A Detail Review of Optical Misalignment and Corrected by ... · A Detail Review of Optical...

IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 4, 2015 | ISSN (online): 2321-0613

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A Detail Review of Optical Misalignment and Corrected by Refocusing

Mechanism Apurv Raval

1

1P.G. Student

1A.D. Patel Institute of Technology, V.V Nagar, Gujarat, India

Abstract— When light rays enter in satellite telescope, it

first travels to the primary mirror than reflects back towards

the secondary mirror and henceforth setting a focal point

after passing through the centrally provided hole on primary

mirror in case of Cassegrain focus. Generally, space borne

telescope are subjected to orbital loads like temperature

excursion, absences of gravity, moisture release of metering

structure etc. which leads to coefficient of thermal

expansion and coefficient of moisture expansion of metering

structure. Due to this there is the change in focal length &

misalignment of optical system which ultimately reduces the

quality of images. The actual location of focal point is very

important for qualitative images. So to get the perfect focal

point, it is necessary to reset the distance between primary

and secondary mirror by means of some actuating

mechanism. This distance can be corrected with the help of

re-focusing mechanism & concept modification of the

mechanism is discussed over here.

Key words: Primary Mirror, Secondary Mirror, Focusing

length, Actuators, Thermal Actuator, Co-efficient of

Thermal Expansion (CTE), Co-efficient of moisture

expansion (CME), metering structure, LVDT, SHWFS,

WFS, WFE

I. INTRODUCTION

Satellite telescope is one of the most important payloads.

Here present generalized ray diagram of optics for

cassegrain focus type telescope.

Fig. 1: Generalized Ray Diagram of Optics

A. Cassegrain Telescope:

This type of telescope has a parabolic primary mirror and a

hyperbolic secondary mirror that reflects the light back

down through a hole in the primary mirror. Folding and

diverging effect of the secondary creates a telescope with a

long focal length while having a short tube length.

II. A BRIEF OVER VIEW OF TYPICAL SATELLITE TELESCOPE

Pleiades HR telescope is successfully launched in year

2008-2009. Its optical performance is checked in year 2011.

The images are taken by Pleiades HR telescope is very fine.

In this telescope thermally driven refocusing mechanism is

implemented first time. This thermally driven refocusing

mechanism has ability to re correct the misalignment

between primary mirror and secondary mirror with few

microns.

Fig. 2: Mechanical Architecture of Pleiades

In above figure mechanical architecture of

PLEIADES-HR camera is shown& Below ray diagram of

the same

Fig. 3: Ray Diagram of Pleiades HR Camera

A Detail Review of Optical Misalignment and Corrected by Refocusing Mechanism

(IJSRD/Vol. 3/Issue 4/2015/188)


Fig. 4: Location of Secondary Mirror

Secondary Mirror is mounted at entry of incoming

light rays. It is connected with thermally driven refocusing

mechanism and mounted with MFD (Mirror Fixation

Device). Whole assembly is directly connected with 3 spider

blades at one end of metering structure.

III. LITERATURE REVIEW

According to, Paul Greenway, Ian Tosh, Nigel Morris, [1]

they worked on development of the topsat camera. In this

paper they show the misalignment problem arises due to

coefficient of thermal expansion (CTE) and coefficient of

moisture expansion (CME) with variation in temperature

during orbital working.

Fig. 5: Ray diagram of Topset & misalignment

According to, Daniel R. Neal, Justine Mansell, [2]

they worked on Application of Shack Hartmann Wave front

Sensors to optical system calibration and alignment. In this

by using SHWFS alignment and measurement of the

performance of 24 inch diameter cassegrain telescope is

carried out. By checking position of spot we can measure

misalignment.

Fig. 6: Focal Spots Generates When Rays Passing through

the Lenslet array On Detector

Fig. 7: Focal Spots Position

According to, Jean-Luc Lamard, Catherine Gaudin-

Delrieu, David Valentini, Christophe Renard et al, [3] they

represent design of the high resolution optical instrument for

the Pleiades HR earth observation satellite. In this paper due

to temperature difference deviation between Mirror 1 and

Mirror 2 within few micron is presented. This can be re-

aligning by using thermal refocalization device included

with Mirror during flight mission. Aluminum ring is

provided with MFD for actuation of Mirror 2 for re-

aligning. This design is based on the temperature controlling

of an aluminum ring located between mirror and structure.

The functioning temperature range is (17°C; 34.5⁰C).

Fig. 8: Optical Arrangement and Path of Rays




Fig. 9: Thermally driven Refocusing Mechanism

According to, Catherine Gaudin-Delrieu, Jean-Luc

Lamard, et al., [4] they show the high resolution optical

instruments for the Pleiades HR Earth Observation

Satellites. In this paper successfully implementation of

thermally driven refocusing mechanism with secondary

mirror is shown.

Fig. 10: Successfully Implementation of Thermally Driven

Mechanism

According to, C.LABORDE, [5] show high

resolution earth observation instruments-how to reach the

best performance. In this research paper best material for

front and back cavity of satellite telescope is presented.

Opto-mechanical design of HR (High resolution and VHR

(Very High Resolution) telescope is shown.

Fig. 11: Suitable Material for Front and Back Cavity

According to, G. Lin, C. J.Kim at el., [6] they

carried out comparative finite element analysis on C-shape

thermal actuator. They describes the design, fabrication, and

testing of a micro actuator, whose bimorph beams curl up to

form a C-shape and reach hundreds of microns from the

substrate, designed by FEM nonlinear analysis and

fabricated on a silicon wafer by surface micromachining

involving polyimide and metal thin films. The bimorph

curled up, and it opens up by either electrostatic or thermal

actuation. The device was operated successfully in liquid as

well as in air to their full range between complete curl up

and flat positions, displacement can achieve up to 200 µm,

& fabricated by surface micromachining techniques.

Fig. 12: Operation of thermally driven container

& it’s working

According to, P.K. Patowari, M.M.Nath, A.S.

Bharali, [7] et al., They carried out comparative study of

different micro-thermal actuators for MEMs application.

They represent a comparative study of three micro-

thermal actuators which differ in their Construction &

material. Model-I is the basic model and Model-II and

Model-III are developed with a view to achieve improved

performance over Model-I. The materials under

consideration are Poly Silicon, Single Crystal Silicon and

Titanium. Comsol Multiphysics software is used for

Modelling and simulation.




For Model-I, in order to achieve higher deflection

at low applied voltage, out of the three materials i.e. Poly-Si,

Si and Ti, the best suitable one is Ti. For low deflection Si is

more suitable. For moderate temperature and deflection, out

of these three materials Poly Si is recommended. Model-II

does not satisfy the basic need i.e. higher deflection in

comparison to the Model-I. Instead it provides much lower

deflection as compared to Model-I.

According to, Amarendra Atre, [8] he has been

carried out multivariable non-linear comprehensive finite

element analysis. The simulation is carried out by using

ANSYS on two arm surface micro machined horizontal

electro thermal actuator.

An indirect method was employed by maximizing

the steady-state deflection for unloaded actuator and

minimizes the steady state deflection for loaded actuator for

same voltage applied.

Electro thermal two-arm polysilicon actuators are

widely employed in optical MEMS application. These

actuators are typically designed for maximum deflection

(unloaded) or force (loaded) output characteristics. The

optimization subroutine is implemented to investigate the

design variables to obtain an actuator geometry that

provides optimum deflection or force output for minimal

power consumption.

Fig. 13: MEMs based thermal actuator

Lt– Length of thin arm

Wt- width of thin arm g- Arm spacing

V- Applied voltage Lf – Length of flexure arm

The optimized thermal actuator shows an 8%

increase in force output from the original geometry for

approximately the same power consumed.

According to, Roger G. Gilberston and John D.

Busch, [9] a survey of micro-actuator technologies for future

spacecraft mission is carried out. They show ten basic

actuator technologies and covers recent micro-actuator

development, their method of operation, design limitations,

comparative performance, and their potential space craft

application.

According to, K. Devendra and T. Rangaswamy,

[10] they carried out thermal conductivity and thermal

expansion coefficient of GFRP composite laminates with

fillers. In this paper shown the method used for

measurement of thermal conductivity on standard ASTM E

1530 specimen. Thermocouples installed on top and bottom

surfaces were used for temperature measurement. Thermal

expansion coefficient relationship is also shown in this

paper.

α = co-efficient of thermal expansion (/⁰С)

∆T = Temperature difference (/⁰С)

∆L = change in length (mm)

L = original length (mm)

According to, A.S.Usmani, J.M.Rotter, S. Lamont,

A.M.Sanad, M. Gillie, [11] they carried out fundamental

behavior under thermal effects. In this paper various cases

of thermal expansion and its theoretical fundamental is

shown. Structural behavior under thermal effects and

deflection was discussed in this paper.

εT=Thermal expansion or (change in length due to thermal

expansion)

α = co-efficient of thermal expansion

∆T = Temperature difference

L = Original length

According to, Ugur Erturun, kaan Erermis, Karla

Mossi, [12] they carried out research on effect of various leg

geometries on thermo-mechanical and power generation

performance of thermoelectric devices. By them different

leg geometries ware modeled and analyzed on two different

temperature gradients. Four types of leg geometry are

analyzed by them (rectangular, trapezoidal, cylindrical &

octagonal) on ANSYS workbench.

Fig. 14: Thermoelectric Four Different Leg Geometry

They found out that in cylindrical and rectangular

prism equivalent stress values ware 43.3 MPa & 49.9 MPa

respectively for the temperature gradient of 100º C.

Maximum equivalent stress ware 94.2 MPa and 85.7 MPa in

rectangular prism and cylindrical legs for temperature

gradient of 300ºC.

Fig. 15: Stylus Profiler used for micron rise




Also in this paper they have shown a measuring

technique of micron increase in height of thermoelectric leg

by using stylus profiler.

According to, M.S.Suen, J.C. Hsieh, K.C.Liu et al.

[13] they carried out stress reduction in V-shape electro

thermal micro actuators. By him stress concentration is

reduced up to 290.71 from 685 MPa. This is achieved by

providing the fillet radius. The stress concentration is

reduced up to 57.66% by providing fillet radius.

The stress concentration of the electro thermal

micro actuator is an important issue in the MEMS structure

resulting from the existence of stress concentration

essentially to change the performance and reduce the

structural life time of MEMS devices.

IV. METHODOLOGY

A. Initial Concept of Thermally Driven Mechanism

In earlier concept of thermally driven mechanism a single

aluminum ring is used for realignment. The working of

mechanism is dependent on heating and cooling of

aluminum ring by heater and radiator respectively. When

heat is given to ring length is increases and mirror moves

up-side. On the other side when ring is cooled it contract

and mirror moves down ward.

B. Modified Concept of Thermally Driven Mechanism

In the modification of above concept two aluminum rings

can be provided and by maintaining of this two ring

temperature, mirror up-down movement can be possible

without need of radiator. In this concept insulation ring is

provided (indicated by green) in between two aluminum

rings which having very low thermal conductivity (made

from FR4 material having conductivity of 0.23 W/mK).

When Inner expansion ring (indicated by red color) is heated

mirror side moves downward. When outer expansion ring

(Indicated by pink) is heated, mirror can be moves upside.

It is checked by CAD software and also performed

experimentally.

V. CONCLUSION

On the basis of literature survey it has been found that a

thermally driven mechanism can used for re alignment of

the optical structure. A thermally driven refocusing

mechanism is already used in Pleiades HR telescope for

solving the problem of misalignment. A single aluminum

ring is used for changing the position of secondary mirror. It

can be possible to provide two aluminum ring for changing

the position of mirror without need of radiator. Also such a

kind of thermallydriven mechanism can be used for micro

positioning of other application, which requires precise and

accurate movement.

REFERENCES

[1] Paul Greenway, Ian Tosh, Nigel Morris, “Development

of the Topsat Camera” Proceedings of the ICSO

(International Conference on Space Optics) 2004.

[2] Daniel R. Neal, Justine Mansell, “APPLICATION OF

SHACK-HARTMANN WAVEFRONT SENSORS TO

OPTICAL SYSTEM CALIBRATION AND

ALIGNMENT Proceedings of the SPIE VoL.4779,

pp.234, 2002.

[3] Jean-Luc Lamard, Catherine Gaudin-Delrieu, David

Valentini, Christophe Renard, “DESIGN OF THE

HIGH RESOLUTION OPTICAL INSTRUMENT FOR

THE PLEIADES HR EARTH OBSERVATION

SATELLITES” Proceedings of the ICSO 2004.

[4] Catherine Gaudin-delrieu, Jean-Luc LAMARD,

Philippe Cheroutre, Bruno Bailly, Pierre Dhuicq,

Olivier Puig, “THE HIGH RESOLUTION OPTICAL

INSTRUMENTS FOR THE PLEIADES HR EARTH

OBSERVATION SATELLITES” Proceedings of the

ICSO (International Conference on Space Optics) 2008.

[5] C.LABORDE, “HIGH RESOLUTION EARTH

OBSERVATION INSTRUMENTS- HOW TO REACH

THE BEST PERFORMANCE”, Proceedings of the

ICSO 2014.

[6] G.Lin, C-J.Kim, S.Konishi And H.Fujita “Design,

Fabrication, And Testing of A C-Shape Actuator” The

8th

International Conference on Solid – State Sensors

And Actuators, and Eurosensors IX. Stockholm,

Sweden, June 25-29, 1995.

[7] P.K.Patowari, M.M.Nath, A.S.Bharali, J. Gogoi,

C.K.Singh, “Comparative Study of Different Micro-

Thermal Actuators for MEMSs Application” Journal of

Advanced Manufacturing Systems.

[8] Amarendra Atre, “Design Optimization of a Surface

Micro machined Electro-Thermal Beam Flexure

Polysilicon Actuator” NSTI-Nano tech,

www.nsti.org,ISBN 0 9767985-2-2 Vol. 3,2005

[9] Roger G. Gillberston and John D. Busch- “ A Survey

OF Micro-Actuator Technologies For Future Spacecraft

Missions” The Journal of The British Interplanetary

Society Vol.49,pp.129-138,1996.

[10] K. Devendra and T. Rangaswamy, “THERMAL

CONDUCTIVITY AND THERMAL EXPANSION

COEFFICIENT OF GFRP COMPOSITE

LAMINATES WITH FILLERS” Mechanica Confab,

Vol.2, No. 5, August-September 2013, pp. 39-44.

(ISSN: 2320-2491)




[11] A.S.Usmani, J.M.Rotter, S. Lamont, A.M.Sanad, M.

Gillie, “Fundamental principles of structural behavior

under thermal effects” Fire Safety Journal 36 (2001),

pp.721-744, March 2001 Elsevier Science Ltd.

[12] Ugur Erturun, Kaan Erermis, Karla Mossi, “Effect of

Various Leg Geometries on Thermo-Mechanical and

Power Generation Performance of Thermoelectric

Devies” Erturun et al. /Applied Thermal Engineering 73

(2014) 126-139.

[13] M.S.Suen, J.C.Hsieh, K.C.Liu, David T.W.Lin,

“Optimal Design of The Electro thermal V-Beam Micro

actuator Based on GA For Stress Concentration

Analysis” Proceedings of the International Multi

Conference of Engineers And Computer Scientists 2011

Vol.II,IMECS 2011,March 16-18,2011,Hong Kong.

[14] Patrice damilano, “Pleiades High Resolution Satellite: a

Solution for Military and Civilian Needs in Metric-

Class Optical Observation” 15th

Annual/USU

conference on Small Satellite.

[15] compliant Mechanisms, design of flexure hinges by

Nicolae Lobontiu, CRC Publication (year 2002), page

no. 394

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