Thermal-Vacuum Testing of the Phoenix GPS Receiver
Contents
1. 80 1200 70 1000 60 800 m o 50 600 F 3 Temperature 40 a 400 5 o t Test Receiver 5 2 o g 30 4 Ref Receiver 200 2 o F 20 o a 10 200 0 400 6 30 6 45 7 00 7 15 7 30 7 45 8 00 Time UTC Fig 3 4 Oscillator offset for the test and reference receiver recorded during the initial thermal test for positive temperatures During the initial thermal test an obvious increase of the frequency offset was recognized with rising temperature cf Fig 3 4 A similar oscillator behavior was observed for the nega tive temperature range Fig 3 5 Surprisingly the decreasing temperature did not result in a likewise decreasing frequency offset but again in an increasing frequency error which indi cated the nonlinear relation between temperature and oscillator behavior The ripples on the measurements encountered through the periods of constant temperature can be attributed to the almost periodic switching of the test chamber s thermal unit in order to maintain the pre adjusted temperature 20 e 1200 ecelvers switched o 1000 10 800 m N x So o 600 p P 3 400 amp 10 4 o 200 6 2 5 E S 20 0 S P 200 t 30 400 40 600 10 00 00 AM 11 00 00 AM 12 00 00 PM 1 00 00 PM 2 00 00 PM Time UTC Temperature TestReceiver A Ref Receiver Fig 3 5 Oscillator offset for the test and reference r2. Overall these tests have demonstrated a proper performance within the tested temperature range of 30 to 70 which covers both the manufacturer s specification and the ECSS rec ommended limits for AOCS space electronics The chip temperatures were generally found to exceed the ambient temperature measured at the base plate of the thermal vacuum chamber by 15 20 In a non powered mode the receiver survived extreme temperatures of 40 and 80 with no subsequent malfunction A linear variation of the receiver power consumption by approximately 8 100K was ob served which may need to be considered in the dimensioning of the power system and elec tronic fuses In comparison with a reference receiver operated in a zero baseline configuration no tem perature dependence of the raw measurements quality and the navigation solution could be identified during quasi static temperature changes dT dt 1K min in the thermal vacuum chamber On the other hand an increased frequency of cycle slips and outages in various tracking channels occurred during accelerated heating and cooling dT dt gt 3K min in the thermal chamber These tracking problems may best be attributed to thermal stress of the employed 10 MHz TCXO reference oscillator Further tests will be required to see whether the problems can be circumvented by a wider setting of the PLL carrier tracking loop Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No par
3. Montenbruck O Markgraf M Leung S Space Adaptation of the GPS Orion Firmware DLR GSOC TN 01 08 Deutsches Zentrum fur Luft und Raumfahrt Oberpfaffenhofen 2001 MG5000 Series User Guide MG5 200 GUIDS User Guide Sigtec Navigation Pty Ltd Issue B T08 14 Au gust 2003 MG5031 33 Design Kit User s Guide MAN 5031 5033 Version 2 0 November 2002 O Montenbruck M Markgraf User s Manual for the Phoenix GPS Receiver DLR GSOC GTN MAN 0120 Deutsches Zentrum fur Luft und Raumfahrt Oberpfaffenhofen 2004 Space Engineering Testing ECSS Secretariat ESA ESTEC ECSS E 10 03A 15 February 2002 Space Product Assurance Thermal cycling test for the screening of Space materials and processes ECSS Secretariat ESA ESTEC ECSS Q 70 04A 4 October 1999 O Holt G Spaceborne GPS Receiver Performance Testing DLR GSOC TN 02 04 Deutsches Zentrum fur Luft und Raumfahrt Oberpfaffenhofen 2002 Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization
4. during the tests Most of the time both receivers were connected to an antenna mounted on Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 5 Thermal Vacuum Testing of the Phoenix GPS Receiver top of the roof of the laboratory building providing an unobscured view to almost the entire hemisphere However due to temporary irregularities encountered in the tracking behavior of both receivers that could be clearly attributed to the excessive cable length of the roof an tenna system a part of the tests was performed with an alternative antenna This antenna was placed in the yard behind the laboratory building in a distance of only a few meters from the building Due to the poor GPS satellite visibility as well as the dramatically increased mul tipath interferences encountered for this second antenna configuration it was decided to switch back to the roof antenna and accept the sporadic signal outages The receiver s interface unit holding the DC DC converter as well as the serial line drivers was placed outside the test chamber and connected to the receiver board via a customized adapter cable The navigation solutions and raw data of the reference receiver and the test receiver were monitored and recorded on a single Laptop The current consumption of the device under test has been recorded on a secon
5. safety reasons and not reactivated until the tempera ture dropped again below 60 C at the end of this cycle After the maximum storage tem perature was reached and held for 20 minutes the chamber has been cooled down to the outside temperature in the laboratory again in 20 C steps In the second part of this test the same procedure has been repeated but this time for nega tive temperatures The chamber was gradually cooled down from approx 22 C to 0 C 20 C and finally 30 C The ECSS recommended minimum non operational test temperature of 40 C couldn t be reached with the present chamber Tests under these extreme temperature conditions have therefore been postponed for the tests in the TVAC chamber To avoid po tential problems caused by condensation of water in the chamber and on the receiver during this test the chamber has been flooded with nitrogen at the beginning of the cooling phase 100 m Receiver switched off Maximum non operation temepartur 60 1 r Mii 3 Jg Maximum operation temeparture 40 20 J RRR lem uu ee Ambient temepariure ___ Temperature C 20 Minimum operation temeparture 40 1 SE ___________ m 6 00 7 00 8 00 9 00 10 00 11 00 12 00 13 00 14 00 UTC time Fig 2 4 Temperature profile recorded during the first maximum minimum temperature cycle Upon reaching the receiver s specified minimum operat
6. used for the TVAC test differed from the setup employed for the thermal test solely in how the temperatures were measured Other than for the thermal chamber the vacuum chamber Fig 2 6 was equipped with a sophisticated multi sensor temperature measurement system which allowed to accurately measure and record tempera ture data at eight different locations inside the chamber and or directly on the test device While four of the temperature probes have been employed to determine the reference tem perature of the test chamber s base plate the remaining probes were used to monitor the temperature of the key components on the Phoenix receiver board GP4020 baseband proc essor SRAM and EPROM memory ICs and R F front end Fig 2 5 shows a picture of the test receiver mounted on the base plate of the TVAC chamber and the temperature probes attached to the critical electrical components At the beginning of the TVAC test the pressure inside the chamber has been constantly de creased to less than 0 1 mbar within a time span of approximately 15min During this phase the receiver was switched on and data have been recorded For the subsequently performed temperature cycles the pressure was further reduced and held constant at a level of about 5 10 mbar Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 8 Th
7. 04 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 17 Thermal Vacuum Testing of the Phoenix GPS Receiver 140 120 100 Oo v e 80 g 2 2 1 3 5 Fr 40 20 0 i 12 00 13 00 14 00 15 00 i 16 00 17 00 i 18 00 19 00 i 20 00 21 00 Time UTC Velocity Temperature C Fig 4 3 Velocity errors for the test device obtained during the thermal cycling test 4 3 Signal to Noise Ratio Throughout all performed tests in the thermal as well as the vacuum chamber the Carrier to Noise Ratio C No exhibited no anomalies or dependency on the ambient temperature or pressure conditions An exemplary comparison of C No readings from both receivers for sat ellite PRN 26 obtained during the second part of the thermal vacuum test is provided in Fig 4 4 55 50 45 40 35 30 Carrier to Noise Ratio dB Test Receiver SV 26 ee Ref Receiver SV 26 20 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 Time UTC Fig 4 3 Carrier to noise measurements recorded for satellite PRN 26 during the thermal vacuum test Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 18 Therm
8. 3 00 Time UTC Fig 3 2 Current consumption of the test device and temperature profile for the temperature cycling test in the vacuum chamber The relation between both parameters was found to be almost linear over the tested tem perature range It could be quantified as a change of approximately 1 4 mA per 10 C tem perature raise This results in a total variation of the receiver s power consumption of ap proximately 8 over the temperature range from 30 C to 70 C Fig 3 3 and might need to be considered during the design and dimensioning of the satellite s power supply system 110 096 107 596 105 096 102 596 100 096 97 596 95 0 92 5 Current cons w r t nominal value 90 0 40 30 20 10 0 10 20 30 40 50 60 70 80 Temperature C Fig 3 3 Relation between current consumption and temperature measurements observed during the thermal cycling test Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 12 Thermal Vacuum Testing of the Phoenix GPS Receiver 3 3 Oscillator Drift The receiver s reference oscillator exhibited a notable frequency variations throughout all tests The changes in the frequency offset were evidently related to the temperature changes but no simple relation between both parameters could be established
9. Space Flight Technology German Space Operations Center GSOC Deutsches Zentrum f r Luft und Raumfahrt DLR e V Thermal Vacuum Testing of the Phoenix GPS Receiver H Lux M Markgraf Doc No TN 04 07 Version 1 0 Date Oct 05 2004 DLR Document Title ii Thermal Vacuum Testing of the Phoenix GPS Receiver Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title Thermal Vacuum Testing of the Phoenix GPS Receiver Document Change Record Issue Date Pages Description of Change 1 0 Oct 04 2004 First release Document No TN 04 07 Issue 1 0 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title iv Thermal Vacuum Testing of the Phoenix GPS Receiver Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title V Thermal Vacuum Testing of the Phoenix GPS Receiver Table of Contents Document Change Record oriana araea aaae De arana aeaa r aaa danaa ahaa daada aoada ioari iii Table of Contents sii cigs cavasiiisssvebivoSi5 cash su usise sev uvessnvestyedavexhdaseddideshaceivesseacssveesesvedensdauves
10. al Vacuum Testing of the Phoenix GPS Receiver 4 4 Raw Data Evaluation The quality of the collected raw measurements was assessed by building double differences between data from two satellites tracked by both receivers the test and the reference device A detailed description of how exactly the raw data were processed during this analyses can be found in 7 Except for various cycle slips and signal outages encountered during the thermal tests which may be readily explained by the above described oscillator behavior the analysis revealed no further dependency of the noise level on the environment temperature and pressure conditions Phoenix GPS Receiver Temperature Tests Double Difference PRN8 PRN27 tst_040720 15 F62 rnx tst 040720 19 F62 rnx 21 Jul 2004 11 16 UTC 4 H sig C1 0 32m DD C1 Pseudorange m eo T 11h 12h 13h 14h 15h 80 sig L1 0 55mm 60 40 20 20 40 b 60 80 2004 07 20 T T T 11h 12h 13h 14h 15h DD L1 Carrier Phase mm sig D1 0 06m s mgr ke DD D1 Doppler m s LL2o0 66660o0ooo 2 DOOOPDODPOOOMND 004 07 20 T j j T i T 11h 12h 13h 14h 15h o o PRN8 PRN 27 o T 70 F coo oo TT Elevation deg op E 1 N oo T 2004 07 20 T 11h o T T T T 12h 13h 14h 15h Fig 4 4 Results of the raw data analyses for the satellite pair PRN 8 and PRN 27 recorded during t
11. around the GP4020 baseband processor of Zarlink which combines a 12 channel correlator for L1 C A code and carrier tracking a microcontroller core with 32 bit ARM7TDMI microprocessor and several peripheral functions real time clock watchdog 2 UARTS etc in a single package Other key components include the GP2015 front end chip a 512 kByte flash EPROM and 256 kByte of SRAM memory A detailed description of the receiver is provided in the Phoenix User s Guide 4 The tested equipment is intended for use in LEO satellites flying at typical altitudes of 400 km to 1 000 km with an approximate orbital period of 1 h This results in a cyclic temperature change with the same period The fastest temperature changes occur at the change from day to night side or the other way round Therefore thermal cycling tests between two ex treme temperatures are recommended to verify the correct functioning of equipment under thermal stress Such tests have not been conducted for the Phoenix receiver before and are therefore a completion of other environmental tests already performed for this receiver type The tests should not only show the mere functionality under TVAC conditions but also as sess a possible temperature dependence of the noise level of the raw data and navigation solution This aspect should be investigated as well as the temperature dependence of other receiver specific data Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No p
12. art of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 4 Thermal Vacuum Testing of the Phoenix GPS Receiver 2 Test Setup and Performance The tests described in this report have been conducted at DLR GSOC in Oberpfaffenhofen Germany in the time frame from July 9 2004 to July 21 2004 As a guideline for the test setup and execution the ECSS standards for testing of space systems 4 5 was em ployed The tests have been performed in close accordance with this standard but with some restrictions due to limitations imposed by the available test equipment described sub sequently in more detail All tests have been conducted with Phoenix receiver unit 19 running software version DO8B July 2004 for LEO satellite applications Because of the small bandwidth of the carrier tracking loop applied in this specific software version the receiver exhibits an increased sen sitivity to external interferences compared to e g the sounding rocket version This simplifies the detection of potential changes in the noise levels on the navigation and raw data during the tests The only modification of the original hardware concerns the back up battery which will not be flown in space and was thus removed prior to the start of the tests To enable an accurate assessment of the tracking and navigation performance during each test run all tests have been conducted in a zero base line
13. configuration In addition to the device under test an identical reference receiver was operated outside the test chamber supplied with GPS signals from the same antenna This specific configuration allows to eliminate the systematic errors that are common to both receivers such as atmospheric propagation delays as well as clock and ephemeris errors by using adequate post processing techniques When forming double differences the only remaining error on the raw data is the measurement noise produced inside the receivers which gives a good indica tion of the current receiver performance Fig 2 1 depicts the test setup employed for the thermal vacuum test Antenna Thermal thermalvacuum chamber Test GPS Indoor DC block receiver Network Power Divider i Ampl Splitter i Reference Power 3 receiver Multimeter Interface Power board Computer Laptop Laptop Fig 2 1 Structural diagram of the test setup for the Phoenix GPS receiver thermal vacuum tests The GPS signals were fed into the receivers through a power divider For the test receiver a further intermediary device a DC block was inserted into the antenna line to decouple the active antenna power supply of both receivers Two different antenna systems were used
14. d computer for post processing purposes During the TVAC tests a third computer was used to display and store the temperature read ings 2 1 Thermal tests An initial series of tests has been carried out in a simple thermal chamber and under normal ambient pressure conditions Fig 2 2 The basic setup for these tests was almost identical to that subsequently used for the thermal vacuum tests which is illustrated above in Fig 2 1 Both setups differed only with regard to how temperatures were measured inside the cham ber During the thermal tests the temperature was measured with the help of a digital ther mometer whose probe was inserted into the test chamber through a small access hole in the wall of the test chamber Fig 2 3 The temperature readings had to be noted down manu ally The temperature of the receiver itself couldn t be measured directly during these tests However due to its low mass as well as the small form factor the test board is expected to adapt its temperature to the ambient temperature inside the chamber in a reasonable short time Thus the temperature readings obtained by the digital thermometer were considered to be almost identical to the actual receiver board temperature Me v gt A aut EY Temperature probe of i Fig 2 2 Thermal test chamber with Fig 2 3 View into thermal chamber The test receiver was placed temperature control unit below onto a block of insulation material a
15. eceiver recorded during the initial thermal test for negative temperatures Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 13 Thermal Vacuum Testing of the Phoenix GPS Receiver Further evidence for a direct correlation between temperature changes and frequency offset is provided by the analysis of the oscillator data collected during the subsequently conducted thermal cycling test Fig 3 6 illustrates the frequency pattern obtained during these test which exhibits a clearly systematic characteristic and repeats itself with the same period as the temperature cycles Particularly strong disturbances were encountered during the heating and cooling phases with relatively large temperature changes 1400 140 A Frequency Offset Temperature 1200 120 1000 100 800 amp 80 Y 600 w 1 60g E s 2 400 40 5 o id 200 209 g E o 2 0 OF 200 20 400 40 600 60 800 80 11 30 13 30 15 30 17 30 19 30 UTC time Fig 3 6 Frequency pattern observed during the thermal cycling test The assumption of a direct relation between temperature gradients and frequency drift could be further verified by computing the derivatives of the frequency changes and plotting the results together with the temperature readings in a common diagram The graph in Fi
16. ermal Vacuum Testing of the Phoenix GPS Receiver The recommended pressure value given in the European standard for space system testing 6 is 10 mBar which could not be achieved in the employed configuration of the TVAC test chamber This pressure difference however is considered of minor importance for the re sults of the test T Fig 2 5 above Phoenix GPS receiver mounted on the base plate of the thermal vacuum chamber The tempera ture probes have been fixed on the critical components by means of Kapton tape Fig 2 6 left TVAC chamber with opened vacuum bell and measurement and recording equipment in the fore ground Even though the ECSS testing standard specifies that a single temperature cycle in the vac uum chamber is sufficient if a complete thermal cycling test has been carried out before it was decided to perform more than only one cycles This decision was mainly taken with re gards to the reduced number of cycles performed in the thermal chamber before As for the thermal chamber the temperature rate of change was exclusively determined by the capa bilities of the cooling heating unit of the TVAC chamber and couldn t be influenced from out side Due to the large size of the vacuum chamber the rate was found to be relatively low compared to the thermal chamber tests The peak value was measured to be approx 1 C min Fig 2 7 shows the temperature profile base plate recorded during the thermal vacuum tes
17. fected in the same way as for the thermal tests Both receivers tracked an almost identical number of satellites throughout the entire test Most likely the tracking problems encountered during the thermal test can be attributed to a pseudo dynamic on the received satellite signals introduced by the frequency variations in the reference oscillator Similar effects have already been observed in previously performed radiation tests where a frequency drift was provoked by radiation This pseudo dynamic is experienced by the receiver in the same way as a physical motion velocity acceleration jerk of the host vehicle that carries the GPS system In case of unusually high or extremely irregular frequency changes caused by large temperature variations this can obviously no longer be handled by the receiver s tracking loops As a consequence the receiver loses Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 16 Thermal Vacuum Testing of the Phoenix GPS Receiver li n Number of tracked SVs Temperature C e Reference Receiver 14 Test Receiver Temperature 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 UTC times Fig 4 2 History of the number of tracked satellites recorded during the first TVAC test lock on individual
18. g 3 7 shows the first order frequency derivatives for the second thermal vacuum test Due to the smaller temperature gradients obtained during these test compared to the tests conducted in the thermal chamber the frequency variations were not as pronounced as for the purely ther mal tests Nevertheless one can clearly discern that sudden changes in the temperature gradient encountered at the beginning and the end of the phases with stable temperatures result in pronounced changes in the frequency drift This behavior has been observed throughout all conducted tests an can be attributed to the reaction of the receiver s TCXO to temperature variations Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 14 Thermal Vacuum Testing of the Phoenix GPS Receiver 100 120 50 90 0 60 Sg 50 305 g 5 5 S 100 0 g S E o o F n O 150 30 200 Test Receiver 60 Temperature 250 90 9 00 11 00 13 00 15 00 17 00 19 00 21 00 23 00 Time UTC Fig 3 7 Derivatives of the frequency offset for the second TVAC test Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 15 Thermal Vacuum Testing of the Phoenix GPS Recei
19. he second part of the TVAC tests Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 19 Thermal Vacuum Testing of the Phoenix GPS Receiver The marginally increased noise level at the beginning an the end of the displayed data arc can be attributed to the low elevation of both satellites at that times resulting in lower C No values an thus slightly increased noise figures This phenomenon is well know and can not be linked to the environmental conditions Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 20 Thermal Vacuum Testing of the Phoenix GPS Receiver Summary and Conclusions The Phoenix GPS receiver is a GPS receiver for space applications based on COTS hard ware A series of thermal tests and thermal vacuum tests have been conducted in close ac cord with established ECSS test procedures to assess the receiver performance under rep resentative space conditions Except for a lithium battery that was removed prior to the tests the receiver was fully equipped with off the shelf components connectors capacitors induc tors polyfuses ICs Different tests were conducted both under atmospheric pressure and under simple vacuum conditions 10 mbar 1 Pa
20. iainys V EI mm 1 1 iere eio ETTR daa 3 2 Test Setup and Performance 444200000000000000nnnnnnnnnnnnnnnnnnnnn nenn nenn nenn nnnnn nun nennen 4 2 1 Thermal tests crece re ev tee LER ae ELDER RV ERR ER TETT 5 2 2 Thermal Vacuum tests ccccccccccccccccececececeeeeeeeeeeceeeceneceseseceeeaesenesseaeeaaessaeseaeeeaeeaas 7 3 Results and Analysis a ne 10 3 1 Component temperatures cccccccccccccecceeecceeeeeeeeeeeeeeeeeeeceeeeeeeeeeeeeeeeeeeeeeeseeeeeeeenas 10 3 2 Current Drairi citer cete te canes Rosi RR PH E canes eR Rue e ee conten 11 3 3 Oscillator Drift ee eere eek eere en ete e RR LR hend he 12 4 Tracking Performance and Navigation Accuracy uunsuuusnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 15 4 1 Tracking performance ae ink 15 4 2 Navigation Solution Accuracy aeneae ee 16 4 3 Signal to Noise Ratio 4422 Reiki 17 4 4 Raw Data Evaluation ssssssssss e ener nnn ennre neis 18 Summary and Conclusions esse unn saca aen cR dann orn a d a FRA E BA EB EE RR ar RR 20 Notation and SyHIDOIs ioa cotone Grad no UE KaL SUM DR Ur Lu Ca ID erlernen 21 ELA CIETE E iie ect sese NE FFEEFIFERHEFEFBETFSEETFEIRERLFETEFELEREERESTERFEFEHRTFELEESFRRRTEREREERFHEBFENEFFEFREREFF 23 Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disc
21. ion temperature of 20 C the test device was again deactivated to prevent potential damage At the end of the low temperature test after the temperature has been held on a constant minimum level for approx 20 min utes the thermal chamber has been switched off Simultaneous to the start of the warming up process the receiver was switched on again and the data logging was resumed The Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 7 Thermal Vacuum Testing of the Phoenix GPS Receiver chamber has been continuously warmed up to room temperature To accelerate the process the chamber door has been opened at 0 C which resulted in an immediate condensation of humidity from the air outside the chamber on the test device Obviously as a consequence of this condensation the receiver stopped outputting data and the power consumption went down to an abnormally low value of about 60 mA at 5 VDC supply power The receiver re sumed normal operation a few minutes later after it had dried again Table 2 1 Summary of the various specified temperature limits Source max temp min temp ECSS testing standard 6 non op 70 C 40 C applicable for qualification testing of AOCS equipment op 60 C 30 C SigTec non op 80 C 50 C Phoenix hardware manufacturer op 70 C 20 C Following
22. losed to third parties without prior authorization Document Title vi Thermal Vacuum Testing of the Phoenix GPS Receiver Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 1 Thermal Vacuum Testing of the Phoenix GPS Receiver Scope This note describes the thermal vacuum testing of the Phoenix GPS receiver which has been conducted as part of a space qualification program for COTS receiver hardware It supplements the technical description of the receiver and further environmental tests e g total ionization dose susceptibility that are provided in independent reports Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 2 Thermal Vacuum Testing of the Phoenix GPS Receiver Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 3 Thermal Vacuum Testing of the Phoenix GPS Receiver 1 Introduction Equipment which is used for space applications needs to meet specific design performance and analysis requirements The purpose of thermal vacuum testing is to quantify the thermal performance of the test device in an environ
23. ment similar to its working environment It should demonstrate the ability of the device to withstand certain thermal stress and work under real istic in orbit conditions with an additional adequate margin The qualification margin should not create unrealistic conditions that lead to failure of equipment and is commonly set to 10 C on the maximum and minimum temperatures for thermal tests Possible problems which can occur under these conditions are outgassing of equipment expansion or contrac tion as well as a change in convection and conductive heat transfer characteristics which might lead to short circuits or overheating of materials Fig 1 1 Phoenix GPS receiver main board Sigtec MG5001 board with standard connectors and backup battery The present study was conducted to assess the performance of a COTS based GPS re ceiver under representative space conditions The Phoenix receiver is a miniature GPS re ceiver that has been adapted by DLR GSOC for high dynamics and space applications It offers single frequency C A code and carrier tracking on 12 channels and can be aided with a priori trajectory information to safely acquire GPS signals even at high altitudes and veloci ties 1 The Phoenix receiver Fig 1 1 employs an almost identical tracking and navigation software as DLR s flight proven GPS Orion space receiver but uses an industrial hardware platform Sigtec MG5001 2 3 with minimal modifications The receiver is built
24. nd connected to the outside world via antenna and interface cables One the left hand side of the chamber one may identify the probe of the digital thermometer Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 6 Thermal Vacuum Testing of the Phoenix GPS Receiver To assure a rapid establishment of a thermal equilibrium within the chamber during the tests the air was permanently kept in motion by means of a fan mounted in the back wall of the chamber As regards the chamber s walls however the temperature may significantly differ form the air temperature especially during the cooling and heating phases To avoid a poten tial falsification of the test results by a direct contact of the test device to the chamber bottom the receiver has been placed on a block of insulating material during these tests as shown in Fig 2 3 In the initial test the temperature inside the chamber was increased in steps of 20 C from room temperature 22 C up to the maximum specified storage temperature of 80 C At each step the temperature was held constant for about 20 minutes in order to ensure a ther mal balance in the receiver and to record a set of reliable data The receiver remained switched on up to the ECSS specified maximum operations temperature of 60 C Thereaf ter the test device was switched off for
25. or even on all channels In general the problem can simply be solved by relaxing the settings of the tracking loop filters which however results in a slightly increased noise level on the raw measurement Since the temperature gradients simulated during the present qualification tests are notably higher than the values typically encountered onboard a spacecraft except for devices directly mounted on the surface of a space vehicle this phe nomena is considered as of minor importance for a use of the receiver in future space mis sions 4 2 Navigation Solution Accuracy As expected from the above analysis the navigation solutions form the test receiver obtained during the purely thermal tests exhibited a large number of pronounced errors These outliers in both the position and velocity fixes were well correlated with the tracking instabilities dis cussed in the previous section and can be ascribed to the same cause the temperature in duced oscillator frequency variations Fig 4 3 shows the velocity errors encountered for the test receiver during the thermal cycling test Outliers occurred most frequently near the tran sition from heating up the chamber to maintaining the maximum operational temperature and during the entire cooling process after the end of the maximum temperature phase In con trast to the thermal tests no such anomalies have been detected during the entire thermal vacuum tests Document No Issue 1 0 TN 04 07 Oct 05 20
26. r No substantial change could be identified in the recorded temperature values for the key components on the receiver board during and after the evacuation of the test chamber This suggests that the thermal balance achieved inside the test board within a few minutes after start of receiver operation does not depend on whether the receiver is operated at atmos pheric pressure levels or in a vacuum environment Obviously no overheating problems have to be considered for the utilization outside the Earth atmosphere and hence no special cool ing or heating precautions must be taken into account Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 11 Thermal Vacuum Testing of the Phoenix GPS Receiver 3 2 Current Drain During all tests the current consumption of the receiver has been monitored and recorded as a key indicator for the physical state of the test device The results have shown that the cur rent drain is clearly correlated with the temperature changes during the thermal cycling cf Fig 3 2 200 100 195 Current 85 190 Temperature 70 185 55 5 180 05 5 E 175 25 8 o E a 3 170 10 E 165 5 F 160 20 155 35 150 T T T T T T T T T T T T T T T T T T T T T T T T T T T 50 9 00 11 00 13 00 15 00 17 00 19 00 21 00 2
27. t of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 21 Thermal Vacu Notation AOCS C A C No COTS DC DLR DUT ECSS EPROM ESA FLL GPS GSOC HD I F LEO LNA N A PLE PRN RAM S SNR SV TCXO TVAC Document No TN 04 07 DLR GSOC um Testing of the Phoenix GPS Receiver and Symbols attitude and orbit control system Coarse Acquisition Carrier to Noise Commercial Off The Shelf Direct Current German Aerospace Center Device Under Test Erasable Programmable Read Only Memory European Space Agency Frequency Locked Loop Global Positioning System German Space Operations Center High Dynamics Interface Low Earth Orbit below 1000 km Low Noise Amplifier Not Available Not Applicable Phase Locked Loop Pseudorandom Noise Random Access Memory Space Signal to Noise Ratio Space Vehicle Temperature Compensated Quartz Oscillator Thermal Vacuum Issue 1 0 Oct 05 2004 No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 22 Thermal Vacuum Testing of the Phoenix GPS Receiver Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 23 Thermal Vacuum Testing of the Phoenix GPS Receiver References 1 2
28. this initial minimum maximum test the thermal cycling test has been started In accordance with the ECSS testing standard 6 the first cycle has once again been per formed between the minimum and maximum specified non operational temperature 30 C to 70 C Outside the manufacturer specified operation temperature range the test receiver was again switched off to avoid a potential damaging of the hardware The recommended dwell time at the temperature minima and maxima given in the ECSS standard 6 is at least 2h For practical reasons this time has been reduced to approximately half an hour Fur thermore the number of subsequently performed cycles has been reduced from 8 cycles as recommended in 6 to 4 cycles for reasons of feasibility The maximum temperature reached during these remaining cycles was 60 C the minimum temperature 30 C The temperature gradient was fully determined by the characteristics of the thermal chamber It was found to have no constant value but was at any time notably below the maximum tem perature rate of change 20 C min specified in 6 for equipment intended for the use within a space vehicle The observed peak temperature rate was approximately 5 C min Through out the entire test the GPS navigation and raw data as well as the current consumption and the temperature measurements have been monitored and recorded for post processing pur poses 2 2 Thermal Vacuum tests As mentioned above the setup
29. ts Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties without prior authorization Document Title 9 Thermal Vacuum Testing of the Phoenix GPS Receiver First Session Second Session Third Session Temperature C 0 00 4 00 8 00 12 00 16 00 20 00 Time hours Fig 2 7 Temperature profile recorded during the tests in the vacuum chamber In total the test receiver has gone through four complete temperature cycles under vacuum conditions in three consecutive test sessions Starting with three cycles between the maxi mum and minimum operation temperatures of 70 C and 30 C respectively the last cycle was carried out between 80 C and 40 C Other than in all earlier tests however the hard ware hasn t been switched off outside the specified operation temperature range during this cycle This latter test was primarily intended to identify a potential upper and lower maximum temperature at which the receiver stops working properly or breaks down For completeness it should be mentioned that the receiver has been power cycled several times at both ex treme temperature levels to verify its ability to reboot under these extreme environmental conditions Document No Issue 1 0 TN 04 07 Oct 05 2004 DLR GSOC No part of this document shall be reproduced in any form or disclosed to third parties
30. ver 4 Tracking Performance and Navigation Accuracy 4 1 Tracking performance A degradation of the tracking performance could only be encountered during the tests in the thermal chamber As seen in Fig 4 1 the tracking capability was seriously affected through phases characterized by significant temperature variations The observed effects ranged form a loss of track on individual channels up to a complete loss of signal across all channels and was encountered throughout all test cycles During phases with constant temperature as well as phases with moderate and almost linear temperature de increase both receivers track almost the same number of satellites which indicates a nominal tracking performance 12 160 10 VU 1 4 Temperature C Number of Tracked Satelites 11 45 12 00 12 15 12 30 12 45 13 00 13 15 13 30 13 45 14 00 14 15 Time UTC tti Reference Receiver amp Test Receiver Temperature Fig 4 1 Number of tracked satellites observed during the thermal cycling test Other than for the thermal tests no such effect could be identified during the test in the vac uum chamber Fig 4 2 shows the number of tracked satellites for the test and the reference device for the first part of the thermal vacuum tests Obviously due to the significantly smaller temperature gradients obtained during these tests the tracking performance of the test re ceiver was not af
31. without prior authorization Document Title 10 Thermal Vacuum Testing of the Phoenix GPS Receiver 3 Results and Analysis The main result of the performed environmental tests with the Phoenix GPS receiver is that the proper and reliable functioning of the device could be successfully demonstrated for the temperature range recommended for space system qualification testing and under vacuum conditions The test receiver hasn t undergone any visible changes nor has it shown any unexpected behavior or even break down during the conducted tests It can therefore be considered as qualified for space applications as far as the thermal vacuum environment is concerned 3 1 Component temperatures The following observations and results apply to the thermal vacuum tests only since meas uring of individual receiver components temperatures was only possible during these tests Fig 3 1 shows the temperature reading for the receiver s key components and the base plate of the test chamber for the third of the four performed temperature cycle 100 90 80 70 60 50 40 30 20 Temperature C 13 00 14 00 15 00 16 00 17 00 18 00 19 00 20 00 21 00 22 00 Time UTC Platte Front End X GP4020 4 Flash AM29LV200BB 4 SRAM IS61LV12816 Fig 3 1 Current consumption of the test device and temperature profile for the temperature cycling test in the vacuum chambe
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