-

__

.S "G ,-

_.; N-_

!!

__z

ii

UJ.

I--

ul

.J

ul

Q

tll

I--

ul

-1

ul

_ww

>>

0 i <

__

Z0÷

uJQ

-I 0

cn

).<u

-I<Zm

n,.

I89

Z0

I-0Zm

I-<Z<

u)

uJ

uJ

uJZ0

i

c_

_J
i,i

Z_._

OZ

Z

c_

C_

-J

,,t >- LiJ

Z

0

O0

I.U

l,i

Z

i,i

..J

L_

m, I.L =_

>.-oo

'=rr", I--

..--I_-'_

L_Z

_--4L.I.J

>.. r._

I---

(._

Z

C__._I

U._ r*',

=EZZ

'-rl..lJ

0

0

L.IJ

or)

1:1.

l---

z

ILl

._I

X

l---

Z

l.J.J

..--I

.--J

I.LJ

X

0

0

x/

I'--

0

m,-

u.J

0

0

C_

00

I-'-

Z

--J

-.I

X

m,,-"

0

0

,,.,,

0

I'--

L.L

0

0

I--

I-i.

0

0

0

0

0

0

Oh

IJ-I

0

0

I.LJ

m,

I--

Z

._.1

..-I

ILl

X

0

t--

0

0

0

0

v'

I--"

0

0

I.L.

00

c_

I'--

Z

ILl

.--J

....I

I._

_._

X

1.61

0

0

>-

v'

I---

r_

0

o

]

J

r_

0

0

0

0

_._

k--

0

0

i,

Oh

ILl

r_

0

0

0

0

>-

1.61

I'--

L.LJ

..-I ...J

.._J .__1

.--._ ,._,

,, I,

i.--i

0

0

CXD

I--"

Z

m,l

x

F--

cO

c_

x

>-

Z

0

m,.*

ILl

0

0

I'--

Z

0

0

L.I_

1.1.1

I--

ILl

or)

!

0o

i-.=1

u_

go
IIIII

F} :=><

ti' L)

ZW

--C-B

OU?

.Z

H

JI

•

O

I

OO

P

L_

2>

,__.)

L'x-2

_--4

C_ O

°

°°

_J

(212

F--

OO

O C-D O O

£r2

L_I

{L3

_JJ

ejO _'_O I I

..

k--

dZ.

w

c_

OJ

C77 G

r.

'4 ">

_J

O_

<

L.Z::

0

_J

dZ_ I CkJ O / / / C_l

o.\\/

/"

/

/

.j/

cO

L_ -.r.----- 0 Ii

0

C_J

i,_-)

J0

I,

/,

F'--

r_0

0

-mY 0

I

:L

ORIGINAL PAGE IS

OE POOR QUALITY

p ,:,

_,,J cD

LL_ i,

o '..fi ,,,

, ,T I_

,±,

m

:R .- " ':2

)_ i" _ 4

O2.

IX2

ZO

r-,-" Z

i,-...i

t,, 0

I"-"

....--I

;4

i,i
,I,

D.J

did

i--i

CO

Z

(2d

2m,.

CD

cO i,I

J

.e

_8

ii ,_J

,,..u

c:m

I

I

I

r'r" m

I'--'-

I

I

0",

0

i

C.)

:K

_i

O0

0

,,D

0

0

-./

I

0

0

°0

Ok:

L_

0 0

0 0

0 0

P_

L_J

_J

CO (_9

-- OJ

I I

£D

Z

F_

__J

G_

__J

O@-

--J r-o

r'_

.,_ OOJ

¢-.,

m-"

0

\

0

0

02_GINA_ PAG_ _._

OF, pOOR QIJAI,ITY,

_J

L.DD_

LD

0 ('_J

oO-J

0 CD

"¢'----- 0

LD

oO

0.1

92

T

0

'4!

oO
i

!

I

!

i

I

i

Two contact positions were provided on the interconnect which

were then welded to the beryllia .metallization. A gold to gold

weld was chosen over soldering due to a manufacturing process

desire to use vapor phase soldering for subsequent assembly

steps. The interconnect has out of plane expansion loops to

minimize the contact stresses. The weld schedule and strength

are shown in Figure 3-65.

Each of the interconnects was mounted to special terminals

using a standard SN62 solder. Posts on the terminals fit

through holes in the interconnect as a mechanical bond (Figure

3-66).

The terminals are commercially available hermetically

sealed feedthrough systems (HSC Series i000 SP30, Hermetic Seal

Corp.) which incorporate a glass bead to electrically isolate

the electrical feedthrough post from the mechanical mounting.

The glass perimeter is covered by metallization which may be

used for solder mountings. In this application, the terminal is

soldered to the feedthrough holes in the primary mirror cup.

Electrical connection between optics is via wire soldered to the

terminals showing on the backside of the cup (Figure 3-37).

3.4.8 Summary

Figures 3-62 and 3-67 summarize the cell stack materials

and bonding methods trades.

93
GaAs

CELL

No.

5

9

10

24

30

36

43

49

56

8O

GOLD PLATED

INTERCONN. TO

BeO CHIF AFTER

THERMAL CYCLING

PULL

VISUAL (lb.)

OK 1.4

mwg

OK 1.3

OK 2.1

OK 1.4

OK 1.5

OK 2,2

OK 2.1

OK 1.9

OK 2.O

FIGURE 3-65 INTERCONNECT TO HEAT SINK WELD TEST RESULTS

* Ribbon removed in therms.

94
IIIII

1

0

_r

C)

\

\

• 95

I!

/

Z0

I--4

I-- ZZ0

I--- Z

._1

I--"

L._

..--1

i.--

0")

.--I

--I

L._!
.m__

-_ =. m

"=_E

'EE

I.I,-

,u

96

.E

_EN

m

F"-_

II!IIii

L

!
!

!

l

!

!

!

!

l

l

l

I

!

I

!

!

I

!

!

3.5 STRUCTURAL DESIGN OF THE MCC

3.5.1 MCC Primary Mirror

The primary mirror built for contract NAS8-35635 was found

to be less stiff than desirable as an unassembled piece. This

resulted in unacceptable distortions when mounted to a

structural assembly, as reflected by the tolerance analysis.

To stiffen the structure, two items were incorporated into

the design. Stiffening rings were designed into the rim of the

mirror and the edge of the flange to provide rigid right angle

joints and minimize deflections.

The spider structure mount for the secondary mirror acts as

an additional stiffener across the bowl of the primary when the

MCC is completely assembled.

3.5.2 MCC Secondary Mirror

The secondary mirror of contract NAS8-35635 was found to be

sufficiently rigid. However, the new secondary design did not

have a similar flat flange at the rim. A stiffening ring was

therefore incorporated at the rim.

3.5.3 Secondary Mounting

The secondary mounting was changed from the "birdcage"

approach (Figure 3-1) in NAS8-35635 to a "spider" approach

(Figure 3-68). A leg was incorporated to provide stiffness in a

third direction if necessary, but was later deleted after testing

showed sufficient strength and stiffness to pass launch dynamic

inputs. The change to a spider was made to decrease effective

blockage of the collection aperture, to decrease the cost of the

mounting system, and to improve the manufacturability of the MCC

element (Figure 3-69). Mounting bosses were incorporated into

the primary mirror flange to facilitate accurate assembly of the

spider to the primary (Figure 3-70). The spider was produced by

wire electrical discharge machining of a stack of plates with the

correct dimensional characteristics.

97
• .. ./,I ̧

i _7,i

m.nl--

98

OR_CINAL PA_2 .T,-*

OE POOR C)U_ _..r"v

,sz

.__2=

z_

O

--w

e_0Z0

ELI

"l-

--.J

_D

4OI

L._

r_ IIIIIIIIIIIIIIIIII
_o

I

_J

L

I::)

.p

L_-
,i:'

1

IOO

OI,,GG'lb!A_: "
I

i

I

l

I

I

I

I

i

I

!

I

I

I

l

I

l

3.5.4 Mirror Manufacturinq Methods

Methods for manufacture of the mirrors are shown in Figure

3-71. The baseline method of electroforming was chosen for

direct comparison of the new design with the model developed in

NAS8-35635 and because surface replication was known to be

excellent.

3.5.5 MCC Element Bondinq Methods

The joints for the cell, interconnects, cover and cone

interfaces were considered under cell stack design. The joints

for the secondary to spider and spider to primary were developed

in parallel with that effort. The options for the secondary to

spider bond are shown in Figure 3-72. Solder was chosen for its

high thermal conduction path to the spider and the manufacturability inherent in the reflow design. Testing in acoustic and

thermal cycling environments (Appendix A) confirmed the

capability. The options for the spider to primary bond are also

shown in Figure 3-72. Adhesive bonding with DYMAX 628T was

chosen for good bond strength, good thermal cycling capability

and ease in assembly.

3.5.6 Complete MCC Element Assembly

An assembly drawing of the MCC element is shown in Figure

3-73. Photographs of the assembly showing the assembly method

to the support structure are shown in Figures 3-74 and 3-75.

Manufacturing methods (Figure 3-76) employed for the production

of MCC elements are described in Appendix B.

101

!
m

l

|I

i==

U

m

m

=D

C

fU

I

m

|I

li

m

o

L=

OI

0

I-0

u-w

Z

IZ

Ooo=_h

_z_

uO0_

_ou_

_Z_

_-_

o

--I

ul

102
IIjIIII

E

I :__ I _]

Ii

=" _I

I_

II ;.o=_,o >=

= _1 P- •-=.___1 _

_ ,.=,

I6o _.-_m_ (2

•i ":--' __-I

I03

I I

°ln

I..I-
104

,-J

r,m

=K

uO

uO0ZZ0Z

_=_ Z

LLJ

i,s

r_

LLJ

UJ

..J

0-!

lIIIIIIIII

r-,.i

aJ

f,.

-s

.r.- '_I

IIIIIII
IIIIIIIIIIIIIIIIIII

105

Z

-'z7"

_" c_C

_L,JZ

__I

",c___j

P,L_

=_Zr--, A

_J
106

ORIGINAL PAGE_

0__ ][_)OR QUALITy

4=JI

C_

be)

c=EO

$.. LCO

°im

t_

_J

e-

¢.DL

-Z_

b-I

t._

C_

_=_

I

t.t.

IIIIIIIlIIIlIIIIIII
IIiIIII

107

V} oE

e- W

C;I I

_t

o_

I=II
3.6 MCC SUPPORT STRUCTURE

3.6.1 Frame Desiqn

The main component of the structure, the tri hex grid

design (THG) (Figure 3-77), was retained from NASS-35635. This

structure was compared with a competing hexagonal structure for

stiffness and manufacturability. The significantly greater

stiffness of the tri hex grid for unit weight (Figure 3-78)

combined with the inherently simpler manufacturability confirmed

the selection of this design as baseline to the program.

I

I

I

Potential materials were reviewed for cost and

manufacturability (Figure 3-79). The Syalon ceramic material

was rejected for difficult process control (shrinkage) which may

have required secondary machining. A Beryllium structure was

defined and found to be manufacturable at a reasonable cost for

a large order of units. However, for potential low cost

applications, a graphite fiber reinforced epoxy (GFRP) system

was selected to explore manufacturability and cost. The

inherent material cost was lower and overall fabrication cost

was found to be less than that for beryllium. (For a more

detailed discussion of processes see MFG-Panel in Appendix C.)

I

I

l

I

I

The GFRP layup methods used in previous contracts and TRW

internal research resulted in a structure higher in resin

content than desirable. Methods to compact the structure walls

and achieve high fiber content (>60%) were considered (Figure

3-80) .

The trapped rubber mold method had been used previously in

commercial applications for squeezing resin from composite

systems. Application to the array was believed to be the best

choice for success.

I

l

I

I

As built, the small GFRP strips and a four element panel

exceeded the goals for stiffness, fiber volume and void content.

The large 37 x 53 cm and 37 x 142 cm panels built under

this contract met most or all requirements as initially

manufactured. Some bowing of the larger panel out of

specification was alleviated through a secondary cure process

wherein the panel was heated to a higher temperature than that

used for cure, stressed to counter any bowing and held for a

specific time. After this, the panel was within specification.

108

I

I

I

I
III!!!!I!I!I!!II!I! I [

X I g_£SEIX I_ I " I l I !

ORIGINAL; PAGE rS

DE POOR QU_,IT_

-i --L

I;

-i"L!L

iol

'll_:ill ':'';'_: I!+' il'-

='!!i!! ++

i

-__ _..

_;_ _- _._._

109

-I!

r-_

,.,,,. x

r.,"

I--"

L,_I

C_

,=i:

-_II WIJ_
L_

i

!

i

i

I

i

i

i_

I

t

I

!:f

i

J

i

I

iI

T

_7" r _ 1 97-!r,;;_'x× I (2 I EL 1 I*_

f_j

X _(X ',

XXX_

J llJ

_ f 00[ :rJ_l C] I t> l re.

- >:

_' _,

r,,. _t_ I' .,.I b4 I

ORIGINAL PAGE IS

OE EOOR QUALITY

| (_; I

=;

C_

X

"lr,/

.-J

.--1

Z

p..

!

e")

r,,"

LIII0
IIIIIIIIIIIIIIIIIII

!_I Li I

-T-

-1"_T _-. -'1_

ORIGINAL PAGE

OF POOR QU_

,c=_ CG_

xaame

IL_J

>

]....< ........

IIi

U

I_I- 0

...I

-_

-N
I

I

I

t: __,_ I

_><."

x><. I

=' _ ><_'_ if

×_> D

3_

_a

= !

,,= _ _ l

=_ I_I _ I_ I_ I

o. _0

==-I I dO= _I ,,>

•_. _ _>I

.= "_o_i_-I I

- :,_ _I
I

I

!

I

!

I

!

I

I

I

LL

I

I

•E f_ e-

_,i eI

I

_1

I-- a- u. --..j ,,Z

N_n z I- _ 5:,<

_. _ ..., < :+,.u_ -,- _ • -> +, >. :E ,";-

+ _ + _o+ ._ '.-' ,.,.,+,.,., ,.,..., _+ _,< =.-. -+ +o + +

,.+ + +>o+"-_l I-.- E _• _+N_ +_ _+. .<-_- ++-<: Zo _ v)

,.>, <_ o, <_ " o z_ _, _,__ . _ ,.+-'_,"'

.., z-- o _0

: o _ o_o._ _ -_ -oz_ _ o=- ,---. "' _ '"

z

' 0,,.

N

, _;_.. __.

113

I

_n

U-

!

!

!

i

I

I

I

I

,I

I

I

I

I

I

I

I

I

I

I

3.6.2 Insert Desiqn

The tri hex grid panel required mounting provisions for the

MCC elements. The natural location for the mounts were at the

triangular sections formed by the THG geometry. The mounts were

designated "inserts" which consisted of two or more components:

a fixed insert in the panel; a fastener for the MCC element; a

sliding insert for flatness control; a snubber for positive

gripping of the MCC element. The design for the NASS-35635

contract consisted of an aluminum female threaded part bonded in

the THG, an aluminum male threaded part to fit in the female

part allowing adjustment of the height above the panel and on

which the MCC was positioned, a washer and a screw threaded for

the interior of the male part which held the MCC in place.

To simplify assembly and manufacture, and decrease weight,

a new part was designed with the intent to use a commercially

available snap fastener to hold the MCC in place. The simplest

process for bonding the fixed insert in place was to co-cure the

insert with the THG manufacturing process. Since the flatness

of the panel could not, at that time, be predicted, a sliding

insert was designed to secondarily bond in place and minimize

any out-of-tolerance flatness achieved during manufacturing

(Figure 3-81).

A commercially available snap fastener was located which

met overall dimensional requirements (Figure C-8). The fixed

insert (Figure 3-82) was designed to be lightweight yet

resistant to pressures developed in the trapped rubber mold

manufacturing process. The insert was triangular and of a

slightly large than nominal THG triangle size to ensure good

bonding over the exterior surface with the graphite fibers. A

triangular sliding insert (Figure 3-83) was designed to mount

into the fixed insert and accurately slide within the hole

provided with little rocking or offsetting. A snubber was

designed which consisted of a washer-like 2 mil piece of kapton

coated on one side with RTV silicone adhesive (General Electric

RTV-142). The washer fit on the snap fastener such that the RTV

faced the MCC element (away from the head of the fastener)

(Figure C-8). The sliding insert mounting surface was modified

with a groove to allow for MCC primary nickel material

overgrowths (Figure 3-84).

115
I

I

II

I

l:I _ I

I I

,,=/_I I

_ _ I .'__I

_ _ _ _ I

= =_

° I

I

I

-_ "I |

_J_i ._ "i _ -_I _ __ z I

116
IIIIIIIIIIIIIIIIIII

117

o

uJ

z_

_'ii=

o,,

m,l

(I") Z

,,i X

Ii

O0I

¢0

i,i

0¢

Ii
oo

_k

118

r-

.,.z

o

w

L

_1o

,_c4

ORIGINAL p_OE ZS

OF. POOR QUALITY

LUZZ

.--1

&;I

e_

I.L

IIIIIIIIIIIIIIIIIII
IIIII!!I ._X

.

Q_ | "-°aJ o o'_ | >=O _ _ O III

119

I

or-E

cop

c-O

tnCO tn

_. e"

-I_0

_JXII C)

¢-

"_ _j

p- ,j_

u'l 4._

OJ "_

C_I

IJJ

¢Y

i,
The sliding and fixed inserts were designed to meet

requirements as shown in Figure 3-85. Materials considered were

plastic, metal, and ceramic (Figure 3-86). Plastics were

selected for easy, least cost manufacturing and best thermal

expansion match to the THG GRFP material.

The plastic material choices needed both high (200°C) and

low (<-170°C) temperature tolerance, low thermal expansion

coefficients, and high tolerance to corpuscular radiation.

Atomic oxygen susceptibility was an unknown, but coatings could

be used if necessary. Of the four plastics finally considered

(Figure 3-87), three were used to manufacture the inserts:

polyetheretherketone, poly(amide) imide, and polyphenylene

sulfide (PEEK, TORLON, RYTON).

Bondinq Methods. Three methods for bonding the sliding to the

fixed inserts were considered: adhesive, welding (plastic

thermal reflow), and staking. The least effort method (adhesive

bonding) was tried first.

The requirements of the bond were resilience, adequate

strength for assembly (>3 ibs push force which was 50% above the

snap fastener maximum push force), and good thermal cycling

stability and reworkability.

A number of adhesives (Figure 3-88) were considered. The

selected choice of Dymax 628T adhesive was based on adequate

strength, good stability under thermal shock and deep thermal

cycling environments, and reworkability with solvents. In

addition, the fast 15 second set time made manufacturing a high

productivity effort.

To provide an absolutely flat surface the THG panel was

suspended by shims above a micro flat table, the inserts were

carefully slid into place, the adhesive was applied, and quickly

cured. The error was less than three mils on any insert.

120

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I1

II

I .'_ IIIIII . ._

ee

c=_ Q3

__ .-_

I l:_•

•a_ '_

I _= __o

Q3

I_____ .: l__

I _'_ .,I "G°"

_;:,__••••••

II

*" 121

c:

|nE

el"

.Dm

c_

Am

I,.. 0O

v

(:E

.B

c_

.m1r.

,.I:

imm

.m

c_E

col

°r..-

,,,=- OO

&,(b

m,-
i

liD

m

i,-.

liD

I= a,_ i

I_ ,m r"r"

W

I=

_=

O

I

II

l

._ _°

._=__

!

!

_ l

0_ ,,_

.,.=_ ..= _

-= I

• " " • • • " • " " i

II

l

.,,,,r

122
Imm i," mImImm i I =$

m_

m

!| _o _ _c_

I= a._

ID0m

MJ I_ I--- _--

Im

_'_

_ ee

ee eN_

- )N

•_'__

0 "-"

u_IIII<IIII

ZEmmEE

mm

x123

coI

aJ

%.-

.rI,

L_

Ct_ 00

L_

n-"
FIGURE 3-88

PUSH STRENGTH (LBS) FOR

ADHESIVES FOR SLIDING INSERT

INSERT MATERIAL

TORLON RYTON PEEK

Dymax 628T* 6-22 4-6 M 6-11

DC93500 - 0-3 X -

RTV 3145" - 5-12 22-28

DC6 1104 - 2-10 X 4-12 M

Lefkoweld Type 46* 4-22 M 18-32 -

RTV 118 . - 2-5 X

Cyanoacrylate* >220 3.5 X 4.5 M

EA 934* 61-65 5-44 4-36 M

X = Cannot Use

M = Marginal

* = All adhesives tested in thermal cycling had greater than

4 Ibs residual push strength.

124

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I

I

I

I

l

i

I

I

I

I

I

I

!

I

I

g

,I

4. ANALYSES

4.1 THERMAL CONSIDERATIONS

4.1.i Thermal Performance For Cell Output

The new design of the MCC element was checked against

thermal analyses for designs from previous NASA contracts. The

essential components of an 8 mil copper optic/radiator have not

changed. Thermal response in a low earth orbit for a typical

element is as shown in Figure 4-1.

4.1.2 Secondary Mirror Temperatures

The temperature reached by the secondary mirror is

important for both possible alignment distortions due to thermal

mismatch and for long term stability of any materials used in

the manufacture of the mirror and support structure.

A simplistic analysis assuming no fin cooling from the

spider showed that the present design should run between 130 and

140°C. This is acceptable for the materials used.

Consideration of the fin effect due to the aluminum spider

should significantly reduce this range.

Thermally induced mismatch between the 80°C primary and a

138°C spider structure would cause a relative growth

difference of only 0.8 mils which is much less than the 2 mil

allowance at the local spider to primary bond interface. Very

little optical distortion can be expected from this source.

125
I

I

" I °_

=_ I

$_ 4-_

I

"_r-'J N x

,_ r,-

"-° I

I I I I I I I I I I I =

* t ' ' "T "T "T

126

(3o)]HnlY'd]dW]l

e.-4

I

5,.

-..s

olm,,
I

I

|

!

i

I

I

!

I

i

I

I

I

i

1

I

i

I

4.2 WEIGHT

Shown in Figure 4-2 is the weight goal for a flight ready

panel compared to the achieved weight of the NAS8-35635 contract

and the new achieved weight of this contract.

Figure 4-3 displays the weight of each piece part of the

MCC panel and summarizes the total average weight achieved per

element.

The THG framework has reached the design weight goals

originally set for it. The insert attachment hardware is

greater than fifty-five percent decreased from the NASS-35635

design but requires a two thirds reduction to meet the design

goal. The MCC elements mounted on the large panel have achieved

the flightweight design goal. The harnessing is 15% less than

the flightweight goal. Altogether, the system weight per

element as presently achieved is only 11% greater than the

flightweight design, that is 14.17 g/element versus

12.60 g/element.

To achieve the design weight goal it is only necessary to

order primary optics nominally 8 mils instead of nominally 9

mils thick as with the current manufacturing process. This has

been discussed with the electroform vendor, Optical Radiation

Corporation, and has been found to be easily achievable with

only small risk of decreased yield. For example the i0 mil

nominal thickness secondary mirrors were actually delivered as 4

to 6 mils thick and primary mirrors as delivered ranged from 6

to ll mils thick.

127
=_

C

128
IIIIIIIiIII

-J0
4.3 PERFORMANCE ANALYSIS

4.3.1 Overall Electrical Achievement

Figure 4-4 shows the capability of the as-built MCC element

configuration for this contract, compared to the goals set for

the MCC technology. Also shown is the projected capability of

the current design when the effect of known manufacturing

defects is eliminated.

4.3.2 _lect_ical Output Corrected for Known Defects

The outputs for the substrings of the 37 cm x 53 cm panel

are shown in Appendix A. At 0° offpoint the average power for

a six element in series substring is 2.14 W after AMO and

temperature correction. This amounts to 0.357 W/element. When

corrected for the poor reflectance of the conic mirror (from

0.66 to 0.98), using the method specified in 3.3.2.13, the power

jumps to 0.419 W. When corrected for mismatch also as described

in section 3.3.2.13, the power achieved is 0.453 W. Performance

at 85°C would be 0.419 W.

An element under 1 sun AMO, 85°C should be capable of

0.162 x .1353 W/cm 2 x pi(2.54 cm) 2 = 0.444 W with a 20%

efficient at 85°C cell in the present design. Correction to

28°c is [I + (57°c) x (.13%/°c)] x 0.444 = 0.47_ w.

The cells used for this small panel were initially 20.6%

efficient at 28°C or 19.1% efficient at 85°C. Allowing for

an increase to 20% efficiency cells at operating temperature,

the current design would achieve (20/19.1) x .453 = .475 W at

28°C at the element level which is very close to the 0.478 W

as expected from the above calculations.

The corrected measurements achieve the capability goals of

the design. There are no unexplained losses in the system.

130
i

I

I

I

FIGURE 4.4: MCC ELEMENT CAPABILITY

NASA NASA

I

I

i

I

I

I

I

I

I

I

i

I

I

I

OPTIC TRAIN

BLOCKAGE

PRIMARY REFLECTANCE

SECONDARY REFLECTANCE

CONIC REFLECTANCE

SCATTER LOSS

GLASSING LOSS

MISALIGNMENT

TOTAL

CELL STACK

CELL EFFICIENCY @ 85++°C

FABRICATION LOSS

TOTAL

PANEL LEVEL

i_ISMATCH

ELEi4ENT PACKING

WIRING & DIODE LOSS***

OFFPOINT ERROR (1.1 °)

TOTAL

OVERALL SYSTEM EFFICIENCY

w/ element

o APPLIES IN MEASURED CONDITION

w/m 2

ACHIEVED

.86

.97

.97

.97

.93

.96

•70(•79)

•138

•89

.123

N/A

.79

.97

.98

.75

.067

(•130)

• 184

(.357)

90.8

3_1_q

ACHIEVED CORRECTED * GOAL

•91 .91 .89

•98 .98 •98

•98 •98 .98

•86* •99 .99**

•96 .96 •96

1.0 1.0 1.0

•99 •99 •99

•714(.81) .822 .80

•194 .194 .200

•98 .98 N/A

•190 .190 .200

.94 .99 .98

•82 .82 .79

.97 .97 .97

•99 .99 .98

•74 .78 .74

•100 .122 .118

.277 .334 .324

136 165 160

++Conversion 28°C to 85°C is .955 factor• Cell average on small panel was .203 @ 28°C.

-Applies in the measured condition•

+Corrected for known manufacturing deficiencies.

*Based on 66% cone reflectance, 0.60 + (0.40 x 0.66) .86

**Based on 98% cone reflectance, 0.60 + (0.40 x 0.98) .99

***Actual losses were negligible• This is shown for comparison to a system design only.

131

I
Based on the achieved weight calculated per element in

section 4.2, the specific power of the design is 29.6 W/kg at

the panel level and 24.7 W/kg at the array system level using

the i00 kW array parameters from NAS8-34131, and the corrected

performance values shown above.

132
!

!

!

4.4 ADVANCED DESIGNS

TO surpass the weight goal of 28 W/kg there are many

categories of change which can have significant impact.

4.4.1 Material Thickness Chanqe

I

I

I

l

I

I

I

I

I

I

U

The optics may be changed from the present 9 mil thickness

to 4.5 mils thickness. Counting only the primary mirror, this

would be equivalent to a 3.8 g per optic drop or 1244 g per

quarter panel for a total of 3307 g remaining or 35.2 W/kg at

the array level.

4.4.2 Material Type Chanqe

With the proviso that the mirror surface could be

replicated and secondarily bonded into place, a 30 mil magnesium

casting could be used to achieve 3.5 g optic drop or nearly that

of the 5 mil copper optic.

The best candidate is to compression mold graphite fiber

cloth whose thermal conductivity is near that of aluminum

structure (66 Btu/hr ft°F) such that no secondary radiator

would be required. Five mils of this material at 1.7 g/cm 3

would total only 0.8 g per primary for a savings over the

baseline of 6.8 g/optic or 2244 g of element weight.

Subtracting from 3168 nominal element weight leaves 924 g.

Combined with the other articles and a 0.5 g element attachment

hardware, the total weight would be 1915 g with .444 W element x

330 = 146.6 W. With 19.5% backup structure, the system watt/kg

is

146.6

or 64 W/kg 1915 g x 1.195

4.4.3 Coatinqs

!

The coverglass may be coated with an infrared reflecting

filter for a potential of ll°C drop or 1.43% improvement.

I

l

I

4.4.4 Advanced Cells

The concentrator may use any advanced cells as they become

available and in a size which may be relatively easy to

produce. A twenty-seven percent efficient cell which has been

reported would increase power to 197.9 W on a quarter panel or

39.8 W/kg.

133

I
4.4.5 Combined

The combined potential of the above design changes could

make the MCC concentrator achieve 1.35 x 1.0143 x 64 W/kg =

87 W/kg.

4.4.6 Manufacturinq

If compression molding were implemented, the piece part

price could be reduced to less than two dollars a part depending

on final complexity.

4.4.7 Offpoint Performance

Quick research into historical analyses discovered that a

focusing refracting lens placed on top of the cone would

increase offpointability by an extra degree. This remains to be

seen with the new element optical design. The lens could be

used in place of the protective glass cover.

134
II

!1

II

I

I

I

i

II

II

i

i

I

!

I

II

I

I

!

5. CONCLUSIONS

The optical design of the miniature Cassegrainian

concentrator (MCC) element has been improved for both offpoint

and onpoint power capability. The cell stack design has shown

no losses under the high short term thermal stresses imposed by

component level test and is projected to be capable of greater

than five years thermal cycle life in low earth orbit. The

structural design met all requirements for stiffness and

flatness and requires adjustable inserts for fine tuning of the

GFRP structure to meet flatness goals. The completed, fully

populated small and large MCC panels deliverable under this

contract perform electrically as expected.

A solid acceptance inspection program to guarantee quality

of all purchased parts, and continued manufacturing process

improvements will make the MCC design a viable low cost

alternative to standard flat panel technology. Minor

improvements to the cell stack design of the MCC element can

make significant improvements in both the performance and

manufacturability of the MCC system.

135

B
6. RECOMMENDED FOLLOW-ON WORK

The following schedule shows recommended follow-on work to

be accomplished prior to acceptance of the MCC array system as a

low risk alternative to flat panel technology arrays.

136

i

I

II

I

I

li

I

If

I

I

II

I

a

I

il

I

i

1

I
O

a=

Z ..j

c_z

X a.0 W _ L _

X"--

u,I 0:

I-v

u-I,-

"T

'...

--_

L'_

,_.-

I

137

I
!

I

APPENDIX A

ENVIRONMENTAL AND ELECTRICAL TEST RESULTS

i. INTRODUCTION

l

I

I

I

I

I

I

I

I

l

I

I

i

I

I

This section presents the parameters and results of selected

environmental and electrical testing performed to support this

contract.

2. ENVIRONMENTAL TESTING

2.1 THERMAL CYCLING

The following tests were_performed.

CONDITIONS TEST ARTICLES RESULTS

A. 200 cycles

-160 to 10°C

20 weld joints to cell, 1 failure due to incipient

cell crack failure

20 solder joints to cell, no failures

6 weld joints to BeO, 1 failure due to Au metallization failure

6 solder joints to BeO no failures

B. 120 cycles

(shock) °

-65 to +124 C

i0 cells mounted on BeO,

i0 silver welds of cells,

15 gold welds to BeO,

3 each Torlon, Ryton,

Peek sliding insert to

fixed insert epoxy bond

no failures no cracks

C. 470 cycles

-150 to+65°C

*(-170 to

+80°C)

small tri-hex panel with

bonded inserts,

*small parts from (B)

above

no failures, partial loss

of epoxy strength but no

effect on capability

D. i00 cycles

(shock)

-80 to +I00°C

Plastic parts as in (B)

except with UV628 bonds,

cone to cover UV bonds,

2 completed unpainted

optic element with

spider bond with UV 628,

sliding inserts with

epoxy 9321

no failures, no visible

degradation

E. i00 cycles

-80 to +80°C

F. 5 cycles

(shock-LN 2

Dip) -196

to 66°C

5 cones with covers,

UV cure adhesive

2 completed optic

elements with SI3GLO

paint (bonds-Dymax

no failures, no visible

degradation, bond strength

greater than glass

no bond failures, no Ag,

SiO coating failures, no

paint failures (passed

UV628, DC93500) tape test)

I

I

G. i00 cycles

+80 to -80°C

(3 openings)

See Figure A-I See Figure A-2

A1
_s

o

.c:

0_ i°°

_ _zI oQ

z_ c_cz _c

A2

L

J

c_

°_w

1--

_Jw

0_

L.¢_

IIIIIIlIIIiIIIiIII
!

I

i

I

I

I

I

I

I

i

I

I

i

I

I

I

I

I

2.2 ACOUSTIC EXPOSURE

The test panel from 2.1G above was subjected to an acoustic

exposure prior to thermal cycling. The acoustic spectrum is plotted

in Figure A-3. Overall pressure level was 146 dB. No failures were

observed as a result of the test.

3. ELECTRICAL TESTING

3.1 CELL ELECTRICAL OUTPUT

The cell data curves for forward one sun, i00 sun, dark forward,

and dark reverse testing are too numerous to present here. All data

is held at the contractor. A summary of the data is provided.

All efficiencies reported below are at I00 AMO sun intensity.

The cells from ASEC all performed between nineteen and twenty

one percent at 28°C with a few stragglers above and below this

range. An additional i00 cells from ASEC produced and received as

replacements for those with contact problems had efficiencies all

above 20% at 28°C. As noted in the text, the Spectrolab cells

averaged 18% efficient with a range of 17.5% to 18.5%. _ The Varian

solar cells averaged 16% with a range of 11% to 18.5%. (Known

contact and batch problems with the delivered lot caused the low

efficiency, but time constraints precluded waiting for another

batch. Cells received for another TRW program all ranged near 20% at

80°C.)

The dark forward characteristics showed no notable changes from

the i00 sun data.

The dark reverse testing for the cells revealed significantly

different characteristics from typical measurements of silicon

cells. The reverse breakdown voltage ranged between 1 and 2 volts

for most samples. No samples exhibited breakdown at any greater than

6 volts. No damage was apparent after reverse testing. For

comparison, 2x4 data for silicon cells typically shows a breakdown

>20V with a range between 5 and 50 V.

A3

I
3.2 SMALL PANEL STRING OUTPUT DATA

The small panel contains MCC elements with copper nickel

sandwich primary mirrors. The best cells of the ASEC quantity were

reserved for this panel. All matching was performed based upon

pre-welded outputs. No equipment was available to match elements

outputs. The MCC elements were arranged in strings of twelve in

series. Measurements were performed on half strings (6 in series) to

avoid some equipment limitations in voltage. After data was gained

on each of the ii half strings, five of the "A" half strings were put

in parallel and measured. The same was done for the "B" half

strings. All data was corrected for solar intensity using a GaAs

concentrator cell transfer standard at 1 sun and corrected for

temperature using the average of two thermistors mounted on the back

of elements and including a known steady state temperature drop of

3°C. Some data may be off by 3 to 5°C at random due to some

transient wind cooling but effort was made to wait for steady state

conditions.

Data for the strings was then corrected for the conic mirror

coating defects as discussed in section 3.3.2.10 using an average

reflectance of 0.70.

Both the data corrected to 28°C and standard conditions and

corrected for the average conic reflectance loss are reproduced here

in figures A4 and A6.

Data for the combined strings are contained in Figures A5 and

A6.

3.3 LARGE PANEL STRING OUTPUT DATA

The large panel contains all nickel MCC elements with various

strings composed entirely of cells from each of ASEC, Spectrolab, and

Varian solar cell manufacturers. Specific kitting may be found in

Appendix B.

Data was measured for individual six element in series half

strings as in 3.2. However a 3 month time lag between measurements

occurred between measurements of elements IA through 4D and 5A

A4

I

I

I

I

I

I

I

I

I

i

I

I

i

I

I

I

I

I

I
lIIlIIIIIIlIIIIIII

A5

I
F--

i

,J

u

A6

._ _, _. _._ _ _,_: ,_ _r- _ _ _

'_ _. _. . _ _

. • • ° . ° _ ° • • • • . • • ° •

_ _ r<r_  ̧ _I_

_ _d _ _ , "_ _:<

_o°_

(_ t_ _ _ _ _ r_ t_ _ _ _ o

I

_ _ _-_ _'_ _'_"1

_ _ _,_i_,_ I

" "i , _' _ _ _ _ _l"l

0

I,

L.IJ

o I

x

,.-_c',<

=_I

rye:-,

="'I __l--

I--

..J

,,0

ORIGINAL PAGE

OF POOR QUALITI
glIIIIIIlIIlII

i

IIil
%0

b.q

q_

$0

_J_

i

t_%

A8

t_

.ii

sl

0 000_

i_"II

IIIIIIII

Z

I-- g

|

O, _._.II _AL P_._Z

OF POOR QUALI]_f

r°.

IiIiIIiI
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

U_

_ c- _. r.I" c- _ , _ ,

l J • ._-_. ' ..:. ri¢-< _.z

_;_: _._ _"_ g._ _,_-

.... _... <%_ _._,.._.

r

%

_JRIGINAL PAGE I$

OF POOR QUALITY

I'Y .,..s ,,.i

• . , . , . . ..: z ..: ..: ....

...: . _:< _ _: _ _ --:-.:--:

._. _'_. , . _ ..: _ _x '

w

-4

-4

-4

q_

v

_,o

A9

_ o _,-_ '_ .... . ,_ _¢:._ _,, .

_, _- _ ,- _._ _ 2_g

.:. <

• . . _, _ 6"- _'- _- _ _

a,....... _ _ _: _ 1"- t",._

! i ! '

I--

f2.

I.a.I

I---

Z

0

I'--

...J

C_

C_

I.l.

t--

l.a.I

C_

C_

¢.D

I--

r'm

_b

I.l.I

¢D

l.l-
°:t

' i

_ _ .O

J

t"

°o,.

• ,_! ._ ,_ .,,_* .,4 o¢ .._*

<1

r_

• ° • " _ _ ,,_ ..4 - -

" • • "_ '_ " .,4 - • •

_-_.r-",:._ . . -_"_-_i_ _'_ o ,

+

I--Z

_N6-!

N

n,

!. '

AIO

ORIGINAL PAGE IS

OE POOR QUAI2T_
I

I

I

I

I

I

I

I

I

I

I

I

I

I

i

I

I

I

through 10D. During that time the panel was stored but not bagged in

the array manufacturing area as well as the test stand. It was noted

that additional contamination of the mirrors was evident. Strings IA

through ID and 2D were remeasured to see this effect. An apparent 1

to 12% loss in output was recorded compared to earlier readings. The

average was near 5%. Also noted was additional conic mirror coating

degradation in terms of actual increases in defect areas. It was not

possible to determine the relative contributions of the contamination

and conic mirror degradation to the total loss recorded. Data for

the remeasured mirrors is noted as strings IA2 through ID2 and 2D2.

As with the small panel data, the large panel data is shown

corrected to standard conditions in Figure A7 and corrected for conic

mirror average loss (0.70) in Figure AS. Note that with reference to

efficiency in Figure A8, an efficiency of 15.5% would represent a 20%

efficient cell in an optic with nominal capabilities as defined in

the main text figure 4-4 "corrected".

3.4 SECONDARY MIRROR TESTING

The secondary proof mirrors (bare nickel) were checked by

bonding each to a dedicated nickel spider and then successively

measuring the short circuit current output of two primary

subassemblies at various pointing angles. Figure A09 shows the

current and normalized output recorded for eight proof secondaries

corrected for intensity only. Figure A-10 shows the normalized data

corrected for conic mirror reflectance of 0.70.

All

I
OpM_MMMMMMMN OFNNNNNNNNN_ O_ MMQ_ONM_NNNNMM_M

.'. ..... -.. ; o ........ o-oo =_ ............ _ ..........

°l.- u_.l

,.,., ,.-._._.":._":._.'_."':.':."':. _ _. _ _,,..._. _. _. _ _. _" "':- _' _" _' _.. ,.,.. • . . .......

o>- _--_--_------ _ "_ ' " "_ o>- N.--.ON ....

L_. t--- _.1--"

_ ........... "_..

ii"- ....... .........." °"-........... .......... °: "-°......

..... ORIGtNAL PAGE Ig

OF POOR '_UAL,IT_f

_ o o=

_ud h-u._ h-Lu _Ud

--_ .......... __ _-_ .......... _ "-_ .......... _ "-,.'5 ..........

gu.h-............ u._-

_= .................... _=, ..........

-- ,_. ,q. ,,_- ,_- ,,_- ._- ,,r ,,_r ,_'- ,_- -- m m un m _,-_ un m un m m _ m m m m m m m u"_ m e_l -- mmmmmmmmmm

oo_o_ooooooooo _ _ _

_ o 9 9 m.o.o.o.o._ 9 _, _ m _ ,_o.o.o._.o.9 9 _._ o. _0_ o.9 9 _.9 9 o.9 _.9

A12

z

o

I--.

--.I

O

C_

z

e_

I--

e_

I---

(:::)

L.I_

I._

t"-

,,_

m,-

0

.._1

Z

'..0

X

m,,,,,

o

I,

I--

I.LI

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

.......... _ .......... _'_'_''"

_ 0__ m_m_ _ _O0_NNm_ _O_m___ ..........

.......... _ .......... _ • ......... _ ..........

___ _=_ ........... _=_ ........... _ _ ...........

_ooo_oooo_o _=_ooo_ .......... ....... _=_RRRRRRRRRR _m_ooo_oooo_o. ........
_ m_mmmmmm_

_ mmmmmmmmmm

ORIGINAL PAGE IS

D]_ _OOR QUALITY

[IIfII

_'cc: ..........

___ooo--oo_--oo

g _=_ ..........,,,,N ............=_,,,,

i,i z

b--

i,i

c_

L.t,.

IIIIIIIIIIII
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

l

I

E

....... oooo _

_ ._z ...... oooo_ = o.oooooooo _ ._z --ooo--ooo_ z-oooooo.ooo

o_ _.............. _=o _-_:_s_ _o_o-_ .......... .... _.O_=o _ ..... ....... _-o_

o_ ........... _ _ ........... _ _ • ._ .... _ . ._ ....

PZ 0 O_ 0

ORIGINAL PAGE IS .....

OF POOR QUALITY

_99999_=_ _ . . ._ ...... 0000

..... o'o_o _ .... _ ......

0

U0

LtJ

(_J

Z

,=[

(-3

I.i.I

LIC_

0

(..3

Z

0

(-3

C_

0

LJLul

I---

(..3

LI.J

m_

o

_.J

×

L_

LJU..
_O _ .......... _ .......... O_ ..........

........... ___

......... _ . . _<__ _ _<__

o=-o ............ W_ ........... _-o ............. o ...........

........... < o ........... < N _ _ =.=._._ =._'_= =

= _

_-_.E_-,.:_ • • ",.: .... _ o ........... _-,-_:N_R_._._._._._._._._. = N_._._._._._._._. _.

...._ ¢n -r' :[ r-_

u_ .... o----ooo ..... o--_ooo _ _ "__; ..... ":...;_ . _ ._._; ..... '-:,_: Z

i

E -- O _, ............ O:=_, .......... N "¢" N&f)-(_ A('_J ) .......... N N OW_ N r'') N t'_'_t_3 r=') N__ &j.j _M ;N, (_ (_, ('_ (_ t"_ (_ (_ t_, t_, I"--'4 I

....... g ,"_

....... PA,JE _S

PO6R Qu .zrg

m m

,==:o o_,_,-.,.-,o o ,=,,=0,o_ ,==:o,o,= ,-.._ o_o o__ ,=, _ =¢=-_,,--,,-,o.,_ o _ o,,..,_ I o_- .......... = oo. .......... =_ =o ,.;o_,:;,..;,:;_,:;,:;,= o=. ..........

Cz: "_" 00_ O0 I',-. m ,:_ _:) 0"_ 0{) _D ;;=

z -oooo-_ooo -_ ......... < ='--:o_c_-_c;c_c_

(-,') F-- u_

_- ._-z -oooo--ooo_. z--,-;o_o,_c_,_o,_ _-" o ...........

_O0_oc_oo

-- _. _ _-_ .......... o _-_ ..........

,.._ tn "5- ,_-

(:3(--} u. _J u-

'_ := ,,=E :%:

I-'0 ...... (J

_-- Z aC.-_ _-_ 0 0 0 m 0 0 0 0 m 0 _: _- ..._ (.a 0 o 0 m 0 0 0 o m 0 F- Z _C--_ C0 0 0 0 m 0 o 0 0 m 0 _:_--.-_ ___ 0 0 0 m 0 0 0 0 m 0

< ..... A16 < ' ' ' < .....
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

- = .... o-oooo _ z o_o_o_ _ _ " ' '_ .... _ --_oooooooo

_ .......... o .......... _ ..... _ .... _ ..... _ ....

_ -- E . ._ ._ .._o>........ .......... o.....

__ o=............ -°°°°'°°°°5 =o ._ooooooooo ......... -N = -oooo--oo05 o_.__

o ........... ._ =o ooooooooo N

-- ,.-;c5c5c5c5.-;c5c5c5c5 _""

U .......... I-" (3 E ;:_ .......... EUE_' ..........

A

La..I

--_

Z

I--"

Z

C_

v

O0

r_

i.-,4

L__
(.D

- I

I

._o....... o....oo_..o___ _'°..........o........ I

£ .... M_..._ o_ .......... Z 00000_000 _ 000o 000 Z 00ooo0_oo0

o ........... _-£ .... _..._ o ........... Z 000000_0o0 _ o000 0o0 _ 000000_00o

_ _m_m_oo_x _mm_m_oo_ 0 _ _O0_mN_ONmX _O0_mN_oNm l

--_-_---------- ==_ ............ _ ............

_ZN_dd_dM_dd_NN_ddd_d_dddM _Z_>___=>____°> ..........

_ _=_ _ _ _=_

_= - .... _ ..... A!8_ ..... <_
EO .......... - __- oz

IIIIIIIIIIIIIII

c_

_ "_oo " ooooooo ........_z _o_£oo_

........... _._-_ ...._ ....

oo_ooo .... _o_ oooo oooo_

...... _._ ..........o

_w_ ww

_ .......... o_ .......... <_o_ ..........

r-,,

LIJ

;E

i-- Z0

CO

oo

,=I:

i,i

r,_

C9

LI-
oRIGiNAL PAGF., IS

oF poor qu,_urr_

_z

-- _ ..... -- .... _ o_ ........... o_ .......... _ ..........

N _ _ _ooo_oooo N o_oooooooo

z _ooo_oooo o _ oooooooo

ooo oooo z o_oooooooo

--ooo--------_o oooo =-----------o-ooo_oo--o o _ _= ---ooo-oooo_ o ...........

_ _E_£_d_£_d _ _ ..........

.......... _ .......... _ _ ............

_- ........... _ =_ .......... N ............

___o___........ _-°°_°°°__ ........... o_ _;==_=___.___ _o_--_-__ .......... ..........

z _oooo_ooo

_N

- z-_oo_o_o_ _ ....... oooooo _ ooo.... _ ........... _ooo_oooo _ oz ........... _ooo_oooo

_< .......................... __ ...........

m_mmmmmmmmmm_ _--_mmmmmmmmmm _mmmmmmmmmm_mmmmmmmmmm_

Lul

Z

hZ

0

C..J

co

L_

(-0

UI

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I
II

_ .|_

I_

IIIIIIIiIIII

.,.J Z00

CONZ

¢3

f_O ¢3

,_. LB 0 I'--

ILl

0--a ,'_ 0

I.I. f.J

nL

_"II Z

Z

I.I.

I.IJ I.I0000

GO

r_

O0

oeoole*_oooeeeeoo_

oo

0

• ..o0 o_.......o..

000

5m

0 c_

00

00

p';

00_

¢M

___o___®...

00N0

......• .... _mm

00

"I0

,-I U

U

V_ e-

%.- _ 0_N

d_-

0__

u

°_,,_

W

°_

00

m0

N

e_

I

A21

I
1n

L__ I

t_Q°

I

°Q1

w

A22 I
I

I

I

I

I

I

I

I

I

I

I

I

II

I

I

I

I

4.0 INSPECTION RESULTS

The small panel was checked and mapped for defects in the

primary mirror coating and for weld joint integrity. Figure All is a

sketch of the defects found.

The large panel was inspected in the same manner as the small

panel. It was noted that 5 mechanically produced nickel conic

mirrors originally machined as test articles with no coatings or

polish found their way onto the panel as noted in Figure AI2. What

is surprising is that the machined parts had relatively small effect

on output of the strings involved. Apparently the coating

degradation is approximately equal in effect to a bare nickel

machined part.

Lack of schedule precluded replacing these machined conic parts.

Figure AI3 presents electrical inspection remarks as determined

during output testing. A number of elements were found to be open or

shorted as shown. The Varian string 10A was not possible to

electrically measure due to the characteristics of the string. Some

elements had essentially 0 current but full voltage capability and

acted as reverse diodes in series with the string. It was not

practical to jumper the effected elements as only 1 element was

actually producing power correctly. This string will be monitored

only for mechanical degradations.

A23

I
\

\

A24

OKIGiNAL PAGE rS

.0_ tK)OR QUALITY

_5

¢MX

_.3

_3Z

i,i

I,

i,!

(.DZ

}..- O

C.)

i,i

¢.D

IIIIIIIIIIIIIIII
IlIlIIi1lI

ORIGINAL P_GE T_

I OF POOR QUALITY I

A25

..J

L_z

0..

t.oX

LL0

V_

I.--

(,_ 0

I'--

LIJ

C_.

C_

L_
I

I

0

] ° I

__ o_

_ _ I

_ _ I

!i ° I

_ I

___. _0

I

I_ _V _'_

_ ®o I

__ o_

_._ I

-_ I

4J_

,-4 ° I

_a

II I_ li ii

i..=i

I

IM

I
i

I

!

!

!

I

I

I

I

I

I

I

I

i

I

I

I

i

I

Appendix B - MCC

ELECTRICAL MANUFACTURING

1. FABRICATION

Items required for fabrication:

CELL I/C

BeO I/C

Spider

Washers

1.1 CELL AND BeO INTERCONNECTS

Approximately 300 interconnects for the cell and BeO cell

mounting were required for the MCC job. Kovar was chosen as base

material due to close match in CTE with the GaAs cell, and by

availability. The Kovar was cut into 0.001" x i" x 6" strips which

were plated with nickel, copper and either silver or gold as

required. Plated strips were then stacked and machined using a wire

electro-discharge process. Cut rates were extremely slow to avoid

fusing strips together and alloying of base material with platings.

Final cut stacks were then separated as individual piece parts.

Stress relief loops were formed in each part using a two piece die;

five parts were formed per cycle. Completed parts were then cleaned

in a solvent bath and protective packaged for later use.

1.2 SPIDER

Approximately 270 spiders were required. Fabrication techniques

were almost identical to those used for the interconnects. Base

material for the spider was chosen as Aluminum; weight was a major

driver. The aluminum plates were stacked as limited by the machine

wire tolerance and, again, a slow burn rate was used to avoid fusing

parts and/or alloying of plating and base material. Cut stacks were

separated and sent to a silver plating bath. The silver plate

allowed the use of solder to bond the secondary mirror to the

spider• The parts were then protective packaged for later use.

BI"
1.3 WASHERS

Approximately 250 Kapton/RTV washers were required for the MCC

job. These washers are used at installation of the MCC element into

the Tri-Hex grid. Commercially available pop-pins (snap inserts)

were used to hold the MCC elements in place. An uneven top surface

of the three elements held by the pop-pins created non-uniform

pressure on the elements, tending to distort the surface or the pin.

Therefore, it was desirable to have a pliable surface between the

element and the pop-pin surface.

This surface was created by making washers the size of the the

pop-pin head. These washers were made from Kapton and RTV. A 0.002"

Kapton sheet was covered with a thin layer 0.001-0.002" of RTV 142.

After cure, the outside diameter of the washers were punched, one

unit at a time. Concentric with the 0.D., an inner circle of

material was removed that matched the pin shaft 0.D., completing the

washer.

82

I

I

tl

i

I

i

I

I

I

II

i

I

I

I

i

I

I

Ii

I
I

I

I

i

I

I

I

I

I

I

I

I

I

I

J

i

I

I

I

2. SUBASSEMBLIES REQUIRED

Washer to Pop-pin

Cell I/C to Cell

BeO I/C to BeO

Coverglass to Cone

Secondary to Spider

2.1 WASHER TO POP-PIN

The completed washer was installed to the pop-pin. Since the

pop-pin shaft 0.D. is much larger at the pressure fitting than the

washer I.D., tooling was required to compress the pop-pin shaft.

This avoided splits to the Kapton washer during installation. The

completed pin washer assembly was then stored for later use.

2.2 CELL AND BeO INTERCONNECT ATTACHMENT

As discussed in section 3.4.2.3, welding was selected for

joining I/Cs to both the cell and BeO pads. Tooling was fabricated

for both of these operations. The cell or BeO were loaded into a

cavity and solvent cleaned. The interconnects as made in section i.i

of this appendix were centered over a locating pin and rotated over

the cell and/or BeO until desired location was achieved (Figure BI,

Left tool). The weld was then made in two places for each interconnect.

The completed joints were then cleaned and the completed assembly was

boxed for later use.

For the cells, all were measured for I/V characteristics prior

to the welding and identified. After a weld schedule had been

developed for each vendor, the cells were then grouped by performance

and welded. It was assumed that performance degradation would be

relatively constant for all cells, by vendor. The cells were

re-grouped by "performance prior to welding," after welding. These

groups were selected to develop a kitting plan to group similar

performance cells at the panel level.

B3
FIGURE B-I. BeO welding tool (left) and conic mirror coarse alignment

tool (right).

_R:)R QUALITY

B4

I

I

i

i

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I

I

i

I

I

I

I

I

I

i

I

I

II

I

I

I

2.3 COVERGLASS TO CONE BONDING

AS discussed in section 3.4.6, several options were evaluated

for joining the cone to the coverglass. This joint was critical in

that the cone must be perpendicular to the glass and that no bonding

material could be allowed on the interior of the cone. Reduced

viscosity bonding materials were ideal for good filleting but

"leaked" under cone to inside surfaces. Higher viscosity materials

did not provide filleting, or the force required for filleting caused

mis-mating of the two components. Dymax 628, a UV curing adhesive

was chosen. This material has a very low viscosity but can be kept

from "leaking" by accelerated cure under intense UV exposure.

A multiple place tool was constructed for this operation (Figure B2)

Five coverglasses were loaded into cavities for loqating and cleaning.

Five cones were then loaded onto the tool and centered by estimation.

Centering spindles made of nylon and match ground to the base ID of

the cone were lowered into the cone and brought down flush to the glass.

The centering nylon could touch only the base of the ID of the cone.

This locked the two components for bonding. A small dot (5 mg) of the

UV adhesive was placed on the side wall of the cone. As the material

ran down the wall of the cone and filleted the coverqlass, it was exposed to high intensity UV light for 10-15 seconds. This operation

was repeated for all four corners of the coverglass. The resultinq

bond was then baked for 30 minutes at 100°C in air to ensure full cure.

Cleanup and rework was accomplished by flushing the bond with

acetone and IPA. Care was taken to avoid contamination of the

interior cone surface.

This bond was tested by thermal cycling sample components in air

from +100°C to -100°C, 200 cycles in duration. Also, sample

components were exposed to acoustic protoqual pressure levels. No

joints showed evidence of delamination or failure.

B5
FIGURE B-2. Conic mirror to coverglass bonding tool.

B6

OE I_DK QUAL[TY_
i

l

I

I

I

2.4 SECONDARY TO SPIDER JOINTS

Adhesive bonding was selected as a baseline process for joining

the secondary mirror the the spider support. This baseline was a

very difficult method. To keep the secondary pointed and true to the

cone, the adhesive layer had to be perfectly flat and continuous.

Low viscosity materials wer e investigated, however, bond strength was

marginal. Paste adhesives resulted in inconsistent bond thickness.

Attempts to eliminate the interface bond and fillet the joint with

paste adhesives were equally unsatisfactory as well as extremely time

consuming to complete.

A secondary system was developed to solder the secondary mirror

to the spider. The aluminum spider was silver p_ated with

nickel-copper base. The interior surface of the secondary,

electroformed nickel, was not prepared. A silver filled solder,

preform was made by wrapping a rod sized slightly larger than the

inside diameter of the secondary with solder wire. Preforms were

then cut from the rod. The spider was locatea on a solder fixture

(Figure B-3, right tool} on its outside diameter. The solder preform was then fluxed in Alpha flux diluted with isopropyl alcohol.

The preform was then located over the spider outside diameter on the

fixture. Installation of the secondary mirror on top of the preform

capped the assembly. The preform was then pushed inside the secondary mirror and held by "spring action" to the inside surface. The

secondary was pressed firm to the spider by slight pressure of a teflo_

pad.

The fixture containing secondary, spider and preform were then

soldered via Vapor Phase soldering on a controlled elevator for time

at temperature. Solder schedules were developed for producing 100%

filleting to the inside surface. Pressure and flux were critical to

achieve wetting to the nickel interior.

None of these subassemblies required rework.

B7
3.1

3. OPTIC ASSEMBLY

Cell Stack Installation

Feed Through Post, Installation

Cone/Core Installation

Painting

Secondary/Spider Installation

CELL STACK INSTALLATION TO PRIMARY MIRROR

The original proposal for installation of the cell stack was to

make one joint at a time, using vapor phase solder techniques.

However, each subsequent joint had to utilize higher temperature

solders to prevent fellow (and misalignment) of the prior joint.

This quickly proved unworkable and expensive. A secondary approach

called for joining the cell to the BeO and the BeO to the primary

mirror in a single vapor phase operation. This method was much more

difficult to tool due to the extremely tight tolerance for placement

of the cell but was chosen over the method above for cost

constraints.

Solder preforms were experimented with and selected at 70% of

the total interface area and at 0.001" thick of silver filled solder

(to avoid gold migration from the BeO). Tooling fabrication was made

to locate the BeO pad and the cell into the Primary. This tool had a

two step cavity (Figure B-3, left tool small cylinder with cavity).

The first cavity held the solar cell, active surface down with its

interconnect. The cell solder preform was then dipped in flux and

placed on the back cell surface. Excess flux here broke cells and

was minimized. The cavity was made slightly less deep than the cell.

The BeO was then placed in the second cavity, over the cell solder preform. The BeO solder preform was then fluxed and added to the Dac_ of

the BeO. This cavity was also slightly less deep than the BeO.

The outside diameter was match ground to the inside diameter of

the primary mirror. A through locating pin aligned the tool to the

primary mirror, where the tool was inserted and pushed flush with the

base of the primary. The undersized cavity created pressure between

all components and the preforms. The tool was then clamped to the

primary by a mating shell with spring loaded tension (Figure B-3,

left tool, hexagonal, with coil interior and leaf exterior springs).

88 •
I

I

i

I

I

I

1

I

I

I

I

I

I

I

i

11

!

I

FIGURE B-3.

ORIGINAL PAGE IS

DE POOR QUALITY,

Cell and BeO insulator to primary vapor phase solder

tool (left) and secondary to spider vapor phase solder

tool (right).

B9
The primary with tool clamped in place, was then soldered in the

vapor phase solder machine. A schedule was developed to ensure good

wetting of the cell and BeO to each other and to the primary. To

maintain schedule, soldering of the cell stacks was done concurrent

with the soldering of the spider assemblies noted in B.4.

The soldered primary was then removed from the vapor phase and

allowed to cool. A vapor degreaser was used to remove the flux from

the tool and completed primary subassembly after soldering and

removal of the clamp. The locating tool was then r_moved. The

primary was then identified with the cell and electrical group

contained within.

This operation caused the worst cell breakage as the GaAs cell

wasvery brittle and had to be held to the center of the primary.

Vent and flux cleaning holes were added to the tool which improved

throughput yields, see attached Figure B-4 This area will be

further evaluated in follow-on contracts.

The completed cell stacks were then protective packaged,

identified, and stored.

3.2 FEED THROUGH POST INSTALLATION

To this point, the interconnected cell and BeO (-)N and (+)P

contacts were floating freely in the primary mirror. Hermetically

sealed feed through posts as used by the printed circuit board

industry were acquired and used to connect the contacts and feed

through the base of the primary to form terminations.

Before assembly, the base of the terminals (ground) were coated

with encapsulent to prevent shorting of the soldered joints. The

back surface of the primary was lightly abraded and cleaned with

acetone to prepare it for soldering. The post was then inserted from

the backside and soldered to the primary mirror using a hand held

iron and silver filled solder. A 50% fillet was required. The

joints were tested for isolation between pin and mirror at 500 V.

Any failures were reworked. Flux was used as required to activate

the surface.

The positive and negative contacts were then made on each

assembly using a hand held iron and a mild flux. The assembly was

held in a fixture so that the operator could make both joints

required without contacting ground (mirror or pin body).

BIO
CO

>--_

LIJ --

CO ©

<0

I

C

0

>E

_u

8 fi_

W

b_

b_

W

Z o

W

°DW

_.1

0

I

_\\\\\\\\\\\\\\\\',_

I I I I I I

0 tO 0 tO 0

W" _0 rO (N O_ _-

(IN3O_J3d)IO]J_](]

I I

0 u_ 0

BII

C_

T-"

O0

_D

©

0

_9

C_

@

@

D

Fh-©

Z

<

@

\L

O©

L_

0

!

H
Because the heated flux tended to splatter and contaminate the

primary mirror, prior to soldering, the mirror was coated with X59

optic cleaner. The cleaner was recommended for use by the TRW optic

lab as its residue is measured in angstroms and it is easily removed.

The toluene base material was coated on the interior of all optics

and removed after soldering with a touch of masking tape applied to a

non mirror surface.

Removal of this material revealed severe plating problems with

the primary mirror plating adhesion.

3.3 CONE AND COVER INSTALLATION

The cone and cover assembly was bonded to the cell using a small

drop of optical adhesive DC93-500. The rightmost tool in Fig. B-I was

used to install and rough center the cone assembly to the primary. The

cone was centered on the cell by visual alignment and tacked in place

by using an elevated temperature cure lamp. After tacking, the assembly

was baked at I00°C for 90 minutes to full cure the adhesive.

Rework for misalignment was easily performed by swelling the

cover adhesive with a chlorinated solvent, manually cleaning, and

rebonding.

3.4 PAINTING

Painting of the optics was probably one of the most difficult

tasks. The paint, SI3GLO a white RTV paint, is difficult to work

with and does not adhere well to nickel or silver plating. Two

surfaces required application of paint - the backside of the primary

mirror and the top side of the spider/secondary assembly.

The primary mirror was placed on a painting aid and bonded in

place with double sided tape. Positions of the optics were mapped to

show identification and the tags were removed. Surface prep included

wipes with acetone and alcohol with one half hour dry times in

between. The posts and the mirror support hole were then masked with

painting aids and the surface was primed with a thin coat of the

vendor supplied primer. The primer was air brushed on in a box coat

to a thickness of less than 0.0003". S13GLO paint was then mixed and

sprayed per the vendor instructions. Approximately 0.001" of paint

was applied per session, with an overnight dry between applications.

The total paint thickness was targeted at 0,003" to 0.004".

812
I

I

I

I

i

I

I

l

I

I

l

I

I

I

I

I

I

I

l

The painted primaries were then removed from the double back

tape by cutting an edge in the tape with an "X-Acto" knife. The

plugs were removed and the flaking paintat these edges was cleaned

with the knife. The part was then bagged and identified from the

map.

Secondary mirror subassemblies were loaded into a custom

fabricated aid for painting. A sheet of neoprene rubber with a best

fit packing factor was cut with through holes that allowed the

secondary mirror outside diameter to "press fit" through. The

neoprene sheet was supported by "lexan" plastic. The spider

assemblies, when placed in the aid, were then masked with masking

tape dots at the to be bonded ends of the spider legs, Cleaning,

priming and painting were achieved using the same procedure as noted

above. The sole exception was that the upper edge of the interior

diameter of the secondary was hard brushed with primer and paint.

The spider assemblies were removed and cleaned using a sharp

knife to remove excess and flaking paint. Special care was taken not

to damage the legs of the spider in removal. The painted parts were

then protective packaged for the next assembly.

3.5 SECONDARY/SPIDER INSTALLATION TO PRIMARY

The secondary/spider assembly self aligned to the primary on

three mounting posts. The interface between the surfaces was cleaned

with acetone and allowed to dry for one half hour. The secondary was

then placed on the primary and three small dots of lightweld 628

adhesive were added. The spiders were quickly tacked in place with

the UV lightsource used in section 2.3 of this appendix. Final cure

was accomplished in an oven at lO0°C for 30 minutes. After cure,

the completed optic was bagged and identified.

B13
4. PANEL ASSEMBLY

Installation of the Floating Inserts

Optic Installation

Harness Fabrication

Series Stringing and Harnessing

Testing and Rework

4.1 INSTALLATION OF PANEL INSERTS

Three candidate materials were installed to the Tri-Hex grid in

the development phase as discussed in the report body. All three

candidates were included on the 66 and 180 optic panels.

Installation of the inserts creates the plane that the optics

rest on and therefore is critical for electrical performance. This

work demonstrated that even though the panel was bowed significantly,

the inserts could create a new plane. The panel was placed on a

granite table with the optic side down. Spacer shims were then added

between the panel and the table rather at random. The inserts were

then slid through the panel from the back side of the panel until

they located on the granite table. (Note: inserts had to be

deburred prior to installation. Burrs were made by the mirror

vendor. )

After insertion, three inserts were selected in the middle of

the panel that made the largest possible triangle. These three

inserts were bonded with UV adhesive noted above, thus creating the

optic plane. With great care not to touch or distort the panel, the

next intersecting and bisecting triangles were selected and bonded.

Soon the panel was sturdy and rested on the bonded inserts; the shims

were removed. The remaining inserts were bonded as these first

triangles, row by row.

The panel was then inverted and epoxy bond (EA9321) added as a

fillet around the top of the insert to add strength to the bond. The

panel was then cured at 100°C for two hours. Rework was

accomplished by solvent and heat gun removal and subsequent rebonding

of the insert on the micro flat granite.

B14
I

I

I

I

I

I

I

I

I

I

I

I

i

I

I

l

l

i

I

4.2 OPTIC INSTALLATION

The first step towards optic installation was development of a

kitting plan. The optics had been identified throughout manufacture

with the original cell output data as well as optic type (several

optics were of Ni/Cu/Ni sandwich construction). Based on original

cell performance data, the optics were kitted to the panel per

attached Figure B-5. Roadmaps were made showing the pedigree of each

optic as it was loaded to the Tri-Hex grid.

After loading, the optic was fastened to the Tri-Hex with the

pop-pin/washer assembly detailed in section 2.1 of this appendix.

Each optic was held by three such pins. Pins were all loaded to the

floating insert and then pressed into position, one at a time such

that the RTV washer captured the lip of the optic, the optics were

all oriented so that the feedthrough terminals were aligned for ease

of series wiring.

4.3 HARNESS FABRICATION

Two harnesses were fabricated for the MCC panels. Both used

rectangular connectors and a three stage potting sequence in a low

boot configuration. There was no ground strap or loop. Fabrication

and cut length instructions are attached as Figure B-6.

Wire used for the harness was a nylon insulated ribbon cable

with 28 Awg wire. The wire was stripped with a laser wire stripper

and separated with a sharp knife. Contact fillers were installed as

required.

4.4 SERIES STRINGING AND HARNESSING

The harness fabricated above was installed to the panel with

lacing ties along the wire bundle. The connector was mounted to the

panel by a twin pair of aluminum plates, mounted with hardware, and

held in place with by clamping pressure across the width of the

Tri-Hex.

Series wiring optic to optic was made with a 26 Awg jumper wire

looped between the Tri-Hex grid and stress relieved. Terminations

were soldered to the terminal feedthroughs using a silver filled

solder and an alpha flux.

BI5
Small Panel:

String

1

2

3

4

5

Large Panel:

1

2

3

4

5

6

7

8

Figure B- 5. MCC PANELS - KITTING PLAN

8

15

15

15

15

68

O tic

Ni

Ni/Cu/Ni

Ni/Cu/Ni

Ni/Cu/Ni

Ni/Cu/Ni

Cell/%

ASEC/19.81-20.1

ASEC/19.81-20.1

ASEC/20.11-20.7

ASEC/20.11-20.7

Set 1

Set 1

Set 1

Set 1

ASEC/20.11-20.7+ Set 1

12

24

24

24

24

24

24

24

180

Ni

Ni

Ni

Ni

Ni

Ni

Ni

Ni

Varian

Varian

Spectrolab 17.51-18.6

ASEC/19.21-20.0

ASEC/19.51-20.0

ASEC/19.51-20.0

ASEC/19.51-20.5

ASEC/19.81-20.1

Set 1 & 2

Set 1 & 2

Set 1 & 2

Set 1 & 2

Set 1

BI6
I

I

I

I

i

I

I

I

I

I

I

I

I

I

I

I

I

I

I

16 Pin (Minimum) Connector- I0 Pin (Minimum) Connector-

(MIN)

PIN# COLOR LENGTH

1 B 65"

2 R 65"

3 B 55"

4 R 55"

5 B 50"

6 R 50"

7 B 45"

8 R 45"

9 B 40"

i0 R 40"

Ii B 30"

12 R 30"

13 B . 20"

14 R 20"

15 B i0"

16 R i0"

(MIN)

PIN_ COLOR LENGTH

1 B 30"

2 R 30"

3 B 25"

4 R 25"

5 B 20"

6 R 20"

7 B 15"

8 R 15"

9 B 10"

i0 R 10"

Figure B- 6. Harness Fabrication Instructions

for 15 x 21 and 15 x 56 Panels

B17
Terminations were made to the harness bundle in accordance with

the attached schematic'Figure B-7. The schematic was developed from

the best fit kitting plan to avoid electrical mismatch degradation.

Terminations to the harness bundle were made using a western union

splice soldered as above and sleeved with a shrink sleeve tubing of

Kynar co-polymer series.

4.5 TESTING AND REWORK

The completed panel assembly was installed on the solar tracker

and tested per procedures noted in the body of the report.

Optics identified with performance problems were removed and

replaced with attrition quantities. Removal was difficult as the

pop-pin is a one way device. The most effective removal technique

was to drill out the pop-pin. A vacuum and shielding were used to

protect the optics and chips were removed as they were generated.

Replacement optics were installed and tested as above.

Thermistors were added to the panel to collect temperature

information during test. Thermistors were bonded to the back of the

primary mirror with conductive epoxy in an area where the SI3GLO

paint had been removed. The paint, however, had left a silicone

contamination which made subsequent bonding with non-silicones nearly

impossible. Abrasion and cleaning resulted in relatively weak bonds.

C-
III

p.I

II

i•

IE

_vvvv

I

B19

I
I

I

BACKGROUND:

APPENDIX C

STRUCTURE MANUFACTURING

I

I

I

I

I

I

Previous NASA contracts and a TRW PMI Program demonstrated

the feasibility of manufacturing a structurally sound tri-hex

grid from a single tow graphite prepreg roving. It was believed

that the low fiber volume/high resin content characteristics of

panels which were previously fabricated could be improved by

utilizing a trapped rubber molding (TRM) expansion process

during cure (see Figure C-l). A major goal of the present

NAS8-36159 contract was to develop this process, resulting in a

higher fiber volume and lower resin content substrate.

Development and co-curing of lightweight molded inserts, thin

uniform wall thicknesses in the substrate and elimination of

tool removal problems were also objectives of this contract.

TECHNICAL APPROACH:

I

I

I

I

I

I

I

I

I

i

I

The graphite prepreg roving materials chosen for evaluation

were 6 K tow T-300/Fiberite 934 (350°F cure) and 6 K tow

T-300/Fiberite 982 (250°F cure) systems. The effect of

different cure temperatures on the TRM process needed to be

established in order to select the best material from which to

fabricate the tri-hex grid.

To establish expected material properties and determine the

structural effect of crossing yarns, six graphite samples were

fabricated using the TRM process. The expandable elastomer

chosen was Dapocast i-i00 silicone casting compound (CTE 10.6 x

10-5in/in/°F) .

The rubber inserts were fabricated in the molds used to layup

the straight and crossover samples by pouring the rubber with

aluminum cores in place which replicated the graphite samples

(see Figure C-2).

Three straight and three crossover samples were

fabricated. The parts were first tested in bending and then

specimens were cut from each part to determine specific gravity,

resin content, void content and fiber volume. Findings are

shown in Figure C-3. Failure of the straight strips occurred in

a buckling mode due to the thin cross section. No structural

degradation was seen in the cross strips at crossover points.

The bending test set up is shown in Figure C-4.

Cl
Z I--

I-- "'

C2
l

I

I

I

I

I

I

l

I

I

i

I

i

I

I

I

I

I

I

Figure C-2. Strip Samples and Tooling.

C3
FIGURE C-3: GRAPIIIIE TRI-II[X SAMPLF FINNING r_

SP[CIFIC RESIN

CURE 20 YARN GRAVITY CONTENT

S_/_.N_ TYPE _ IIIICKNESS(In} _ (%)

3A CROSS 350 .020- .023 I.$461 Z3.0

38 STRAIGIIT 350 .021 - .024 l. 6367 23.5

4A CROSS 350 .019 - .022 1.6367 22.5

40 STRAIGIIT 350 .023 - .027 1.6412 21.7

SA CROSS 250 .019 - .029 1.5248 27.3

SB SIRAIGIIT 250 .O27 - .030 1.5407 29.3

VOID FIBER

CONTENT VOLUME MAXIMUM

(%) (%) BENDING LOAD (LB)

2.9* 67,9 42.50**

O.O 70.1 19.75

0.0 72.1 20.BS

O.O 73.1 20.15

3.9* 66.7 29.35

0.0 64.3 . 21.50

t

NOTE THAT SAME NUMBER SAHPLES WERE CUBED CONCURRENTLY.

* VOIDS,WERE FOUND IN S/N 3A AND 5A SINCE SPECIMENS WERE CUT TO INCLUDE A CROSSOVER POINT, VOIDS WERE

STILL LESS TIIAN THE ALLOWABLE VALUE OF 4%.

** _IE IIIGI MAXIMUM LOAD FOR S/N 3A WAS DUE 10 A LIP WIIICII EXISTED ON Tile EDGE OF TIlE SAMPLE CAUSED BY TIlE

INITIAL FABRICATION IECIINIQU[.

F

I

I

I

I

I

m

I

I _ 1.0§ _.. 2 PL

_c_L_J _J

5,0

o

l

t

_--SEE FIGURE C-3

it

L_

-I--I 11

F

V

II

/

OBSERVED

FAILURE

LINE

FIGURE C-4: CROSS STRIP SAMPLE IN TEST FIXTURE

C4

SBIM

_/_-- EQUALLY 2 PL A/R

//

I

-1F-o,, +:oI

'-r
I

I

I

I

I

I

I

i

I

I

I

I

I

I

I

I

I

I

I

TRIM AND PANEL LAYUP DEVELOPMENT:

Five mini-panels (5.0" x 6.0") were fabricated-two 350°F

cure and three 250°F cure-to develop the optimum wrapping

technique and tooling approach, verify the ability to co-cure

inserts with the panel, and determine the degree of wall

compaction which could be attained in a tri-hex structure (see

Figure C-5). During fabrication of the mini-panels, the optimum

debulking (compaction) schedule was developed and it was found

that debulking after the third, sixth, eighth and ninth course

resulted in a uniform structure. It was necessary to debulk

around wrapping pins after each course. Debulking was performed

using .24" thick x .5" wide stainless steel Starrett shim stock.

Two major tooling innovations were proven out on the

mini-panels. The first was to fabricate a two piece rubber hex

for expansion molding (see Figure C-6). Initially, all rubber

pieces were installed on the layup plate and the tows were

wrapped in between them. This was done since it was physically

impossible to drop full size rubber pieces between the tows

after wrapping without trapping some fibers underneath. A

disadvantage of having all rubber pieces on the mold is you are

essentially working blind since tows cannot be seen. This slows

down the wrapping. The two piece rubber approach was based on

the fact that two rubber pieces with the same volume as a single

piece should perform the same thermally. This was proven to be

true. The two piece hexes were fabricated by placing 1.500"

diameter aluminum plugs in the mold before pouring the rubber

(Figure C-7). The aluminum plugs were removed, the outer hex

rubber was released and the central rubber core then poured in

the same mold. The two rubber pieces were then separated and

the outer hex cut through on one side for ease of installation

in the layup.

The second major tooling breakthrough was the development

of screw pins as wrapping pins (see Figure C-8). Initially,

.125" diameter dowel pins, snug slip fit in the layup plate,

were used as wrapping pins. The tri-hex grid tended to lock

around the pins during cool down making part removal very

difficult. By modifying 10-32 socket head cap screws into

wrapping pins, we took advantage of the "screw jack" effect

which could be used toremovepins from the backside of the

layup plate, thus eliminating part removal problems.

C5
@ •

Figure C-5. Mini Panel with Tooling.

C6

0_" POOR QU_

I

I

i
!iI!II!

C7

Z

e_

...I

c_

c_

e_X

LI_I

"-r"

Fc,,,,- 000

I--

Fe_!

r_

c_

LIC_

i,i 0Z0

I'-- O

p--f

..J

C_

--J

LI.I

I-- x

}--- 0

e_

e_

I-- LJ-
.OE POOR QU;_.L£'rY

figure C-7. Rubber Insert Mold.

C8

!

!
I

I

I

I

I

, i

I

1

I .___

I

I

I

I

I

I

I

I

I

I

I

I

I

/--_0- sT.."THP ,IF

-L ExI gTl,,_-

! il' " I

t:.o_.

v

.17.._:r. ooL _'

_..

Too L. __ i I "

.. "_

,50 ............ "

(:' . _ II ...... -TI-""'F-s F_._., "TO

I II. II (.zo_ s_co_, _v_f_c_

oe -I

c'6oA_

"FIGURE C-8: THE SCREW PIN CONCEPT ALLOWED EASY DISASSEMBLY

OF THE THG LAYUP TOOL AFTER CURE.

C9
The first three mini-panels used machined epoxy glass

triangular inserts as placeholders. Production type injection

molded thermoplastic inserts for element mounting were co-cured

with panels number four and five (see Figure C-9). Inserts were

molded from 30% graphite fiber filled PPS (RYTON), PEEK and

TORLON. It was found the PPS was easiest to mold, requiring

very small gates. These gates had to be enlarged slightly for

injection of PEEK material and enlarged to the maximum for

TORLON. Inserts were tooled to the layup plate using .203"

diameter teflon pins for location and 6-32 socket head cap

screws for angular clocking and tie down.

The method whichevolved as the easiest way to fabricate

the several hundred rubber pieces required for the 15" x 21" and

15" x 56" panels was to pour the rubber into an open mold

overfilling slightly, and then clamping a caul plate with holes

to it. This allowed excess rubber to extrude out and controlled

thickness. De-airing of the initial Dapocast mix was found to

be critical and allowing air to rise to the surface before

covering with the caul plate helped cut down on voids. The thin

cross section of the outer hex contributed to voids in some

parts. This cross section should be increased slightly for any

future fabrication by decreasing the diameter of the aluminum

inner hex mold plug. It was found that post curing the Dapocast

up to 400°F causes a color change from yellow to rust, but

there is no degradation in properties unless continually used at

this temperature. It also happened that one Dapocast mix

resulted in "soft" rubber pieces. They had a Shore hardness of

30 A versus a normal value of 50 A. These soft pieces exhibited

no detrimental difference in CTE when used for TRM.

The overall TRM Process Development Plan is shown in

Figure C-10.

PANEL FABRICATION:

I

l

I

I

I

I

I

I

I

I

I

l

I

I

I

Based on the properties achieved in the strip samples and

evaluation of the mini panels, it was decided to use the

T-300/982 resin system for fabricating the 15" x 21" and 15" x

56" panels. Since this is a 250°F curing system, less

internal stress due to thermal growth is built into the panel.

The 15" x 21" layup tool and panel configuration is shown in

C10

I

I

I

I
III I, II

E=

I II

U_

I=

:b.

I

U_

I.-.

I®r_

I=

I

I®III

na

I

._="G=

II

lu

.J<• _Z ,"_Z

wO wO

>- ..j< .J<:

._-_ 0_ Oo < =EE =E

E

z_ z_

n0 Ow

uJ I.-G. i-a. 0 m om 0 "_n- Zrr ZI- (J -- In- I.-

uJ rr Z uJ

uJ (n

I...Z

U..

Z

Q. ua Z

I-wZi

ul Xi

U.

Cll

L

>-

-Im

I,M<

o'_

.pL._
E

O

m

W

.E

2

=_

I=..

.

,"- t_ eC12
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

Figure C-11. The wrapping pattern is a six tow sequence (one

course) repeated 9 times resulting in a total of 18 tows in each

internal wall. The outer frame has a consistent pattern, but

does not have the same number of tows at every location. To

give a better appearance to the frame and further stiffen the

structure, the frame was covered with T-300 6K tow unidirectional tape (MT3-103-3) around the periphery. This tape has a

350°F curing resin so it is not fully cured at the 260°F

curing temperature, but it has reached the glassing temperature

(Tg) and is securely bonded from the resin in the roving.

The graphite tows were drawn through a series of dies

(.052", .043" and .033" diameters) utilizing the technique

developed on a previous PMI program. This rounds out the flat

fibers and makes it easier to uniformly wrap around inserts and

pins. A 108 style bleeder cloth was placed on top of the layup

and the caul sheet was clamped down with 1/4-20 socket head cap

screws threaded into the layup plate. Rails and inserts were

.450" high, but some rubber pieces were slightly higher so this

extra clamping helped to eliminate loose tows. The panel was

turned over so the bleeder side was down and resin would be

soaked up during the three hour, 260°F, vacuum bag cure. The

15" x 21" panel was easily removed from the mold and met all

requirements (see Figure C-12). The panel is shown in Figure

C-13 with the 15" x 56" layup tool.

Since the tri-hex pattern repeats, the 15" x 21" layup tool

was simply extended to accommodate the 15" x 56" panel. The

layup procedure was the same as the 15" x 21", but the cure

cycle was modified. In an effort to reduce thermal stresses in

the part, it was cured for three hours at 200°F (beyond the

Tg), wrapping pins were removed and the part was postcured for

two hours at 260°F. When removed from the mold, the part was

inspected and found to have a .240" bow. The walls of the grid

tapered from .015"-.028" and this unbalanced condition was

suspected as the cause of the bow. It was decided to build a

second panel using a controlled compaction technique to

guarantee an equal number of tows above and below the center

line of the panel. The second panel was bowed .310" even though

the walls were more uniform (.016"-.026"). This taper was

C13
C

C

C

0

o_c

i.l,-i itl I

0

1"-.

0

\

\

0 0 0

0 0

C14

®

....... f_..

_-_-_ _ _.

_.___.+i

F

ORIGINAL PAGE I$

_0]__:K)I_ QUALITY

O

\\1

i'I
IiIIiiIIIIIIIIIiIII

f

ORIGINAL PAGE IS

OF POOR QUAL;y

0

_ ._ ___§-

- _g

_×

C15

J
Figure C-13.

DRIGINAL PAGE Tg

'_)_ I_)OR QUALITY

15"x 21" Panels with 15"x 56" Layup Tool

C16 III
I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

partially due to rubber triangle inserts allowing fibers to get

underneath during wrapping. Longer pins to secure these inserts

would eliminate this problem. The layup process is shown in

Figures C-14, C-15, and C-16.

The decision was made to straighten both panels to gain

data points even though panel #2 was planned for use as the

deliverable article since it had a more uniform structure. They

were heated to 310F for 16 hours while restrained in the

direction opposite the bow as shown in Figure C-17. Panel #2

was placed back into the oven at 360 ° for 16 hours to further

straighten it. The results are shown in Figure C-18. In

summary, panel #i was flat within .020" after one straightening

and panel #2 was flat within .040" after two straightenings.

RESULTS/CONCLUSIONS:

a. All tri-hex grid specifications for this contract have

been met or surpassed (see Figure C-12).

b. The TRM technique was extremely successful in

increasing the fiber volume of the tri-hex grid

structure.

C. Injection molded thermoplastic inserts can be

successfully co-cured with an epoxy based prepreg

roving.

do

eo

A tri-hex grid can be easily removed from the mold

when screw pins are used.

Thermally induced residual stresses are built into the

15" x 56" structure as a result of aluminum layup tool

expansion during cure, causing the panel to bow. A

graphite layup plate and caul sheet is recommended for

fabricating any tri-hex grid panel with a length or

width dimension greater than 30".

C17
Figure C-14. Drawing TOW Through Die.

C18

ORIGINAE PAGE IS

OF, POOR QUALITY

III
IIIIIIIIIIIIIIIIIII

\

Figure C-15. Layup Process.

C19
Figure C-16.

ORIGINAL PAGE IS

OE POOR QUALIT_

Rubber Inserts Installed in Panel.

C20

III
I

FIGURE C-17: STRAIGHTENING SETUP.

m Caul Plate Weight

o12" x Ig" x 60" r2oO" x 2°0" x 20"

Al Sheet Al Bar

m Both Sides , Panel

\ _____ >.-- _" _

I _>/ _ __

m . .50" x .50 = x 20"

A1 Bar 2 P1

I ,

m FIGURE C-18: 15" x 56" FLATNESS RESULTS.

I _-_ _° I

m

I + -

m PANEL #

I

m

m

m

(Deliverable

m Article)

I

AFTER AFTER FIRST AFTER SECOND

DIMENSION INITIAL CURE STRAIGHTENING STRAIGHTENING

A .000 .000 N/A

B .000 .020 N/A

C .140 .010 N/A

D .050 .000 N/A

E .000 .010 N/A

A .000 .000 .000

B .025 .000 .000

C .310 .080 .040

D .050 .010 .010

E .000 .000 .000

I

C21