A method for thermal ambient tests of space technology equipment
Contents
1. 373 710 2 676 5 303 149 114 100 564 0 004 120 711 115 410 393 861 2 539 4 748 107 070 120 604 0 107 Sai C B A Steinhart coefficients C 8 410311x10 2 395800x10 1 392714x10 Table 3 Steinhart Hart coefficients for the sensors Steinhart Hart coefficients Sensor ALC B C CF 1 1 392714x10 2 395800x10 8 410311x10 2 1 389369x10 2 402207x10 8 103822x10 3 1 391608x10 2 396213x10 8 384731x10 4 1 391828x10 2 398144x10 8 333081x10 5 1 394587x10 2 393127x10 8 601122x10 6 1 391608x10 2 396213x10 8 384731x10 7 1 391046x10 2 398763x10 8 340808x10 8 1 391398x10 2 397475x10 8 343215x10 9 1 391446x10 2 397680x10 8 327609x10 m a o Q S a Nn o a4 50 100 Temperature C Figure 3 Example of the temperature resistance relationship for sensor 1 18 The residuals for each sensor were evaluated from the mean temperature values calculated from the Steinhart Hart eguation and the temperature valus measured by the standard themometer at the temperature points using Eguation 2 27 AT sensori Tsensor i Ei T sta A 2 where AT sensori is the residual for respective sensor Tsensor i IS the temperature value of respective sensor using Steinhart equation Tsid is the temperature reading from the standard thermometer given by Equation 3 27 T sid Tsid ind 4 Tsta 6T res OT stab 3 where T std ind IS the tem2. 8 where OTinhom IS the temperature inhomogeneity Tref is the reference sensor mean temperature Ti is the mean temperature from any specific location The deviation of each sensor from the reference location L9 are given in Table 6 Spatial inhomogeneity results for the three temperature locations according to Equation 8 are given in Table 7 26 Table 6 Temperature deviations of locations from the reference location L9 Figure 6 Measurement Deviation from reference location C location 40 C 23 C 85 C LI 0 04 0 18 0 83 L2 0 63 0 52 0 56 L3 0 43 0 09 0 87 L4 0 50 0 09 0 97 L5 0 36 0 01 0 19 L6 0 44 0 20 0 06 L7 0 45 0 14 0 01 L8 0 16 0 07 0 40 Table 7 Spatial inhomogenities Temperature point 40 C 23 C 85 C Spatial inhomogeneity C 0 63 0 52 0 97 The temperature deviation of locations from the UVRL in the chamber at 85 C is given in Figure 7 Location L4 registers the highest temperature deviation and location L7 registers the lowest temperature deviation from the center of the useful volume Table 6 0 97 C 187 C BC 56 C 40 C 0 19 C 0 06 C 0 01 C F ron Figure 7 Local temperature deviation from the UVRL at 85 C 7 27 4 2 Evaluation of temporal instability 4 2 1 Evaluation of temporal instability for the whole useful volume Temporal instability for a
3. Non exclusive license to reproduce thesis and make thesis public I Sinai Mwagomba date of birth 23 11 1983 1 herewith grant the University of Tartu a free permit non exclusive license to 1 1 reproduce for the purpose of preservation and making available to the public including for addition to the DSpace digital archives until expiry of the term of validity of the copyright and 1 2 make available to the public via the university s web environment including via the DSpace digital archives as of 19 12 2014 until expiry of the term of validity of the copyright A method for thermal ambient tests of space eguipment developement and validation title of thesis supervised by PhD Riho Vendt and Professor Ivo Leito 2 Lam aware ofthe fact that the author retains these rights 3 This is to certify that granting the non exclusive license does not infringe the intellectual property rights or rights arising from the Personal Data Protection Act Tartu 11 12 2014 52
4. C2 14 84 C3 Figure 6 Sensor locations in the thermal chamber 25 4 Characterization of the thermal chamber In order to meet the specific objectives in characterizing the thermal chamber a step by step method of how results were obtained results and discussions are given for each parameter The characterization of the thermal chamber was done in the temperature range of 40 C to 85 C The range was chosen on the basis that the minimum and maximum measuring extreme temperatures for testing space eguipment were chosen and the third one at normal room temperature 23 C was also chosen The factors that contribute to the measurement uncertainty of temperature measurements in the thermal chamber including temperature inhomogeneity temperature instability radiation effect and loading effect were evaluated The temperature rate of change in the thermal chamber was also evaluated with different loading setups typical of loads that will be tested 4 1 Evaluation of spatial inhomogeneity In this thesis the spatial inhomogeneity was evaluated as the maximum deviation of temperature of each of the eight corners of the cube where the sensors are located from the central reference sensor Temperature values were taken from each sensor and spatial inhomogeneity was evaluated from the mean values of each sensor and the mean values of the reference sensor where spatial inhomogeneity is given by Equation 8 9 lOTinhoml Max T rep Til
5. The CDHS has a crucial role in a satellite mission It has a microprocessor that is used for coordinating the satellite and for logging and storing of data on three flash memory devices mounted on the board It also has sensors that are used for altitude determination of the satellite 31 33 Figure 11 shows the CDHS board in the chamber during the tests Figure 11 CDHS board in a thermal chamber during tests 5 2 Summary of the thermal ambient test Thermistor temperature sensor was mounted onto the specimen on the TRP microprocessor chip and the temperature of the test object during the test cycles was recorded in time using Labview software to track the actual temperature of the specimen A test program with four cycles that was developed using S mpati software was used in the test Figure 5 In order to maintain good contact between the test material and the sensor copper sensor block and thermal paste were used as described in section 4 6 The eguipment was placed in the useful volume of the chamber on an insulating material to ensure that the board does not touch the metal surface of the chamber shelf which could short circuit the board The USB data cable for powering the 39 board and for data logging from it together with sensor cable were passed through the cable hole on the side of the chamber and the cover was properly replaced The door of the chamber was properly closed 5 3 Initial functional test The specimen wa
6. and also the deep space as a very low temperature heat sink about 3 K 3 6 7 A satellite orbiting the Earth also has the Earth as a large source of infrared radiation 7 Also during launching of satellites high temperatures are experienced by the satellites in the launching space vehicle With such temperature variations of very wide ranges the parts used to build up the eguipment to be used in space must be tested to check if they will stand the effects of temperature in their lifetime in space If the pieces of eguipment are not tested and will not stand the effects of temperature they will fail get cracked and damaged and a large amount of money time and effort will be wasted In order to test the space eguipment there is a need for a controlled environment where the parameters that affect the pieces of eguipment are controlled to simulate similar values as in the environments where the objects will be used The environment where testing of the specimen is to be done has to be controlled so that the samples will be tested at various specific parameters A climatic chamber is one of the facilities that allows selectively specified temperature and or relative humidity values to be realized in a closed volume in a working range It is used for testing different eguipment under various thermal and or relative humidity conditions However one of the important problems of today s temperature controlled environments to users is to establi
7. 0 49 L4 0 51 0 18 0 60 L5 0 37 0 09 0 58 L6 0 44 0 11 0 38 L7 0 45 0 05 0 39 L8 0 17 0 15 0 02 L9 0 00 0 09 0 38 28 Table 9 Temporal instabilities of the whole useful volume Temporal instability C 0 a 0 4 2 2 Evaluation of temporal instability at individual measuring locations The temporal instability of temperature in the chamber was also evaluated for each location This was done by analyzing how the temperature varied in each location after temperature stabilization in the chamber was achieved Three standard deviations were calculated from 1500 temperature values that were taken at each location on each day at the rate of one value per minute in three different weeks These standard deviations were pooled to get reproducibility which characterized the variance of temperature in each location by Equation 10 26 n Ds n 1 5 7 Iss nm m n k l 10 where nj is the number of replicate measurements on each day kis the number of days siis the standard deviation given by Eguation 4 The reproducibilities for each location at the three calibration temperature points are given in Table 10 Table 10 Reproducibility of temperature at each location Location Reproducibility C 40 C 23 C 85 C LI 0 08 0 06 0 05 L2 0 14 0 07 0 04 L3 0 03 0 05 0 05 L4 0 06 0 04 0 04 L5 0 06 0 05 0 03 L6 0 04 0 02 0 03 L7 0 0
8. Kaspars Laizans for all the help he offered to acguire the reguired materials used in the task Thirdly I would like to thank Indrek Siinter for the help he offered to do functional test of CDHS during thermal ambient tests I would also like to thank Tartu Obsevatory for allowing me to do my research there I would also like to thank all the ESTCube 1 team members for all the support rendered Last but not least I would like thank Astrid Pung for helping with proof reading the thesis and translating the summary of this thesis into Estonian language 48 10 Appendices Appendix 1 Sensor calibration block design diagram All dimensions in mm LH N vw 49 Appendix 2 Labview software Block diagram File Edit View Project Operate Tools cb Physical Channeli Window Help n 259 sole gt 15pt Application Font gt Zax inv 49 Sad el Se ah Waveform Chart a Virite To Measurement File Signals Ulx Read vi Units perature Y Appendix 3 Labview software user interface File Edit View Project Operate Tools Window Hi 15pt Dialog Font lt osamo A Waveform Chart 1983 1982 Physical Channel 1981 Dev0 T0 7 Dev0 70 on Units SE J oegc R 19 78 i 1 12 15 34 255 20112014 20 11 2014 50 Appendix 4 Sensor block design diagram All dimensions in mm 51
9. hot start 2225505 kesiin anakan bana ban Gia naa ea 12 2 4 6 Functional and performance tests Ja 13 3 ystem development sammuks kaal aal kaka Bus 14 3 1 HardWare sssri M RS EN BB 14 3121 System arehiteetuTe Aa aetud ojamaa BNN SNN taju ike ues 14 31 24 Ehermaal Chambers eeta eda Naa 14 GOES Data NO Er MAA A BTS nes Lo brates LET S 14 3 1 4 Temper t re Sensors tara tac clan nian Dum una 15 SUDAN baso ae aa ana bm 15 3 1 6 Calibration GE SEMSOTS 1 03 girs serta Aa Meh ab Ran karjala BE anes 15 3 2 Software develop MEME NA LEAN OR kama conse oes 22 3 21 Labview software tsaiari os Ben Ra Be mall EU KN 22 322 Sampai SONW Area Rain 24 3 3 Useful volume and location of sensors mo o iwoWo amp oi dak santunan 24 4 Characterization of the thermal Chamber 4 sesak as alle 26 4 1 Evaluation of spatial inhomogeneity Jooaa 26 4 2 Evaluation of temporal instability oWo o Woo oo raas sendava te 28 4 2 1 Evaluation of temporal instability for the whole useful volume 28 4 2 2 Evaluation of temporal instability at individual measuring locations 29 4 3 Evaluation of radiation effect Lan asas cad ius ANE RN ie 30 4 4 Evaluation OF loading effect s gwen te LEAN ANE 131 4 5 Estimation of measurement uncertainty for temperature of the chamber 33 A Sel Model equation a Akaa PARU NN NA SBB OO 4 5 2 Standard uncertainty of contrib
10. sensors L stab 0 3 C year was given in the sensor manufacturer s data sheet The standard thermometer used had the resolution of 0 001 C expanded uncertainty of 0 02 C at 95 confidence level with coverage a factor k 2 from its calibration certificate and long term stability of 0 005 C year The combined standard uncerainty of each sensor at every calibration point was found by combining the uncertainty due to repeatability of measurements from the sensors uncertainty of the fit of calibration graph the resolution of the measurements from the sensors long term stability of the sensors temperature gradient between the standard thermometer and sensors and the contributions due to resolution calibration uncertainty and the long term stability of the standard thermometer The combined standard uncertainty of the sensor is given in Eguation 7 Table 5 gives the uncertainty budget for sensors ensor 2 2 2 2 2 2 2 te S or Urep Urr 2 Ures sensor t Ulong sensor Ugrad t Ures std tua Ulong std 7 where Uc Sensor is the combined standard uncertainty of the sensors Urep is the repeatability uncertainty from repeated measurements of the sensors ufi is the uncertainty of the fit of the calibration curve Ures sensor 18 the uncertainty due to resolution of the sensors Ulong sansor IS the uncertainty due to long term stability of the sensors Ugrad i the uncertainty due to temperature gradient difference b
11. spatial inhomogeneity ii temperature instability iii radiation effect iv loading effect 2 2 1 Evaluation of spatial inhomogeneity Spatial inhomogeneity is expressed as the maximum deviation of the temperature of a corner or wall measuring location from the reference location of the useful volume i e the center of the working space 9 2 2 2 Evaluation of temporal instability Temporal instability for air temperature is evaluated from the registration of the temporal variation of temperature over a period of time of at least 30 minutes after steady state conditions have been reached Steady state conditions are considered to be reached when systematic variations of temperature are no longer observed 9 For the measurement of the temporal instability at least 30 measurement values are to be recorded in 30 minutes at more or less constant time intervals The measurement needs to be performed at least for the center of the useful volume or for the reference measuring location and for each calibration temperature 9 2 2 3 Evaluation of radiation effect At air temperatures in the thermal chamber differing from ambient temperature the inner wall of the chamber always has a temperature which deviates from the air temperature 9 The temperature sensors and indeed the test objects in the thermal chamber therefore have a slightly different temperature from the air temperature due to radiation effect The difference between these two
12. the temperature in the useful volume of the chamber Tread sensor IS the temperature read from the sensor in the useful volume OT sensor 18 the deviation due to sensor calibration OTinn is the temperature deviation due to chamber temperature inhomogeneity dTinst is the temperature deviation due to chamber temperature instability OTraa is the temperature deviation due to chamber temperature radiation effect ST oad is the temperature deviation due to loading effect 4 5 2 Standard uncertainty of contributing components All relevant contributions to uncertainties were taken into account and uncertainty budget was estimated Contributions to uncertainty included the combined standard uncertainty from calibration of the sensors spatial inhomogeneity temporal instability radiation effect and loading effect For the loading effect each loading setup was considered separately Equation 14 gives the formula used to calculate the uncertainty Uc Tcnamper Vue Sensor t Uinn Uinst T Uraa Uload 14 where Ue chamber is the combined standard uncertainty of temperature in the useful volume of the chamber Uc sensor 1S the combined standard uncertainty from sensor calibration Uinn IS the uncertainty due to inhomogeneity Uinst 18 the uncertainty due to instability Urad IS the uncertainty due to radiation effect Uload IS the uncertainty due to loading effect 33 Table 14 gives the sources of uncertainty distributi
13. with four cycles 100 Temperature C 60 L L L 0 200 400 600 800 1000 1200 Time min Figure 5 Thermal testing profile for acceptance testing created in S mpati software A Start and end of program where functional tests are done B Dwell times where cold and hot start and functional tests are done 3 3 Useful volume and location of sensors A cube of 27 liters giving the central useful volume with sides of dimensions 300 mm in the thermal chamber was characterized For useful volumes of less than 2000 L at least nine measuring locations are to be selected i e the measuring locations form the corner points and the spatial center of a cuboid spanning the useful volume 9 Eight sensors were located in the corners of the cube formed and one sensor was placed in the center of the cube The sensor in the center of the cube was the reference sensor and the center of the cube was the useful volume reference location UVRL Temperature read by the reference sensor was the reference temperature T ef Each sensor was connected to a specific channel of the data logger The arrangement of sensors in the thermal chamber the sensor locations the sensor numbers and the 24 data logger channels to which the sensors were connected are given in Figure 6 where Li is the location number Si is the sensor number and Ci is the data logger channel number 129201 S2 C1 usi co 81 CO 155504 S5 C4 L3 53
14. 4 0 03 0 03 L8 0 06 0 06 0 04 L9 0 02 0 02 0 03 29 Figure 8 gives a picture of temporal instability at each location in the thermal chamber at 85 C Table 10 3 Figure 8 Thermal chamber temporal instability of each location at 85 C Comparing instability for the whole useful volume in Table 9 and that of individual locations in Table 10 it is noted that the temporal instability for each location is of the order 10 times smaller than that of the whole useful volume Lower uncertainties can therefore be achieved with individual sensors placed at the reguired measurement location The instability for the whole useful volume was used in evaluation of uncertainty to avoid underestimating the combined uncertainty 4 3 Evaluation of radiation effect Radiation effect was evaluated by placing two sensors at the reference location center of useful volume One sensor was covered by a radiation shield made from aluminum foil Readings were taken from the two sensors virtually simultaneously The temperature readings taken by shielded sensor represented the temperature values in the thermal chamber without radiation effect and those taken by unshielded sensor represented the temperature values influenced by radiation Mean values were calculated from ten sets of temperature values taken from both sensors at each of the three temperature points The difference between each mean value from sensor with shield 30
15. C 0 6 0 5 0 8 Circuit board C 0 6 0 5 0 8 4 6 Evaluation of temperature reference point on test objects A temperature reference point TRP is a point located on the test object which provides a simplified representation of the unit temperature Temperatures at the TRP are used to verify reguirements by analysis and test 28 It is reguired that the same position on the test objects where temperature values are taken when characterizing the thermal chamber is to be used when testing eguipment A temperature reference point TRP must be selected on the unit external surface and unambiguously identified in the respective mechanical interface control drawings 29 In this study reference points were determined on all the three tests loads which shall also be used as reference points for testing similar test objects On the circuit board the central location on top of a chip S5 was chosen as a TRP This position was chosen because the measurement of chip temperature is essential to the evaluation of thermal performance for the design application and manufacture of the module 30 Also when the circuit boards are switched on the temperature of the chips is slightly higher than the temperature of all other components on the circuit board The temperature of chips on circuit boards is therefore of uttermost importance On the P POD and ESTCube 1 satellite dummy experiments were carried out to determine the TRP It was still ver
16. Lewi and J Smeyers Data Handling in Science and Technology Handbook of Chemometrics and Oualimetrics part A Elsevier Science B V Amsterdam 1997 27 DIN 50011 12 Artificial climates in technical applications air temperature as a climatological guantity in controlled atmosphere test installations 2009 28 EADS astrium General Design and Interface Reguirements Iss 3 1 UK 2010 29 ECSS Secretariat Space Engineering Thermal Control ESA ESTEC Requirements amp Standards Division Noordwijk Netherlands 2012 30 J Yin High Temperature SiC Embedded Chip Module ECM with Double Sided Metallization Structure Doctoral Thesis Virginia Polytechnic Institute and State University 2005 45 31 1 Siinter Software for the ESTCube 1 command and data handling system Masters The sis University of Tartu 2014 32 S de Jong G T Aalbers and J Bouwmeester Improved command and data handling sys tem for the delfi n3xt nanosatellite in 59 International Astronautical Congress Glasgow Scotland UK 2008 33 J R Wertz and W J Larso Space mission analysis and design 3rd ed Microcosm Press El Segundo California 1999 46 Meetod kosmosetehnoloogia seadmete katsetamiseks temperatuurikeskkonnas v ljat tamine ja valideerimine Sinai Mwagomba Kokkuv te Temperatuurikeskkonna katse on ks nendest uuringutest mida tehakse kosmosesse saadetavate seadmet
17. Observatory Temperature Reference Point Universal Serial Bus Useful Volume Reference Location 1 Introduction Different pieces of eguipment in life are used in various environments where other factors like temperature vibration humidity air pressure and others affect the parts that form the eguipment in distinct ways In space satellites make one orbit around the Earth in about 90 minutes in sun synchronous low earth orbit 1 which extends up to 2 000 km altitude above sea level 2 In low earth orbit when the satellite faces the sun the solar cells temperature on the external surface of the satellite rises up to 100 C But when the satellite passes from the sunny side of the Earth to the dark side the temperature plummets to about 100 C 3 In short there is a swing of about 200 C between cold and heat in the low earth orbit in space that satellites experience in every 90 minutes Nowadays temperature inside the satellite is controlled in the range of 40 85 C and nanosatellites parts and components are designed to operate in this temperature range The satellite sub assemblies are therefore reguired to stand this temperature range 3 5 As one goes into the higher orbits satellites experience even higher extreme temperatures in every rotation when they face the sun and lower extreme temperatures when they are in the eclipse since the satellite faces the sun as an extremely hot source of thermal radiation about 5776 K
18. UNIVERSITY OF TARTU Faculty of Science and Technology Institute of Chemistry Sinai Mwagomba A method for thermal ambient tests of space technology eguipment in a thermal chamber development and validation Master s Thesis Supervisors Ph D Riho Vendt Research Associate Tartu Observatory Professor Ivo Leito Institute of Chemistry University of Tartu Tartu 2014 Table of contents Kas Aa Ora na ama Nun 4 1 Introductions e E E A O EE AE EA AEA js 5 2 Overview of existing MEMOS nasa enale vallas s kaikki lll at 8 2 1 Measuring locations and useful volume erreeveneeenenennnne nne 8 2 2 Characterization methods for thermal chambers Jk 8 2 2 1 Evaluation of spatial inhomogenetty en 8 2 2 2 Evaluation of temporal instability Joan 9 2 2 3 Evaluation of radiation GITCCL 22 2 osake saak aa laun amalan 9 2 2 4 Evaluation of loading ESC Soe ion hasan anna vea naa 10 2 2 5 Evaluation of measurement uncertainty vrreneereeneeemee 10 2 3 Selection OL SCMSOTS 2 ana BNN uu 10 2 4 Thermal ambient tests of space equipment in order to get qualified and accepted 11 2 4 1 Number of temperature Cycles xx bea bikin cies nan nan nana cdeceveseadane 11 24525 Extreme TEMIPEPALUTSS LA PLS LL AL NN 12 2 4 3 Rate of temperature NAN Sita stats Dab 12 244 well times Saos ea ln aa nm an ba 12 24 5 Gold start and
19. and each value from sensor without shield was calculated The radiation effect was evaluated by the formula below 9 IST radiation lt Max Tie Thel 11 where OT radiation IS the radiation effect on temperature of the chamber Tie is the temperature of the sensor with low emissivity i e with radiation shield The IS the temperature of the sensor with high emissivity i e without radiation shield The highest temperature difference between the temperature read by the unshielded and shielded sensor from the three sets of measurements was considered to be the radiation effect The radiation effect results for the three temperature points are given in Table 11 Table 11 Radiation effects Temperature point 40 C 23 C 85 C Radiation effect C 0 50 0 24 0 63 4 4 Evaluation of loading effect In thermal ambient testing of space equipment different kinds of equipment are tested at different levels of satellite development Individual circuit boards for specific purposes on the satellite and other subassemblies are individually tested Then the whole assembled payload is also tested These specimen give different loads to the thermal chamber that affect the chamber temperature differently It is required that the loads that are used in characterizing thermal chambers should be similar to the loads that will be tested later in the characterized chamber 8 In this study the loading effect on chamber temperatur
20. ate with the computer at the end of all the four cycles The test was repeated two times and the results were reproducible apart from the fact that the second flash memory device out of the two working devices was noted to have stopped working Figure 12a shows the temperature measured by the sensor on the TRP ofthe test object the set profile and the difference of the two The figure also shows the time when the functional test were performed 40 Figure 12b shows the reguired temperature margins 5 C by the standard 10 and the uncertainty region The uncertainty is presented as expanded uncertainty at 95 confidence level with coverage factor k 2 Table 15 pem BA WE O O OOO Temperature C NOOR Lk 30100 13000 Time s Figure 12a CDHS thermal cycling Chamber set profile CDHS board temperature Difference between set profile and CDHS board temperature A Functional Test B Hot start C Cold start Temperature C Figure 12b Uncertainty and reguired limits CDHS temperature Uncertainty region Reguired limits 41 6 Conclusions A method for thermal ambient tests of space eguipment has been developed in this study Sensors were installed in the thermal chamber and a Labview software for data acguisition using a data logger was developed The thermal chamber at Tartu Observatory was characterized Different sources of uncertainty were investigated and uncertainty budget for th
21. chamber was procured This device has to be investigated in order to compile uncertainty budget as is usually the case with most commercial eguipment The characteristics that contribute to temperature measurement uncertainty need to be validated The chamber cannot be used as it is without being checked for such a purpose of space eguipment testing which reguire to meet the specified reguirements before satellites can be accepted for launching All reguired parameters that affect operation of satellites in space 10 including temperature need to be tested before launching Once a satellite is launched there is no way to modify its hardware It is of paramount importance that eguipment to be used for testing be characterized with specific loads as will be analyzed by the user preferably in the environment where application will actually be done The main objective of this thesis is to develop a method for thermal ambient testing of space eguipment that meets the reguirements of the above mentioned standard 10 The goal includes 1 selecting and installing suitable temperature sensors in the climatic chamber and connecting them to computer via data logger 11 developing a software for data acguisition iii characterizing the climatic chamber to be used for thermal ambient testing of space equipment iv evaluating temperature measurement uncertainty budget for specific loads that will be tested at TO v testing a sample space equ
22. e 1 resistance temperature detectors RTDs 2 thermocouples TCs and 3 thermistors Each of them have specific operating parameters that may make it a better choice for some applications than others There are several considerations when selecting a temperature sensor 12 Some of the factors are i Type of application ii Cost budget per sensor iii Distance from sensor to the display 10 iv Measurement range A sensor must be able to withstand the temperature without getting damaged by heat Different sensors are sheathed with different materials to suit the temperature range they are measuring Also sensors perform well in their measuring range v Size of sensors Sensors come in different sizes and shapes and the one that fits the specific purpose is chosen vi Data acquisition methods 2 4 Thermal ambient tests of space equipment in order to get qualified and accepted For space equipment to qualify and get accepted for launching it has to pass a series of pre launch tests in qualification and acceptance tests stages 10 Thermal ambient test is one of the environmental tests done in both the qualification and acceptance stages An environmental test is a test conducted on flight or flight configured hardware to assure that the flight hardware will perform satisfactorily in one or more of its flight environments Examples are acoustic thermal vacuum and electromagnetic compatibility EMC tests Environmental testing
23. e Institute of Electrical and Electronics Engineers Las Vegas Nevada January 21 23 1992 44 15 BIPM International vocabulary of metrology Basic and general concepts and associated terms VIM 2008 16 NASA Hardware Reguirements Document for the Human Research Facility Rack 2 Workstation R2WS 2000 17 EVS EN 60068 2 14 Environmental testing Change of temperature Part 2 14 2009 18 Installation and Operation manual Simpati software Version 4 06 2011 19 Weiss Technik Temperature and Climatic Test Chambers Greizer Germany 2010 20 Measurement User guide rev 13 Massachusetts USA 2014 Measurement Computing Corporation MCC USB Temp Multi sensor Temperature 21 Siemens Matsushita Components Temperature Measurement Miniature Sensors data sheet B57861 2006 22 Nexus SOVMTX Miniature PTFE coaxial cable data sheet Iss 2 Draveil France 1999 23 M Jim nez R Palomera and I Couvertie Analog Signal Chain in Introduction to Embedded Systems using Microcontrollers and the MSP430 University of Puerto Rico Mayagiiez Puerto Rico pp 537 595 2014 24 Automatic Systems Laboratories ASL F100 Precision thermometer user manual Brentwood N America 2011 25 FLUKE Corporation 287 289 True RMS Digital multimeters User manual Rev 1 7 08 Eindhoven Netherland 2007 26 D L Massart B G M Vandeginste L M C Buydens S De Jong P J
24. e chamber was established for specific loads that are tested at different levels of satellite development A sample space technology eguipment was tested using the method in the thermal chamber The method achieves expanded measurement uncertainty of 2 C for the temperature measurement range 40 85 C at 95 confidence level k 2 The uncertainty achieved by the method complies with the reguirements for testing space eguipment in thermal ambient testing However the uncertainty can further be improved The major contributing components to the combined standard uncertainty for this method are spatial inhomogeneity and temporal instability Uncertainty can therefore be reduced if further studies are done to investigate the causes and solutions for improvement of these parameters 42 A Method for Thermal Ambient Tests of Space Technology Eguipment in a Thermal chamber Development and Validation Sinai Mwagomba Summary Thermal ambient test is one of the series of analyses that are carried out on eguipment to be launched in space in order to check their capability to withstand the environmental conditions to be encountered in orbit while maintaining the desired performance It is also one of the reguirements to be fulfilled for the space technology facility to be gualified and accepted for launching The aim of this work was to develop a method for thermal ambient testing of space eguipment at Tartu Observatory to validate it and come u
25. e measurements was evaluated for three different loads An ESTCube 1 circuit board an aluminum dummy for ESTCube 1 with four circuit boards in it and an ESTCube 1 dummy with four circuit boards in an ESTCube 1 P POD These loads are typical of the loads that will be tested in the thermal chamber using this method The DKD R 5 7 9 standard for calibration of thermal chambers states that the loading effect can be evaluated by taking readings from the useful volume reference location UVRL in an empty chamber and also in a loaded chamber The loading effect can then be evaluated as the maximum 31 average difference between the two setups In this study this approach was not used because in order to load the chamber with loads the chamber door had to be opened and the metrological conditions of the chamber in the empty chamber and the loaded chamber are not the same any longer and cannot be compared to estimate the loading effect An independent reference was needed that does not get influenced by changed conditions Two measuring locations in the useful volume the UVRL and location L2 Figure 6 were randomly chosen and the temperature difference between these two locations was calculated for the empty chamber and also for the chamber loaded with the three loading setups The temperature deviation between the two locations in the empty chamber was subtracted from the temperature deviation between the two locations in the loaded chamber to c
26. e puhul kontrollimaks nende v imet vastu pidada orbiidil valitsevatele keskkonna tingimustele See on htlasi ks kohustuslikest katsetest mille alusel kvalifitseeritakse seade kosmosek lbulikuks K esoleva t eesm rgiks on Tartu Observatooriumis kosmosetehnoloogia seadmete temperatuurikeskkonna katseteks vajaliku metoodika v ljat tamine selle valideerimine ning m tem ramatuste allikate osakaalu hindamine Tartu Observatooriumis kasutatakse temperatuurikatsetel kosmoses valitsevate tingimuste simuleerimiseks t stuslikku termokambrit WKL 64 mille t ienduseks ehitati temperatuuri anduritest ja arvuti hendusega andmeh iveseadmest koosnev m tes steem Andmeh iveks arendati ja rakendati spetsiaalne tarkvara Kambris tehtavate temperatuurim tmiste jaoks hinnati m tem ramatuse allikaid ning meetodi rakendamiseks koostati m tem ramatuse koondtabel Meetod v imaldab temperatuuri laiendm ramatust 2 C m tepiirkonnas 40 85 C usaldusnivool 95 kattetegur k 2 Saavutatud m tem ramatuse tase vastab kosmoseaparatuuri temperatuurikatsetele esitatud n uetele Meetodit rakendati kosmoseaparatuuri katsetamiseks temperatuurikambri erinevate t itemahtude puhul 47 9 Acknowledgements First of all I would like to thank my supervisors Ph D Riho Vendt and Professor Ivo Leito for all the support advice and guidance throught the duration of doing my thesis Secondly I would like to thank
27. ensors The units input allows to set the units for particular data that is intended to be acguired The parameter reader reads the physical guantity selected in the parameter selector from the sensors The time delay function enables to set the freguency of logging the data with the default freguency of 1 value sec Data logging is initiated and stopped using the read Start Stop function Time out function makes sure that a program ends smoothly when stopped After the parameter reader acguires the data it is displayed in a waveform on the user interface using the waveform chart function and also displayed numerically using the data display function The write to file function writes the data acguired to a file that is saved in a folder automatically created in the computer by the software The screenshots for the software block diagram and the user interface are given in Appendices 2 and 3 respectively 23 3 2 2 S mpati software For setting and controlling the thermal chamber parameters a S mpati software version 4 06 provided by manufacturer of the thermal chamber was used 18 Two programs for thermal cycling were created within S mpati software using the S mpati Symbolic editor one for gualification and the other one for acceptance thermal ambient tests The programs are used to set maximum and minimum extreme temperatures of the tests and the dwell times at the extreme temperatures Figure 5 shows the planned program for acceptance tests
28. etween the standard thermometer and sensors Ures std IS the uncertainty due to resolution of the standard thermometer Ucal IS the uncertainty from the calibration of the standard thermometer Ulong std 1S the uncertainty due to long term stability of standard thermometer 21 Table 5 Uncertainty budget for the sensors Standard Ouantity Source of uncertainty Uncertainty Distribution Sensitivity uncertainty C coefficient C Urep sensor repeatability 0 021 normal 1 0 021 Ures sensor sensor resolution 0 00001 rectangular 1 0 000006 Ufit calibration curve fit 0 053 normal 1 0 053 Ulong sensor Sensor long term stability 0 3 rectangular 1 0 173 gradient between standard Ugrad thermometer and sensors 0 14 rectangular 1 0 1 Ures std standard thermometer 0 001 rectangular 1 0 0003 resolution Ucal standard thermometer 0 01 normal 1 0 01 standard uncertainty k 1 Ulong sd standard thermometer long 0 005 C rectangular 1 0 003 term stability year The evaluated combined standard uncertainty of all the sensors is 0 2 C for the entire measurement range 40 85 C 3 2 Software development In order to characterize the thermal chamber and during thermal ambient testing of space equipment data must be acquired from the sensors in the thermal chamber There is also a need to control the thermal chamber as desired A computer was used in data acquisition and controlli
29. haracterize the loading effect on temperature in the chamber Three loading effects were evaluated from 1500 temperature measurements taken at the rate of 30 seconds per value after temperature stabilization was achieved in the chamber on three different days The largest calculated loading effect was used for the estimation of uncertainty due to loading effect The temperature differences between the two locations are given in Table 12 for both the empty and loaded chamber for the three loading setups at three temperature points The loading effects are given in Table 13 Table 12 Temperature difference between the reference locations Temperature point 40 C 23 C 85 C Chamber condition Empty Loaded Empty Loaded Empty Loaded P POD C 0 40 0 65 0 21 0 33 0 58 0 92 ESTCube 1 dummy C 0 43 0 62 0 21 0 32 0 57 0 79 Circuit board C 0 40 0 51 0 22 0 32 0 58 0 73 Table 13 Loading effects Temperature point 40 C 23 C 85 C P POD C 0 25 0 12 0 34 ESTCube 1 dummy C 0 19 0 11 0 22 Circuit board C 0 11 0 10 0 15 32 4 5 Estimation of measurement uncertainty for temperature of the chamber 4 5 1 Model eguation To get the actual temperature from the sensors in the chamber when doing measurements the following model was obtained T chamber Tread Sensor OT Sensor Tinh OTinst OT rad STioad 13 where T chamber IS
30. how the effect of loading on the rate of change of temperature with the ESTCube 1 dummy and the four circuit boards in the protective P POD 100 U 80 spa a 70 A o 5 50 s S 30 m 20 p a 0 A 10 E 8 og 5000 10000 15000 E io 5000 10000 15000 20000 30 40 50 A Time s Time s Figure 10 Rate of change of temperature with P POD load Chamber set point Empty chamber UVRI Loaded chamber UVRP Loaded chamber TRP The rate of temperature change in the chamber was slower with loaded chamber setup The rate of temperature change was noted to be even slower on the surface of the test object Table 17 gives the average rate of temperature change in an empty chamber and in the loaded chamber at the UVRP and in loaded chamber on the test object TRP of each of the three loading setups 37 Table 17 Rates of temperature change in the empty and loaded chamber Average temperature rate Loading setup Reference point C min Empty UVRL 16 5 UVRL 15 5 Circuit board TRP 15 0 UVRL 14 0 ESTCube 1 dummy TRP 8 0 UVRL 13 5 P POD TRP 7 2 38 5 Thermal ambient test of sample space technology eguipment In the second part of this study the characterized thermal chamber was used for thermal ambient testing of a sample space technology eguipment 5 1 Test specimen An ESTCube 1 satellite non flight command and data handling system CDHS board was used asatest object
31. ions that a measuring instrument or measuring system is reguired to withstand without damage and without degradation of specified metrological properties when it is subseguently operated under its rated operating conditions 15 For eguipment to be launched in space the temperature cycles are reguired to span from extreme temperatures of 40 C as lowest extreme temperature and 85 C as highest extreme temperature 3 5 2 4 3 Rate of temperature change The rate of temperature change refers to the speed at which the temperature in the thermal chamber increases or decreases while thermal cycling the specimen under test For eguipment to be launched in orbit the rate of temperature change is reguired to be less than 20 K min 5 2 4 4 Dwell times Dwell times refer to the duration necessary to ensure that internal parts or subassembly of a space segment eguipment have achieved thermal eguilibrium from the start of temperature stabilization phase 1 e when the temperature reaches the targeted test temperature plus or minus the test tolerance 10 For eguipment to be launched in space the specimen is reguired to be exposed to dwell times of at least 2 hours at each extreme temperature in thermal ambient tests 10 2 4 5 Cold start and hot start Cold start refers to switching on the specimen into operational mode at the minimum extreme temperature Hot start refers to switching on the specimen into operational mode at the maximum ext
32. ipment using the developed method and its estimated uncertainty The climatic chamber to be characterized enables creating environment with controlled parameters such as temperature and relative humidity The scope of this study is only the temperature characterization of the chamber and the relative humidity characterization of the chamber is not carried out The chamber is hence herein referred to as a thermal chamber During testing of sample space technology equipment there is need to conduct functional tests of the sample space equipment under test to check its functionality during testing The functional tests depend on the particular equipment that is being tested and are out of the scope of this study This thesis has five chapters Chapter 2 gives the literature review of the subject Chapter 3 discusses the system development for this method The characterization procedure for the thermal chamber and its results are given in Chapter 4 Chapter 5 discusses the thermal ambient testing of sample space technology equipment using the method Chapter 6 gives the conclusions and recommendations for improvement Drawings and schemes are given in the appendices 2 Overview of existing methods 2 1 Measuring locations and useful volume As a rule calibrations are carried out through measurements in several locations in the useful volume 9 The useful volume of a thermal chamber is the partial volume of the thermal chamber spanned by the measu
33. ir temperature is determined from the registration of the temporal variation of temperature over a period of time of at least 30 minutes after steady state conditions have been reached 9 In this task the temperature instability was evaluated by taking 1500 measurement values at the rate of one value per minute in three different days in different weeks from the center of the useful volume i e at reference point and from all the corner sensors after the stabilization of temperature in the chamber was achieved The temperature instability was evaluated three times from the mean temperature values of all sensors and mean temperature values from each sensor in each location where Temporal instability is given by Eguation 9 9 l T instab lt Max T mean Ti 9 Where OTinstab IS the temperature instability Tmean IS the mean temperature of all the sensors T is the mean temperature from any specific location The analysis that gave the highest instability out of the three analyses was used to estimate the instability of the chamber The temporal variations of each sensor from the mean value are given in Table 8 and temporal instability results for the three temperature points are given in Table 9 Table 8 Temporal variations of the locations from the mean temperature Measurenent Deviation from refence sensor C location 40 C 23 C 85 C L1 0 04 0 09 0 45 L2 0 62 0 43 0 17 L3 0 43 0 18
34. ir temperature with exactness as they affect each other all the time 2 2 4 Evaluation of loading effect The loading effect is defined as the maximum average value when the differences between the average maximum temperatures achieved between the empty chamber and the loaded chamber from each measurement location are calculated and when the difference between minimum temperatures achieved between the empty chamber and the loaded chamber from each measurement location are calculated 8 A calibration is carried out at least for the reference measuring location with and without load and the maximum difference is taken as the half width of a rectangularly distributed uncertainty contribution 9 Thermal chambers are normally calibrated and characterized in the empty state 9 The investigation of the loading effect can be performed with a customer specific load or using a test load the volume of the latter amounting at least to 40 of the useful volume 8 2 2 5 Evaluation of measurement uncertainty The combined uncertainty to be evaluated is composed of the uncertainty of the measurement of temperature using the reference measuring sensors the contributions of the temperature instability radiation effect influence of ambient conditions temperature inhomogeneity as well as the loading effect 8 9 11 2 3 Selection of sensors There are many different types of sensors available for measuring temperature The three most common types ar
35. is normally combined with functional testing to a degree which depends on the objectives of the test 13 Thermal ambient test is carried out to ensure that the specimen design withstands the environment it will encounter during launching and during its lifetime in space without degradation of its performance 10 It determines the ability of components equipment or other articles to withstand rapid changes of ambient temperature and also its ability to withstand the maximum and minimum temperatures it experiences during its operation 10 13 Thermal ambient testing consists of thermal cycling the entire experiment assembly in an operating mode This test is performed to detect problems early in the hardware development It checks the functional capability of the electronic components in a simulated on orbit temperature environment 14 2 4 1 Number of temperature cycles Temperature cycles refer to the transition from an initial temperature to the same temperature with excursion within a specified range 10 The number of thermal cycles to be carried out 11 depends on whether the test is gualification test or acceptance test For eguipment to be launched in space it is reguired that the specimen shall be subjected to 8 temperature cycles in one gualification test and 4 cycles in one acceptance test according to ECSS space engineering testing standard 10 2 4 2 Extreme temperatures Extreme operating conditions refer to condit
36. libration of the sensors a sensor calibration block was designed and machined The block was 20 mm long with diameter of 20 mm and was made from a cylindrical copper rod Copper material was chosen because of its good heat conductivity Ten holes of 2 5 mm diameter were drilled around the central 7mm diameter hole The design drawing for the sensor calibration block is given in Appendix 1 The probe of the standard thermometer was 6 5 mm in diameter and was placed in the central hole of the copper block Nine thermistor sensors that were being calibrated were placed in the holes around the probe of the standard thermometer Thermal paste was used to fill the gaps in the holes of the block to make sure there was good contact and effective heat transfer between the copper block and the sensors The sensor 16 calibration block with the sensors was placed in the center of the thermal chamber Thirty temperature and corresponding resistance values were taken from the F100 standard thermometer and the Fluke multimeter respectively at each of the eleven different temperature points ranging from 40 C to 120 C Figure 2 shows the sensor calibration block that was used the arrangement of the sensors in the block and the position of the calibration block in the chamber during calibration Reference gt Thermometer Probe Calibration Block Figure 2 Sensor calibration block in the chamber and the arrangement of sens
37. ng of the chamber Software programs were therefore developed and used for the purpose 3 2 1 Labview sofware A custom made software was developed by using the tools of Labview for data acquisition using a computer from the sensors via a data logger The software makes it possible to acquire data virtually simultaneously form multiple sensors via the data logger This is useful because in order to effectively characterize the thermal chamber and also when testing space equipment temperature values from multiple sensors need to be taken at virtually same time at the same rate and within the same time duration The program makes it possible to set the time interval when data should be acquired The trends of data acquisition can be seen graphically from the front 22 panel of the program user interface The program automatically saves the data acguired to a specific file in the computer Figure 4 shows the block diagram of custom made software Waveform Chart Parameter Data Selector Display Write to File developed in Labview and illustrates the main features of the program Physical Channels Read Start Stop Figure 4 Labview software block diagram Physical Channels on Figure 4 refer to the channels of the data logger from which data is acguired The parameter selector makes it possible to select the type of physical guantity for example resistance or voltage e t c that one wants to log form the s
38. nt 3 1 Hardware 3 1 1 System architecture The system setup of the method for thermal ambient tests in the thermal chamber is presented in the system architecture in Figure 1 Sensors Data USB Cable Logger p Labview Software hed Pe in eny Climatic Po E 1 Chamber Software Ethernet Cable Figure 1 System architecture Temperature data from the thermal chamber is logged into a computer file using the Labview software program via a data logger The thermal chamber is controlled and the desired parameters are set using the S mpati software 18 3 1 2 Thermal chamber A Weisstechnik WKL 64 thermal chamber at Tartu Observatory was automated and its useful volume was characterized using the unloaded chamber characterization method with the loading effect evaluated It has operational temperature range of 40 C to 180 C The chamber has internal dimensions of height 400 mm width of 470 mm and depth of 345 mm 19 3 1 3 Data logger A commercial Measurement Computing USB Temp data logger is used in this task It supports data acguisition from thermocouples RTDs and thermistors The logger has the capability to read two samples per second It supports Visual Studio Java Labview and DASYLab programming environments It can acguire temperature and voltage data from the sensor
39. ons and the standard uncertainties at the three calibration points for each contribution Table 14 Uncertainty components of the chamber temperature Source of Temperature Uncertainty Sensitivity Standard Ouantity uncertainty point C Distribution coeffcient 1900 1 C Uc Sensor Sensor All 0 2 normal 1 0 2 calibration Toe 0 5 0 3 Spatial 423 C 0 5 rectangular 1 0 3 Uinh inhomogeneity 85 C 1 0 0 6 20 C 0 6 0 4 Temporal 23 C 0 4 rectangular 0 3 Uinst instability 85 C 0 6 1 0 3 40 C 0 5 0 3 Radiation 23 C 02 rectangular 1 0 1 Urad effect 85 C 0 6 0 4 Toe 0 3 0 1 Loading 423 C 0 1 rectangular 1 01 Uload Effect P POD 85 C 0 3 0 2 Loading Effect 40 C 0 2 gt ESTCube 1 23 C 0 1 rectangular 1 0 1 Uload e payload 85 C 0 2 0 1 40 C 01 0 1 Loading Effect 23 C 0 1 rectangular 1 0 1 Uload Circuit Board 785 C 02 0 1 4 5 3 Combined standard uncertainty The combined standard uncertainties were calculated for all the three calibration temperature points for the three loading setups 14 Table 15 shows the combined standard uncertainties according to Eguation 14 34 Table 15 Combined standard uncertainties for three loading setups with coverage factor k 1 Temperature point 40 C 23 C 85 C P POD C 0 6 0 5 0 8 ESTCube 1 dummy
40. or blocks and thermal paste was used to fill the gaps in the holes for good contact and efficient heat transfer between the block and the sensors Thermal paste was also used to attached the sensor blocks with sensors to the test material Thermal paste helps to attach sensors properly and also to offer good heat transfer between test object and the sensor blocks The sensor block design drawing is given in Appendix 4 Y nn E W 1 Fel pe i ig H i amp i lt b Figure 9a Sensor mounting on circuit board Figure 9b Sensor mounting on the P POD 36 4 7 Evaluation of rate of temperature change in the thermal chamber It was noted Table 14 that among inhomogeneity instability radiation effect and loading effect the smallest component contributing to uncertainty was the loading effect However loading was observed to affect the rate of temperature change in the chamber The rate of temperature change in the chamber was investigated with an empty chamber and a chamber loaded with the three loading setups which are typical of space eguipment that are tested in thermal chamber at different levels of satellite development The items included an ESTCube 1 size circuit board an ESTCube 1 payload dummy with four circuit boards in it and the complete ESTCube 1 payload in protective P POD The temperature of these materials was cycled starting from 40 C to 85 C and from 85 C to 40 C Figure 10 s
41. ors in the block The Steinhart Hart coefficients for each sensor were calculated using Eguation 1 The residuals the temperature difference between temperature values read from the reference thermometer and temperature values calculated from Steinhart Hart eguation 26 were calculated for each sensor Table 2 gives the mean temperature and resistance values measured from standards the calculated temperature values from sensors Tea using the equation and the residuals as an example for sensor 1 The Steinhart Hart coefficients for all the sensors are given in Table 3 Figure 3 shows the relationship between temperature and resistance for the temperature sensors 17 Table 2 Example of the calibration data for Sensor 1 TIC R O TIK UT mK MR MR Tia C Res C 40 896 112480 000 231 895 4 312 11 631 1573 253 40 883 0 013 31 479 59500 000 241 671 4 318 10 994 1328 726 31 525 0 046 20 740 30720 000 252 410 3 962 10 333 1103 158 20 693 0 047 10 509 17190 000 262 641 3 807 9 752 927 454 10 479 0 030 0 414 10078 000 272 736 3 667 9 218 783 296 0 440 0 026 23 123 3305 300 296 064 3 378 8 103 532 087 23 039 0 084 40 218 1581 900 313 368 3 191 7 366 399 726 40 236 0 018 60 385 735 200 333 535 2 998 6 600 287 515 60 403 0 018 84 663 303 450 359 880 2 827 5 715 186 680 84 793 0 130 100 560 200 900
42. p with an uncertainty budget A commercial Weisstechnik WKL 64 thermal chamber in Tartu Observatory was used in the task to simulate the temperature environment that satellites encounter in space The system for the method was developed Temperature sensors were installed in the chamber and were connected to the computer via a data logger for registering temperature readings A software for data logging was developed and implemented The uncertainty sources of temperature readings in the chamber were validated and the uncertainty budget for the method was evaluated The method achieves expanded measurement uncertainty of 2 C in the temperature measurement range 40 85 C at 95 confidence level k 2 The achieved uncertainty level complies with the requirements for testing space equipment in thermal ambient tests The method was applied for testing of actual space equipment at different chamber loading setups 43 8 List of references 1 A Globus J Crawford J Lohn and A Pryor Scheduling Earth Observing Satellites with Evolutionary Algorithms In Conference on Space Mission Challenges for Information Technology SMC IT 2003 2 N L Johnson Medium Earth Orbits is there a need for a third protected region 61 International Astronautical Congress Prague CZ 2010 3 L Jacgues Thermal Design of the Oufti 1 nanosatellite Master Thesis in Aerospace Engi neering University of Li ge 2009 4 P
43. perature reading indicated by the standard thermometer AT sq is the correction of standard thermometer from its calibration OT res is the parameter to take into account the resolution of standard thermometer OT stab IS the parameter to take into account the long term stabiliy of standard thermometer The standard deviation of the residuals was estimated and used as the uncertainty of the fit of the calibration curve This uncertainty was ug 0 053 C with coverage factor k 1 for the whole calibration range After determining the Steinhart Hart equation coefficients the sensors were connected to the data logger channels and the coefficients for each sensor were written in the Steinhart Hart equation in the memory of the data logger in respective channels With the same setup of the calibration sensor block in the chamber Figure 2 calibration of sensors proceeded via the data logger in order to establish treceability of temperature values measured using the logger In this process 200 values were measured from the sensors and from the standard thermometer at the rate of one value per minute at three temperature points 40 C 23 C and 85 C The temperature points were chosen such that the minimum extreme temperature and maximum extreme temperatures that will be used in testing space equipment were used in calibration A third temperature point at 19 normal room temperature 23 C was also chosen in the middle of the calib
44. ration range The repeatability of the sensor readings at each temperature point was estimated by calculating the standard deviation of repeated measurements from the sensors using Eguation 4 11 N 1 olx Vu 1 Ge x k 0 4 where o x is the standard deviation of the measurement values Xp are the individual measurement values N is the number of measurements X is the mean of measurement values given by Eguation 6 11 n a x ae n k k41 6 where n is number of measurements Xx are the individual measurement values The repeatabilities of readings for all the sensors are given in Table 4 Table 4 Repeatabilities of readings from the Sensors Calibration point Repeatability C 40 C 0 004 23 C 0 004 80 C 0 021 The highest repeatability from the three temperature points was used in the uncertainty budget The resolution of the logging device data logger was used to estimate the uncertainty due to resolution in reading temperature values from the sensors The deviation difference between the temperature values measured by the sensors using the data logger and the temperature values measured by the standard thermometer was estimated and used to evaluate uncertainty due to 20 temperature gradient between the standard thermometer and the sensors 26 This uncertainty WAS Ugrad 0 14 C for the whole temperature range The long term stability for the
45. reme temperature The specimen shall be tested for cold start at the minimum extreme temperature to check for cold start capability and also for hot start at maximum extreme 12 temperature to check for hot start capability of the specimen Both cold and hot starts shall be performed at the end of dwell times The test starts with the specimen off 14 2 4 6 Functional and performance tests Functional testing is a series of electrical or mechanical tests conducted on flight or flight configured hardware at conditions egual or less than design specifications Its purpose is to establish that the hardware performs satisfactorily in accordance with the design specifications 16 Depending on the situation and the type of eguipment under test there are various functional tests of various complications and depth 16 Functional and performance tests shall be performed before the start and after the thermal ambient test They shall also be performed as a minimum at hot and cold operating temperatures and during the whole duration of respective number of cycles at the end of each dwell time Functional and performance tests for space eguipment to be launched in low earth orbit shall only start after a dwell time greater or egual to 2 hours at the maximum and minimum extreme temperatures 9 16 The specimen shall be visually examined and electrically and mechanically checked as reguired by the relevant specification 17 13 3 System developme
46. ring locations of the sensors used for calibration According to the arrangement of the measuring locations the useful volume can considerably differ from the total volume of the chamber The calibration of the chamber is valid only for this useful volume 9 Spatial interpolation of the determined values is permissible only for the workspace The extrapolation of the measurement results outside the workspace is not allowed 8 A measuring location is the spatial position in which a temperature sensor is arranged in the useful volume for calibration A measuring location thus is a small volume which is defined by the dimensions of the sensor elements 9 For greater useful volumes the measuring locations are to be arranged in the useful volume in the form of a cubic lattice with a maximum lattice constant of 1 m 9 2 2 Characterization methods for thermal chambers There are three main ways how thermal chambers can be characterized 1 unloaded 2 loaded and 3 characterization in individual sensor locations in the thermal chamber 9 The process of characterization of unloaded chamber relates to the empty useful volume spanned by the measuring locations in the thermal chamber and to the useful volume with a test object in the loaded thermal chamber characterization method Characterization in individual sensor locations relates to each location idependently without covering the whole useful volume All these methods cover the evaluation of i
47. s 20 14 3 1 4 Temperature sensors In this topic the sensors used had to meet the following reguirements 1 Very small size sensors Small size sensors enable fast time response Small sensors can also be installed even in very small areas 11 Sensors that work in temperature range of 40 C to 85 C iii Accuracy 1 iv Resolution 0 01 C v Long term stability lt 0 1 C year vi Fast time response Different types of thermocouples RTDs and thermistors were analyzed and the best choice of the sensors for the purpose were miniature thermistors An NTC EPCOS B57861S302F40 miniature thermistor was chosen for this task It has working range of 55 C to 155 C and diameter of 2 4 mm and meets the specified technical requirements given above 21 3 1 5 Sensor cables In order to conduct this study there was a need for cables that could stand the maximum and minimum extreme temperatures from 40 C to 85 C without getting damaged and that would have the size that would suit the miniature sensors chosen Miniature Nexans 157284 coaxial cable was chosen for the purpose The cable has copper conductor plated with silver with Fluorinated Ethylene Propylene jacket material and has operating temperature range from 90 C to 200 C The outside diameter of the cable is 1 17 mm 22 The cables were soldered to the sensors and the connection pins were soldered at the other end of the cables for connecting the sensor
48. s to data logger Thermo shrink was used to cover the joints 3 1 6 Calibration of sensors Thermistors work on the principle that a change in temperature causes a change in the resistance of the sensors However the relationship between temperature and resistance is not linear There was a need to calibrate the sensors The temperature resistance curve of thermistors can be described by different equations The most commonly used equation is the Steinhart Hart Equation shown below 23 15 A Bfin R C In R 1 UN where T is temperature in Kelvin R is resistance in ohms A B and C are the Steinhart coefficients The calibration of the sensors in this work was done according to Equation 1 and the coefficients A B and C were determined for each sensor The Automatic Systems Laboratories F100 precision standard thermometer was used as a reference thermometer for measuring temperature values of the sensors and Fluke 287 True RMS multimeter was used to measure resistance values for the sensors under calibration Table 1 shows the specifications of the equipment used for the calibration of the sensors 24 25 Table 1 Specifications of the calibration standards 24 25 F100 standard thermometer Fluke 287 multimeter Resolution 0 001 C 0 01 kQ Accuracy 0 02 C 0 05 2 Q Operating Range 200 C to 850 C up to 500 MQ Stability lt 0 005 C Year lt 1 2 Year For effective ca
49. s visually examined and functional tests were carried out before starting thermal cycling The performance of the specimen was recorded The board was able to communicate with the computer apart from the fact that one of the three flash memory devices was not functioning 5 4 Thermal cycling The specimen was thermal cycled with 4 cycles spanning in the extreme temperatures of 40 C as the minimum extreme temperature and 85 C as the maximum extreme temperature The specimen was exposed to dwell times of 2 hours at each extreme temperature 5 5 Functional tests during and at the end of thermal cycling The specimen was tested for cold start at the minimum extreme temperature in the first cycle after a dwell time of two hours to check for cold start capability and then it was allowed to run during the ramp up to higher extreme temperature where it was powered off and on again to check for hot start capability During both cold start and hot start tests the specimen was able to power up During thermal cycling it was observed that the CDHS had done several resets During the period of resets communication with the computer was lost Unplanned resets have also been observed on the actual ESTCube 1 satellite that is now in space The reason for the resets was discovered to be a software problem Functional and performance tests were also performed at the end of the thermal ambient test The test object was functioning well and was able to communic
50. sh with accuracy the metrological characteristics of those temperature controlled environments 8 There are however a lot of factors that affect the temperature in the chamber that lead to uncertainty of measurement results The chamber therefore has to be characterized in order to precisely validate the performance and the influence of all factors that affect the temperature in the chamber and to know its working conditions It is also difficult to characterize climatic chambers using a manual way as it reguires many temperature sensors from which temperature values have to be taken simultaneously and at short intervals for example a minimum of nine sensors for climatic chambers of volume of less than 2000 liters 9 To date standard guidelines have been established by European Cooperation for Space Standardization ECSS in Space Engineering Testing standard 4 giving reguirements to be met for space eguipment testing The reguired temperature margins for thermal ambient testing of space eguipment are specified For eguipment to be used in space thermal ambient tests are reguired to be carried out to meet the temperature margin of 5 C in the measurement range 10 These margins have to be accurately met if space missions are to be successful However the standard does not describe how the reguirements can be achieved through testing For the purpose of thermal ambient testing of space eguipment at Tartu Observatory TO a commercial thermal
51. temperatures depends on the surface emissivity size and position of the sensor in the chamber It also depends on speed of air at the sensor and the difference between air temperature and thermal chamber wall temperature 9 There are three ways how the radiation effect on temperature in thermal chambers can be evaluated 1 using two calibrated sensors one with high emissivity and another with low emissivity in the reference location of the useful volume The temperature read by a sensor with low emissivity represents chamber air temperature without radiation effect and the sensor with high emissivity slightly indicates the temperature with radiation effect 11 using two similar calibrated sensors one with a radiation shield applied and another without a shield in the reference location of the working space The sensor without a radiation shield measures the temperature with radiation effect and the sensor with a radiation shield reads the temperature which is not affected by radiation iii recording the wall temperature and there after an approximate air temperature with a sensor with low emissivity or with radiation shield In this task the radiation effect was evaluated by method ii because it does not require the exact emissivity of the sensors to be known and no special sensors are needed for the purpose as is reguired in method i The last method can easily introduce errors as it is not easy to differentiate wall temperature with a
52. umpkin Inc CubeSat Kit User Manual San Francisco USA 2005 5 ALMA Space European Student Earth Orbiter Satellite Experiment interface document Part A EID A 2013 6 J A Angelo Encyclopedia of Space and Astronomy Facts on the file Science library New York 2006 7 J A Angelo Satellites Facts on the file Science Library New York 2006 8 M L DONA Methods of Calibration and characterization of Temperature Controlled Environments U P B Sci Bull Series C Vol 72 Iss 2 197 210 2010 9 Deutscher Kalibrierdienst DKD Calibration of Climatic Chambers ed7 DKD Braunschweig 2009 10 ECSS Secretariat Space Engineering Testing ESA ESTEC Reguirements amp Standards Division Noordwijk Netherlands 2012 11 Joint Committee for Guides in Metrology JCGM 100 2008 Evaluation of measurement data guide to the expression of uncertainty in measurement JCGM 2008 12 T Al Hawari S Al Bo ol and A Momani Selection of Temperature Measuring Sensors Using the Analytic Hierarchy Process JJMIE Vol 5 451 459 2011 13 ALCATEL Space Payload verification and test requirements Proteus Unser s Manual document PRO LB O 003 ASC chap 6 2003 14 W M Foster H Thermal Verification Testing of Commercial Printed Circuit Boards for Space flight NASA Technical Memorandum 105261 presented at Annual Reliability and Main tainability Symposium sponsored by th
53. uting components oooaaa 33 4 5 3 Combined standard uncertainty nana 34 4 6 Evaluation of temperature reference point on test objects JJJ c 35 4 7 Evaluation of temperature rate of change in the thermal chamber 37 5 Thermal ambient tests of sample space eguipment errreeneeeeneneeeeee 39 Di Ve TOE SPS CHM T ssh ui ue pas See BA te vad i iO tts lhe el SN la 39 5 2 Summary of the thermal ambient test veerreenee nen nene nee naeene nne 39 235 Littal Tone HON AL TESS aden han sakinah NAN aa 40 She etal even ee tian aan et vanana On OR on akan 40 5 5 Functional tests during and at the end of thermal cycling cee eee eee eee eens 40 6 Conclusiones rsen E EEA E EEEE EEEE EEE BB Nan 42 Te SUMMA Ea Saxe E R T uu E R ante 43 S Eist Of Tete ETS Anna sa ba aii EN RN AR Re e ei E EROE 44 D2 STROM ODE AA Si we BEN Na ena NE BN wena hada klaadi ok 47 LO Acknowledgements aru ba Wetter NE TENUN state 48 TA ASOT ADP aa AAA rn eg Mates meee necaetdawead us 49 List of abbreviations CDHS EMC ECSS GUM NTC P POD RTD TO TRP USB UVRL Command and Data Handling System ElectroMagnetic Compatibility European Cooperation for Space Standardization Guide to the expression of Uncertainty in Measurement Negative Temperature Coefficient Poly Picosatellite Orbital Deployer Resistance Temperature Detectors Tartu
54. y crucial to monitor how the temperature affects the chips on the circuit board while it is inside the payload A sensor was mounted on the circuit board on the TRP and the board was placed in the P POD and dummy Six sensors were mounted on the P POD and ESTCube 1 dummy one sensor on each of their six surfaces The setups were placed in the chamber until temperature stabilization was achieved Readings were taken from the sensors Table 16 gives the mean temperature values from the sensors at 85 C with expanded uncertainty at 95 confidence level with coverage factor k 2 as an example Table 15 35 Table 16 Measured temperature values on P POD at 85 C coverage factor k 2 Board TRP PSI Under PS2 PS3 PS4 PS5 PS6 Back C C C C C C C 85 2 84 2 85 2 84 2 84 2 85 2 84 2 Sensor 2 and 5 gave temperature values that are close to the temperature of the chip inside the P POD The position of sensor 5 PS5 was chosen as the TRP for the P POD and payloads Figures 9a and 9b show the TRPs for the circuit board and P POD and the mounting of the sensors In order to offer good contact between the test material and the sensors copper sensor blocks were used The copper blocks were designed and machined to be as small as possible while allowing the sensors just to fit it The sensor blocks have 2 5 mm inner diameter and 6 mm outside diameter and 6 mm in length Sensors were placed in the sens
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