Thermo-mechanical studies of the Narrow Angle Camera of the …ggilles/TFE/TFE.pdf · 2007-06-04 · Thermo-mechanical studies of the Narrow Angle Camera of the ESMO satellite GILLES

Thermo-mechanical studies of the Narrow AngleCamera of the ESMO satellite

GILLES GaëtanThird year civil engineering in physics

Academic year 2006-2007

1

I would like to thank all the people who assisted me in the development ofthis work :

• Jean-François Vandenrijt, coordinator of the NAC team, for the con-tinuous management, his advice and the re-reading of this work ;

• Pierre Rochus, my promoter, for the follow-up of the work ;

• Guy Janssens, director of GDTech, Anne Mawet, Olivier Fanielleand Sébastien Mortier, for their assistance in the use of the softwareSamcef ;

• Emmanuel Mazy and Jean-Yves Plesseria, for their technical ad-vices ;

• Tanguy Thibert, concerning the thermal part of this work ;

• Claude Jamar, director of CSL, for his moral support ;

• my brother Thierry for the correction of the English spelling and gram-mar.

Contents

1 Introduction 51.1 What is SSETI ? . . . . . . . . . . . . . . . . . . . . . . . . . 51.2 What is ESMO ? . . . . . . . . . . . . . . . . . . . . . . . . . 61.3 The different teams of the ESMO . . . . . . . . . . . . . . . . 91.4 Composition of the NAC team . . . . . . . . . . . . . . . . . 101.5 Organisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.5.1 Communication between the teams . . . . . . . . . . . 101.5.1.1 Chat channel . . . . . . . . . . . . . . . . . . 111.5.1.2 FTP server . . . . . . . . . . . . . . . . . . . 111.5.1.3 News server . . . . . . . . . . . . . . . . . . . 11

1.5.2 Workshops . . . . . . . . . . . . . . . . . . . . . . . . . 121.5.2.1 ESMO WS 1 . . . . . . . . . . . . . . . . . . 121.5.2.2 ESMO WS 2 . . . . . . . . . . . . . . . . . . 131.5.2.3 ESMO WS 3 . . . . . . . . . . . . . . . . . . 14

1.5.3 iCDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2 Evolution of the NAC 152.1 Call For Proposals . . . . . . . . . . . . . . . . . . . . . . . . 152.2 Evaluation of team proposal . . . . . . . . . . . . . . . . . . . 16

2.2.1 Technical feasibility . . . . . . . . . . . . . . . . . . . . 162.2.2 Manpower/Background . . . . . . . . . . . . . . . . . . 162.2.3 University support/Academic credit . . . . . . . . . . . 172.2.4 Funding/Industrial links . . . . . . . . . . . . . . . . . 172.2.5 Selection decision . . . . . . . . . . . . . . . . . . . . . 17

2.3 Expert review . . . . . . . . . . . . . . . . . . . . . . . . . . . 172.4 Requirements for the NAC . . . . . . . . . . . . . . . . . . . . 19

2.4.1 Functional requirements . . . . . . . . . . . . . . . . . 192.4.2 Performance requirements . . . . . . . . . . . . . . . . 192.4.3 Operational requirements . . . . . . . . . . . . . . . . 192.4.4 Interface requirements . . . . . . . . . . . . . . . . . . 192.4.5 Structural requirements . . . . . . . . . . . . . . . . . 19

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CONTENTS 3

2.4.6 Reliability/Availability/Maintainability/Safety require-ments . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.5 Design after WS1 and difficulties of the project . . . . . . . . 20

3 Design of the tube 233.1 Evolution of the optical design . . . . . . . . . . . . . . . . . . 243.2 Carriage of the lenses in the tube . . . . . . . . . . . . . . . . 243.3 Interfaces between the lenses and the mount . . . . . . . . . . 25

3.3.1 "Sharp-corner" interface . . . . . . . . . . . . . . . . . 253.3.2 Tangential interface . . . . . . . . . . . . . . . . . . . . 26

3.4 Design of the mounts . . . . . . . . . . . . . . . . . . . . . . . 273.4.1 Characteristics of the lenses in the optical design . . . 273.4.2 Case of concave surfaces . . . . . . . . . . . . . . . . . 283.4.3 Case of convex surfaces . . . . . . . . . . . . . . . . . . 283.4.4 Shape of the interfaces . . . . . . . . . . . . . . . . . . 293.4.5 Gap in the event of dilatation . . . . . . . . . . . . . . 30

4 Finite elements analysis 324.1 Modal analysis by Samcef Field . . . . . . . . . . . . . . . 33

4.1.1 Analyse data . . . . . . . . . . . . . . . . . . . . . . . 334.1.1.1 Behaviour . . . . . . . . . . . . . . . . . . . . 334.1.1.2 Material . . . . . . . . . . . . . . . . . . . . . 33

4.1.2 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354.1.3 Solver and result . . . . . . . . . . . . . . . . . . . . . 35

4.2 Mechanical study by Spectral . . . . . . . . . . . . . . . . . 374.2.1 Vibration environment . . . . . . . . . . . . . . . . . . 374.2.2 Random vibration tests . . . . . . . . . . . . . . . . . . 374.2.3 *.psd file structure . . . . . . . . . . . . . . . . . . . . 384.2.4 Additional commands in the *.dat file . . . . . . . . . . 394.2.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.2.5.1 Excitation in the direction x . . . . . . . . . . 404.2.5.2 Excitation in the direction y . . . . . . . . . . 424.2.5.3 Excitation in the direction z . . . . . . . . . . 43

5 Thermal considerations 455.1 Calculation of radiative transfers . . . . . . . . . . . . . . . . 46

5.1.1 Recall : view factors . . . . . . . . . . . . . . . . . . . 465.1.1.1 Definition . . . . . . . . . . . . . . . . . . . . 465.1.1.2 Properties of view factors . . . . . . . . . . . 46

5.1.2 Application to the NAC . . . . . . . . . . . . . . . . . 475.1.2.1 Ideal case . . . . . . . . . . . . . . . . . . . . 47

CONTENTS 4

5.1.2.2 View factor between two disks . . . . . . . . . 495.1.2.3 Rectification of the view factors (lens with a

convex surface) . . . . . . . . . . . . . . . . . 515.1.2.4 Numerical results . . . . . . . . . . . . . . . . 53

5.1.3 Radiative transfers . . . . . . . . . . . . . . . . . . . . 535.1.3.1 Calculation of the flux qi and qij . . . . . . . 555.1.3.2 Numerical results . . . . . . . . . . . . . . . . 55

5.2 Evaluation of the maximal temperature variation admissiblein the tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575.2.1 CTE of the different lenses and the tube . . . . . . . . 575.2.2 Dilatation of the lenses and the tube . . . . . . . . . . 575.2.3 Shrinkage of the lenses and the tube . . . . . . . . . . 595.2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 59

6 Opening system of the shutter 606.1 Shape Memory Alloy . . . . . . . . . . . . . . . . . . . . . . . 616.2 Frangibolt device . . . . . . . . . . . . . . . . . . . . . . . . . 616.3 High Output Paraffin actuator . . . . . . . . . . . . . . . . . . 646.4 Comparison of models . . . . . . . . . . . . . . . . . . . . . . 66

7 Conclusion 677.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 677.2 Personal enrichment of the work . . . . . . . . . . . . . . . . . 68

A Acronyms and Abbreviations 69

B Current dimensions of the NAC 70

Bibliography 72

Chapter 1

Introduction

Contents1.1 What is SSETI ? . . . . . . . . . . . . . . . . . . . . 5

1.2 What is ESMO ? . . . . . . . . . . . . . . . . . . . . 6

1.3 The different teams of the ESMO . . . . . . . . . . 9

1.4 Composition of the NAC team . . . . . . . . . . . 10

1.5 Organisation . . . . . . . . . . . . . . . . . . . . . . 10

1.5.1 Communication between the teams . . . . . . . . . 10

1.5.1.1 Chat channel . . . . . . . . . . . . . . . . 11

1.5.1.2 FTP server . . . . . . . . . . . . . . . . . 11

1.5.1.3 News server . . . . . . . . . . . . . . . . . 11

1.5.2 Workshops . . . . . . . . . . . . . . . . . . . . . . 12

1.5.2.1 ESMO WS 1 . . . . . . . . . . . . . . . . 12

1.5.2.2 ESMO WS 2 . . . . . . . . . . . . . . . . 13

1.5.2.3 ESMO WS 3 . . . . . . . . . . . . . . . . 14

1.5.3 iCDF . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.1 What is SSETI ?SSETI gathers more than 500 students from more than 15 universities lo-

cated in European countries and Canada. The students are undergraduates,

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CHAPTER 1. INTRODUCTION 6

graduates or PhD students and they are designing and building satellites inclose collaboration with the Education Department of ESA.

The first SSETI satellite, SSETI Express, was launched in October 2005 -seen as a technology demonstration carrying three Cubesatellites, a propul-sion module, a colour camera and an amateur radio transponder. Next inline is the ESEO - planned to be launched in late 2008. Following the ESEO,the next potential satellite is the European Student Moon Orbiter.

Figure 1.1: SSETI Express Figure 1.2: ESEO

1.2 What is ESMO ?In March 2006, the Education Department of ESA approved the ESMO

mission proposed by the SSETI association for a Phase A Feasibility Study.If it can be realized, the ESMO will be the third mission to be designed,built and operated by European students through the SSETI association,and would join many other contemporary missions to the Moon (SMART-1,Chandrayaan, etc.).

The ESMO mission objectives are :

• Education : prepare students for careers in future projects of the Eu-ropean space exploration and space science programmes by providingvaluable hands-on experience on a relevant and demanding project ;

• Outreach : acquire images of the Moon and transmit them back to theEarth for public relations and education outreach purposes ;

• Science : perform new scientific measurements relevant to lunar scienceand the future human exploration of the Moon, in complement withpast, present and future lunar missions ;


• Engineering : provide flight demonstration of innovative space tech-nologies developed under university research activities.

The ESMO spacecraft would be launched in 2011 as an auxiliary payloadinto a highly elliptical, low inclination GTO on the new ASAP by either Ar-iane 5 or Soyuz from Kourou. From the GTO, the spacecraft would use its

Figure 1.3: Ariane 5 rocket.

on-board propulsion system for lunar transfer, lunar orbit insertion and orbittransfer to its final low altitude polar orbit around the Moon. A miniaturisedsuite of scientific instruments (also to be provided by student teams) wouldperform measurements during the lunar transfer and lunar orbit phases overthe period of a few months, according to highly focused science objectives.The core payload would be a high-resolution narrow angle camera for opticalimaging of lunar surface characteristics. Optional payload items are consid-ered, including for example a LIDAR or Cubesat subsatellite for a precisegravity field mapping.

Two different spacecraft designs are being studied in parallel and traded-off by the student during the Phase A : one based on a hybrid solid/liquidpropulsion system, and one relying upon solar electric propulsion. The formerwould allow a rapid transfer to the Moon within a few days, but with areduced payload, whereas the latter would take up to 12 months for thelunar transfer phase with the benefit of giving greater payload accomodationand wide launch window flexibility. Other technologies include miniaturisedavionics, a lightweight structure and a solar array. The mission would need to


Figure 1.4: Configuration of the sub-systems in ESMO (chemical propulsion).The NAC is surrounded with red.

be supported by a Global Educational Ground Station Network for TT&C, asingle large ground station for payload data downlink from lunar orbit, andthe several student-run Mission Control Centres. The mission would endin 2012.

The preparation for the Phase A included a Call For Proposals to Europeanstudent teams for the spacecraft subsystems, the ground segment and thescientific payload. The deadline was 15th August 2006 and a team selectionprocess was made by the Education Department and the SSETI associationduring September 2006, closely followed by a study on the ESMO in theESTEC CDF. The CDF is a state-of-the-art facility equipped with a networkof computers, multimedia devices and software tools, which allows a team ofexperts from several disciplines to apply the concurrent engineering methodto the design of future space missions. It facilitates a fast and effectiveinteraction of all disciplines involved, ensuring consistent and high-qualityresults in a much shorter time. It is primarily used to assess the technicaland financial feasibility of future space missions and new spacecraft conceptsproviding :

• a new mission concept assessment

• space system trade-offs and an option evaluation

• a new technology validation at system/mission level

as well as :


• a payload instrument conceptual design

• a scientific requirement definition and consolidation

• education and training

The CDF was established at the ESTEC in November 1998 within the frame-work of the General Studies Programme. Concerning the mission ESMO, theobjective of the CDF study was to review the students’ proposals and makea selection of suitable proposals for possible implementation into the ESMOmission.

Student workshops took place at the ESTEC in October 2006 and January2007, with the latter performed in the CDF accompanied by training of thestudents in concurrent design methods and tools. The go/no-go decision toimplement the ESMO mission and proceed to launch will be made followingthe Phase A study review to be conducted by the Education Department,ESA technical experts and the SSETI association in July 2007.

1.3 The different teams of the ESMOEach team is constituted within a university and comprises a person in

charge, the coordinator. A primary team deals with the development of asub-system of the satellite. However, one or more backup teams can work onthe same sub-system as a primary team. Moreover, if the primary team doesnot fulfil requirements of the mission, a backup team can replace it and sobecomes the new primary team.

The different sub-systems can be grouped together in the following way :

1. Science/Payload : The core payload on-board is a Narrow AngleCamera (NAC) used in order to acquire images of the Moon, andpossible other objects, from the lunar orbit for scientific and outreachpurposes. In addition to the camera, there will be a small sub-satellite(CSAT) — called Lunette — on-board, as science payload. Thesmall sub-satellite will perform gravity mapping and thereby providefull maps of the lunar gravity field. Other instruments, such as a LI-DAR (LIDAR) and a microwave radiometer (URM), are also studied,but constitute backup payloads.

2. Energetics & Platform : This includes the propulsion, the electricalpower (EPS), the structure (STRU) and the thermal control (TCS).


Concerning the propulsion system, two cases are considered and studiedin parallel : a chemical propulsion system (CPROP) and an electricalpropulsion system (EPROP).

3. Avionics : This refers to the attitude and orbit control (AOCS), thecommunications (COMM), the on-board data handling (OBDH) andthe mechanisms (MECH).

4. Ground segment : This includes the mission analysis (MIAS), theflight dynamics (FD), the ground stations (GS) and the simulations(SIM).

Finally, a specific team (SYS) takes charge of the global administration ofthe project and is generally composed of young employees of ESA.

1.4 Composition of the NAC teamInitially, our team was composed of three persons :

• Jean-François Vandenrijt, assistant of CSL and coordinator of theteam ;

• Philippe Franssen, student in third year civil engineering in physicswho is in charge of the optical design of the camera ;

• Gaëtan Gilles, student in third year civil engineering in physics whois in charge of the thermo-mechanical design of the camera ;

In March 2007, a new student, Rémy Woine, from ISIL, integrated the team.He is in charge of the electronics of the camera.

1.5 Organisation

1.5.1 Communication between the teams

The conception of a satellite by European and Canadian universities needsa particular infrastructure in order to guarantee an effective cooperationbetween the different teams. This infrastructure includes :

• a chat channel ;

• a FTP server ;

• a news server.


1.5.1.1 Chat channel

The chat channel allows teams to know about the evolution of the project,the changes in the administration, the new proceedings, etc. These pieces ofinformation are given by members of ESA and the SYS team. I have takenpart in these chats which take place every Tuesday at 14 o’clock (generalchat) and Thursday at 17 o’clock (ESMO chat). The duration of a chatsession is approximatively one hour and a half.

1.5.1.2 FTP server

The FTP server is an arborescent structure of folders where all the files anddocuments provided by the different teams are placed. It also allows eachteam to consult very easily data, information, ..., from another one when itis required.

Concerning the documents, a part of them was provided by SSETI and hadto be updated regularly by Philippe Franssen and me. These documentscontain all our information and results about :

• preliminary functional specifications ;

• product tree ;

• requirements ;

• data, electrical and mechanical interfaces ;

• key parameters ;

• power, mass and data budgets ;

• design justifications.

In addition to the documents, we had to transmit to the SYS team in thenews server (see 1.5.1.3) a biweekly report which summed up what we didand why, what were the effects on the system, which documentation wasupdated, etc.

1.5.1.3 News server

The news server is a web forum in which each team also has a folder. Itallows an interaction between the teams. All the questions and answers areconserved and can be consulted by all the teams.


1.5.2 Workshops

The workshops are meetings held at the ESTEC for a week. These meetingsallow the teams to discuss and make technical decisions, reach compromisesaccording to demands, etc. Moreover, meetings with experts of ESA can bearranged in order to obtain their advice and opinions.

Figure 1.5: ESTEC

1.5.2.1 ESMO WS 1

WS 1 took place in October 2006. This was the kick-off workshop follow-ing the selection of the ESMO teams as a result of the CFP during summerand autumn. The results from the CDF study, performed during the timebetween the selection and the workshop, were discussed together with theproposed ESMO design. The first steps towards defining the basic require-ments and interfaces were taken by the teams after discussions. Invited ESAexperts held presentations, giving the students important knowledge and in-formation regarding the space environment and the process of designing aspacecraft, during the first days of the workshop. These initial days withpresentations were followed by working sessions, during which the studentsbegan defining their detailed requirements and interfaces for the separatesubsystems. The ground segment and mission analysis teams visited ESA’sSpacecraft Operational Centre, in Germany, for discussions dealing with theirtasks. The SSETI Association held a General Assembly for one of the days.Changes of the statutes together with the books from 2005 were presentedand approved by the assembly.


Participation of the NAC team to the WS1

The participants were Jean-François Vandenrijt and Gaëtan Gilles.During this WS, I presented our project to ESA members and the otherESMO teams. Afterwards, we asked for a meeting with an expert of ESAin order to obtain his advice about potential colour filters in front of thedetector, the number of lenses in the optical design, etc. We also discussedabout another project of camera which consisted of four sensors. One of themwould be qualified for space in order to guarantee the capture of imagesand the others would be «off the shelf» sensors in order to test differenttechnologies. Finally, discussions with other teams were undertaken in orderto provide information and to fix requirements for the NAC.

1.5.2.2 ESMO WS 2

In January 2007, the teams were invited to come and gain practical hands-on experience of spacecraft design and concurrent engineering using theirproposals and designs as a basis. They were able to use the expertise andfacilities available within the CDF to achieve a first coherent system design.

Significant progress was made in defining the two different spacecraft op-tions (chemical and electrical propulsions) for the lunar transfer. These willbe traded-off against each other at system-level during the Phase A studyperformed by the students. The main benefits for the students in using theCDF is that they learnt to work together in an interdisciplinary team environ-ment, making the necessary trade-offs and compromises in order to achievethe overall mission objectives within tight mass and cost constraints. Thisgave them a better understanding of the reality of a spacecraft system designas well as broadening their knowledge of all the other parts of the system bysubjecting them to the whole design iteration process.

The students also experienced various roles within the design process withsome taking part in splinter meetings and alternate design options, whileothers took on the roles of subsystem specialists and the system engineers incoordinating the design. Training on the use of the CDF model was given tostudents on the first day of the workshop by the CDF staff, and this allowedthem to use the model effectively during the design sessions, enabling a rapidsystem design process.


Participation of the NAC team to the WS2

Because of the exams of January, only Jean-François Vandenrijt wasable to take part in the second WS. As we said, this one intended to learnthe functioning of the CDF and to prepare the members of ESMO for theiCDF (see section 1.5.3). After the WS2, Jean-François Vandenrijt gaveto Philippe Franssen and me all the explanations in order to take part inthe iCDF.

1.5.2.3 ESMO WS 3

The upcoming WS will be held in July 2007 and will consist of the PhaseA PRR. At this point, the ESA management will make a go/no-go decisionon the project.

1.5.3 iCDF

The iCDF has the same objectives as the CDF study, but in which thestudents take part by using the Internet. A special infrastructure wascreated in order to organise that. There were four sessions in which I tookpart and which took place at the end of March and in April.

Before each session, each team had to connect with the server of ESAand update a specific datasheet. Afterwards, thanks to the chat channel,we debated on Thursday from 15 o’clock to 18 o’clock on which had to beimproved. Generally, these improvements consisted of reductions of the massor the consumed power in some systems.

The two first iCDF sessions concerned the case where the only payload wasthe NAC and the propulsion was chemical (first session) or electrical (secondsession). As the two last sessions, the payload was the NAC and the Cubesatin case of a chemical propulsion (third session) and in case of an electricalpropulsion (fourth session).

Chapter 2

Evolution of the NAC

Contents2.1 Call For Proposals . . . . . . . . . . . . . . . . . . . 15

2.2 Evaluation of team proposal . . . . . . . . . . . . . 16

2.2.1 Technical feasibility . . . . . . . . . . . . . . . . . 16

2.2.2 Manpower/Background . . . . . . . . . . . . . . . 16

2.2.3 University support/Academic credit . . . . . . . . 17

2.2.4 Funding/Industrial links . . . . . . . . . . . . . . . 17

2.2.5 Selection decision . . . . . . . . . . . . . . . . . . . 17

2.3 Expert review . . . . . . . . . . . . . . . . . . . . . . 17

2.4 Requirements for the NAC . . . . . . . . . . . . . . 19

2.4.1 Functional requirements . . . . . . . . . . . . . . . 19

2.4.2 Performance requirements . . . . . . . . . . . . . . 19

2.4.3 Operational requirements . . . . . . . . . . . . . . 19

2.4.4 Interface requirements . . . . . . . . . . . . . . . . 19

2.4.5 Structural requirements . . . . . . . . . . . . . . . 19

2.4.6 Reliability/Availability/Maintainability/Safety re-quirements . . . . . . . . . . . . . . . . . . . . . . 20

2.5 Design after WS1 and difficulties of the project . 20

2.1 Call For ProposalsIn June 2006, ESA launched a «Call For Proposals» for the ESMO mission

to the European and Canadian universities. CSL proposed a NAC project :

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CHAPTER 2. EVOLUTION OF THE NAC 16

it consisted of two mirrors separated by invar bars and which focus on thelight originally from the Moon to a CCD detector. This last one is cooledby an external radiator. At last, in order to process the pictures, proximity,memory and compression electronics were also planned. The dimensions ofthe instrument were 450 x 200 x 170 mm. As to the external radiator, itslength was 270 mm (see figure 2.1).

Figure 2.1: Design of the NAC before the CDF.

2.2 Evaluation of team proposal

2.2.1 Technical feasibility

The mass budget was considered reasonable even if it looked a bit pes-simistic. However, the sizing of the camera was critical since 450 mm wasalready more than half of one dimension of the whole spacecraft. Takinginto account other space-consuming subsystems (propellant tanks, thermalradiators, etc.), the camera’s size was estimated to be too large. Whetherit was because of a wrong assessment, the envisaged hardware was not ableto fulfil the size requirements. It was therefore highly recommended thatstructures, electronics and other equipments of the payload are shared in anintegrated way, if relevant, with other spacecraft subsystems.

2.2.2 Manpower/Background

The education of the proposed students was estimated relevant for thepurpose of the activity, but some experience in the critical optics area waslacking. However, the fact that CSL, which supports and backs up the pro-


posal, has extensive experience in space missions and instruments, and thatmost of the necessary tools are available at CSL, was emphasized.

2.2.3 University support/Academic credit

It was estimated excellent. The professor is very supportive and the projectis a part of the Masters course. He has relevant and substantial expertise inthe field.

2.2.4 Funding/Industrial links

It was also estimated excellent : fully funded and supported locally byULg and Liege Espace ; links to Liege Espace and other local industries forspecialist software.

2.2.5 Selection decision

The camera is a requirement included in the Call of Proposals and thistopic is fairly well addressed in the proposal. CSL was selected as primaryteam for the NAC of the ESMO payload.

2.3 Expert reviewAfter the selection of the ESMO teams in September 2006, an expert review

followed in order to determine the necessary changes to bring in the sub-systems of the satellite.

The CCD sensor was replaced by a CMOS detector. This last one hasa drastic increased radiation robustness and needs low-resources proximityelectronics. Moreover, the necessary power is approximately 10 W, in op-position to the CCD sensor which needs 25 W. At last, the CMOS detectordoes not require to be cooled.

The design was also changed. The project was too large and weighty. Thedesign proposed by the CDF was inspired by the instrument AMIE of themission SMART-1. It consists of a box extended by a tube in which a set oflenses is placed.


Figure 2.2: Design suggested by theCDF.

Figure 2.3: AMIE camera (missionSMART-1).

The dimensions of the instrument were reduced to 300 x 100 x 100 mm.As to the mass budget, it transited from 5 kg to 2.3 kg (see table 2.1).

Parameter Value (g)Previous design mass budget Mirrors 600

Structure (Al) 2000Invar bars 260FPA 1000Proximity electronics 300Memory and compression electronics 300Structure feet (Ti) 150Radiator 370Other (screws, connectors, ...) 150Total 5130Additional 20% margin 6156

New design mass budget (CDF) Lenses 200Optical System Assembly 100Structure (Al) 1100FPA 100Proximity electronics 400Compression electronics 100Structure feet (Ti) 150Other (screws, connectors, ...) 150Total 2300Additional 20% margin 2760

Table 2.1: Evolution of mass budget according to CDF.


2.4 Requirements for the NACThe sub-system requirements were fixed during the ESMO WS1 in October

2006. They must be satisfied and so will control the global design of thecamera.

2.4.1 Functional requirementsThe NAC shall map lunar surface characteristics for educationoutreach purposes.The NAC shall take at least 5 pictures per day of the lunarsurface for a period of at least 4 weeks.The NAC shall take images from a polar lunar orbit with aperilune of 200 km.

2.4.2 Performance requirementsThe NAC shall use a detector of 1024 x 1024 pixels.The NAC shall use lenses to focus light on the detector.The images taken by the NAC shall have a spatial resolution of10 m at 200 km.The total power consumption shall be less than 10 W.

2.4.3 Operational requirementsThe NAC shall take pictures of the Moon on request.The NAC shall be pointed with enough precision during the timeexposure.

2.4.4 Interface requirementsThe images from the NAC shall be transfered to the OBC (wherethey shall be compressed) with a spacewire.The NAC shall be attached to the structure of the spacecraftso as to obtain enough precision in the pointing.

2.4.5 Structural requirementsThe NAC shall have a maximum mass of 2.5 kg.The dimensions of the NAC shall be 300 x 100 x 100 mm.


2.4.6 Reliability/Availability/Maintainability/Safety re-quirements

The NAC performance shall be tested before launch.The structure of the NAC shall be sufficiently thick in orderto survive the radiations during the mission.

2.5 Design after WS1 and difficulties of the pro-ject

After the WS1, the design of the camera was very similar to the proposalof the CDF. Initially, the camera is composed of a tripod on which a tube is

Figure 2.4: Representation of the tripod, the tube and the optical baffle ofthe NAC.

fixed. In order to reinforce it, we put stiffeners. The tripod and the stiffenersconstitute the FPA. Indeed, this part of the structure also serves to carry thedetector (placed on the axis of the tube) and the proximity electronics. Inorder to protect this last one from radiation, a box covers the FPA.

Figure 2.5: Representation of the NAC with the tube, the baffle and theprotective box (the shutter does not appear).


As we said in the requirements, the structure of the camera shall be suffi-ciently thick in order to survive the radiations during the mission. Of course,the thickness depends on the used material. In order to have a lightweightcamera (the camera shall have a maximum mass of 2.5 kg), I envisagedto use the aluminium alloy 7075 T6 Al-ZnMgCu, which has a density of2.8 g/cm3 and a good resistance (the yield tensile strength is approxima-tively 570 MPa). In the mission project ESEO, the recommendation is tohave a minimum thickness of 3 mm in the case of aluminium in order to pro-tect electronics against radiation. We chose to follow this recommendationand gave this thickness to the box of the camera since, as we said, this oneaims at protecting electronics.

Concerning the global dimensions of the camera, these ones shall be 300 x100 x 100 mm, which limits the size of the different elements of the structure.We foresee a 100 mm side for the box. So we can allow ourselves a 200 mmtube length. However, we wanted to add at the extremity of the tube anoptical baffle in aluminium for the shake of the optical system. This bafflewill be covered by black coating and intend to reduce the effect of parasitelight during the imaging phase of the mission. Ideally, the length of the bafflemust be as long as possible, but it will be limited in order to preserve therequired global dimensions. In order to add a baffle, a quarter of the tube(50 mm) will be inside the protective box, the remaining three quarters (150mm) being outside. That permits to have a 50 mm optical baffle.

We also envisaged the presence of a shutter which will close the apertureof the baffle during the launch and the cruising phase in order to protect thelenses from contamination and solar light. This shutter will open thanks toan actuator during the mission, permitting in this way to take images of theMoon. Once again, it affected the mass budget, but also the power budgetbecause of the actuator. Indeed, we will see in chapter 6 that each sort ofactuators needs some power (25 W for a frangibolt device and from 5 to 10W for a HOP actuator) to be activated.

One of the main difficulties was the design of the tube. Indeed, this onewill contain the lenses which will focus light on the CMOS detector and musttherefore be designed according to the optical system which must satisfy aspatial resolution of 10 m at the perilune of the polar orbit (200 km). As aconsequence, a first optical design, obtained in November 2006 by PhilippeFranssen, was necessary before starting the design of the tube. Moreover,the gradual improvement of the optical system required suitable changes inthe structure, in particular in the mounts of the lenses. The optical de-


sign also created problems concerning the mass budget of the camera. InFebruary 2007, it was necessary to replace aluminium alloy by titanium alloy(Ti-6Al-4V) for the tube and the FPA. The reason is that aluminium de-forms itself very easily in the presence of temperature gradients, which risksdamaging the lenses in the tube. Titanium, which has a CTE of 8.9 10−6 K−1

(against 24 10−6 K−1 for aluminium), is more suitable in order to avoid largestrains due to temperature variations. However, the material has a densityof 4.43 g/cm3 and is therefore heavier than aluminium, which affected themass budget of the camera. I had to review the thickness of the tube in orderto keep a weight below 2.5 kg : it evolved from 7 mm when the material wasaluminium to 5 mm. Concerning the other parts of the camera, i.e. the boxand the baffle, I kept them in aluminium in order to avoid a weight biggerthan 2.5 kg.

Another difficulty of this project was that we sometimes had to wait in or-der to obtain necessary information from the other teams. For example, theNAC perfomance shall be tested before launch. That includes in particularthe resistance of the camera to the vibrations during the launch of ESMO.In order to provide launch opportunities to micro Auxiliary Payload, ARI-ANESPACE has developed a circular platform called ASAP 5 to carry anddeploy small and medium satellites. Before the launch, the satellite will beplaced on this platform and subjected to vibration tests in order to check thateach sub-system resists. All the characteristics about spacecraft mechanicalenvironment qualification and acceptance tests are given in a manual, whichpermits to do simulations by computer. With the help of the software Sam-cef, I wanted to simulate the random vibration tests and I had to take intoaccount the amplifications at the level of the camera1. So I had to knowthe configuration and the mass of the different sub-systems in the satellite inorder to estimate these amplifications. In March 2007, I discussed with theSTRU team in order to obtain this information, but this one has not beenable yet to give me all the details of the configuration.

1The accelerations are applied at the base of the satellite, but the camera is placed onthe top of this one.

Chapter 3

Design of the tube

Contents3.1 Evolution of the optical design . . . . . . . . . . . 24

3.2 Carriage of the lenses in the tube . . . . . . . . . . 24

3.3 Interfaces between the lenses and the mount . . . 25

3.3.1 "Sharp-corner" interface . . . . . . . . . . . . . . . 25

3.3.2 Tangential interface . . . . . . . . . . . . . . . . . 26

3.4 Design of the mounts . . . . . . . . . . . . . . . . . 27

3.4.1 Characteristics of the lenses in the optical design . 27

3.4.2 Case of concave surfaces . . . . . . . . . . . . . . . 28

3.4.3 Case of convex surfaces . . . . . . . . . . . . . . . 28

3.4.4 Shape of the interfaces . . . . . . . . . . . . . . . . 29

3.4.5 Gap in the event of dilatation . . . . . . . . . . . . 30

As we previously said, the design of the tube is very dependent on the opti-cal system constituted by the lenses. The tube must be designed according tothis system of lenses in such a way that the optical requirements of the NAC,such as the resolution of the images, are fulfilled. In order to satisfy theserequirements, we must introduce constraints on the lenses (seats, retainers,spacers, etc.) which will permit to fix them in the positions established bythe optical design. Moreover, we must check that the lenses cannot havedisplacements superior to 20 µm and are not damaged in case of dilatationof the tube.

23

CHAPTER 3. DESIGN OF THE TUBE 24

3.1 Evolution of the optical designThe first optical design (November 2006) contained a system of seven lenses.

There were two models of this design : a 200 mm model and a 250 mm model.Afterwards, the length of the system (and in consenquence the length of thetube) was fixed at 200 mm and the number of lenses was reduced to six. Thissecond design (February 2007) is based on corrections and improvements ofthe first one. It is lighter and simpler, and it is based on real glasses andstandard curvatures – so it is more realistic. Each brace of lenses constitutesa barrel and the tube must be designed according to the characteristics andtolerances of the lenses.

Figure 3.1: Seven lenses optical design (November 2006).

Figure 3.2: Six lenses optical design (February 2007).

Finally, the last optical design in process (April 2007), also composed ofsix lenses (three barrels), needs a tube with a length of 210 mm.

3.2 Carriage of the lenses in the tubeEach barrel will be maintained in the following way. On one side of the

barrel, we will place a seat that has the role to hold up the brace of lenses.On the other side, a retainer will be screwed. Finally, a spacer will be placedbetween the two lenses in order to maintain them at a distance fixed by theoptical design. So the seat, the retainer and the spacer create constraints onthe lenses in the direction of the optical axis. These constraints must be spec-ified depending on the shape of the lenses, their tolerances, etc. Moreover,we must foresee a gap between the lenses and the mount in case of dilatation.


Indeed, if the lenses were in contact with the mount and the temperatureincreased, the lenses would risk being damaged because of dilatation.

Figure 3.3: Elements 1 and 2 represent the seat and the retainer. As toelement 3, it matches to the spacer separating the two lenses of the barrel.

3.3 Interfaces between the lenses and the mountWe will consider only two cases of interfaces.

3.3.1 "Sharp-corner" interface

The most simple interface between a mount and a lens is a "sharp-corner"interface. The inside radius of the mount at the interface is equal to :

ys =A

2

where A is the clear aperture of the lens.

Figure 3.4: "Sharp-corner" interface


3.3.2 Tangential interface

When the lens is convex, it is better to use a tangential interface as repre-sented on figure 3.5.

Figure 3.5: Tangential interface

The contact height, i.e. the distance between the contact point P1 and theoptical axis, is given by :

yc =A + DG

4

where A is the clear aperture of the lens and DG is its diameter. The insideradius of the mount at the interface is :

ys = yc −DG − A

4

We define the half-angle cone by :

ϕ =π

2− arcsin(yc/R)

So the axial location of P1 is :

∆x = R− x1

where :x1 = x2 − xs

xs = ys/ tan ϕ

x2 = R/ sin ϕ


3.4 Design of the mounts

3.4.1 Characteristics of the lenses in the optical design

The characteristics of the lenses are given in table 3.1. R1 and R21 are the

two radius of curvature of the lens, e is its thickness and D is its diameter.

R1 [mm] R2 [mm] e [mm] D/2 [mm]Lens 1 57.32500 -207.82000 7.88504 16.05850Lens 2 -195.62000 1056.80000 5.43524 16.05850Lens 3 51.14000 361.30000 4.64227 11.00000Lens 4 -91.03100 57.95100 6.84621 11.00000Lens 5 -70.85000 51.27100 4.00000 9.00000Lens 6 81.43000 -122.78000 6.99935 9.00000

Table 3.1: Characteristics of the lenses according to the optical design.

Actually, the diameter D corresponds to the clear aperture of the lenses.As a consequence, the real lenses will have a higher diameter. So we canrewrite the table in the following way :

R1 [mm] R2 [mm] e [mm] A/2 [mm] DG/2 [mm]Lens 1 57.32500 -207.82000 7.88504 16.05850 18.05850Lens 2 -195.62000 1056.80000 5.43524 16.05850 18.05850Lens 3 51.14000 361.30000 4.64227 11.00000 12.00000Lens 4 -91.03100 57.95100 6.84621 11.00000 12.00000Lens 5 -70.85000 51.27100 4.00000 9.00000 11.00000Lens 6 81.43000 -122.78000 6.99935 9.00000 11.00000

Table 3.2: Characteristics of the lenses after the increase of their diameter.

where A is the clear aperture and DG is the diameter.1When R1 is negative, it means that the surface is concave. Equally, when R2 is

negative, it means that the surface is convex.


Figure 3.6: Scheme of a lens.

Thereafter, we will name Si1 (respectively Si2) the surface of the i-th lensthat has the radius of curvature R1 (respectively R2).

3.4.2 Case of concave surfaces

For these surfaces, we will choose a sharp-corner interface with the mount.The concave surfaces of the optical design are S21, S22, S32, S41, S42, S51 andS52. Table 3.3 gives the inside radius of the mount at the interface ys foreach surface.

Surface A/2 [mm] DG/2 [mm] R [mm] ys [mm]S21 16.06 18.06 -195.62 16.06S22 16.06 18.06 1056.8 16.06S32 11 12 361.3 11S41 11 12 -91.031 11S42 11 12 57.951 11S51 9 11 -70.85 9S52 9 11 51.271 9

Table 3.3: Inside radius of the mount for the concave surfaces.

3.4.3 Case of convex surfaces

The other surfaces of the lenses, i.e. S11, S12, S31, S61 and S62, are convexand it is preferable to use tangential interfaces with the mount in this case.Table 3.4 gives all the required characteristics according to subsection 3.3.2.


Surface A/2 [mm] DG/2 [mm] R [mm] yc [mm] ys [mm] ϕ [°] ∆x [mm]S11 16.06 18.06 57.325 17.06 16.06 72.69 2.285S12 16.06 18.06 -207.82 17.06 16.06 94.71 -0.619S31 11 12 51.14 11.5 11 77.00 1.194S61 9 11 81.43 10 9 82.95 0.493S62 9 11 -122.78 10 9 94.67 -0.326

Table 3.4: Characteristics for the convex surfaces.

3.4.4 Shape of the interfaces

The following figure shows the profile of the interfaces between the lensesand the mount for the three barrels.

Figure 3.7: Shape of the interfaces for each barrel.

If we take the system of axis illustrated on figure 3.8, the points Pi (i =1, 2, ..., 24) will have the following coordinates :


P1 P2 P3 P4

x [mm] -207.81 -207.18 -202.98 -202.82y [mm] 16.06 18.06 18.06 16.06

P5 P6 P7 P8

x [mm] -201.95 -201.95 -195.52 -195.52y [mm] 16.06 18.06 18.06 16.06

P9 P10 P11 P12

x [mm] -151.89 -151.66 -148.24 -148.24y [mm] 11 12 12 11

P13 P14 P15 P16

x [mm] -147.73 -147.73 -138.83 -138.83y [mm] 11 12 12 11

P17 P18 P19 P20

x [mm] -72.35 -72.35 -66.3 -66.3y [mm] 9 11 11 9

P21 P22 P23 P24

x [mm] -64 -63.75 -57.98 -57.82y [mm] 9 11 11 9

Figure 3.8: System of axis used to determine the coordinates of the pointsPi.

3.4.5 Gap in the event of dilatation

As we said, we must foresee a gap between the lenses and the different in-terfaces in case of dilatation. However, we must also consider the tolerancesof the lenses. Indeed, these ones cannot be subjected to too great displace-ments in order not to damage the optical performances. The tolerances ofeach lens are 0.02 mm for each space direction. So we chose to let a gapbetween the lenses and the mount of 0.005 mm in the direction of the opticalaxis and in the direction perpendicular to the optial axis. The coordinatesof the points Pi become :


P1 P2 P3 P4

x [mm] -207.815 -207.192 -202.980 -202.815y [mm] 16.065 18.065 18.065 16.065

P5 P6 P7 P8

x [mm] -201.955 -201.955 -195.515 -195.515y [mm] 16.065 18.065 18.065 16.065

P9 P10 P11 P12

x [mm] -151.895 -151.664 -148.235 -148.235y [mm] 11.005 12.005 12.005 11.005

P13 P14 P15 P16

x [mm] -147.735 -147.735 -138.825 -138.825y [mm] 11.005 12.005 12.005 11.005

P17 P18 P19 P20

x [mm] -72.355 -72.355 -66.295 -66.295y [mm] 9.005 11.005 11.005 9.005

P21 P22 P23 P24

x [mm] -64.005 -63.758 -57.978 -57.815y [mm] 9.005 11.005 11.005 9.005

Figure 3.9: Gap between a lens and its mount.

Chapter 4

Finite elements analysis

Contents4.1 Modal analysis by Samcef Field . . . . . . . . . . 33

4.1.1 Analyse data . . . . . . . . . . . . . . . . . . . . . 33

4.1.1.1 Behaviour . . . . . . . . . . . . . . . . . . 33

4.1.1.2 Material . . . . . . . . . . . . . . . . . . . 33

4.1.2 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4.1.3 Solver and result . . . . . . . . . . . . . . . . . . . 35

4.2 Mechanical study by Spectral . . . . . . . . . . . 37

4.2.1 Vibration environment . . . . . . . . . . . . . . . . 37

4.2.2 Random vibration tests . . . . . . . . . . . . . . . 37

4.2.3 *.psd file structure . . . . . . . . . . . . . . . . . . 38

4.2.4 Additional commands in the *.dat file . . . . . . . 39

4.2.5 Results . . . . . . . . . . . . . . . . . . . . . . . . 40

4.2.5.1 Excitation in the direction x . . . . . . . 40

4.2.5.2 Excitation in the direction y . . . . . . . 42

4.2.5.3 Excitation in the direction z . . . . . . . 43

The aim of this chapter is to verify that the stresses of the camera caused bythe vibrations during the launch remains in the domain of linear elasticity(the plasticity of materials must be avoided). The vibration environmentis described by ASAP 5 manual (see [9]). In order that the structure ofthe instrument is compatible with the levels requested for qualification and

32

CHAPTER 4. FINITE ELEMENTS ANALYSIS 33

acceptance tests, we used the software Samcef Field (modal analysis) andthe module Spectral of Samcef (evaluation of the stresses).

4.1 Modal analysis by Samcef Field

In a first time, we made a modal analysis in order to determine the firstmodes of the camera and the corresponding eigenvalues. This analysis isnecessary in order to know which modes will be excited afterwards.

4.1.1 Analyse data

After modeling the instrument in Samcef Field, we must introduce allthe data necessary for the analysis.

4.1.1.1 Behaviour

In a first time, we must specify the behaviour of the different parts ofthe camera. Figure 4.1 shows the window which permits to introduce thecorresponding data.

Figure 4.1: Introduction of behaviour in Samcef Field

4.1.1.2 Material

After introducing the behaviour, we must specify the properties of the usedmaterials.


Figure 4.2: Model of the camera in Samcef Field : the brown parts aremade up of titanium ; the grey parts are made up of aluminium.

The tube and the FPA of the NAC will be made up of a titanium alloy(Ti-6Al-4V). For the rest of the camera, we will use an aluminium alloy(7075 T6 Al-ZnMgCu) in order to reduce the weight of the camera. Table4.1 gives the necessary mechanical properties of these alloys to introduce inSamcef Field (see figure 4.3 and 4.4).

Ti-6Al-4V 7075 T6 Al-ZnMgCuDensity ρ [kg/m3] 4430 2800Young’s modulus E [MPa] 114 000 73 000Poisson’s ratio ν 0.33 0.33yield tensile strength σ0 [MPa] 1 100 570

Table 4.1: Properties of Ti-6Al-4V and 7075 T6 Al-ZnMgCu alloys.

Figure 4.3: Introduction of mechanical properties of Ti-6Al-4V.


Figure 4.4: Introduction of mechanical properties of 7075 T6 Al-ZnMgCu.

4.1.2 Mesh

The following step is the mesh of the structure. We choose an averagemesh size of 7 mm. The elements are tetrahedronic and linear, and areautomatically generated. This gives a number of degrees of liberty close to16270 and a number of nodes close to 5000, i.e. close to the limit of SamcefField.

Figure 4.5: Mesh of the camera. Figure 4.6: Mesh without the box.

4.1.3 Solver and result

After the mesh is created, the calculations can be done. We calculated thefirst ten modes of the camera whose corresponding frequencies are taken backin table 4.2.


Mode number Frequency [Hz]mode 1 294.304mode 2 369.776mode 3 1164.326mode 4 1501.698mode 5 2367.142mode 6 2609.564mode 7 3146.143mode 8 4187.945mode 9 4385.657mode 10 4398.343

Table 4.2: Ten first modes of NAC.

We can see that the first frequency is superior to 100 Hz, which is generallyrequired for the instruments in a satellite.

We also illustrated in figures 4.7, 4.8, 4.9 and 4.10 the first four modes ofthe camera. We will see in section 4.2.2 that, during the random vibrationtests, the range of frequencies is [20 2000] Hz. Therefore, only these modeswill be excited.

Figure 4.7: Mode 1 (294.304 Hz). Figure 4.8: Mode 2 (369.776 Hz).

Figure 4.9: Mode 3 (1164.326 Hz). Figure 4.10: Mode 4 (1501.698 Hz).


The first two modes correspond to bending modes of the tube respectivelyround the y-axis and z-axis. As to the two other modes, they correspond tobending modes of the tube and the box round the y-axis and z-axis.

4.2 Mechanical study by Spectral

In order to study the distribution of the stresses in the camera, we had touse the module Spectral of Samcef. This study was made with the helpof GDTech.

After the determination of the first modes of the camera, Samcef Fieldprovides a file *.dat which contains all the data related to the modelisationof the camera, the behaviour and the properties of materials, the mesh, etc.One only needs to get back this file and add it to some additional commandsspecific to Spectral. We must also create a file *.psd which provides toSpectral the PSD of the vibration environment.

4.2.1 Vibration environment

In order to show that a designing is acceptable, the tests with the qualifi-cation levels, which are the most restrictive, shall be succeeded. The valueswhich are given in ASAP5 manual are applied at the interface between thesatellite and the rocket, i.e. at the base of the satellite. As a consequence,we must take into account the amplifications between the base of the satelliteand the instrument. As we said in chapter 2, we asked the STRU team in-formation about the configuration of the different sub-systems in the satellitein order to estimate these amplifications, but it was not available yet. So theteam suggested using a safety factor of 1.5.

4.2.2 Random vibration tests

The random vibration test levels for the qualification and acceptance areas follows :

• Qualification : 0.0727 g2/Hz flat PSD between 20 Hz and 2000 Hz.

• Acceptance : 0.05 g2/Hz flat PSD between 20 Hz and 2000 Hz.


Figure 4.11: Qualification and acceptance levels in random vibration tests.

The random vibration tests must be performed along the 3 satellites axes.The test durations are two minutes per axis for qualification and one minuteper axis for acceptance.

A notching procedure may be agreed based on a preliminary low level run.

4.2.3 *.psd file structure

The *.psd file structure is the following :

• First line : Number of control frequencies.

• Second information : List of control frequencies, expressed in rad/secif unit time is the second. Control frequencies are specified in ascendingorder.

• Third information : Number of excitations.

• Fourth information : For each control frequency and according totheir orders, we give the lower triangle of the excitation matrix, lineby line. The terms of the excitation matrix are expressed in varianceby rad/sec, if unit time is the second. For instance, according to theInternational unit system (SI system), one acceleration PSD will beexpressed in (m/s2)2/(rad/s).


According to the vibration environment described previously, we obtain thefollowing structure for the *.psd file :

2.12566E+03 0.12566E+05

1.11135E+07 0.00000E+00.11135E+07 0.00000E+00

4.2.4 Additional commands in the *.dat file

The additional commands in the *.dat file are the following :

1. .DGEIRDY 12 ISTOP 2 NOP1 0

This command gives general integer data. The signification is :

• IRDY 12 : Indicator of random response calculation ;

• ISTOP 2 : Stop after calculation of the quadratic means of com-parison stresses ;

• NOP1 0 : Standard printout.

2. .DGRTEQ 120

where TEQ - corresponds to the equivalent stationary duration, ex-pressed in seconds if unit time is the second, during which excitationis applied.

3. .CATNPAS 20 F1 20 F2 2000

This command is relative to control frequencies. We have :

• NPAS - : Number of control frequencies uniformly spaced over alogarithmic scale between extreme frequencies defined using F1and F2 parameters ;

• F1 - : Minimum frequency in Hertz ;

• F2 - : Maximum frequency in Hertz.


4. .BASI 1000000 C x V 1.5 N 1 T 1

This command is relative to prescribed accelerations. We have :

• I - : Node member ;

• C - : Component number [x must be replaced by 1 (direction x),2 (direction y), 3 (direction z), 4 (rotation round direction x), 5(rotation round direction y) or 6 (rotation round direction z)];

• V - : Value of the amplification factor associated with the accel-eration ;

• N - : Component number of the excitation matrix associated withthe degree of freedom involved ;

• T - : Printing of quadratic mean, central frequency and peakfactor.

5. .AMMI 11111 V 0.01

This command is relative to modal damping. We have :

• I - : Number of the mode involved (11111 allows the selection ofall modes) ;

• V - : Is the value of the critical damping fraction (0.01 for 1%).

4.2.5 Results

The upper face of the protective box of the camera will be fixed on thestructure of the spacecraft. The following results were obtained by clampingthe three rotational motions of the camera and the translatory motions intwo directions, the excitation being applied on the third one.

4.2.5.1 Excitation in the direction x

The following figures represent the distribution of the equivalent Von Misesstresses, the view being oriented in different directions.


Figure 4.12: View in the direction[1 1 1].

Figure 4.13: View in the direction[−1 1 1].

When the excitation is applied on the direction x, i.e. the direction of thetube, the maximum stress is 12.33 MPa. We can see in figure 4.16 thatthe more stressed parts of the camera are the corner of the tripod and thebottom of the stiffeners. Since the excitation is applied in the direction x,it is normal that the FPA undergoes the most significant stresses. Concern-ing the resistance of the camera, we know that the yield tensile strength ofTi-6Al-4V is equal to 1 100 MPa. The maximum stress is therefore widelybelow this value.

Figure 4.14: View without box andbaffle in the direction [1 1 1].

Figure 4.15: View without box andbaffle in the direction [−1 1 1].


Figure 4.16: View in the direction [−1 1 1] (zoom).

4.2.5.2 Excitation in the direction y

This time, the maximum stress is equal to 19.18 MPa and the more stressedpart is the extremity of the tube close to the FPA (see figure 4.21). Since theexcitation is applied in the direction y, the tube undergoes bending. We cancompare the situation with a beam fitted at its extremity and submitted toa transversal force. In this case, we have actually a significant stress at thefitted extremity.



Finally, concerning the resistance of the camera, the maximum stress isonce again less than the yield tensile strength.


Figure 4.19: View in the direction[1 − 1 − 1].


Figure 4.21: View in the direction [1 − 1 − 1] (zoom).

4.2.5.3 Excitation in the direction z

In case the excitation is applied in the direction z (perpendicular to theupper face of the box), we can see that the maximum stress is equal to 25.56MPa, i.e. more significant than in the directions x and y. But this valueis always below the yield tensile strength value. Finally, like in the case ofan excitation in the direction x, the corner of the tripod is the most stressedpart of the camera (see figure 4.26).






Figure 4.26: View in the direction [1 1 1] (zoom).

Chapter 5

Thermal considerations

Contents5.1 Calculation of radiative transfers . . . . . . . . . . 46

5.1.1 Recall : view factors . . . . . . . . . . . . . . . . . 46

5.1.1.1 Definition . . . . . . . . . . . . . . . . . . 46

5.1.1.2 Properties of view factors . . . . . . . . . 46

5.1.2 Application to the NAC . . . . . . . . . . . . . . . 47

5.1.2.1 Ideal case . . . . . . . . . . . . . . . . . . 47

5.1.2.2 View factor between two disks . . . . . . 49

5.1.2.3 Rectification of the view factors (lens witha convex surface) . . . . . . . . . . . . . . 51

5.1.2.4 Numerical results . . . . . . . . . . . . . 53

5.1.3 Radiative transfers . . . . . . . . . . . . . . . . . . 53

5.1.3.1 Calculation of the flux qi and qij . . . . . 55

5.1.3.2 Numerical results . . . . . . . . . . . . . 55

5.2 Evaluation of the maximal temperature variationadmissible in the tube . . . . . . . . . . . . . . . . . 57

5.2.1 CTE of the different lenses and the tube . . . . . . 57

5.2.2 Dilatation of the lenses and the tube . . . . . . . . 57

5.2.3 Shrinkage of the lenses and the tube . . . . . . . . 59

5.2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . 59

45

CHAPTER 5. THERMAL CONSIDERATIONS 46

5.1 Calculation of radiative transfersThe camera will be externally insulated and maintained at a 20 °C temper-

ature. However, when the shutter opens, the first lens and the cross-sectionof the tube, as well as the internal surface of the optical baffle, will see thecold space. So the camera will have radiative transfers with the cold space.This chapter is aimed at estimating the transfered flux.

5.1.1 Recall : view factors

5.1.1.1 Definition

Let be two surfaces Ai and Aj which constitute an enclosed space. The

Figure 5.1: Definition of the view factor.

view factor from surface Ai to surface Aj is defined by :

fij =1

πAi

∫Ai

∫Aj

cos θi cos θj

r2dSidSj

where r is the distance from a point of Ai to a point of Aj, and θi (re-spectively θj) is the angle between r and the surface normal of Ai (respec-tively Aj).

In fact, the view factor fij depicts the part of the radiation which gets awayfrom surface Ai and arrives to surface Aj. So we have 0 ≤ fij ≤ 1.

5.1.1.2 Properties of view factors

Here are some properties of view factors that we will use thereafter.

Property 5.1.Aifij = Ajfji


Property 5.2. If we have an enclosed space of N surfaces, the conservationof energy implicates that :

N∑j=1

fij = 1

j represents all the surfaces seen by i ≤ N .

Property 5.3. If Ak is a convex surface, we have :

fkk = 0

5.1.2 Application to the NAC

Figure 5.2 shows the different surfaces which see the cold space, i.e., aswe said, the surface of the first lens, the cross-section of the tube and theinternal surface of the baffle.

Figure 5.2: S1 : internal surface of the optical baffle ; S2 : cross-section ofthe tube ; S3 : surface of the first lens.

We will determine the view factors between the surfaces and between asurface and the cold space.

5.1.2.1 Ideal case

In a first time, we consider an ideal case where the surface of the lens isplane. Moreover, we introduce a fictive surface S0 at the extremity of theoptical baffle1. This fictive surface will help us in the calculation of the viewfactors.

1The view factor fi0 (i = 1, 2, 3) represents the part of the radiation which gets awayfrom Si to S0, i.e. to the cold space.


Figure 5.3: Ideal case : S3 is a plane surface.

Let name R the radius of the optical baffle, h its length and r the radiusof the lens. The surfaces are given by :

S0 = πR2

S1 = 2πRh

S2 = π(R2 − r2

)S3 = πr2

Using property 5.2, we obtain the following system of equations :f10 + f11 + f12 + f13 = 1f20 + f21 = 1f30 + f31 = 1f01 + f02 + f03 = 1

The view factors f00, f22 and f33 are null because the surfaces are plane.About f23, each beam getting away from S2 cannot reach S3. So we havef23 = f32 = 0.

The system can be written in the following way (see property 5.1) :f10 + f11 + f12 + f13 = 1f20 + S1

S2f12 = 1

f30 + S1

S3f13 = 1

S1

S0f10 + S2

S0f20 + S3

S0f30 = 1

So we have four equations and six unknowns. Two equations are missing inorder to solve the system.


5.1.2.2 View factor between two disks

Let take two disks which are parallel and have the same axis (see figure5.4). If we fix :

R1 =r1

h

R2 =r2

h

X = 1 +1 + R2

2

R21

the view factor from disk 1 to disk 2 is given by (see [5]) :

f12 =1

2

X −

√X2 − 4

(R2

R1

)2 (5.1)

Figure 5.4: Parallel disks with the same axis

In case the two disks have the same radius (r1 = r2 = r), we will obtain :

f12 = f21 =1

2

[X −

√X2 − 4

](5.2)

where X = 2 + (h/r)2.

Thanks to these relationships, we can determine the view factors f20 and


f30. Indeed, we have, according to the equation (5.1) :

f30 =1

2

X −

√X2 − 4

(a2

a1

)2

where

a1 =r

h

a2 =R

h

X = 1 +1 + a2

2

a21

About f20, we can write :

f0,2∪3 = f02 + f03

Indeed, generally speaking, if Uj are disjointed surfaces, we have2 :

fi,Uj=

∑j

fij

Since S2 and S3 are disjointed, the relationship is correct. So, we have :

f0,2∪3 =S2

S0

f20 +S3

S0

f30

According to the equation (5.2), f0,2∪3 is given by :

f0,2∪3 =1

2

[X0 −

√X2

0 − 4

]with

X0 = 2 +

(h

R

)2

and we obtain :

f20 =S0

S2

f0,2∪3 −S3

S2

f30

2Otherwise, we havef1,2∪3 = f12 + f13 − f1,2∩3


So it remains four unknowns — f10, f11, f12, f13 — which are given by :

f12 = S2

S1(1− f20)

f13 = S3

S1(1− f30)

f10 = S0

S1− S2

S1f20 − S3

S1f30

f11 = 1− f12 − f13 − f10

5.1.2.3 Rectification of the view factors (lens with a convex sur-face)

Actually, the surface of the first lens is convex. The effect is that we cannotwrite f23 = 0. Moreover, the other view factors are modified, except for f10.

Figure 5.5: Rectification : S3 is convex.

If the bend of the lens is not important, f20 does not change either.

Figure 5.6: We plot on the scheme the straight line linking the point P andthe extremity of the baffle, and the tangent of the arc of circle at the pointP . If the gradient of the tangent is lower than the gradient of the straightline, f20 will change. Otherwise, f20 will have the same value as the idealcase.

At last, f3′3′ = 0 because the surface is convex.

Let name S3′ the convex surface of the lens and R its curvature radius. We


have :S3′ = 2πRδ

whereδ = R

[1− cos

(arcsin

( r

R

))]

Figure 5.7: Geometry of the surface S3′ .

We see that the radiation getting away from S0 and cutting S3′ cuts S3 too.So we can write :

f03 = f03′

i.e.

f3′0 =S3

S3′f30

In the same way, we can say that each beam getting away from S3 and cuttingS1 cuts S3′ too. So

f31 = f3′1

i.e.

f13′ =S3′

S3

f13

Finally, we know that :f10 + f11 + f12 + f13′ = 1f20 + S1

S2f12 + f23′ = 1

f3′0 + S1

S3′f13′ + S2

S3′f23′ = 1

so we have the following relationships :

f23′ =S3′S2

(1− f3′0 − S1

S3′f13′

)f12 = S2

S1(1− f20 − f23′)

f11 = 1− f10 − f12 − f13′


5.1.2.4 Numerical results

We have the following datas :

R = 23.5 mmr = 16 mmh = 50 mmR = 57.325 mm

Considering the dimensions, we can check that f20 will not be affected by thebend of the lens.

The following table gives us the view factors in the ideal case (secondcolumn) and when we rectify (third column). We observe that there areno big differences between the two cases.

Ideal case Rectificationf11 60.38 % 60.23 %f12 10.76 % 10.72 %f13 09.05 % 09.23 %f23 00.00 % 00.30 %f10 = f1,cold space 19.81 % 19.81 %f20 = f2,cold space 14.65 % 14.65 %f30 = f3,cold space 16.91 % 16.58 %

Table 5.1: View factors

Remark : In the table and in case of the rectification, we renamed S3 thesurface S3′ .

5.1.3 Radiative transfers

The radiative transfers between the surfaces and the cold space can beimitated by an equivalent wiring diagram (see figure 5.8).


Figure 5.8: Equivalent wiring diagram of the problem.

The "voltages" Vi (i = 0, 1, 2, 3 3) match to εi

αiEb (Ti) where :

• εi is the emissivity of Si ;

• αi is the absorptivity of Si ;

• Eb (Ti) is the energy that a black body could radiate at the same tem-perature Ti.

qi (i = 0, 1, 2, 3) is the flux emitted by the surface Si and qij (i, j = 0, 1, 2, 3and i 6= j) is the flux transfered from surface Si to surface Sj. The "resis-tances" Ri (i = 1, 2, 3) match to 1−αi

αiSi, and the resistances Rij (i, j = 0, 1, 2, 3

and i 6= j) to 1fijSi

where fij is the view factor from Si to Sj.

If we assume that we have grey bodies, we can write εi = αi and so :

Vi = Eb (Ti)

Ri =1− εi

εiSi

In this way, we can calculate the flux emitted (or received) by the differentsurfaces and the flux interchanged between the surfaces thanks to the electriccircuits theory.

3The case i = 0 corresponds to the cold space which is modeled by a black body at5 K.


5.1.3.1 Calculation of the flux qi and qij

In order to determine qi and qij, we use Kirchhoff’s circuit laws, i.e. Kirch-hoff’s Current Law (KCL) and Kirchhoff’s Voltage Law (KVL). We obtainthe following system :

0 R1 0 0 R10 0 0 0 0 00 R1 0 −R3 0 0 R13 0 0 00 R1 −R2 0 0 R12 0 0 0 00 0 0 R3 0 0 0 0 0 R30

0 0 R2 0 0 0 0 R20 0 00 0 −R2 R3 0 0 0 0 −R23 00 1 0 0 −1 −1 −1 0 0 00 0 1 0 0 1 0 −1 −1 00 0 0 1 0 0 1 0 1 −11 0 0 0 1 0 0 1 0 1

q0

q1

q2

q3

q10

q12

q13

q20

q23

q30

=

V1 − V0

V1 − V3

V1 − V2

V3 − V0

V2 − V0

V3 − V2

0000

Since we want to maintain the temperature of the system at 20 °C (293 K),the "voltages" V1, V2 and V3 are given by :

V1 = V2 = V3 = 2934 σ

and V0 by :V0 = 54 σ (cold space = black body at 5 K)

where σ is the Stefan-Boltzmann constant (σ = 5.67 10−8 Js−1m−2K−4).

5.1.3.2 Numerical results

We have the following data :

Emissivity ε11 0.9

ε22 0.3

ε33 0.9

View factors f10 0.1981f12 0.1072f13 0.0923f20 0.1465f23 0.003f30 0.1658

Dimensions R 0.0235 mr 0.016 mh 0.05 mR 0.0573 m


So we obtain :

R1 = 15.05 m−2

R2 = 2 507.08 m−2

R3 = 135.41 m−2

R12 = 1 263.54 m−2

R13 = 1 467.51 m−2

R23 = 358 154.58 m−2

R10 = 683.75 m−2

R20 = 7 334.22 m−2

R30 = 7 350.24 m−2

V0 = 0.000035 Wm−2

V1 = 417.882 Wm−2

V2 = 417.882 Wm−2

V3 = 417.882 Wm−2

The fluxes are equal to4 :

q0

q1

q2

q3

q10

q12

q13

q20

q23

q30

=

−0.70350.62710.01930.05710.59740.0309−0.00120.0504−0.00010.0558

W

We can see that the total flux lost to the cold space is :

qlost = −q0 = 0.7035 W

It is this loss of flux which will have to be compensated for maintaining thetube at 20 °C.

1emissivity of a black coating2emissivity of titanium3emissivity of glass4When qi is negative, it means that surface Si receives the flux. When qij is negative,

it means that the flux is transfered from surface Sj to surface Si.


5.2 Evaluation of the maximal temperature vari-ation admissible in the tube

As we said in chapter 3, we must foresee a gap between the lenses and themount in case of dilatation. This gap was chosen equal to 0.005 mm in thedirection parallel and perpendicular to the optical axis. So we are going todetermine the maximal temperature variation admissible in the tube in orderto protect the optical system.

5.2.1 CTE of the different lenses and the tube

The tube is made up of titanium alloy which has a CTE of 8.9 10−6 K−1.As to the lenses, their CTE is resumed in table 5.2.

Type CTE [1/K]Lens 1 BK7G18 7 10−6

Lens 2 F5 8 10−6

Lens 3 UBK7 7.1 10−6

Lens 4 SF5 8.2 10−6

Lens 5 NBK10 5.8 10−6

Lens 6 SF10 7.5 10−6

Table 5.2: Radius and coefficient of thermal expansion of the lenses

5.2.2 Dilatation of the lenses and the tube

The tube dilates on the thickness according to the law :

∆e = αtubee0∆T

where ∆e is the variation of thickness, αtube is the CTE of the tube and e0

is the initial thickness. Equally, the lenses dilate on the diameter accordingto the law :

∆φ = αlensφ0∆T

where ∆φ is the variation of diameter, αlens is the CTE of the lens and φ0 isthe initial diameter.


Figure 5.9: Dilatation of the lens and the tube

We must avoid that :∆e + ∆φ > 0.01

or otherwise the tube risks damaging the lenses. So the maximal temperaturevariation is fixed by :

(αtubee0 + αlensφ0) ∆Tmax = 0.01

i.e.∆Tmax =

0.01

αtubee0 + αlensφ0

The following table gives the maximal temperature variation admissible foreach lens :

Lenses Radius of the lens [mm] Thickness of the tube [mm] ∆Tmax [K]BK7G18 18.06 5.435 33.20F4 18.06 5.435 29.64NBK7 12 11.495 36.67SF5 12 11.495 33.43NFK5 11 12.495 41.88SF10 11 12.495 36.20

Table 5.3: Maximal temperature variations.

We can see that the second lens will be the first one which will risk beingdamaged because of dilatation. The corresponding maximal temperaturevariation is 29.64 K.


5.2.3 Shrinkage of the lenses and the tube

We must also consider the case of a shrinkage of the elements. Indeed, ifthe temperature decreases, the gap between the lenses and the mount willincrease. However, we must take into consideration the tolerances of thelenses, i.e. the maximal displacements that the lenses can have withoutdegrading the optical performances.

So we must avoid that

|∆e|+ |∆φ| > 0.01

We consider the modulus because ∆e and ∆φ are negative. Of course, weobtain the same values as previously, though the temperature variations arenegative.

5.2.4 Conclusion

As we said, the tube will have to be ideally maintained at a temperature of20 °C. However, local variations of temperature are always possible : in prac-tice, the tube will not perfectly be maintained at the wanted temperature. Sothe previous calculation gives us an estimation of the maximum temperaturevariation which can appear locally, i.e. 29.64 °C above and below 20 °C.

Chapter 6

Opening system of the shutter

Contents6.1 Shape Memory Alloy . . . . . . . . . . . . . . . . . 61

6.2 Frangibolt device . . . . . . . . . . . . . . . . . . . . 61

6.3 High Output Paraffin actuator . . . . . . . . . . . 64

6.4 Comparison of models . . . . . . . . . . . . . . . . . 66

In order to protect the lenses against pollutants during the launch and thesolar light during the travel in space, we will place a shutter at the extremityof the baffle. The opening system of the shutter will be realised thanks toa spring and an actuator. As long as this last one is not set in action, theshutter will be maintained closed. But, at the moment when the actuator isengaged, the system will be free and the spring will drive the opening of theshutter. About the moment of this last one, it must still be established.

The reason of that study has its importance for the mass and power budgets.Indeed, the opening system must be in such a way that the weight of thecamera does not exceed 2.5 kg. Moreover, the actuator will have to consumepower. It is therefore necessary for this consumed power to be provided bythe electrical power system. Finally, the dimensions of the actuator must bein such a way that the camera can be enclosed in a space of 300 x 100 x 100mm.

In this chapter, we envisage two sorts of actuators which use shape memoryalloys : the frangibolt and the HOP actuator.

60

CHAPTER 6. OPENING SYSTEM OF THE SHUTTER 61

6.1 Shape Memory AlloyA SMA is a metal that «remembers» its geometry. After a sample of SMA

has been deformed from its original atomic configuration, it regains its orig-inal geometry by itself during heating (one-way affect) or, at higher ambienttemperatures, simply during unloading (pseudo-elasticity or superelasticity).

The three main kinds of SMA are the copper-zinc-aluminium, copper-aluminium-nickel, and nickel-titanium (NiTi) alloys. NiTi alloys are generallymore expensive and possess superior mechanical properties when comparedto copper-based SMAs.

6.2 Frangibolt deviceThis system is used in the aerospace sector in order to replace the pyrotech-

nic uncoupling (bad for the structures). The SMA piece is warmed up, whichleads to a coming back to the initial form and exerts a pressure on the screwthat breaks and, as a result, disorganizes a unity.

Figure 6.1: Frangibolt concept.

The frangibolt mechanism offers enormous application versatility. Figure6.2 shows a few of the joint designs which can be used.


Figure 6.2: Examples of fixation with frangibolt mechanism.

However, the disadvantage of frangibolt mechanism is that, after actuation,elements are liberated and can damage the other sub-systems in the satellite.So an enclosure is necessary in order to maintain free elements. The figure6.3 shows a generic design of enclosure in which the frangibolt can be helddown and retained after actuation.


Figure 6.3: Example of enclosure

Specifications of FC2-16-31SR2

The model FC2-16-31SR2 is the smallest frangibolt actuator produced byTiNi Aerospace. The small envelope and minimal power consumption (25Watts @ 28 Vdc) are ideal for applications with stringent size and powerrequirements. This model is also the fastest frangibolt capable of operatingin less than 10 seconds.

Figure 6.4: FC2-16-31SR2 model


Max load support and release 2200 NMax joint length 4.4 cmOperational voltage 22 to 36 VdcMinimum operating temperature - 65 °CMaximum operating temperature 80 °CHeater resistance 31 OhmsMass 20 gPower consumption 25 W @ 28 Vdc

Table 6.1: Specifications of model FC2-16-31SR2.

6.3 High Output Paraffin actuatorThe volumetric expansion of paraffin that occurs during the solid-to-liquid

phase change provides the motive force for HOP actuators. Significant hydro-static pressure is generated by constraining the expansion within the actuatorbody. This pressure is transformed by the actuator to mechanical work inthe form of a linear shaft motion.

Figure 6.5: Structure of HOP actuators

Starsys HOP actuators use thermal energy, provided by an electric heateror a passive source, to create a controlled extension of the actuator shaft withminimal moving parts. Actuation temperature is determined by paraffin se-lection. Electrically activated models use high melting temperature paraffins(60 - 80 °C), which preclude premature actuation from high environmentaltemperatures. Passive control actuators use specially formulated paraffinswith melting temperatures at the control temperature.


Figure 6.6: Examples of HOP actuators

Specifications of some HOP actuators

IH-5055 EH-3525Mass 50 g 35 gPower/Voltage 10 W @ 28 V 5 W @ 28 VResponse time 2̃10 sec. @ 24 °C 2̃00 sec. @ 24 °COutput force 220 N 154 NOperating environment -180 to 115 °C -120 to 80 °C

Table 6.2: Specifications of HOP actuator models.

Figure 6.7: IH-5055 model. Figure 6.8: EH-3525 model.


6.4 Comparison of modelsThe FC2-16-31SR2 frangibolt is more lightweight than IH-5055 and EH-

3525 HOP actuators. However, as we said, we must foresee an enclosure in thecase of the frangibolt. As a consequence, we can estimate that, as far as themass budget, the considered actuators are equivalent. Concerning power, thefrangibolt requires a more great consumption than HOP actuators. A debatewith the EPS team will be necessary in order to establish the maximumpower which can be provided to the actuator.

Chapter 7

Conclusion

Contents7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . 67

7.2 Personal enrichment of the work . . . . . . . . . . 68

7.1 SummaryThe aim of this work was the feasibility study for the NAC of ESMO. The

two critical items in this study are the mass budget and the global dimensions.The corresponding requirements are a maximum mass of 2.5 kg and a 300 x100 x 100 mm structure.

The current mass budget is given in table 7.1. We can see that the requiredmass is satisfied. Concerning the dimensions of the camera, we can see inappendix B that the requirements are also obtained : the box has a side of100 mm and the part of the tube outside the box plus the optical baffle havea length of 200 mm, which gives therefore a 300 x 100 x 100 mm structure.

In July 2007, the camera project will be presented during the third WS.As we said in the introduction, the WS3 will consist of the PRR and decideor not the continuation of the ESMO mission. If it is accepted, the projectESMO will therefore be in Phase B.

Let add that improvements can be made at a late time. Indeed, we couldtake off mass by creating holes in the parts of the tube where there areno lenses, which would reduce the mass of the camera. So a mechanicalstudy should be made with these changes in order to verify the resistance

67

CHAPTER 7. CONCLUSION 68

Quantity Total mass Total mass with Remarkwithout margin [kg] 20% margin [kg]

Lenses 6 0.0707 0.08484Box and tube 1 1.269 1.5228FPA 1 0.319 0.3828Proximity 1 0.25 0.3 estimatedelectronic value (TBC)Screws 16 0.0096 0.01152 estimated

values (TBC)Connectors 2 0.1 0.12 estimated

values (TBC)Shutter 1 0.1 0.12 estimated

value (TBC)Optical baffle 1 0.108 0.1296Total 2.23 2.67

Table 7.1: Current mass budget

of the camera to the vibrations. Another possibility would be to excavatethe stiffeners. Moreover, as we can see in the mass budget, we foresee twoconnectors. Holes in the protective box of the camera will therefore haveto be created for these connectors. Finally, let note that, in the mechanicalstudy, we did not consider the presence of the lenses in the tube, or thepresence of electronics. In this last case, we need a first design which is atthis time taken in charge by Rémy Woine. The recognition of the lensesand electronics in the mechanical study could require changes in the designof the tube or the FPA.

7.2 Personal enrichment of the workThis work brought me a good experience for many reasons. At first, it

was the opportunity to manipulate the software Samcef and in particularits module Spectral. Then, that gave me an idea of the way in which amission is designed, in particular in a Phase A Feasability Study. Moreover,such work is different from an ordinary end of study work : we must facedifficulties specific to such a project (communication and compromises withthe other teams, changes in the design due to modifications in other sub-systems or in another part of the camera, etc.). Finally, the workshop let memeet people from other European countries and from Canada.

Appendix A

Acronyms and Abbreviations

ASAP Arianespace Support for Auxiliary PayloadsCCD Charge-Coupled DeviceCDF Concurrent Design FacilityCFP Call For ProposalsCSL Centre Spatial de LiègeCTE Coefficient of Thermal ExpansionESA European Space AgencyESEO European Student Earth OrbiterESMO European Student Moon OrbiterESTEC European Space Research and Technology CentreFPA Focal Plan AssemblyFTP File Transfer ProtocolGTO Geostationary Transfer OrbitLIDAR LIght Detection And RangingNAC Narrow Angle CameraOBC On-Board ComputerPRR Preliminary Requirements ReviewPSD Power Spectral DensitySMA Shape Memory AlloySMART Small Missions for Advanced Research in TechnologySSETI Student Space Exploration and Technology InitiativeTBC To Be ConfirmedULg University of LiegeWS Workshop

69

Appendix B

Current dimensions of the NAC

Figure B.1: Dimensions of the tube.

70

APPENDIX B. CURRENT DIMENSIONS OF THE NAC 71

Figure B.2: Dimensions of the box, the optical baffle and the FPA.

Bibliography

SSETI[1] SSETI website : www.sseti.net

Actuators and SMA

[2] TiNi AEROSPACE website : www.tiniaerospace.com

[3] Nimesis website : www.nimesis.com

[4] Starsys website : www.starsys.com

Thermal control

[5] Pierre Rochus & Véronique Rochus. Contrôle thermique spatial.

Optics

[6] Paul R. Yoder, Jr. Mounting Optics in Optical Instruments. SPIEPress, 2002.

[7] Optical Glass. Data Sheets. SCHOTT North America, Inc.

Mechanics

[8] Charles Massonet & Serge Cescotto. Mécanique des matériaux.De Boeck Université, 2001. 2nd edition.

72

BIBLIOGRAPHY 73

[9] ASAP 5 User’s Manual. Arianespace. Issue 1 - Revision 0 - May 2000.

[10] Properties of materials : www.matweb.com

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