Large Program - NASA Technical Reports Server (NTRS)

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Large

Phase and

Program

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Miss_Archi, e_: ....

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Craig

A.

CONTRACT OCTOBER

Roge_£_Warren

NAS_ 1991 -_:5

_

_=

HI/15

_

.

NASA Contractor

Large

Phase

Technology

and

Mission

Craig

A. Rogers

and

Virginia

for

Langley Research Center under Contract NAS1-18471

National Aeronautics Space Administration

and

Office of Management Scientific and Technical Information Program 1991

Antenna

Assessment

Architecture

Polytechnic

Blacksburg,

Prepared

4410

Deployable

I:

Virginia

Report

Warren Institute

L. Stutzman and

State

University

Program

TABLE EXECUTIVE 1.

.

3.

.

OF CONTENTS

SUMMARY

INTRODUCTION 1.1

Mission

1.2

Technology

1.3

LDA

MISSION

to Planet

Objectives

REQUIREMENTS

AND

ANTENNA

FUNDAMENTALS

3.1

Overview

3.2

Main

3.3

Candidate

Reflector

AND

AND

Overview

4.2

Deployable

Trusses Truss

4.2.2

Ring

Technology

4.2.3

Design

4.2.4

New

4.3.1

4.3.2

CONFIGURATIONS

EVALUATION

Deployable

Reflector

CANDIDATE

Configurations

4.2.1

4.2.5

REQUIREMENTS

Shapes

PERFORMANCE

4.1

4.3

Needs

Program

REFLECTOR

DESIGN

Earth

Truss

Technology Review

and Performance Truss

Concepts

Overview

Evaluation for the LDA

4.2.4.1

Truss

Concepts

for a Segmented,

4.2.4.2

Truss

Concepts

for Furlable

4.2.4.3

Ring

Selected

Truss

Radiometer

Concept Structural

Rigid

Reflector

for a Membrane

Panel

LDA

Reflector

Strips Reflector

Configuration

Surfaces Rigid

Facets

4.3.1.1

Design

4.3.1.2

Manufacturing

Furlable

Evaluations Considerations

for Rigid

Facets

Surfaces

Ul

PRECEDING

PAGE

BLANK

NOT

FILMED

4.3.3

4.4

4.5

4.6

6.

Preliminary

4.3.2.2

Panel

Deployment

Membrane

Analysis

Sizing

Analysis

of Furlable

4.3.3.1

Design

4.3.3.2

Manufacturing

Surfaces

Evaluation of Furlable

4.4.1

Practically

Inextensible

Membrane

4.4.2

Membrane

Design

Material

4.4.3

Deployable

Motion

and

Reflectors Selection

Alternatives

and Controls

4.5.1

Introduction

4.5.2

LDA

4.5.3

Antenna

Motion

4.5.4

Actuator

Technology

4.5.5

Power

4.5.6

Vibration

Control

4.5.7

Summary

of Motion

4.5.8

Scan

4.5.9

A Scan

Motion

Train

AND

Requirements Systems

Considerations

Technology

Kinematics

Electromagnetic

SUMMARY

Segments

Reflectors

4.6.1 .

4.3.2.1

Selected

Scenario Designs Electromagnetic

Configurations

CONCLUSIONS

REFERENCES

iv

EXECUTIVE

The Large

SUMMARY

Deployable

availability Mission (OAET) Year

of critical

long term

The

goal

from

Program

for passive

of GCTI

specific

documentation

the 1987

goals

Sally

and understanding

Ride report

The

for the fin'st phase

of the LDA

technologies

Develop preliminary study team.

mission

study

wide

range

.

2. 3.

team

generic was

of skills

Principal Virginia

technologies

program

composed and

of university

experience,

Investigator: Polytechnic

Dr. Warren Stutzman, and State University

Dr. Craig Institute and Department

and

Astro

was

The study approach involved geosynchronous wide-scanning

The study

(rather

than

specifications)

team performed

a detailed

with

precise,

concepts

for

wide

the

Mission

the

to

referring purpose

deployable

scanning

presented

radiometer

concept

of

passive

to the study

presented

team

to the

reflectors.

researchers

Engineering,

of Mechanical

and

technologists

with a

Company, Aerospace

of Mechanical Virginia

Engineering,

Engineering,

Polytechnic Virginia

Institute

Polytechnic

Inc. Company,

Inc.

Inc. Inc.

from

determining radiometer

and enhance

to:

A. Rogers, Department State University

Aerospace

received

large,

industry

of Electrical

Mr. Ed Derby, Composite Optics, Dr. Brian Lilly, ANT Technologies,

as goals

for

the following:

Dr. John Hedgepeth, Consultant, Astro Mr. John Rule, Composite Optics, Inc.

Thomson,

large

including

Dr. Harry Robertshaw, Department Institute and State University

Additional input NASA Langley

will be required

is a concept

observations

were

for each

to support

Mr. Mark

8. 9.

the

as a system".

Administrator,

global

for

architecture

5. 7.

and demonstrate

to enable

of the earth

of the radiometer

4. 6.

which

needed

to the NASA

space-based

Determine the critical and prioritize them.

Evaluate

sensing

the technology

Review the technology state-of-readiness radiometers up to 60 GHZ.

•

to investigate

microwave

"is to provide

to the endeavor of making long-term, understanding earth system processes. The

was initiated

and for the NASA Office of Astronautics, Exploration and Technology Technology Initiative (GCTI) which is scheduled for initiation in Fiscal

observations,

Earth,

(LDA)

technologies

to Planet Earth Global Change

1991.

Planet

Antenna

the Electromagnetic

Advisory

basic operational parameters from which specific structural which

specific

technology

review, V

technologies evaluated

Panel

convened

by

and configurations for a requirements were used could

be evaluated.

the feasibility

and technology

readiness team

for a dual-reflector

also developed

IV launch

radiometer

a system

vehicle.

The

design

study

with a target

resulted

largest

deployable

stiff

IV or Space

Shuttle

A passively

controlled

thermal

controls

Segmented

'stiff'

requirements Several

with

an areal

density

concepts

have

the reflector

surface

accuracy

surface

identify

suitable

deployment

variations,

thermal

suitability

for ground

An

deployment

active

investigated •

Further

study

team

accurately support design and

goals,

the

requires

a deep

truss

and

at 40 GHz. designed

developed

to meet

using

a gore

The

manufacturing

quantify edge

scheme

surface

the surface

or

maximum

accuracy

strip

approach

to

width

to satisfy

the

techniques;

accuracy

distortions

and

for

stiff reflectors

constitutive

model

design

as a function

deployment

in the following

using

that a specific

mission

a reliable

of manufacturing

load

variations;

and

designs. antenna

assessment

mission

point

the

alloys

has been

studies.

can then With

design

vi

configurations. meter antenna for a 20-30 is needed focus,

be proposed these

to efficiently

of the

for which and

and

technology

or determination

specifications

can be completed.

designs. m antenna.

in order

state-of-readiness

of a mission

be determined. and

focus

and

selection

configurations can

memory

for further

area:

architecture Upon

shape

formulated

review and assessment of 20-30 of remote sensing requirements

electromagnetic

technology

in diameter.

testing.

configurations.

requirements

in a Titan

reflectors may be possible for sizes up to 40 meters basic fundamental investigations are still needed to

scheme;

also concluded

determine specific

control

detailed

been

develop

stresses,

is needed

Technology Determination

4. The

been

from a 40-meter

can be stowed

reflector)

configuration

Detailed EM analysis of the baseline Examination of alternative radiometric

.

2. 3.

The

of 2.4 kg/m 2.

membrane several

and a detailed

study

reflector.

to stow in a Titan

be reduced

which

(parent

requirements

3 m 2 have

down

is 12 m.

materials;

mechanical

meters

on the truss structure.

requirements

Practically inextensible in diameter. However,

20-25 radiometer

about

should

configuration

the accuracy

reflectors

'furlable'

deploying

40-meter

scaled

conclusions:

configuration

dual reflector

is approximately

to satisfy

radiometer

in the following

The deployable dual-reflector radiometer baseline to a 20-25 meter baseline. The

size of 40 m for the main

for a deployable

specific

to

of specific structural

requirements,

a

1.

INTRODUCTION

1.1

Mission

to Planet

Earth

In August of LEADERSHIP

1987, Dr. Sally K. Ride published "A Report to the Administrator" and America's Future in Space, which defined four potential U.S. space

and evaluated

them

retain

space

study

and

leadership evaluation,

exploration States

in light

and each identified

obtain

Exploration Outpost Humans program

all time

The

changes

The principal

function,

concept

accurate

- than

Mission

to Planet

Implementation proposed While

current

needed

scope

- either

the United four

selected

to Planet from

Earth,

a

space

to

Toward

with data from comprehensive

that

end,

Science

develop

of human

the

and

is to how

to evolve

of the Earth

gathered

of an integrated

by describing

be expected

to eventually

is that data

can be compared which are more

goal of this initiative System,

they may

or as a result

Earth

of Space

The

Earth

on

System,

the capability

activity."

over

a decade

or more

earth-based observations - and presumably more

guiding

principle

approach

behind

to observing

Applications)

initiative

the

the earth. has

been

[1-2]. of Aeronautics, particularly

will be necessary of CSTI

The

afforded

understanding

in order

naturally,

to Planet

(Office

us.

and how

a fundamental

is the adoption

1992

(Office

for and

restore

of Mission

use the perspective

will affect

interact,

models.

Initiative

missions,

efforts

the 5-year for the (GCTI)

OAET

near-term

technology

present-day

Year

activity."

of the entire

to that system,

occur

of this OSSA

for Fiscal

OSSA's

how they

of the Mission

Earth

if adopted,

is in support

changes

is to develop

might

would, of space

initiatives in science

on a global scale. Specifically, the mission is "an how forces shape and affect its environment, how that

those

global perspective for global change

any

report

understanding

of changes

that

candidate

achievements

and

System

that would

planet planet,

and how

challenge

from a space-based to produce models

in this

scientific

and of the consequences to predict

which

to regain

on the Moon to Mars

our home our home

components scales.

four

NASA's

desire

Earth

by the task group)

is changing,

the nation's

identified

on sphere

of the Solar

described

a comprehensive

and

group

proposal

to Planet

3.

(as described

its various

task

are:

2.

program

"builds

by the report

study and characterize initiative to understand environment

stated,

aggressive

Mission

technology

Dr. Ride

in a particular

4.

program

The they

space

of leadership

.

The

[1-1]. which is a bold,

to a position

initiatives

of the current

entitled, initiatives

[ 1-2].

the

Exploration,

and

Civil

Technology

to progress

To ensure

Space

into

availability

the next

Technology) era

of earth

of the technologies

programs

Initiative

support

(CSTI),

observation, which

new beyond

will be required

Mission to Planet Earth, OAET is developing a Global Change Technology Initiative for initiation in Fiscal Year 1991. The goal of this initiative is to provide the technology to

enable

understanding In July of 1988,

and

enhance

of the earth an Ad Hoc

the

long-term

observation,

documentation,

and

scientific

was formed

to determine

as a system. Review

Team

on Space

Technologies

what

technologiesmust be developedin the nearterm to supportMission to PlanetEarth. In their report entitled "Technology for the Mission to PlanetEarth" they describedthe major space segmentsfor the mission [t-2]. The threeproposedmission classesthat form the spacesegmentsfor the Mission to PlanetEarth are the Earth ObservingSystem(EOS), the Earth SystemExplorer missions,and the advanced GeostationaryEarth Scienceplatforms. Eachof thesespacesegmentsdescribedin detailedin the report "Technologyfor the Mission to PlanetEarth" are given below. EOS, a seriesof low earthpolar orbit platforms,eachcontainingmultiple scientificinstruments, is being planned to begin deploymentin the mid-1990s. Subsequentlauncheswill provide growth in the number and quality of remote sensingcapabilitiesthrough the year 2000, and continuousoperationof the systemat full capacityuntil at least2010. The EOS mission will createanintegratedscientificobservingsystemthatwill enablelong-termmulti-disciplinary study of the earth. The secondspacesegmentis a proposedseriesof Explorer-classmissionscalled Earth Probes, andthe useof well-establishedinstrumentsmountedon long-termplatforms suchas the space station. In additionto thepowerful synergismswithin EOS, thereare someobservingneedsthat require other low earthorbit (LEO) configurationsor dedicatedspacecraft. The third possible spacesegmentof a total systemfor global earth observationconsistsof advancedplatforms in geosynchronousearth orbit (GEO). Foremostin the advantagesthese platformswill offer overotherplatformsis thecapacityfor high temporalresolution,limited only by instrumentdesign andcost, to be brought to bearon the study of rapidly changing,global atmosphericphenomena.This type of orbit also would provide a fixed referencegeometryfor a given earth location, facilitating data analysisand interpretation; this advantagehas been demonstratedby operational geosynchronoussatellites,in service since 1974, which carry imager/sounderinstrumentsproviding high-resolutionvisible and infrared imagesof the earth. The infrared channelsof the sounding instrumentsyield frequent temperatureand moisture prof'flesover large areasof the earth. Another major advancewould be passive-microwave sensingof regionsof precipitation. For the technology program described in this report, the passive-microwave The

Ad

Hoc

sensing

instrument

Team

on Space

Review

for the geosynchronous Technologies

stated

microwave sounding is not now available because spatial resolution at GEO altitudes." This specific

current

earth

in their

focus

orbit

report

is

advanced that

on

the

platforms.

"the capability

of

of the large antenna required for adequate technology need is the motivation for this

program.

1.2 The

Technology objectives

technologies another

Needs

of the must

ad hoc group

measurement

of

technologies

have

Ad

Hoc

be developed

Review

of the Committee

precipitation so far remained

Team

on Space

in the near term to support and

soil

on Space moisture

unobservable

Research as from

2

high space

Technologies Mission

was

to Planet

(COSPAR), priority

they new

but should

to determine

what

Earth.

with

have

Along identified

technologies.

be developed

the These

to measure

global changeparameters. To determinethe technologyneedsaccurately,the scienceneeds,priorities, andrequirements must be def'med. Once the sciencerequirementsare specified, specific mission and system planningis thenpossible. The technologyreview teamidentified a lack of coherentarchitecture as hamperingtheir discussionof the Mission to PlanetEarth andGCTI's supportof it. "The committeefelt hamperedin their ability to assessOAET's GCTI plans becauseof insufficient mission andsystemplanning andanalysis." Adequatedefinition of architecturewas viewed as prerequisiteto their addressingmany technologyissues. NASA however, has had a basic assumptionthat full implementationof Mission to PlanetEarth will includeplacing observation platformsin GEO. This assumptionhasinfluencedNASA's selectionof key technologiesto be emphasizedin the GCTI. NASA's scientistsand technologistsfeel that a major advantageof GEOs for earthobserving platformsis the ability to acquirecontinuousobservationswith high temporalresolution,i.e., to be able to stare at a scene. Earth systemprocesseswhich require high temporal resolution observationsalso require high spatial resolution. Despite the substantiallygreateraltitude of GEOs over the orbits of the EOS and the Explorer-classmissions,the phenomenaobserved require the highest possible spatial resolution. This in turn meansgreaterrequirementsfor precisionpointing and platform control. Technology developmentsin precision pointing and vibration control for remote sensing instrumentsare important for the accuratepointing of multiple instruments and for large radiometric antennas. In the technologyreview teams' report they often used an 80 meter diameter antennaas a baselinefor evaluating the technologyissues. The goal of the GEO platform is to allow simultaneousandcontinuousobservationof theearthby multiple instruments with minimal interference. Advancedsensorsand detectorarrayswould permit remote sensingacrossthe electromagnetic specmamfrom the microwave to the ultraviolet. Three regions of the spectrum, the submillimeterrange(300 to 3000 GHz), the millimeter range(30 to 300GHz), andthe thermal infraredrange(5 to 20 microns),areespeciallycritical for understandingglobal climatechange. The region from 1 to 200GHz was cited as being particularly usefulfor metrology. The technologyreview teamalsoidentified a particular needfor large precisionantennas.They madethe following argumentsconcerningthe technologyneedsfor large antennasystems. "Largeprecisionantennaswouldenablemicrowavesoundingwith adequatespatial resolutionfrom geosynchronous orbit. Sinceit is estimatedthat abouthalf of the earth'srainfall occursin short-lived,small-scalestorms,resolutioncorresponding to the size of these storms (10 kin) is neededto provide complete rainfall monitoringdata. Observationsat 36 GHz with anearthfootprint of 10km require an antennadiameterof 40 meters. Theselarge antennaswould requireprecision shapecorrectionandsteeringto allow coverageof the globe,eithermechanically or throughreceiverarmyadjustments.Measurementsaboveabout36 GHz require solid surfacereflectorswhile lower frequencymeasurements can uselarge mesh reflectors. Unfilled aperture or interferometric techniquescould provide an 3

alternative approachfor the large antennasneededfor frequenciesless than 36 GHz. Special microwave-transparentstructuralmaterials may be necessaryto achievethe instrumentperformancerequirements. Array feedswill be required for effective offboresightpointing andscanning." Another related orbit

technology need Technology

environments.

developing should

and characterizing

include

subelements materials structures.

scaling

up

for large may

new and

platforms

the

High

structural

materials

characterizing

precision

not provide

Conclusions:

is advanced materials for both low earth and geosynchronous research in long-life materials and structures will be aimed

priority

promising

new

reflector

support

and

required

specific

items

for long-term

stiffness

associated

with

operation.

material

systems

structures;

into

1.3

LDA

Program

The NASA Concepts,"

and

thermal

stability

the

science

aspects

of these

Contract a program

for very

of the

for a Large

Deployable

application

of large

Antenna modular

(LDA).

The focus

reflectors

concepts/designs

for accomplishing

the mission.

components

Phase

and selection

and sketches.

this

which

the

II will consist

of a point design,

The specifications

effort,

possess

team

was

Virginia

The

charged

primary

Tech

expertise

implementation

made

mission

complete

with

objective

assembled

mission

of technology and vibration

a part

of the

identifying technologies of the LDA

suitable

detail

evaluation

Large

technologies,

of existing

hardware

specifications

the completion

of this

for follow-on

development

and

technologists

industry

and electromagnetic as well

technology

of critical

engineering

such that after

of university

readiness

(6 - 60 GHz)

Science Geophysical of the most feasible

and testing

procurement

structures,

to the focus program

and

is technology

frequency

the Earth definition

with preliminary

a team

in the areas of controls,

of these

wave

of the development

shall be of sufficient

has

of this effort

missions from oriented toward

task, these specifications can be used to initiate a new of a test article to demonstrate technology readiness. For

been

to millimeter

radiometers for future NASA Global Observation Platform (ESGP). Phase I of the program was to support

have

large

Task is entitled "Definition of Large Deployable Space Antenna Structure involving the detailed definition, assessment, and selection of conceptual

for

antenna

items

available

Objectives

designs the

All

structural

currently

included the passive microwave remote sensing which resulted in a number development needs, including advanced sensors and detectors, precision pointing controls, and advanced materials. Deployable Antenna program.

at

This research

technology.

as innovative

This

approaches

to

mission.

is to demonstrate

by means

of ground

test articles

that the technology is available for a large-deployable wide-scanning radiometer. To this end, the focus of the Phase I and II efforts is to develop concepts and configurations for such a flight article,

determine

the

state-of-readiness

technologies,

perform

articles

will demonstrate

which

can be specified

trade

in a future

studies

of the and

technology,

down-selection

the state-of-readiness RFP.

4

evaluate of alternate

and design

and

prioritize

technologies,

such items

to a degree

the

critical

select

test

that they

The test article(s)requirementsare straightforwardto determinewhen the objective of the test articles is kept in mind. It is necessaryto accommodateanticipatedmission requirements associatedwith the critical componenttechnologies. The plan for determiningthe test article requirementsfollows. 1.

Evaluateall the radiometerconfigurationsproposedby the EM Advisory Board Determine

.

.

the essential

ground-test

article

Beginning

with

NASA-LaRC, for each .

5.

critical

mission

Virginia

test article

component

architecture Tech,

technologies

specifications

the EM Advisory

component,

needed

performance

as

Board,

compiled

determine

criteria,

to be demonstrated

and

Develop

the technologies

As a starting adopted.

point,

Please

the following

note

article

that as the trade

studies

of the parameters

listed

presently

from

The

global

the

science

expended requirements

missing mission

to determine and

achievable

design

the list (e.g.,

control

been

the overall

objectives Because

upon

and

and designs there

parameters)

and

set.

of the radiometer of the complexity

specifications.

in turn,

1.3-1 begin

and

by

which

A great

will

circulate

selected

in (2)

Fig.

1.3-1

were

to appear,

that

some

are many

will be impossible

will be determined in a somewhat science and structural communities

requirements

who,

in Table

Likewise, related

agreed

goals

progress

and specifications

have

specifications.

hardware requirements the electromagnetics,

design

will be inconsequential.

requirements

requirements

that demonstrate

test

on

specifications

etc. Tech

configurations(s)

iterated

the design

Circulate the selected design specifications to Virginia to NASA-LaRC AMRB for comment and review test article

in a

must

parameters

instrument(s) of the instrument,

are

be added.

to f'trmly deal

that

determine

of

effort

and

until

is being

the necessary

the science

and

iterative fashion. Interaction between will be needed to achieve realistic and

I _,_Focal

Focal Length 60m

q.

./"7

Surface 0.1ram

Accuracy RMS

!

I_.. I-

Main Reflector 40m I_.

Diameter

1

_1 "-I Offset 40m

I y

Figure 1.3-1. Initial Test Article Requirements

6

Point

Table Test

1.3-1

Article

Design

Parameter

Goal

Frequency

Range

6 to 40 GHz

Bandwidth

Antenna Focal

Size

Consideration least two feed

for placement of at assemblies should be

given

6 to 40 GHz

to cover

Aperture)

1.0 to 2.5 (present Configuration

Offset

Dual

Reflectors

array

feed

40 m (see Fig. Surface

Reflector

GHz)

60 m

F/D

RMS

(60

40 m (Circular

Length

Antenna

Goals

Accuracy

goal is 1.5) with

an

1.3-1)

0.1mm

Surface

Lightweight

Membrane,

approx.

1 kg/m 2 Assembly

Deployable

Package

Volume

(Entire

Instrument)

Thermal Mechanical

Titan

Differential

IV (4.4

m x 15 m)

I00 °

Scan

As required

7

to achieve

scan

steering. Goal the mechanical

is to minimize motion of the

main

reflector,

subreflector

and

feed system

and

2.

MISSION

NASA

AND

Langley

September sensing

hosted

1988 issues

selected of low determine

were

vertical

water

of rapidly

evolving

vapor

events

periods

-

of the GEO

the antenna A resolution

system. From GEO very of 20 km is a long range

Without

that need

microwave

preempting

be a modest

A single

sized

from

antenna

from

out of reach

for quite

not

sensing

process

to feed

feeds

sometime.

of the

surface

GHz

(with

resulting

a hopeful

problem

designs

antenna

can

systems

Table

2-1

gives

design

from

1).

complete with

This in turn leads

global

scan

increasing

arrive

because

technology

6 to 220 GHz

characteristics

challenging Another

aspect parameter

to a narrower

(see

line

4).

can be tracked

based

of interest

mechanical

reflector

a

design,

large

especially

at the classes of the large

of antennas feed

network

microwave Also, there

from

Panel

concluded

that microwave

GHz).

be that

It may

turn

out

two completely

that

separate

and 60 to 220 GHz. of a 40-m

beamwidth large The

seems

and RF front ends is equally to an upper frequency limit of

to 60

or it could

6 to 220 GHz

diameter

circular

reflector

(see line 2).

number

required

at midband in electrical

Therefore,

of beamwidths wide

scanning

antenna. (see size

to accomplish

of scan

is required

is perhaps

the

most

of the design. to the radiometer

approaches,

Table 2-2, part a, gives physical b gives beam efficiency values smooth

upward

without

designer

is that of beam

efficiency

power in the main beam to that in the entire pattern solid angle). Beam efficiency by system configuration and surface roughness. Since surface accuracy is a strong of candidate

to

observations

For narrow beam types of reflectors.

channels

the EM Advisory

(+ 8.6 °) an increasingly

frequency

earth

events LEO

A 40-m diameter was selected because it results in a 20 krn ground resolution line 3 of the table). Note that as frequency increases the 40-m antenna increases (see line

been

is used

permit

is the radiometer

the necessary

6 to 60 GHz,

and

GEO

from

we can quickly

of similar

evolve,

goals

have

the reflector.

In addition,

be used

eventually

in

remote

beams are needed for ground resolution. This, of course, requires a large aperture

risk technology

to cover

extension

(GEO)

From

possible

components much above 60 GHz for use in the feed assembly distant in the future. Therefore, we have redirected our attention 40

6 to 220 GHz

the

orbit

as hurricanes.

narrow antenna goal at 6 GHz.

are high

used

with multiple

Platforms

meetings,

sounding

geostationary

such

remote

Arrays

array

Panel

Microwave

which introduces loss and noise problems for the radiometer. antennas, this leaves reflector antennas; there are, of course, many could

Geostationary

from

atmosphere.

something

the design

to be considered.

channels

precipitation

taken

At the heart

antenna.

the

and

data

meteorological

for long, continuous time constellation of satellites.

Frequency

through

These

Science

EM Advisory

Some channels are at atmospheric windows (frequencies surface observation, while other channels are off window

sounding

the atmosphere.

for Earth

and subsequent

discussed.

these parameters. allowing earth

temperature,

through

Workshop

At that workshop

for ESGP

for

REQUIREMENTS

the Technology

[2-I].

to observe attenuation)

frequencies

ANTENNA

feel for the numbers

must

distances for two electrical lengths for typical reflector illumination

and the same random

on the null locations

a basic

surface

for the smooth

error cases.

reflector 8

(M.C.

The beam Bailey,

(the ratio

of

is affected determinant

be introduced

early

on.

of RMS surface errors. Part for the cases of a perfectly efficiency

NASA

LaRC).

calculations Remote

were sensing

engineerswould like to haveabout95 percentbeamefficiency [2-1]. The tablerevealsthaton the order of X/50 surface accuracyis required which is about 0.1 mm for our 40 (60) GHz antenna. The parametervaluesfor the baselineantennadesignshownin the previouschapter(Fig. 1.3-1) were arrived at from remote sensingrequirementsdescribedabove,constraintson technology developmentin the future, subcontractorreview, NASA input, andEM Advisory Panelreview. The dual offset reflector with an array feed is not "the" design,but one which is rather simple in structureand hassomeevidenceof providing electronic scancapability. Table 2-1 Design Goal andCharacteristicsof a 40-meterReflectorin GEO Frequency 6

10

18

22

31

60

Main Reflector (wavelengths)

800

1,333

2,400

2,933

4,933

8,000

Half power beamwidth degx 10.2

8.16

4.90

2.72

2.22

1.32

0.82

Ground resolution(km) (23dB beamwidth)

60.2

36.1

20.0

16.4

9.7

6.0

Beamwidthsof scanfor

+105

+175

+316

+388

+652

±1054

1.00

0.60

0.33

0.27

0.16

0.10

+8.6 ° Surface error required in mm for k/50 RMS

Table of a 40-meter

Characteristics a. RMS

Surface

f I

Reflector

Antenna

Error _,

(GHz)

2-2 Circular

_./20

(mm)

I

_./50

mm

mils

I

mm

mils

6

50

2.50

98

1.0

39

37

8.1

0.41

16

0.16

6.4

50

6.0

0.30

11.8

0.12

4.7

220

1.5

0.075

3.0

0.03

1.2

b. Beam

Efficiency

Smooth Reflector 98%

L/20 Surface Error [

-70%

_./50 Surface Error [

-93%

3. REFLECTOR CONFIGURATIONS

FUNDAMENTALS

Conventional

design

antenna

developed design,

for (3)

the

consists

application

Mechanical

of

at hand

design

AND

these

CANDIDATE

steps:

(1)

(communications,

and

construction,

Performance

radar, and

(4)

specifications

or radiometry),

Measurement

are

(2) Electrical of

electrical

and

mechanical performance. This is a serial process with each step being completed before the next. In this project these steps have not been performed in a serial fashion. The research and development and

effort

mechanical

has been

designs

ongoing

were

while

performed

remote

sensing

at the same

requirements

time.

This

evolve.

was

nature of the program; it is complex and pushes the state-of-the-art components. This requires that the steps be performed iteratively. That implications of a particular electrical must be relaxed or electrical design This

section

antenna

3.1 The

identifies

design

was

reflector

configuration changed.

reveal

fundamentals

and

an inferior

candidate

electrical

because

of the

in many technology is, as the mechanical

design,

remote

configurations

sensing

from

goals

which

the

initiated.

Overview ESGP

antenna

design

design

problem

holds

that are most

many

challenges

challenging

elements

associated

antennas. Therefore, the design launch and long life in space.

then

for wide scanning. Scanning can, of course, be accomplished assembly, as is usually done on the ground. However, mechanical in space. is required;

experiments

that require

Figure

illustrates

3.1-I

a stable scanning

is that it provides

waves. 3.1-1c)

The reflector merely a parabolic reflector

rapid

However,

performance

efficiency

the reflectors

fundamentals.

no focusing

for waves

is lower

and

a large

arriving

from

such

as gain

degradation

array

directions loss

and

offers

feed

the incoming a plane wave

but with the poorest It focuses (but not

than

of Fig. 3.1-1

in the

process

must

design

be

of large

by slewing the motion creates

other

undistorted

is required

waves. arriving

to collect

The

the arriving

At the other extreme (Fig. parallel to the axis of the

than along

pattern

scanning.

the axis of the parabola,

distortion

scan properties. to a point) and

occurs.

The

parabola

The spherical reflector has scan capability. Its

that of the parabola. scanning

motion.

antenna

Electronic

feed).

trade-offs

A flat reflector

acts to redirect sharply focuses

case of no main reflector (or array

fundamental

the

scanning.

platform.

offers the best aperture efficiency of Fig. 3.1-1b is a compromise. aperture

the

with

wide

Drives and controls are required. Momentum compensation for this is a major problem on ESGP which also carries laser and other

penalty

reflector.

in mind

two

space entire

many problems antenna motion

dearly

the

size and ii) its required

It is important reflectors reflector

to have

but

are: i) its large

These would also be challenges for earth-based tempered with a goal of simplicity to facilitate

With

Also,

necessary

The

offers instantaneous beam positioning can be avoided by switching between

is achieved most

scanning

elementary (either

in the ways method switched

and even multiple beam fixed feeds as illustrated 10

illustrated

in Fig. 3.1-2

is to physically or phased)

move

for the the feed

is the alternative

that

possibilities. Mechanical motion in Fig. 3.1-2b. A full array feed

a) Flat reflector:

b) Spherical reflector:

Full scanning, no focusing

Figure

3.1-1.

a) Movement

Figure

(Fig.

3.1-2.

3.1-2c)

Scanning

of Reflectors

of the feed assembly

Implementation

b) A switched feed

of Scanning

solution

without

(assuming

full

spectrum

mentioned approach We are,

above, illustrated therefore,

configuration. reviewed.

of scanning full

methods

mechanical

Movement

available

slewing

is no clear

cut

answer

represented

is to be avoided

11

the appropriate

to compensate

are

to our

of the Main Reflector

in that

weighted

in Fig. 3.1-2 will require a very left with using a hybrid approach

There

c) Full array feed

no motion)

elements can be properly amplitude and phase well as main reflector surface distortions). The

Limited scanning, focused

Partial scanning, partial focusing

Properties

is the best

c) Parabolic reflector:

for scan degradation

in Fig.

if possible.

large array and or with finding design

problem

3.1-3. The

associated a clever in the

For

(as

reasons

electronic-scan feed network. electronic scan

literature

we have

Electronic

Mechanical

complexity

complexity

Only electronic scanning

Full slewing of antenna system Switching of feeds in under illuminated

Mechanical movement of feeds or

Mechanical movement of feeds and

aperture

subreflectors

subreflectors

Hybrid electronic/mechanical

Figure 3.1-3.

3.2

Main

There

The Trade-offs

Reflector

are a few

summarize

plane

waves

properties The

Shapes

classical

of Fig. 3.2-1

(the

focal

are summarized

parabolic

torus

of

Fig.

3.2-2

spherical

reflector

than

plane

cylindrical

which

scanning may resolution.

reflector aperture

has

along

reflector

of Fig.

because

use.

it focuses

to high gain (high

circular

3.2-4

has

array

been

aperture

In this section

incoming

aperture

a straight

feed along

used

by feed

we

(on-axis)

efficiency).

azimuth

cross-section the axial

Arecibo

displacement. larger

and

multiple

simultaneous

in applications the

with a reflector

12

in

efficiency

and separate

has

example,

scan

associated

circle

3.2-3

A linear

For

cross-section

of reduced

of Fig.

achieves

the costs

a

the focal

efficiency.

is stationary be worth

are in common

popular

This leads

the penalty

parabolic cross-section in elevation. steered to scan the beam.

important

that

is the most

point).

With

be placed in the azimuth obtained from each feed.

The

shapes

Scan

on the figure.

in elevation.

parabolic

reflector

types.

reflector

to a point

cross-section

The

main

the fundamental

The paraboloidal

in Scanning Reflector Antenna Systems

beams

may

can be

in azimuth

focal

and

line can be phase

where

1000-foot

parabolic feeds

scanning diameter

Potential than a paraboloid

for

is more spherical wide

angle

for the same

Y

Parabo

X

(Q_I¢) Civic

•Scanning

in

displacing

feed

the focal • Phase gain

point errors

AZ

and

may

however, arrays

accomplished

switching)

in the

by

linearly

plane

through

F. induced

loss and pattern

-Arrays

EL

(or feed

be used

this requires

in the aperture

during

scan

cause

degradation. to correct amplitude

3.2-1.

in AZ accomplished

switching)

along

gain aperture

phase

and phase

errors,

weighting

reduction

•Scanning

and

paraxial

or beam

phase

by feed movement

focal

arc with no scan

(or feed induced

degradation.

in EL identical

•Cylindrical

can be large.

Figure

•Scanning

to parabolic

errors

in

case.

AZ

plane

degrade

performance.

Paraboloidal

Reflector

Figure

3.2-2.

Parabolic

Torus

EL

AZ

AZ

• Scanning •Undistorted a linear •Scanning Figure

scanning

array

in AZ accomplished

(or feed

feed.

in EL identical 3.2-3.

by phase tilting

Parabolic

scan to parabola. Cylindrical

induced

• Spherical Reflector

Figure

13

in AZ and EL accomplished switching) gain

phase 3.2-4.

along reduction errors

Spherical

paraxial

or beam

degrade

by feed

focal

degradation.

performance.

Reflector

movement

sphere

with

no

3.3

Candidate

After

an extensive

Configurations literature

reflector

antenna

represent

the range

development, of possible

scanning 3.3-1.

methods

with

the

search

accompanied

several

candidate

configurations promise

configurations

available

of wide

scan

Table Candidate .

Switched

Partial

Dual

2.2 Array-Fed 2.3 Cylinder .

Electronic 3.1 Dual

Diagrams

of the configurations

companies

were

selected.

all reflector They

are

Feed

Corrected Torus

Type

Electronic

Tri-Reflector Dual

Reflector

Scanning (Foldes

Reflector

with partial

2)

Spherical

(Foldes

Type Type

1) 3)

movement

Scanning Parabolic,

Array-Fed,

3.2 Array-Fed

Dual

3.3 Array-Fed

Cylindrical

are given

Reflector

in the following

14

Gregorian (Foldes

Type

Reflector 3)

Reflector

figures

(Figs.

The

summarized

Reflector (Foldes

involved

shapes

3.3-1

Mechanical,

2.1 Array-Fed

capability.

or Moveable

1.2 Tri-Reflector 1.3 Gregorian 1.4 Parabolic

including

with

Configurations

Feed

1.1 Bifocal

.

by contacts

3.3-1-10).

with

candidates

and different in Table

o

.o_ LU_O

t--

•-_

_

rr

05 [..-

o -.--. tO.

0 OJ

0 ¢_ r.-

ea "-a

.--

¢00g

o 0

ON c-

o °-0

0

_r-

n-

.__8 i.k¢_

E

_

o

_

0

_

'_

L,L

m

c_

"0

0

r"

0") °

°

_>

g_

0

0

,-'-

• 0

15

--

U.

16

1?

._=_

o

=

E

_

0

0

.o _

_

E o _

_E o

_ ._ o

0

0

0

"l_

= o

0

_

.=_

} •-=

ogo _

___o_ _ 0.

18

..Q "13 0 t--

0

._o _. mE

,-. 9

o

t_

_8 o_

-

_

°

[

.__-_ _ .=- >o.

e_

_-___ __

8o

•

19

_

_._

_ _ _

0_

o O3

_

.__ 14.

4.

DESIGN

4.1

PERFORMANCE

I of the "Definition oriented

towards

the objectives

definition

will discuss

Technologies

considered

surfaces,

to the more

Many

of

the

inclusion

range

technology

evaluated

been

4.2

The

Phase

or further

been

LDA

configurations.

a LDA

evaluated

design

goals

listed

that

antennas.

based

upon

This best

in Table

reflector

their

is to say that

utilizes

its unique

1.3-1.

In the case was the

approaches to accommodating large deployable space warrants further study and will have utility in future into

Trusses

I LDA

Truss

Technology

study

has progressed

for precise

for the

approach

membrane

have

into

for the LDA.

and furlable

studied.

support

Overview with

of a reflector

semi-rigid solid surface. One may ask for reflector surfaces are often integrated is used

inextensible

by the design

an instrument.

considered

i.e. pactruss

chapter

included

such

However, not all the technologies described in this chapter will be carried of the specific performance requirements as described in Chapter 1.

Deployable

required

designs

has

was judged not to meet the stated performance requirements an attempt the maximum size of the antenna or component that would enable

Deployable

4.2.1

and physical

program

for accomplishing

to support

of conceptual

and is judged

to be utilized

missions. II because

Concepts"

concepts/designs

technology

state-of-the-art,

in this

designs

Smactures

antenna

i.e. practically

This chapter contains several novel design structures. In each case, the technology space Phase

feasible

current

discussed has

Antenna

the existing

concepts,

physical

of interest

the technology to determine

from

exploratory

characteristics

Space

of the most

and evaluating

technologies

technology

Deployable

the technologies

in preliminary

performance where made

of Large

of the LDA

This chapter

each

EVALUATION

Overview

Phase been

AND

small

solid

is attractive

used at extremely dishes by hinging

dishes

Hexagonal

Panel

and the resulting

[4.2-2]

panel-only,

concepts

on

that an area

is composed

communication

structure Ingenious segments

concepts

that

if a truss is even necessary, with the reflecting surface

flying

high frequencies. between adjacent

the assumption surface

shown

structure

will be rigid

or

since supporting structures itself. Indeed, this approach

satellites.

can be made

truss

of a segmented

The

dimensionally

simplicity stable

of this

enough

to be

concepts have been devised for deploying larger as in the TRW Sunflower [4.2-1] and the Harris in Figs.

also use well established

4.2-1

fabrication

and

4.2-2.

techniques

Integrated-structure,

and appear

or

to be of low risk.

They are, however, structurally "thin," so that small fabrication or thermally induced errors in individual parts grow into large distortions for large sizes. In addition, such structures are difficult

to test in a one-g

produce

deflections

It is therefore component measurements The

difficult

parts

experience

environment.

that are large

to passively

with enough

obtained

during

and information

Their

flexibility

in comparison achieve

precision ground obtained

to those the

desired

or by "trimming"

combines

with

acceptable

for the present

accuracy,

the gravity

either

the structure

by

loading

to

application.

fabricating

by adjustments

the

based

testing. by studies 20

and

tests over

the past two decades

have

on

_4s-- i

Deployed Figure 4.2-1. TRW Sunflower

Stowed

Deployable Reflector Concept

11

Figure 4.2-2. Harris Hexagonal Panel Deployable Reflector Concept

2l

shown

that

structural

high-precision

configurations

surfaces

than

this notion intuitively achieved with careful constructed

from

2-meter

struts

showed

an expected

had

surface

error

by testing should

in a one-g

be able

Numerous As

field

concepts

previously

for remotely

a deep-truss

support

efforts;

panel

Single-fold package

the robustness

segments

length,

poses a severe breakdown and surfaces Dynamics [4.2-11-15].

to nest,

truss

with

by a robot.

Another individual shown periphery using

a robot.

possible, One

precision that have

for

worst

of 20

of 100 cases

of the deflections

100 micrometers;

been

flew

gravity

with solid

devised

caused

compensation

reflector

for deploying

integral

surfaces large

but structurally

on the SEASAT

simplified

has been studied This arrangement

thereby

saving are

exist.

dishes

thin support.

spacecraft.

The

10.75

double

are

surface,

intelligent would

only

meter

the

deployable

Research

modules require

of the fact

truss

surface

has

for achieving

than

the

vehicle

available

configuration.

in both directions.

been

demonstrated

this is proposed

This

by General

that

and some each

aid in control

which

is

later

can be assembled Center

being

canister locking effort module

in the report.

to the deployed

on such robotic

reflectors in remote its associated support

in a deployment

would

and testing.

and by Martin Marietta with the Box Truss doubly curved panels onto a deep support truss

at Langley

would

smaller

on the launch

and the panels

deploying

hinging

diameters

the reflector

large segmented of a panel and

canister

for

structures

a concept

stowed

integration

truss geometries are notoriously difficult to attached. Stowage of flexible mesh reflector

truss

separately,

analysis,

was by

volume.

depending

to divide

fold

be made The

by One

for possible use with reflector antennas. One has the advantage that it allows the doubly

package

useful

is in progress

These

to its neighbors.

concept

variation

is supported by a deployable truss. A feature of this truss is that the radiating panels are stowed and deployed while

can be stowed

4.2-4.

Use

The

analysis

antennas

have

however,

Research

of this

large

Not only is

of magnitude.

10 to 15 meters,

deep,

of the reflector

development

with

error of 43 micrometers.

or panels

concept for constructing modules, each consisting in Fig.

lengths

error of about

it will be necessary

truss

for

7].

an RMS

using their Geo Truss [4.2-8-11] Autonomous deployment of rigid,

supporting

suitable

random

concepts

concepts

has yet to be accomplished, The

more

4, 5, 6 and

that very high precision is tetrahedral-truss structure

problem because double fold stow with rigid reflector panels

integrally

much

[4.2-3,

analyses have shown of a 20-meter-diameter

of the configuration

approximately

reflectors,

are

Refs.

This structure, which supported an L-band antenna (7L = 20 cm) 2.5 mm maximum deflection. This was achieved and demonstrated

truss-stiffened

For larger

"deep" See

Furthermore,

structure

A similar deployable truss concept of these is shown in Figs. 4.2-3. curved

surface

aperture radar antenna to the LDA application

to the truss. to better than

careful

RMS

deploying

several

with

have

an RMS

segments

long synthetic that is crucial

which

that by an order

adjacent

antenna

attached accurate

showed

mentioned,

between

are ones.

of 72 micrometers.

to decrease

hinging

"thin"

obvious, but also detailed fabrication. A simulation

micrometers, an RMS

that

are the

which each but

moves

around

to its neighbors. seems

would

the The

to be easier

be hinged,

of the canister extensively

assembly.

locations employs truss section. It is

than

so far as

motions. studied

for

various

high-precision applications is the Pactruss shown in Fig. 4.2-5. The deploying truss in this concept is very strongly synchronized and offers reliable deployment with a few actuators. The design

of the Pactruss

is flexible

in that its geometry 22

can be altered

to make

it compatible

with

i

Stowed Figure 4.2-3. Synchronously

Deployable Concept

23

B (Crest) for Stiff Panel Reflectors

Figure 4.2-4. Sequentially

Deployable Segmented

various

geometries.

types

compatible The

with rectangular

triangular,

This version parallelogram Figure

4.2-7

double-fold

of reflector or more

depicts Pactruss

stiff panel

correctly,

is compatible units on the

The

segments.

segments

form

Pactruss The

the geometry of the truss which hybrid

of the Pactruss,

or flexible

the paraUelogram

with surface

a hybrid

square

Reflector

form

strips

shown

of furlable

of the Pactruss

in Fig. 4.2-6, reflector

is shown

is composed

of six single-fold will stow around

PACTRUSS

i0

f,

,

f,,

Y U[|_UYI

panels in the

radial

beams

a central

if the figure. and six

body

_0 t_ll'

)t_w__

°

I_AN VI[W

24

I!._

I_ I'l AN V IL W U| i't IIyI

Figure 4.2-5. Pactruss Concept with Triangular Form

such

CONCEPT

0

PARIIAII

material.

in Fig. 4.2-5.

of hexagonally shaped stiff are tilted 60 degrees as shown

configuration

is

D

51t)Wt'i)

_o

Elevation

View

Perspective

View

Figure 4.2-6. Views of Pactruss for Offset Paraboloid as a feed

structure

or cryogenic

for descriptions 4.2.2

Ring

Several

of recent

Truss

types

which are held reported below. The

inflatable

a rim

that

torus

very

reliable.

sandwich

technology composite [4.2-18]. Inflatable viewed suitable

balloon, with

of precision

have

structures, as being materials needed

difficult

to "tune

Another

ring-type

wheel. As shown by stays or spokes.

while

is not a truss Examples which

ring

The

Mylar-film

being

vigorously

for very up,"

even

structure

See Ref. [4.2-16]

sheets

and

forces.

of membrane

Some

the reflector include

by

slow

the ECHO

in the space

age.

an aluminum

during

ground

that is capable

stow

without

in a radial

for lower

In addition, testing.

passive

core.

More

foil

frequency

inflatable

Adjustments

of supporting

was developed

fashion

inflation was

antennas,

are

with and

is

satellite,

a

composed recently,

antennas, in orbit

a membrane

and 25

are

by Astro deployed

once

seem

reflector

fabricated,

are

to be impossible. surface

is the wire

that is deployed state to provide

utilized

for Rockwell by

are generally

herein. The available coefficient of thermal

The folding ring approach has been at Langley Research Center.

wires

surface

Its shell

in Fig. 4.2-8, the wire wheel is composed of a folding ring The spokes also load the ring in compression in its deployed

ring

designs

since the early 1980s developing a Kevlar-epoxy on orbit after inflation. See Refs. [4.2-17] and

promoted

high precision.

reflectors

of these

membrane

inapplicable for the high frequencies being considered lack the long-term dimensional stability and super-low

folding

segments

early

support

is deployed

trusses

launched face

support

assembly

of inflatable was

for the

by distributed

but it does

load.

the appropriate stiffness and precision. of the hoop-column antenna structure A deployable

with hex-panels.

applications.

developed

work in Europe has been underway surface which is cured and hardened

expansion

The

been

configuration

a compression

100-foot-diameter of a thin

proper

type

and is compatible

Review

structures

in the

carries

intuitively

evaluations

Technology

of ring

equipment,

in the design

in the late 1970s.

a circumferential

scissors

252 Nodes 1014 Struts 264 Redundants

Stows around a central body

/

/

Pactruss

Singlefold beams

Each beam and Pactruss sector is unique for an offset configuration. Figure 4,2-7. Five Ring Hybrid Pactruss mechanism. launch 4.2.3

The

vehicle Evaluation

A simple

ring

payload

segments

space

flame

structures

which

can

be no longer

than

the

bay radius.

of Deployable

two-dimensional

are

analysis

Truss has been

performed

26

to estimate

the structural

depth

that wiU

be required for the 40-meter-diameter LDA configuration to passively maintain the required accuracy. The derivation of the equation used for this analysis was based on the lattice rectum equation

for the rise

height

of a shallow,

circular

arc.

The

f'mal form

of the equation

is:

AEL _ h -- -_

(4.2-3)

8(zXS)

where:

h is the beam AS is the rise L is the length AE is the strain

(truss) height

depth

of the arc segment differential between

the outermost

STOWED

0RUM

J,

surfaces

of a beam

ROTATION

°°* *// HIM

HINI;t

UPPER

RIM

TUSI¢

_

NN_,

(truss)

.."

_

STAY

GORE

LOWER STAY

PARTIAl.

. LOWER

DEPtOYMENT

STAY

'_R

)

RIM

TUmE

_

RIM

Figure 4.2-8. Wire Wheel Schematic

c_n. 27

STAY

For the required LDA shown that a specific deviation

from

the

configuration, RMS accuracy ideal

approximately valid localized undulations

feature

A8 can be set to 0.3 mm. This is because experience has (0.1 mm in this case) can be achieved if the maximum is approximately

whether the deviations of the surface.

three

are

due

times

to gross

the

RMS

changes

value.

This

in curvature

Shown in Fig. 4.2-9 is the relationship of the strain differential Ae to the depth, h, for the LDA to maintain a maximum deformation Ae of 0.3 mm.

required

is

or more

structural

40

35 30

25 40m Truss Depth H, m; 20

15

10

selection of truss depth of approximately 3.3 meters. _

5 _1

Microstrain

limitation imposed

by

I

I

I

I

I

I

I

I

10

15

20

25

30

35

40

45

0 0

5

Ditferential

Strain Through

50

Depth, Microstrain

Figure 4.2-9. Truss Depth and 4.0 m Panel Thickness vs. Microstrain to Limit A_ to 0.3 mm

The value of AE that is chosen represents the maximum through the depth of the structure for any reason. This maximum thermal length errors, and microstrain extensive stated structural

LDA

depth

differential that is anticipated will be a combination of the

distortion between the truss front and back, fabrication imperfections such as scatter in the CTE of the composite material. Experience has shown that 5

is a reasonable thermal insulation

in the

strain value

value for Ae, although achievement of this value may require of the structure due to the 100°C maximum thermal differential

baseline

requirements

is approximately

list.

With

the

maximum

Ae set

to 5 microstrain,

3.3 meters.

Therefore, the structural configuration required is a truss with a minimum depth of 3.0 to 3.5 meters. This depth is required to insure that the LDA requirements for passive accuracy control can be maintained.

A mass of this depth

will be composed

4.4-meter-diameter

of the

launch

convenient

STS

or Titan

vehicles,

for packaging.

28

of members which,

that are shorter

incidentally,

than

will prove

the

to be

4.2.4

New

New

Truss

truss

Concepts

concepts

generated.

for

that

one new

compatible

with

truss

has been

panel segments, furlable reflector surfaces.

semi-rigid

reflector

As explained in Section 40-meter-diameter LDA

4.2.3, a truss configuration.

highly

At least

are

the LDA

articulated.

Such

achieve

high

payload

dimensions

a doubly

a structure

reliability.

curved

The

truss

of the Titan configuration

be used to create

high

double-fold

stiffness.

a variety

4.2.4.1

Truss

studied

in some

PSR capacity,

depth

strongly folded

current

as part

rigid

membrane

type

during

vehicle.

elements

of the reflector.

concepts:

depth is required that the structure

its diameter

Finally,

for the will be

deployment

exceeds

It must such

been

to

all of the

also deploy

as standoffs

into

need

the truss should

not

be very

sections, are, in general, based on the Pactruss. satisfy the needs for reliable, highly synchronized deployment

is very

flexible

into

doubly

curved

in that its geometry

area

trusses

is readily

and

altered

to

geometries.

for a Segmented,

the Pactmss

launch

have

precision.

geometry,

the Pactruss

reflector

for one-piece

synchronized since

structural

in the following to simultaneously

of reflector

Concepts

be very

for support

packaging

requirements

for each of three

and a ring truss

be doubly

of the proper

In addition,

accommodate

must

performance

of 3.0 to 3.5 meters characteristics dictate

IV or any other

shape

achievement

The truss concepts, described The Pactruss can be designed deployment,

strips

structure These

must

LDA

conceived

so that additional

a parabolic

stiff to promote

the

Rigid

of NASA's

supports

Panel

Precision

hexagonaUy

LDA

Reflector:

Segmented shaped

The

Reflector

reflector

Pactmss

(PSR)

panels

has

program.

of optical

been In the

precision

on

three points. This panel configuration dictates a triangular Pactruss geometry such as that shown in Figs. 4.2-7. The PSR approach to attachment of the hex-panels to the truss, however, requires extravehicular

activity

Hexagonally One method 130 or more

for deployment segments

be

Due to the limitations 40-meter LDA accordion-folded meter

A concept

with

robotic

was

assembly

techniques.

and

would

be

Pactruss are

for deployment

shown

in Figs.

panels

to fill

meters

approach

have

been

A minimum the

into five rings in diameter

The depicted

chosen

and

of the

task might

more

in Figs.

4.2-5;

for further

Rectangular into the surface of 13 rows

40-meter-diameter

that are appropriate

4.2-10

panels

deployment 4.0

be staggering.

canister

reflector panels. rows on tracks built

configurations

of square

would

in Fig. 4.2-6.

required

be about

to be too complex.

rectangular

segmented into long

Additionally,

will

mechanized

also considered

such as that shown

geometry

truss.

panels complexity

the

of hex-panels,

panels

conceived

since

mechanical

with rigid, and deployed

Pactruss square

rectangular been

The

accomplished

this approach

geometry

onto a backup

is required

is 40 meters.

reasonably however,

or advanced

shaped panels do not readily lend themselves to autonomous deployment techniques. has been described in Ref. [4.2-2] and is shown in Fig. 4.2-2, but this approach is

not appropriate aperture

by Astronauts

of the

panels can be of a rectangular

and columns

LDA

for the LDA

study

aperture. requirements

of 3.1 Two have

and 4.2-11.

onto the truss

29

is shown

in Figs.

4.2-12(a-d).

This

o |

o.- = 0 O.

0 U.,.

/

/ u.O

,_,

'5 0-

0 U.

u.O

3O

deployment width must Fig.

concept is however not appropriate be less than the payload maximum

4.2-12(a)

is rotated

90 degrees

for a 40 meter aperture, diameter of 4.4 meters.

so that a larger

panel

stack

because the panel stack If the package shown in

height

is possible,

the stowed

• 6 x 6 Bay Paclruss support structure slaown

Accordian-lotdeO

l

panels

• 6 x 6 Rigid Panel Array Pactruss wilh an alongalsd

configuration

Plan View

Figure 4.2-12(a).

Square

panel deployment

concept

- slowed

Elevation

• 3 bundles

of 6 panels

attached

Figure 4.2-12(b). Square panel deployment

to Pactr,

JSS surface

battens

concept, partially deployed

surface Iongerons Deployment

tracks along

X

_

Panel bundles rotate 90_

\ Elevation

Figure 4.2-12(c). Panel deployment

concept, Truss deployment 31

complete

Pactruss

is then limited

to less

than the allowable

2 times as long as its deployed will be utilized more efficiently The

concept

Deployment 4.2-12(b). lined

provides

diameter.

A stowed

Pactruss

is about

depth. If the panels are rectangular, the payload cross-section and the panel stack height limit is the length of the payload bay.

the possibility

of truly

autonomous

deployment

with

relative

simplicity.

of the Pactruss synchronously unfolds the bundled rows of panels as shown in Fig. Once this is accomplished and the Pacmass is fully deployed, the bundled rows are

up along

one edge

to be perpendicular unfolded

payload

of the truss,

to the

accordion

style

truss

in tracks

panels

face

parallel

as shown

on the truss • Simultaneous • Sequential

deployment deployment

to the truss in Fig.

face

as shown

of all rows of two

rows

face.

4.2-12(c). in Fig.

They

must

The

panels

then

be rotated

may

then

be

4.2-12(d).

shown at a time

is an option

Figure 4.2-12(d). Square panel deployment concept, Reflector deployment Figure

4.2-13

shows

panels

in the launch

how vehicle.

the Pactruss Although

would

be stowed

autonomous

separately

deployment

from

the

3.1 meter

of this configuration

is probably

3.1m

2,0 m

Rigid panel reflector surface 145 panels 3.1 mx3.1 Paclruss 4.0 cm diameter

members

4.4m

IE = 15.3m

Figure 4.2-13. Primary Reflector Stowed on Titan IV 32

square

m x 6.0 cm

impractical,

the figure

illustrates

that

a 40 meter

diameter

rigid

paneled

primary

reflector

with

6.0 centimeter thick panels will fit into a Titan IV with little volume remaining for other constituents of a complete radiometer space craft such as the secondary reflector, feed and feed support

structure,

panels would of 145 panels

bus and

solar

arrays.

Composite

Optics

has

indicated

that

3.1 meter

require a shell and rib structure of about 12 centimeters thickness. 12 centimeters thick alone exceeds the maximum payload length

the geosynchronous launch capability. Obviously, a 40 meter diameter segmented, instrument will not be feasible until one of the following situations applies: New

.

launch

2.

Orbital

3.

Materials

4.2.4.2

Truss

vehicles

assembly

such

from

several

with several Concepts

as HLLV

orders

for

originally conceived by Composite a cigar-shaped bundle for stowage. 40-meter-long deployment. The

strips

rectangular

launch

Pactruss

vehicles

is deemed

greater

panel

Reflector

acceptable

swain

Strips:

The

accuracy/stability

are available.

furlable

concept

reflector

Optics, Inc. (COI) as a one-piece dish that can be rolled For the LDA configuration, the reflector must be cut

that can be rolled

geometry

rigid

are available

of magnitude

Furlable

square

The stack height of a Titan IV in

onto parallel

designs

tracks

described

built

into the supporting

in the previous

section

truss

and

was into into

after its

shown

in Figs.

4.2-10 and 4.2-11 are appropriate for the deployment of long, narrow, furlable strips. The rectangular truss configuration, however, requires that each furlable reflector strip have a unique figure whether it occupies a row or a column in the surface pattern of the truss. It would be desirable aperture. strips.

to have only one type of furlable strip, such as a gore, that is repeated throughout the Therefore, only one mandrel would need to be made for fabrication of all the furlable

A plan view

of a gored

truss

geometry

for an offset

aperture

is shown

in Fig. 4.2-14

The

truss

would be made from adjacent tapered beams that are identical except in length. The long edges of the beams radiate from the apex of the parent parabola. The design of a gored truss is aided by an aperture

geometry

that is significantly

together to one point at the apex. geometry; however, other geometries gored approach to deployable truss Stowage

of the Pactruss

with

furlable

furlable

packages

can be attached

vehicle

as shown

in Figs.

4.2-15.

offset.

This keeps

the truss

It may be possible to design may be found to be appropriate design. strips

is much

to the outer Figure

more

longeron

4.2-15

efficient

struts

depicts

which

furlable

edges

from

converging

such a truss using Pactruss upon careful review of the

than

with

rigid

stow vertically strips

that

panels.

The

in the launch

are one

truss

bay

wide. When the truss is deployed, the bundles of furlable strips end up in the proper position for deployment by rolling out onto tracks or ruling surfaces built onto the truss face. More detailed concepts for actual deployment forthcoming sections of this report. 4.2.4.3 designed PacRing, precision

Ring using

Truss

Concept

Pactruss

of

for a Membrane

geometry

and is shown

furlable

Reflector:

strips

A new

in Fig. 4.2-16

like the Pactruss, is highly synchronized during without the guy wires or spokes often associated 33

onto

concept

a

truss

are

for a ring

with its deployment deployment and with ring trusses.

discussed

in

truss has been sequence.

is capable

The

of high

Furled reflector (typical, others

gore not shown)

._..,

1.7m • Truss • Fuded

Figure

4.2-14.

Gored

Truss

Plan

with identical reflector

View

tapered

gores

beams

of different

roll out towards

aperture

lengths axis

Concept

A

I 4.4m

Furlable Pactruss 4.0 cm diameter

reflector

surface

12 bundles o! reflector strips 3.5×40 m

members A

L Figure

4.2-15•

Primary

-,e--35 -=, 18.3 m

Reflector

Stowed

on

Titan

IV

34

m7.0 m

! Figure 4.2-16. Pacrlng Support for Deployable Membrane Antenna 4.2.5 The

Selected

Radiometer

conclusion

radiometer

of the

can achieve

studies of the rigid within a Titan IV.

reflector

paneled

parametric

studies

described

in Section

4.2.4.1.

within the other constraints configuration, when stowed

4.3

bay.

The deployed

Reflector

4.3.1

Rigid

Configuration

studies

the required

Therefore

payload 4.2-18.

Structural

by the

surface

configuration

were

is that

that a 40 m diameter

with

determined

contractors

only

for the 40 m diameter

concluded

conducted

It was

various

precision

the rectangular that

aperture

paneled

the maximum

a rigid

aperture.

aperture

mass

paneled

Packaging will not stow

configurations

diameter

possible

of this study is approximately 28m. The maximum aperture with the feed and secondary, occupy about 14m of the Titan IV radiometer

is depicted

in Fig. 4.2-17

and

it is shown

stowed

in Fig.

Surfaces

Facets

Various

concepts

surfaces

commonly

for large

deployable

used are either

antennas

a continuous

(LDA) mesh

facets. For upcoming remote sensing applications, frequencies on the order of 40 GHz are desirable.

been

developed. of rigid,

Two

deployable

continuous

surface

reflector apertures of up to 40 meters and For these targeted frequencies, mesh surfaces

have inadequate reflectance characteristics which drives Surface accuracies for adequate performance at 40 Ghz

35

have

or an assembly

the design to a continuous solid surface. need to be on the order of. 1 mm RMS.

Focal

Point

i

÷/

l! I

I !

!

I

I 42 m

÷

i L

\Ve_ex

Flgure

4.2-17•

28 meter

LDA

radlometer

spacecraft

structural

36

Concept

--!

I

i-- H

=0.6m

=13.7m

9.5m

t 1.6m

4.4m _ 1.15m

I'

Figure 4.2-18. 28 meter radiometer structure stowed In Tltan IV

37

Composite four types. 1.

Optics

The

has manufactured

single-surface,

Communication

Spacenet,

Kevlar

Satcom,

and

graphite/epoxySizes

of these

from

2.5

to 6.1 kg/m 2.

produced accuracies

The

receive

used

and

used

that are of the following

as used

on the

master

mold,

After

reducing

for lay-up

this

from

type

from

subreflectors

with

1.0 to 3.3 meters

manufacturing

which

a

support

rib

accuracy

induced

reflective structure

Ford

with

continuous

skins is also

thermally

Compare

honeycomb this

design

shell bonded approach

.015"-thick graphite/epoxy This design yields a much of 0.11 mm RMS. 4.3.1.1 shows Astro

Design both

stowed

Pactruss.

the truss.

The

This stowed

facet

on the next

With

this deployment

and

point

employing

stable

stresses

created

front

shell

and

a

densities

reflectors

where

ranging which

achieving

are

surface

of this kind of accuracy achieved was 0.06 mm a highly

graphite/epoxy

accurate mold

in the graphite/epoxy

plaster

is replicated.

mold,

it is used

and

COI

the

cured

skin

or shell

is laid

on it and

and backup rib structure can be adjusted during of 0.070 mm RMS for 2.2 m reflectors and 0.053

can vary significantly by the design approach. of 3.4-3.8 kg/m _-. These designs use a graphite

to graphite

to the

The

Astro

the deployed

concept

utilizes

arrangement

as closely

E,

skin/Nomex

design

used

honeycomb on

the

DBS.

rib support This

structure.

design

uses

a

skin bonded to a backside rib support structure as shown in Fig. 4.3-1. reduced areal density of 2.2 kg/m 2, yet maintains a surface accuracy

Evaluations:

the

Anik

or shells.

areal weight of many graphite/epoxy reflectors ACTS reflector designs exhibit areal weights

skirt/Nomex

Satellite

Superbird,

areal

surface

to the

involves

thermal

mapped. The final accuracy of the shell manufacturing to achieve surface accuracies mm RMS for 3.3 m reflectors. The The

Broadcast

Kevlar

in aperture

of rigid

a high temperature

of the antenna

A backup

of surface

the manufacturing

Advanced

shell.

from low-density graphite/epoxy has evolved of better than 0.1 mm RMS is feasible.

Attaining

the

reflectors.

on the Direct

At Composite Optics, Incorporated, (COD, the most recent demonstration has been the 3.3-meter transmit antenna for ACTS where the accuracy RMS.

on

transmit

Satellites.

back

range

reflector

(ACTS)

reflectors

hyperbolic

stiffened

reflectors

reflectors

reflector

gridded

GSTAR

Gridded-shell-stiffened

.

Satellite

membrane-sfifened

Dual-shell-stiffened

.

continuous-surface

honeycomb-shell-stiffened

Technology

The single-surface, (DBS).

.

many

Aerospace

square, shows

deployment

arrangements rigid-facet

the rigid

concept

for a rigid-facet segments

facets

which

to be packaged

shown

in Fig.

surface

attached

deploy

sequentially

by stacking

4.3-2 to the on

one rigid

as possible.

concept,

two

antenna

aperture 38

sizes

of 40 meters

and

15 meters

were

Figure 4.3-1.2.1

Meter skin stiffened antenna for Direct Broadcast Satellite (DBS)

39

ORIGINAL OF POOR

PAGE 18 QUALITY

Slowed Stowed

truss

panels

10 packages

-

of 10 panels

each,

4.0 m)

),,

__,A,__

Panels

,Packages unfolded onto truss edge

onto

unfolded truss

I

Deployed

antenna

face

:

40m

I

t

Figure 4.3-2. Deployment investigated. the 40-meter The

goals

more facets

facet

condensed includes

required

I

Concept for Rigid Panels

For these aperture sizes, a 3.1-meter and 2.0-meter and 15-meter-aperture reflectors, respectively. for the rigid

maintaining

I

I

facet

surface

design

accuracies

were

me surface

thickness

of 0.1 mm RMS.

packaging and stowage the depth of draw which

to maintain

a minimum

square

facet

Minirnizing

facet

and

was

areal

the facet

baselined

density

thickness

for

while enables

within the launch vehicle. The total thickness of the is dictated by the F/D and the thickness of the facet

accuracy

requirements.

Feasibility of meeting a minimal areal density was also investigated. For the 40-meter-aperture antenna, a 1.0 kg/m 2 areal density was targeted to maintain a reasonable overall total launch weight.

As-manufactured

for performance A simple and

finite

3.1- meter

reflective

shell

surface

requirements element square and

accuracies

of this LDA

model facets.

was

for the rigid

were

set up to represent

element

used

orientation

the rigid

facet

concepts

plate

elements

for the backside

onto

at 0.1 mm RMS

were

for both the 2.0used

rib structure.

The

to model four

the

support

A 1-g load was assumed to compute the surface to meet the targeted surface accuracy. Several

on both configurations.

Figure 4.3-3 shows the resultant (.75-inch) thick shell consisting quasi-isotropic

baselined

A total of 40 "CQUAD4"

44 "CBAR"

performed

were

application.

points were all modeled to be simply supported. standard deviation in order to size the reflector iterations

facets

The

results

were

as follows.

design concept for the 3.1-meter square facet having a 1.9-cmof 0.25 ram-(0.01 inch) thick graphite/epoxy skins laid up in a 1.9 cm-thick

core.

For

the

purposes

of this

sizing

analysis,

aluminum core properties were used in the finite element model. The backside rib structure consists of a perimeter ring stiffener with two separate ribs crossing through the center. These ribs have a cross-section of a box beam with a 1 mm (.04 inch) wall thickness and cross-section 40

3.1

MET

NOTES:

Figure 4.3-3. 3.1 Meter square facet shell stiffened concept dimensions required The

of 5 cm (2 inches) to meet

resultant

the surface

areal

density

wide

and 10 cm (4 inches)

accuracy calculations

target

with

deep.

This deep

the four-point

for this configuration

simply

box beam supported

section

was

attachment.

as follows: Weight

Shell

skins

Shell

core

Backside

Item (2)

3.1-Meter 8.3

Interface Total The

2.0-meter

5.9

1.6

7.9

4.6

0.8

0.5

0.2

0.2

ribs

Tie clips fittings

Weight square

(Areal facet

Density)

was

23.1

of the same

(2.4 kg/m 2)

design

same

modeling

techniques

were

were

.2 cm

For each of draw desired.

(.08 inch)

thick.

of the two concepts,

The

resultant

areal

thick

in Fig.

as on the 3.1-meter

density

for the 2-meter

was computed

of draw varies depending where maximum draw on the antennas 41

facet

quasi-isotropic

4.3-3.

It had

graphite/epoxy

square

facet.

The

concept except the cross-section was smaller The wall thickness of the box beam members

the total facet thickness

for each case. The amount For these purposes, the

inch)

used on this concept

backside rib structure was the same as the 3.1-meter with 3.8 cm x 3.8 cm (1.5 in. x 1.5 in.) box beam.

10.4 (2.6 kg/m 2)

as the 3.1 meter

a 1.3mm-(.5 inch) thick shell consisting of .25mm-(.01 skins bonded to a 1.3cm-(.5 inch) thick core. The

2.0-Meter 3.5

panel

which

was

2.6 kg/m 2.

includes

the amount

on the antenna the draw is was used in the overall

thicknessdeterminationwhich is at the locationclosestto the vertex. The total panelthicknesses are summarizedas follows for eachconcept.

Maximum Draw Shell Thickness Rib Thickness

3.1-Meter SquareFacet 1.96cm 1.90cm 10.16cm

2.0-Meter SquareFacet 2.18 cm 1.27cm 3.81 cm

Total Thickness

14.02cm

7.26 cm

The resultsof thesepreliminary studiesshow thatattaining arealdensitiesof 1.0 kg/m2 are optimistic.

However,

of previous

COI

current

reflector

which

areal Panel

concept.

criteria

densities

reflectors, designs.

the 3.1-meter design

areal

of 2.0 kg/m 2 seems

densities

These

preliminary sensitive

1.

A four-point

interface

2.

Quasi-isotropic

3.

Aluminum

core

properties.

When

considering

these

baseline

future

studies

thinner

panel

design.

may

also require

antenna

sizing

to the results

Based

on the areal

improvements reduction,

studies

over

especially

results

many

of the

in the case of

are based

on the listed

obtained.

laminates

design

the rigid

These

criteria,

facet

several

design,

further

thereby

iterations

producing

could

a reduced

be performed areal

density

panel design a six-point additional ijaterface seem o

if an increased number attachment with three support

support

to offer

at the where

the most

center

assume is

all laminates

possible

where

directionalized

when

Another

of the panel

to reduced

were feasible. along each

would

areal

option

weight

(shell the

orientation

and

The core,

core COI

selection could

or using

is another propose

ribs)

backside

and panel

structure

area requiring a quasi-isotropic 42

since

be

graphite/epoxy

investigation.

tri-cell

be a center Additional

truss

supports

thickness.

core

further

designed

the cross-sectional

further

option could be thereby giving

The baseline

However,

could

higher-modulus

the design

point to the

graphite/epoxy fiber system is ideal due to its near-zero

orientation.

are quasi-isotropic. rib

One edge,

would

be supported.

laid up in a quasi-isotropic

or P120). This would benefit beam ribs could be reduced.

,

of the panel.

the center benefit

of attachments truss interfaces

The design concepts shown baseline the P75 high- modulus which is a 75- million-modulus fiber. This fiber selection CTE characteristics

in and

include:

The interface attachment to the truss is presently a four-point attachment withone at each of the comers of the rigid facet. There could be considerable improvement

.

too

densities

to the truss

graphite/epoxy

to optimize

of 2.0 kg/m 2 offer

thicknesses

are very

feasible.

made

optimization

using

material properties

In place of

concepts

the

a

more

(e.g.,

P100

of the box

of aluminum same

parent

graphite/epoxy material as the shell skins. This benefits the structure by offering uniform sandwich CTE. The core can also offer improved core shear modulus improves

the sandwich

approach

1.5 lb/ft 3, thereby

shows .

COI's

Additional

stiffness.

reducing

graphite/epoxy design

4.3-5 and 4.3-6. viable alternatives

In addition,

tri-cell

options

could

it is anticipated

the areal

densities

of the rigid

core and its possible be studied

which

These options require further requiring investigation.

( .00;8

facets.

use in applications

are

analysis

SKIt/

UPPER

that the core

REFLECTOR

SHELL

in future

studies.

They

f

--RIB

/x_

_

_

VENT

TH