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Challenges in Spacecraft Reflector Technologies –

A Few Potential Applications of Smart Materials

B. S. Munjal*

Scientist / Engineer-SG / Head, Structures Systems Division * Space Applications Centre (SAC), Indian Space Research Organization

Ahmedabad. 380015. INDIA

Email: bsmamsd@sac.isro.gov.in

1.1 Introduction

Intelligent / Smart / Adaptive structures are the state-of-the-art technologies

being used for a few ground & some space borne structures and structural

systems. Although intelligent materials systems and structural concepts may be

applied to the design and implementation of buildings, dams, bridges, pipelines

and ground based vehicles but recent efforts have shown the possible

applications in potential domains of advanced aircrafts, launch vehicles,

spacecraft antennas and large space borne systems. Until now, this has

remained as an area not fully explored although, as a matter of fact, it has lot of

built–in future potential.

Smart structural systems, a buzz word of today, have the tendency to get

adapted to the new environment by changing their shapes and sizes respectively

by using the concept of sensing, actuation and control almost, as smart as,

human body having the reflex action using nerves, muscles and brain. Smart

materials should be able to both sense and communicate with outside

intelligence in order to meet functional requirements. In SAC, efforts are being

made to develop Smart spacecraft reflectors and Light weight spacecraft

reflectors for futuristic applications.

1.2 Advances in Space Domain

Weight and power consumption are at premium in satellites, hence there is

always a requirement of state-of-the-art light weight, high specific stiffness,

high specific strength and low thermal expansion materials for spacecraft

reflectors. Size of the component is also a major consideration in spacecraft,

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hence there is a requirement of small size composite reflectors operating at high

frequencies. To meet the above requirements; the intelligent and adaptive

contemporary materials to some extent come to our rescue. As matter of fact,

the applications of smart materials and smart structural systems in space

domain have there own formidable challenges and a few of them have been

enumerated as follows:

1.2.1 Formidable Challenges in Space Domain

In order to meet the communication and broadcasting needs of the twenty-first

century, antenna reflectors are generally required to have shaped surfaces. It is

a well known fact that maintaining precision surface shape for spacecraft

antenna reflector is a challenging task. The surface errors are introduced by

manufacturing errors, thermal distortions in orbit, moisture, loose structural

joints, material degradation and creep. Lot of R & D is required in the

development of advanced methods for precision control of piezoelectric smart

structures with temperature and hysteresis compensation.

Piezoelectric smart structures have potential aerospace related applications,

such as active shape control of deployable space antenna reflectors, active

vibration control of flexible solar arrays and position actuation of space-board

precision scanners and mirrors among many others. However, piezoelectric

materials exhibit nonlinearities, such as hysteresis, which adversely affect

precision control of the structures activated by piezoelectric actuators. Also

variations in temperature affect the properties of piezoelectric actuators . To

design control methods to compensate for the nonlinearities associated with

piezoelectric actuators poses a challenge for control engineers and researchers.

Conventional linear control designs cannot solve these issues. Therefore, lot of R

& D is ongoing to develop advance control methods, such as the technique using

neural networks and sliding-mode based robust controller to compensate for

hysteresis in smart actuators.

A major issues stems from the fact, that once the antenna is deployed on orbit,

the radiation pattern cannot be modified. If the shape of the antenna is allowed

to change, however, this issue can be addressed. A few illustrations of

contemporary ideas like inflatable / umbrella type reflectors, which may

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overcome these key issues in future for the communication satellites of 21 st

century are shown in Figs 1.1 & 1.2 : (Few are early artist's concepts only).

Fig 1.1 : Spacecraft antennas of 21St century

Fig 1.2 : Spacecraft antennas of 21St century

Schematic diagram (not to scale) of the 14-meter Inflatable Antenna Experiment

(IAE) that was flown from the Space Shuttle. This is a joint JPL, NASA/Goddard

and L'Garde program. Ultra Light weight structures and space observatories as

proposed by NASA (National Aeronautics and Space Administration) is gist are as

follows:

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1.2.2 Ultra Light Structures and Materials - An overview at NASA

The Ultra-Lightweight Structures and Space Observatories (ULSSO) thrust

develops revolutionary technology in structures, materials, and optical systems

to enable bold new missions of discovery for deep space missions . NASA is

studying future missions requiring very large space observatories. Long-range

plans are aimed at detection and characterization of planets in orbit around

nearby stars to search for the chemical signatures of life. Achieving this ,will

require arrays of space telescopes that have 1000x the light collecting area of

the largest ground-based telescopes in operation today. Technologies are sought

that enable very large telescopes for imaging extra-solar planets, studying the

formation of large-scale structure in the early universe, and continuously

monitoring the Earth form distant vantage points. Technologies are sought that

enable large deployable and inflatable antennas for space-based radio

astronomy, high-bandwidth communications from deep space, and Earth remote

sensing with radar and radiometers; solar sails for low cost propulsion, station

keeping in unstable orbits, and precursor interstellar exploration missions;

gossamer technology for kilometer-scale membrane spacecraft that weigh less

per unit area than a sheet of paper.

Revolutionary advances in ultra-lightweight structures and materials technology

are needed to enable a broad range of futuristic NASA’s missions. Applications

include large aperture telescopes and antennas, solar sails and telescope

sunshields, large solar arrays and solar concentrators, Earth and planetary

balloons, planetary entry vehicles, and spacecraft operating in extreme

environments. Technology breakthroughs in this area will also enable gossamer

spacecraft, which are very large, ultra-lightweight, highly-integrated systems

that can packaged into a small volume for launch. Technologies of specific

interest are:

Large (> 20 m) deployable and inflatable rigidizable booms and trusses.

Innovative methods for in-space manufacture and self-assembly of

lightweight structural elements and membranes. Membranes that can be

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made to grow like a biological system and that can ‘self-heal’ is a long-term

demand.

Thermal protection for hypersonic vehicles.

Highly - integrated multifunctional membranes that incorporate electronics,

MEMS devices, sensors, actuators, power sources, or other spacecraft

components in thin-film materials.

Ultra – lightweight, high- strength membrane materials for solar sails,

sunshields, inflatables, and balloons. Materials should be resistant to

ultraviolet radiation, particle radiation, and extreme temperatures (lifetime >

10 years).

High surface precision thin-film materials and reflective coatings for

membrane optics.

Nano-particle (i.e., organoclays, carbon nanotubes, etc.) containing

composite materials with substantially higher strength-to-weight ratio or

thermal conductivity than state-of–the–art composites. Ideas should not be

limited to filling polymers with nano-particles, but should include concepts

such as chemically linking nano-particles together to form molecular ‘net-like’

structures. Applications include ultra-lightweight structural elements,

electrically conductive elements, and efficient thermal management devices.

Proposals are sought for the development of adaptive systems applicable to

large, ultra-lightweight structures and apertures. Adaptive systems are needed

for measuring and correcting surface figure and wave front errors for large

telescopes and antennas, for controlling the dynamics of large flexible

structures, and for enabling gossamer spacecraft that can reconfigure

themselves in response to changing environmental conditions or mission phases.

Technologies of specific interest are:

Smart inflatable structures with embedded actuators and sensors for

controlling structural geometry and dynamics.

Innovative methods for shape control of large membrane mirrors and

antennas such as non-contact actuators.

Concepts and components for active, adaptive wave front control systems

with correction to < 1 wave length.

Materials with controllable surface properties that could adapt to changing

environmental conditions or mission needs.

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Novel concepts for gossamer spacecraft that could enable mission that were

previously considered impossible, while keeping cost and risk within

acceptable limits. An example concept is a gossamer spacecraft capable of

modifying its shape or other functional characteristics so that it can adapt to

different mission phases, such as atmospheric entry, descent, landing, and

surface exploration.

Large telescopes and structures 10 times the size of the Rose bowl in Pasadena,

California, that can be compacted and deployed in a single small launch vehicle

and then inflated once they are in the orbit, are a major part of the future of

earth and space exploration.

As part of the Gossamer spacecraft initiative, which is chartered with developing

technology for large telescopes and space sails new ways are being explored to

put large structures in space. The results of these investigations eventually

would be breakthroughs in ultra-light, inflatable materials that will substantially

reduce mission costs and enable large, ultra light objects to observe the Earth

and far reaches of the Universe. One of the proposed studies at Jet Propulsion

Laboratory (JPL), NASA with illustrations is shown in Fig 1.3 :

Fig 1.3 Inflatable space stations research as JPL,NASA

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According to Mr Artur Chmielewski, Manager of JPL Space Inflatables

Technology, “without new technology and new materials, we can’t go forward in

our missions to peer deep into the cosmos and look for earth–like planets and

other stars”.

NASA’s recent studies on Space Solar Power Satellites (SSPS) for generating

large amounts of electricity from large-scale, space based solar power systems

are shown in Figs 1.4 & Fig 1.5. :

Fig 1.4 Morphology of various SSPS concepts

Baseline1.2GWAbacusssatellite Cylindrical SSPS concept

Fig 1.5 Morphology of various SSPS concepts

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SSP Exploratory Research and Technology (SERT) of NASA has also proposed

the concept of Integrated Symmetrical Concentrator (Fig 1.6) to harness Solar

Energy :

Fig 1.6 Symmetrical Concentrator

1.2.3 Frontiers in Aerospace Technologies– Present & Future

The ultra light weight concept of structures presently can be monocoque (from

French mono – ‘single’ + coque – ‘shell’), semi-monocoque, sandwich,

corrugated, gossamer (a filmy substance consisting of cobwebs spun by spiders)

type structures, isogrids / waffle (fine honey comb weaving) type structures.

Ultra high precision reflectors for Ku band with RMS specifications like (0.25

mm) and Ka band reflectors with RMS specifications like (0.10 mm) would be

required in future as high stability structures with lay up fibers of high specific

strength Carbon-Carbon vanes (99 % of Phenolic Resin is converted into Carbon

by infiltration method for bonding with the M55J / M18 fibers of the prepregs) to

the accuracy of 5 microns accuracy. Inflatable structures and foldable

composites including Ultra long balloons are the requirements of the 21st century

Stratellites (A high altitude futuristic Air ship that when in place in stratosphere

as a stationary platform can be used for transmitting various types of wireless

communications currently transmitted through cell towers and satellites. For

stratellites dry adhesives would be developed and would have self launching

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capability at low earth orbit (20 Kms or so) & would not require launch vehicles

to reach stratellites). Space elevators made up of chirals / carbon nano tubes

would be developed by NASA using tethers and would be working using the

concept of Laser torch. A few illustration (Fig 1.7 – Fig 1.10) are as follows

showing the concept of stratellites, space elevators, Gossamer (thin film type)

spacecraft structures, inflatable antennas & aluminized Kapton solar sails getting

developed at NASA Langley Research center :

Fig 1.7 An idea of a Stratellite

Fig 1.8

An idea of the Space Elevator

Fig 1.9 Gossamer spacecraft – Solar sails, . Fig 1.10 –

5m dia. Inflatable Antenna

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The performance requirements of structures of space domain are as follows:

structural integrity

Low response to loads / disturbances

Dimensional accuracy / precision

Low inter system coupling

Jitter control

Stiffness

Agility

High Design Efficiency

Thermal Characteristics (Conductivity & Surface properties)

Electric / Electromagnetic permeability properties

Fast realization

Flexibility to incorporate the changes

Following are the methods of achieving the above mentioned design

requirements :

Contemporary materials similar to High modulus polyethylene (Dyneema)

with density of 0.97 gm /cc, vis-à-vis, CFRP AT 1.8 gm /cc.

Innovative types of construction

Efficient structural forms / joints / fastners

Optimum design modeling simulation

Load reduction

Adaptive / Smart structures

Multi-functional structures

Strategy for design / development fabrication

Inflatable

Following is the on-orbit behavioral requirements of the space structures:

Dimensional Stability & accuracy

Low response to the disturbances – internal & External

High Damping (Preferred is always passive damping as in active damping

the error in feed back control loop can lead to instability of the space

structure)

Viscoelastic damping to reduce settling time of the appendages.

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High Agility

Following are the real challenges in then design of space structures :

is the Dimensional stability & accuracy because of high heat dissipation

characteristics.

Following are the standard strength of material parameters considered in the

choice of high specific strength & high specific stiffness space materials :

E, EI, K, M, f, {F}, Ε/ρ, 3 √ Ε/ρ, σ/ρ, √σ/ρ, α, σ, σ c r, φ, δ, ρ,

State-of-the-art, high damping alloy viz., Thermoelastic Martensitic Alloy e.g

PROTEUSTM stands out as the contemporary material with good vibration

damping effect in a wide temperature range due to martensite-martensite

interface movements. Other mechanisms which may contribute significantly to

the amount of damping are, such as the movement of twin-boundaries in Cu-Al-

Ni and in NI-Ti alloys. A typical illustration of a spacecraft reflector under

development and testing using PROTEUSTM is illustrated in Fig 1.11.

Fig 1.11 Spacecraft reflector developed using high damping alloy PROTEUSTM

Now focusing & narrowing on applications of smart structures and intelligent

structural systems related to spacecraft antenna domain , presently, following is

the scenario in gist:

1.2.4 Present Scenario in Antenna reflector domain

Presently , the composite reflectors made up of Graphite and Kevlar being used

in INSAT / GEOSAT missions are Prime Fed type Parabolic reflectors or shaped

offset reflectors without any usage of smart materials . Even the next generation

Dual gridded shaped composite reflectors are being used without any concept of

reflector skin smartness or reconfigurability of the reflector surface . However,

Future Indian space missions will require smart space borne reconfigurable

antenna reflectors working on Ka-Band radio frequencies for telecommunications

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and higher frequencies for earth observation and scientific applications , which

would require modern reflector shape changing capabilities for catering to

different land masses with the same reflector. Presently , without the use of

dedicated antenna pointing mechanisms for rigid body movement of reflector

surfaces, it is a limitation in the design of spacecraft reflectors .

The need for high precision thin shell reflectors will also crop up for futuristic

satellite reconfigurable reflectors capable for Q/V–Band applications which will

need contemporary shape adjustment techniques.

Recent studies on smart structures world over, have found potential applications

in Large Deployable spacecraft antennas for mobile internet / mobile tele-

conferencing type applications, Large space mirrors and in large Inflatable space

antennas for deep space missions.

Moreover, applications are also possible in futuristic Radio Frequency Filled

Apertures / Antennas in space of very large diameter. In addition to this, the

applications of Meta materials & micro machined structures are also being talked

about in quasi optic multiple frequency applications viz millimeter wave antennas

(300 G Hz to 1 Tera Hz frequency). Fig 1.12 shows NASA’s concept of Large

Deployable Reflectors (LDRs) .

Fig 1.12 Piezo films in LDRs for reflector profile adjustments.

Fig 1.13 shows NASA’s concept of Inflatable antenna and the use Piezo films to maintain the requisite profile of the antenna .

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Fig 1.13 : Applications of Piezo films in Inflatable structures in NASA

Smart materials such as PZTs, PVDF Films and Shape Memory Alloys (SMA),

Magnetostrictive materials like Terfinol-D rods, Electro-Rheological Fluids (ERF),

Memory Metal Fibers (MMF) etc, have attracted many researchers around the

world for obtaining vibration control, shape control, thermal control in aerospace

structures. Active and passive vibration control of thin flexible structures using

Magnetostrictive powder has been studied by various researchers including the

concept of quite coats & smart constrained layer damping criteria ; where a

viscoelastic layer is sandwiched between a piezoelectric layer and the substrate.

In this particular case, the vibration energy is damped due to shear deformation

in the viscoelastic layer, which derives smartness when the vibration of the

structure is fed back to regulate the axial motion of the piezoelectric layer.

Moreover, for plates, in the concept of enhanced constrained layer damping, a

viscoelastic layer is constrained between a smart piezoelectric layer and the base

substrate which is being controlled. In this particular case, the smart damping

takes place due to cyclic shearing of the viscoelastic layer and it gets enhanced

by active component of the damping which is through the transfer of control

movements.

A review on shape control is given by H Irschik. Andoh Fukashi presented shape

control of singly curved and doubly curved reflector with a limited number of

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discrete actuators and optimized the actuator location. Gupta V.K et. al.

developed finite element formulation based on degenerate shell element for

piezo actuation in shell structure and also performed the experiment on doubly

curved shell structures.

For a space antenna structures, for instance, the required surface accuracy

depends on its frequency band of operation. Because the frequency used

currently tends to be higher and higher, the demand on the surface accuracy

becomes severer. The structural thermal deformation induced by temperature

change ranging from -150°C to + 150°C on orbit and the in-process member

length errors are cited as the main causes of deterioration of surface accuracy.

In general, the precise measurement of antenna configuration is required for

high precision shape control of antenna structure. However, since it is difficult to

place sensors and actuators to all structural components, the techniques of

highly precise measurement by a small number of sensors become more and

more important. Furthermore, low frequency vibrations tend to occur easily in

these space structures due to the rapid temperature change of surrounding

environment or the altitude control of structures or due to three axis movements

of spacecraft gyros. Since those vibrations do not decrease in the environment

of micro gravity and high vacuum, the performance of a satellite main part or an

electric device may drop remarkably. Therefore, it is crucial to suppress those

structural vibrations by some active or passive control techniques on real time.

Recently, research on the static shape control and the vibration control for

applications in space structures has been proposed. In static shape control

domain, highly precise shape control becomes possible only under the condition

of a large number of sensors and actuators. However, accurate shape estimation

and shape control using a small number of sensors and actuators are still

difficult for a deformed structure with respect to arbitrary disturbance enacted

on it.

For the realization of next generation space structures, such as a space antenna

with higher performance, the development of highly precise shape

estimation/control techniques only employing a limited number of sensors and

actuators is indispensable. Second, for vibration control, many researches using

the conception of modal sensor and modal actuator to control the dominant low-

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order modes have been carried out based on the modal analysis of structural

vibration. These kinds of traditional approaches can only be applied to some

simple structures, like a beam structure. Also, they usually need to attach a

sensor, such as a PVDF film; on the whole surface of a beam and the

computational cost is comparatively high. Therefore, the techniques for realizing

highly precise vibration measurement and control using limited number of

sensors and actuators have not been developed yet for large-scale and

complicated structures.

Applications of similar but practically feasible concepts for small size doubly

curved parabolic antennas surfaces, is still an area unexplored fully.

Recently only, in addition to vibration damping domain, work has been carried

out in the domain of using THUNDER (Thin Layer UNimorph Ferroelectric DrivER)

actuators, Power Pack actuators & curved Strip actuators for investigating beam

shaping in the domain of Mechanically Active Antenna (MAA) surfaces in space

segment based on the concept of smart aperture antennas. Fig. 1.14 shows a

typical Mechanically Active Antenna under development at Ohio State University,

USA for steering the antenna beam from North America to South America.

Lately, this has opened new vistas for innovative materials to handle the design

challenges posed by the futuristic antennas of high radio frequencies in terms of

ultra high precision designs...

Fig 1.14 A typical Mechanically Active Antenna under development

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Fig. 1.15 shows a typical model of 0.3 m dia. doubly curved smart antenna at

Ohio State University, USA using piezoceramic strip actuated approach using

Four Thunder PZT actuators for 11.8 GHz of frequency of signal .

___________________________________________

Fig 1.15 A typical model of 0.3 m dia. MAA antenna at Ohio State University, USA

1.3 Biomimic Systems

Advanced research in materials science resulted in man-made materials, such as

plastics and composites. Selection of unusual shapes in the design of structural

components and ideas of embedding sensors to monitor complex strain fields

then took hold. Furthermore, materials with unusual properties were discovered:

properties by which material behavior can be varied depending upon the phase

of the material (e.g., shape memory alloys, such as NiTiNol, whose phases

change at critical temperatures), the poling direction (as in piezoelectric

materials such as PZT),and the level of electric field (electrorheological fluids).

These discoveries have opened up the design space to such an extent that

possibilities of designing structures that can not only monitor themselves but

also adapt to the environment are now contemplated by the research

community.

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This is the background that has ushered in an era of research efforts leading to

“smartness” in structural design. Not unexpectedly, a variety of names, such as

smart materials, intelligent materials, and adaptive structures, have been

proposed.

Clearly, the dictionary definition of “smart” (brisk, spirited, mentally alert,

bright, knowledgeable, shrewd, witty, clever, stylish, being a guided missile,

operated by automation) is not quite adequate in this context. The engineering

community has adapted the term smart structures, over nearly a decade now,

and the words have come to mean a certain extraordinary ability of structures or

structural components in performing their design function. Smartness, in this

context, implies (a) the ability of structural members to sense, diagnose and

actuate in order to perform their function (closed-loop smartness) and/or (b)

unusual micro or macro-structural design that enhances structural integrity

(open-loop smartness). A closed-loop smart structure or component is one which

has the ability to sense a variable such as temperature, pressure, strain, and so

forth, to diagnose the nature and extent of any issues, to initiate an appropriate

action to address the identified issues, and to store the processes in memory

and “learn” to use the actions taken as a basis next time around. The attributes

of smartness may thus include the abilities to self-diagnose, repair, recover,

report, and learn.

1.3.1 Smart Systems

Smart structures have the capability to sense, measure, process, and diagnose

at critical locations any change in selected variables, and to command

appropriate action to preserve structural integrity and continue to perform the

intended functions. The variables may include deformation, temperature,

pressure, and changes in state and phase, and may be optical, electrical,

magnetic, chemical, or biological. The question of structural integrity arises

when defects develop, cracks form and propagate, or vibration occurs at

resonance or flutter. Some examples are earthquake response of buildings,

cutting tool chatter, rotor critical speeds, and turbine engine blade flutter.

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Efforts are also being directed toward the development of "smart," or

responsive, materials. Representing another attempt to mimic certain

characteristics of living organisms, smart materials, with their built-in sensors

and actuators, would react to their external environment by bringing on a

desired response. This would be done by linking the mechanical, electrical, and

magnetic properties of these materials. For example, piezoelectric materials

generate an electrical current when they are bent; conversely, when an electrical

current is passed through these materials, they stiffen. This property can be

used to suppress vibration.

1.3 A new era

Certain materials possess a property by which they experience a dimensional

change when an electrical voltage is applied to them. Such materials are known

as piezoelectric because of the converse effect; that is, they generate electricity

when pressure is applied. Perhaps the best-known such material is Lead-

Zirconate-Titanate (PZT); in fact “PZT” is commonly used to refer to piezoelectric

materials in general, including those of other compositions.

When manufactured, a piezoelectric material has electric dipoles arranged in

random directions. The responses of these dipoles to an externally applied

electric field would tend to cancel one another, producing no gross change in

dimensions of the PZT specimen. In order to obtain a useful macroscopic

response, the dipoles are permanently aligned with one another through a

process called poling.

A piezoelectric material has a characteristic Curie temperature. When it is heated

above this temperature, the dipoles can change their orientation in the solid

phase material. In poling, the material is heated above its Curie temperature

and a strong electric field is applied. The direction of this field is the polarization

direction, and the dipoles shift into alignment with it. The material is then cooled

below its curie temperature while the poling field is maintained, with the result

that the alignment of the dipoles is permanently fixed. The material is then said

to be poled.

When the poled ceramic is maintained below its Curie temperature and is

subjected to a small electric field (compared to that used in poling), the dipoles

respond collectively to produce a macroscopic expansion along the poling axis

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and contraction perpendicular to it (or vice versa, depending on the sign of the

applied field).

The working temperature of the PZT is usually well below its Curie temperature.

If the material is heated above its Curie temperature when no electric field is

applied, the dipoles will revert to random orientations. Even at lower

temperatures, the application of too strong a field can cause the dipoles to shift

out of the preferred alignment established during poling.

1.5 Research Element

Presently, in space segment domain, all the spacecraft components including

antenna feed chain components, mounting brackets for satellite reflectors, mast

mounted long wave guides / plumb lines, spacecraft reflectors etc, are all opted

for frequency based designs, basically, with a view to decouple the fundamental

system level frequency of the spacecraft w.r.t the sub-system frequencies

respectively.

Adequate stiffness ( frequency > 50 Hz) is provided for all subsystems including

the flimsy composite spacecraft reflectors to cater to launch conditions. All

these sub-systems face severe during launch vibration loads (in plane 20 g and

30 g out of plane ) approx., depending upon the launch vehicle. They are also

subjected to post launch thermal loads coupled with milli g vibrations

generated due to movement of three axis gyros of the spacecraft, altitude

correction exercises and thermal load variations.

In order to handle the design challenges of the futuristic small size, high

precision ,radio frequency Satellite Communication reconfigurable antennas of

the space segment for the Indian space research programme in particular, the

need was felt for investigating the applications of smart materials to meet the

structural, mechanical and electrical design specifications in a practical and

feasible way; purely from the realistic applications point of view.

Efforts, have been envisaged in understanding tomorrow’s design challenges for

developing a high precision, thin, space qualified futuristic reflector for high

Radio Frequency signals (Q/V bands) with following desirable design

specifications :

Diameter of Spacecraft reconfigurable reflector, say less than 1.0m,

First Eigen frequency of ~ 50 Hz (pre-launch – stowed condition)

Preferable total mass of < 3 Kg

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In-orbit stability RMS < 30 μm

Pointing error < 0.01o

These futuristic mechanically active reflectors may also modify the radiation

pattern by actively changing the shape of the reflector when on-orbit thermal

distortions deform the reflector shape.

As per the above design specifications, the geometry of the high precision thin

reconfigurable shells can be something as shown in Fig 1.18 :

Fig 1.18 Basic layout of the high precision thin shell

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[19] Intelligent network for science and technology MIMR 95, MATETOPIA, 21 (JAPAN) [20] Alaster McDonach, Peter T. Gardiner, RON 5 Mc Ewen, Brian culshaw , second

european conference on smart structures and materials held at the Glasgow Hilton Glasgow scotland, 12-14, Oct 1994, SPIE,P SPIE, proceedings series, volume 2361.

[21] K P Gowd Adaptive materials for aerospace Manufacturing Technologies, proceedings of the 13th national Convention of Aerospace Engineers , Edited by NK Naik , Kanchan Biswas, G C Popli , page 23-30.

[22] Jim Scragg, Development of Intelligent structures , Proc. ESA symp. Space applications of Advanced structural material Noordwijk (NL) 21-23 March 1990.

[23] Y Furuya and H Shimada , Shape memory Actuators for Robotic applications, Materials processing engineering Tohoku University, sendai, 980 Japan.

[24] B S Munjal, H V Trivedi and P V B A S Sarma, ‘Vibration Damping on Graphite and Kevlar Composites using Piezoceramic Powder coatings: A Review’, The Shock and Vibration Digest, Vol. 39, No. 1, January 2007,pp 3-18, SAGE publications.,UK.

[25] B S Munjal, H V Trivedi and P V B A S Sarma “Concept of Parabolic Reflectors made up of Composites with thin hybrid PZT coated layers”, JIMSS (An international Journal of Intelligent Material Systems & Structures) ,Vol.19,Nov.11,pp 1281-1294(2008)DOI 10.1177/1045/39X07085515, SAGE Publications, UK

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[26] B S Munjal, A C Mathur, S B sharma, D subramanyam, ‘Development Efforts w.r.t. Mechanically Active Antenna Reflector using PZT Patches for IC-EC Coverage- A Novel Futuristic Concept’, Proceedings of the 59th International Astronautical Congress, IAC-08-B2.1.12,29TH September-3rd October 2008, Glasgow, Scotland, UK.

[27] B S Munjal, ‘Finite Element Analysis of Smart Skin Spacecraft Reflectors using Smart / Intelligent materials and Smart structural Systems’, PhD Thesis submitted to Gujarat University, Ahmedabad , India in April 2006.

[28] B S Munjal, H V Trivedi and P V B A S Sarma Parabolic Spacecraft

Reflectors -A Shape Deformation Investigation Using Discrete Unimorph PZT Actuators’, Journal of Structural Engineering Structural Engineering Research Centre, CSIR Campus , Taramani, vol. 34, No.5 December 2007-January 2008 pp.

[29] B S Munjal, H V Trivedi and P V B A S Sarma “Investigation of MLF for PZT powder coated Composite laminates using ASTM Standard”`,Journal of Spacecraft Technology, Thermal Systems Group, ISRO Satellite Centre, Vol.18, No.1 January 2008, ISSN 0971-1600, pp 48-60.

[30] B S Munjal, H V Trivedi and P V B A S Sarma ‘Piezo actuated Parabolic

Aluminum reflectors- A Shape deformation Investigation’, National conference on Smart structures and MEMS systems for Aerospace Applications, Research Centre Imarat (RCI), Vigyanakancha, Hyderabad. session 6, AB50, 1-2, December 2006.

[31] B S Munjal, H V Trivedi and P V B A S Sarma ‘An experimental

investigation of composite loss factor for CFRP/GFRP Laminates with smart material coatings at ambient temperature’, National conference on current trends in technology (NUCONE-2006) Nov 30- Dec 2,2006) pp49-53.

[32] B S Munjal, H V Trivedi, A C Mathur and P V B A S Sarma ‘Finite Element

& Experimental shape studies of parabolic antenna reflectors using discreet piezoelectric actuators’, session XIX (19th ) Mechanical Design of Antennas session , International Conference on Antennas Technology (ICAT-2005), Feb 23-24, 2005, Space Applications Centre, ISRO, Ahmedabad.

[33] B S Munjal, H V Trivedi and P V B A S Sarma ‘Graphite and Kevlar Composites with thin Piezoceramic Powder (SP4 & SP-5A) coatings using RF Plasma Etching Technique for vibration Damping benefits’, Plasma Processing Update, Golden Jubilee Issue, July 2006, pp 41-42.

[34] B S Munjal, H V Trivedi and P V B A S Sarma, ‘Surface Activation of Hydrophobic Graphite Composite Laminates by RF Plasma Etching for Piezoceramic Powder Coated Spacecraft reflector’, Proceedings of the CASST-2007 Symposium IISc Bangalore, Jan 18-20, 2006.

[35] B S Munjal, H V Trivedi ‘Shape Investigations of Parabolic Antenna Reflectors using Piezoelectric Actuators – FEA using ATILA ’, National conference on current trends in technology (NUCONE-2007) Nov 30- Dec 2,2007.