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Operations of the thermal control system for Alpha Magnetic Spectrometer electronics following the beta angle of the International Space Station
Nuclear Instruments and Methods in Physics Research A 767 (2014) 235–244
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Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Operations of the thermal control system for Alpha Magnetic Spectrometer electronics following the beta angle of the International Space Station Kun Wang, Jinbo Li, Zheng Cui, Naihua Wang, Qie Sun, Lin Cheng n Institute of Thermal Science and Technology, Shandong University, 17923 Jingshi Road, 250061 Jinan, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 15 May 2014 Received in revised form 7 July 2014 Accepted 9 August 2014 Available online 10 September 2014
The Alpha Magnetic Spectrometer (AMS) has been running and measuring cosmic rays on the International Space Station (ISS) since May 19, 2011. The thermal control system (TCS) plays an important role in keeping all components and equipment working in an operational temperature range. Since the AMS started working on the ISS, AMS thermal engineers have been monitoring the on-orbit status of the TCS. During normal operation, the local temperature of AMS components regularly varies along with the β angle of the ISS. Based on the collected temperature data, the general characteristics of local temperature variations of TCS for AMS Electronics following the β of the ISS are discussed with the statistics of the orbit-averaged temperature and the orbit standard deviation of temperature. Furthermore some temperature anomalies at specific β are also studied. & 2014 Elsevier B.V. All rights reserved.
Keywords: Alpha Magnetic Spectrometer electronics Thermal control system Beta angle Regularity Temperature anomaly
1. Introduction The Alpha Magnetic Spectrometer (AMS) project is an international physical experiment whose aim is to use the unique environment on the International Space Station (ISS) to study the universe by searching for anti-matter and dark matter while performing precision measurements of cosmic rays composition and flux [1,2]. More than 48 billion cosmic-ray events (up to May 1, 2014) have been measured by six detectors since AMS started running on 19th May, 2011. Detailed information about the six detectors can be found in the referenced literature [3–8]. The first result of AMS experiment was published in 2013 [9]. The first result provides the largest set of cosmic-ray positron data, increasing the total world sample a hundredfold, while presenting a striking confirmation of positron fraction indicated in previous satellite experiments [10]. AMS will be working for the whole life of the ISS. Normally the ISS flies in the sun and the eclipse of earth, with the orbital period of about 91 min and altitude varying between 241 and 434 km. In this space environment, about 2500 W heat must be dissipated radiatively during operation. In addition to this, thermo-optical characteristics of materials are slowly degrading. For this reason, the temperature of all equipment must be controlled within its
n
Corresponding author. Tel.: þ 86 531 88393000. E-mail address: [email protected] (L. Cheng).
http://dx.doi.org/10.1016/j.nima.2014.08.010 0168-9002/& 2014 Elsevier B.V. All rights reserved.
own allowed range and furthermore, stability of the temperature of components is also required. Based on the issues mentioned above, an efficient and reliable thermal control system (TCS) is required in AMS to keep all components working within their allowed temperature range. On-orbit operation of AMS has proved that the TCS provides strong support for this experiment. In long-term monitoring, the AMS thermal group finds that the local temperature of AMS regularly varies along with the angle between the ISS orbit plane and sunlight (β angle) in normal operation. The AMS thermal group has also been trying to find the characteristic of local temperature change of AMS to give an approximate prediction of AMS local temperature at a certain moment with predictable thermal factors. In the preliminary simulation, the mean effective radiation temperature (MERAT) method was adopted, which means the external thermal factors were simplified as a MERAT which was provided by National Aeronautics and Space Administration (NASA), USA. In the simulation, the thermal status of AMS electronics in the operation of startup, running, power outage, and heater activities in worst hot and cold cases selected from 259 possible cases was given, which had proved that the TCS can support AMS effectively when working on the ISS. But the thermal status in general situations was not specifically given. In this paper, based on the collected temperature data, the general regularity of the temperature dependence on β will be investigated, and temperature anomaly at specific β will be studied.
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Table 1 Thermal limits (1C) of electronic elements.
β = 0° β < 0°
β > 0°
12°
Fig. 1. The sun's position relative to AMS at different β angles.
Fig. 2. Variation of β in 2012.
2.
β Angle of the ISS
The β is a very important parameter for the ISS external thermal factor. The regularity of β can be calculated with the parameter of the ISS orbit. Put simply, the angle between the ISS orbit plane and equatorial plan is 51.51 and the angle between equatorial plan and the ecliptic plane is 23.51, which results in a β angle of the ISS varying in the range [ 751, 751]. For AMS, different values of the β correspond to different configurations of Sun illumination, shown in Fig. 1. Since AMS is inclined to the port side of the ISS by about 121, when the β 4121, the sun illuminates AMS on the port side; when the β o 121, the sun illuminates AMS on the starboard side. However there is an express logistics carrier panel (ELC2) at the starboard side of AMS, and if the β is low enough, the ELC2 panel will shade AMS to a different extent. The author cannot get the specific dimension of the ISS but based on the observation of temperature data and approximately when β o 231, the ELC2 panel starts to shade the bottom of AMS from the sun; when β o 601, the AMS will be completely in the shadow of ELC2 during a certain period of an orbit. Fig. 2 presents the β variation in 2012. In fact, the variation of the β in each year is almost the same. The highest β always occurs between the end of May and the beginning of June, the lowest β always occurs between the end of December and the beginning of January.
3. TCS for AMS electronics The electronic system is a fundamental system that provides power supply\distribution, data collection and command interface [11,12]. Both passive thermal control hardware and active thermal control hardware are utilized in the AMS electronics thermal
xCrates J-group Crates xPD TTCB HV Bricks
Operational warning
Operational limits
Non-operational limits
Low
High
Low
High
Low
High
15 15 20 15 15
45 60 43 45 45
20 20 25 20 20
50 65 48 50 50
40 40 40 40 35
80 80 80 55 65
control [13]. The TCS protects the electronics from exceeding the allowed temperature range when AMS is running on the ISS. Relevant thermal limits are shown in Table 1, the low operational warning is also the minimum switch-on temperature of corresponding electronic elements. The two main radiators are arranged on RAM and WAKE side of AMS to dissipate heat generated by electronic boxes, shown in Fig. 3. The electronic boxes are mounted and fixed with screws on the inner sheet of the RAM radiator and the WAKE radiator. Heat pipes are used in radiators to diminish the temperature difference and homogenize the temperature distribution. A total of 40 heat pipes with various shapes are embedded into the interlayer of the main radiators: 16 are on the RAM radiator and 24 are on the WAKE radiator. Heaters are used on AMS main radiators including 38 heater patches and 132 thermostats (including spares) in order to keep the temperature of crucial electronic boxes above the required limit in cold conditions. There are two sets of heaters mounted on the RAM radiator. Set #1 includes 16 heaters, ten of which are glued onto the radiator while the other six are glued onto the walls of the boxes of J-group crates i.e. J, JT and JPD. Set #1 heaters aim to keep all the electronic boxes above the minimum nonoperational temperature with the exception of the J-group electronics, which has to be kept above the minimum switch-on temperature. The second heater set includes 9 heaters, which are glued onto the radiator directly. Set #2 heaters aim to bring all the electronics sitting on the RAM radiator panel to the minimum switch-on temperature together with the first set. The two sets work in parallel to reach this goal when AMS is on the ISS truss location. The WAKE radiator panel is equipped with 6 heaters glued onto the inner side of the panel itself. This heater set aims to warm all the electronics that are mounted on the WAKE radiator panel, with the exception of the Power Distribution System (PDS) box, to the minimum switch-on temperature together with the support of the PDS heaters set. Heater activities are controlled by means of PDS switches and mechanical thermostats. Two types of thermostats comprise the heater circuit: the control thermostats and the safety thermostats. The control thermostats regulate the normal (absence of failures) activity of the heaters cabled together, and the corresponding set points are 18 1C/ 12 1C. The tolerance on the set points is 71.7 1C. The safety thermostats have higher set points, namely þ42 1C/ þ 48 1C, and interrupt the heater circuit in case of failure if the temperature underneath the heater patch (close to the safety thermostat) exceeds þ 48 1C. Almost all visible surfaces on the inside and outside of the AMS are thermal-control finishes to increase emissivity and decrease absorptivity of surfaces. In addition, multilayer insulation (MLI) covers electronic units to minimize the thermal radiation to the inside detectors. On the main radiators, a total of 57 thermal sensors are arranged to collect the temperature of electronic units and main radiator panels: 28 thermal sensors are on the RAM radiator and
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Fig. 3. Radiators on AMS. The dimensions of AMS is about 3 m 3 m 3 m, with weight of about 7 tons. On a spacecraft, the ram side faces to the velocity vector, the wake side faces to the opposite of the velocity vector. When facing to ram direction, the left and right sides are respectively called port and starboard sides nautically. In addition, in the Cartesian coordinate of the ISS, the x-axis points to ram direction, the y-axis points to starboard direction, and z-axis points to the core of the earth.
Fig. 4. Arrangement of electronic boxes and thermal sensors on main radiators. The sensors marked as RR1-RR4 and WR1-WR4 are selected in this paper, each one is at a corner of the main radiators, and surrounded with several electronic boxes. In addition, about the names of electronic boxes, “E” represents Electromagnetic Calorimeter (ECAL), “R” represents Ring Imaging Cherenkov Detector (RICH), “S” represents Time of Flight detector (ToF), “U” represents Transition Radiation Detector (TRD), “UG” represents the TRD gas system, “T” represents Silicon Tracker. The six kinds of boxes are “Crates” referring to the readout/monitor/control electronics boxes. “TT” represents Tracker Thermal, “TTCBP” represents Tracker thermal control box primary, “TTCBS” represents Tracker thermal control box secondary, “J” represents Main Data Computer (MDC) and data handling interface, “JT” represents trigger and central data acquisition, “PD” represents power distribution, “HV” represents high voltage brick, “M” represents monitoring, “PDS” represents the power distribution system. The “CCEB” represents Cryo-Cooler Electronics Box which stopped working after the upgrade of AMS. (a) RAM radiator (b) WAKE radiator.
29 on the WAKE radiator. There are four sensors on each corner of the main radiators respectively RR1–RR4 and WR1–WR4 to record the local temperature of the radiator panel. The arrangement of electronic boxes and thermal sensors on the inner sheet of the main radiators is shown in Fig. 4.
4. General regularity of the TCS for AMS electronics 4.1. Method The AMS TCS gives a read out of temperature values once in a minute. In long-term monitoring, the quantity of temperature data
is extremely large. In this paper, based on the collected data, i.e. more than 1.4 million records for each sensor in total, from May 19, 2011 to January 31, 2014, the arithmetic average value and standard deviation of the local temperature in one orbit are calculated. Because of the illumination-varying characteristic, the local temperature of AMS has an oscillating behavior with the same period of the orbit around an average, and with and amplitude slowly varying with time, an example of which is shown in Fig. 5. In this case, the orbit-averaged temperature could represent the temperature level in a certain period, while the standard deviation could represent the variation range of local temperature in one orbit. In this paper, the relationship between orbit-averaged temperature and the β will be given, along with the orbit standard deviation versus the β.
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Fig. 5. Examples of temperature measured by RR3 and WR3 sensors in 8 h, plus the orbit averaged temperature. The period clearly visible corresponds to the ISS orbiting time of about 91 min.
Normally, the RAM side of the ISS faces to the velocity vector, the solar arrays rotate around the main truss of the ISS automatically following sunlight and locked parallel to the velocity vector to minimize the air resistance. According to the routine report of the ISS activity, for more than 90% of the time the ISS is in this normal operation. Using the above-mentioned method, the variation of temperature versus the β can be observed. Since there are 57 thermal sensors, most of which are used to read out the temperature of electronic boxes, eight sensors (RR1– RR4, WR1–WR4) are used to measure the temperature of the radiator panel. The RR1–RR4 sensors are located at the four corners of the RAM radiator, and the WR1–WR4 sensors are located at the four corners of WAKE radiator, Each of the sensors is surrounded with several electronic boxes. These eight sensors are more easily affected by various thermal factors, in normal operations of the ISS and AMS, β is the main external thermal parameter. In this paper, the data from the eight sensors will be utilized. 4.2. Results and discussion The results of orbit-averaged temperature versus β are shown in Fig. 6, the temperature dependence on the β is displayed. The duration of special operations of the ISS accounts for about 10%, which is shown as limited dots beyond the main trend, these dots will not significantly affect the general temperature dependence on β. According to the figures, the intervals of temperature variation of RR1–RR4 sensors at the entire β interval are respectively [ 5 1C, 5 1C], [ 2 1C, 5 1C], [ 2.5 1C, 75 1C], [ 4 1C, 3 1C]. The temperature of both RR1 and RR3 sensors which are located on the starboard side of the RAM radiator shows a similar variation with the β, with the highest temperature occurring when β ¼ 301, and in the interval [ 401, 101], a rapid rise and drop of temperature occurs. This is because in this β interval, the Sun illuminates the starboard side of AMS. In addition, at a specific period in an orbit the solar radiation can reach the starboard side of the inner sheet of the RAM radiator. Detailed discussion of this effect is in the next section. The temperature of RR2 remains stable in the entire β interval. For RR4, the temperature remains stable when β o201, however a rapid rise occurs when β rises from 201 to 301, and this relatively high temperature remains when β 4301, caused by the solar illumination on the port side of the inner sheet of the RAM radiator. The reason why the RR2 sensor which is at the same side as RR4 does not present a rapid temperature rise is because AMS is inclined to the port by 121, and this inclination means the solar illumination can hardly reach the point of the inner sheet of the radiator where RR2 is located.
The temperature of WR1–WR4 sensors shows a relatively uniform variation, the temperature variation range of these four sensors at entire β interval are respectively [0 1C, 15 1C], [0 1C, 17 1C], [0 1C, 14 1C], [ 5 1C, 13 1C]. It is obvious that the temperature interval of each RR and WR sensor is different from others, this phenomenon comes from two points. One is the different heat generated by different electronic units, the other is the influence from heater patches. The temperature of the four sensors goes up slowly when the β increases from the extremely negative value, with the highest level reached at about β ¼ 251, and the temperature slowly goes down for β 4 251. This is because the starboard thermal radiator panel of the ISS can reflect solar irradiation to AMS on the port side and wake side when the β is negative, and the reflection around β ¼ 251 is the greatest. The investigation about the influence of the starboard thermal radiator position to TCS for AMS electronics will feature in future research. The temperature value is not the same in different periods with the same β. The temperature difference between the highest and lowest temperature at the same nominal β is within about 7 1C. One reason is that the solar flux varies between 1322 W/m2 at aphelion and 1424 W/m2 perihelion. In a year, the ISS passes one value of β ( 501 o β o501) many times but with different solar flux levels, which causes the orbit-averaged temperature in the statistics at the same β to fall within a range rather than be a fixed value. It can be concluded from the statistics that, for electronic units, the hot case is when the β is between 301 and 201 in normal operation, while the cold condition is when the absolute β value is very high ( 4601). Figs. 7 and 8 display the approximate temperature distribution that is calculated using cubic spline interpolation. The comparison of the temperature distribution on the main radiators between the hot case and the cold case is visualized. The highest temperature on the RAM radiator occurs at the TMPD2 box and the highest temperature on the WAKE radiator occurs at the PDS box. According to the two figures, it is evident that all the electronic units on the radiators are in the requested temperature range in both normal hot and cold conditions. The statistics of the orbit standard deviation of temperature is presented in Fig. 9. The results show that the RR1–RR4 sensors do not display a similar variation of the orbit standard deviation with β. The RR1 sensor gives a smooth variation of orbit standard deviation following the β, but that of RR2 sensor shows an unstable variation. The largest orbit standard deviation of both of the two sensors occurs when β ¼301. The largest orbit standard deviation of RR3 occurs when β ¼ 201, however for RR4, the largest orbit standard deviation occurs when β ¼ 301. Considering the orbit-averaged temperature of RR3 and RR4 sensors at the two β, temperature anomaly occur here, and will be analyzed in the next section. The four WR sensors present uniform variation of orbit standard deviation except that there is a turning point when β ¼551, which means that the WR3 temperature fluctuates more, within a single orbit, as β increases. This anomalous behavior will be discussed in the next section.
5. Temperature anomaly discussion Based on the regularity in last section, temperature anomaly possibly occurs at RR3 and RR4 when the β is respectively 201 and 301, since both orbit-averaged temperature and orbit standard deviation of these two sensors show variation anomaly during a certain β period. Fig. 10 shows the temperature curve of RR3 and surrounding electronic boxes in a long-β interval. It is obvious that the orbithighest temperature of RR3 sensor in one orbit goes suddenly
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Fig. 6. Orbit-averaged temperature of the selected sensors. (a) RR1, (b) RR2, (c) RR3, (d) RR4, (e) WR1, (f) WR2, (g) WR3 and (h) WR4.
higher when β is in the interval ½ 301; 151, which usually lasts about four days, however the surrounding electronic boxes do not show the same phenomenon as RR3.
The change of thermal sensor temperature usually occurs for the following three reasons: change of thermal load of electronic units, change of heater activity and change of solar illumination.
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Fig. 7. Temperature distribution on RAM (left) and WAKE (right) radiators at β¼ 301. The temperature data in use is recorded on May 12, 2012.
Fig. 8. Temperature distribution on RAM (left) and WAKE (right) radiators at β¼ 701. The temperature data in use is recorded on June 5, 2012.
Here the sudden temperature change of RR3 is not caused by the first two reasons, since thermal load change will cause a sudden temperature change of electronic boxes, and heater activity change will influence a group of sensors in the area where heat can be transferred easily via heat pipes. When the β is around 201, the sunlight reaches AMS on the starboard side directly. Since the radiator is connected with the vacuum case by the unique support structure (USS), but not fitted together tightly, plus the RR3 sensor is located at the starboardbottom of the RAM radiator, in one orbit, there is a particular moment when the solar illumination can reach the inner side of the RAM radiator. The sudden rise in temperature of RR3 is caused by the solar illumination on the inner sheet of the RAM radiator (see Fig. 11). The inner sheet of the radiator is 0.5 mm-thick aluminum board with very little heat capacity and the electronic boxes are covered with MLI. However, the inner surface of the radiator is covered with white paint, so the sheet can be easily warmed. The detailed temperature variation of RR3 with surrounding electronic boxes is shown in Fig. 12. In the figure, T6 and S3 reach the highest temperature in an orbit at point 1, which means if the sun cannot shine on the inner side of the RAM radiator, point 1 is the highest temperature in one orbit. The sun starts shining on the inner side from point 2, and the temperature of RR3 reaches the highest point at moment 3. According to the thermal sensor arrangement, the E1R0PD Lower sensor is the closest sensor to RR3, though this electronic box is covered with MLI, the thermal sensor is easily influenced by temperature rise of RR3 and this is
why for E1R0PD Lower sensor at moment 3 is warmer than that at moment 1. RR1 displays a similar behavior for the same reason. This effect occurs at very specific position of the Sun relative to the ISS. If the β o 301, the ELC2 panel will block the sunlight from illuminating RR3, if the jβjo 101, the TRD detector will block the sunlight as well. However, the situation of RR4 is different from RR3 and the unusual temperature phenomenon of RR4 occurs when the β is around 301 (see Fig. 13). RR4 is located at the port-bottom position of the RAM radiator and only the port solar array panel could block the sunlight to AMS when β is extremely high which is why the temperature anomaly for RR4 occurs when 201 o β o 401. The temperature anomaly for RR4 generally lasts about five days. The detailed temperature variation of RR4 and surrounding sensors is shown in Fig. 14. The detailed information of the unusual temperature phenomenon is similar to that of RR3. The CCEB Power side sensor is the closest sensor to RR4, the sudden rise of temperature of RR4 influences the CCEB Power side sensor. The temperature anomaly for WR3 sensor mentioned above can be interpreted according to Fig. 15. The amplitude of temperature measured by this sensor rises when the β goes up to β 4 571 and the orbit-minimum temperature goes down stably, but the orbit-maximum temperature goes up. This phenomenon lasts longer than the above two because it occurs during the entire extreme-positive-β period, i.e. β 4 571 which usually last about nine days. Meanwhile, the temperature of the other sensors shows less and less amplitude. Bigger amplitude causes higher orbit standard deviation.
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Fig. 9. Orbit standard deviation of temperature of the selected sensors. (a) RR1, (b) RR2, (c) RR3, (d) RR4, (e) WR1, (f) WR2, (g) WR3 and (h) WR4.
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Fig. 10. Temperature variation of RR3 sensor when the β dropped from 01 to 301.
Fig. 11. Sunlight reaches the inner side of RAM radiator.
Fig. 13. Temperature variation of RR4 sensor when the β dropped from 401 to 151
Fig. 14. Temperature curves of RR4 and surrounding electronic boxes when β ¼ 301. At point 1, the electronic boxes reach the orbit-highest temperature with the solar illumination on outer sheet of RAM radiator, and the sun stops illuminating the outer sheet of RAM radiator after point 1 in the current orbit. At point 2, the sun starts to illuminate the port side of the inner sheet of the RAM radiator, which rapidly warms up only the RR4 sensor, and at point 3, the sun stops illuminating the inner sheet of the radiator, RR3 sensor reaches its orbit-highest temperature.
Fig. 12. Temperature curves of RR3 and surrounding electronic boxes when β ¼ 201. At point 1, the sun stops illuminating the outer sheet of RAM radiator, the electronic boxes reach the highest level; at point 2, the sun starts to illuminate the starboard side of the inner sheet of RAM radiator, but only the RR3 sensor is warmed up rapidly since no MLI is covered on the sensor; at point 3, the sun stops illuminating the inner sheet of RAM radiator, and at point 4, the sun starts to illuminate the outer sheet of RAM radiator again in a new orbit.
Fig. 15. Amplitude of WR3 temperature and surrounding sensors. According to the temperature curves, the amplitude of WR3 temperature is getting greater following the β increases, meanwhile the amplitude of the rest sensors is getting smaller.
Detailed temperature curves of WR3 and its surrounding sensors are shown in Fig. 16. On point 1 and point 5, the temperature turning at the three sensors of WR3, T4 and S2 is synchronous. The TTCBP box is not mounted on the WAKE radiator but fixed on the USS and is very close to the inner sheet of the WAKE radiator. The temperature turning at point 5 on the TTCBP is synchronous with the others, however the bottom of the temperature curve is smoother. In the figure, the sun (firstly on the ram side of the ISS) starts to illuminate the inner sheet of the WAKE radiator in an orbit at point 1, because much greater heat
capacity of electronic elements than the aluminum sheet, WR3 temperature rise much more rapidly. Since the β in this case is about 621, the solar illumination is easily blocked by the thermal radiators of the ISS and the port solar arrays. Between points 2 and 3, the sunlight falling on inner sheet of the WAKE radiator is blocked by solar arrays. After point 3 (the sun has moved on the wake side of the ISS), the sun illuminates the outer sheet of the WAKE radiator, but at point 4, the lower USS beam shades the WR3-sensor area, which causes a short and rapid temperature drop. At point 5, the WAKE radiator starts to be shaded by the
K. Wang et al. / Nuclear Instruments and Methods in Physics Research A 767 (2014) 235–244
starboard thermal radiator of the ISS, and soon after, the ISS goes into the eclipse of earth. The above discussion is based on specific examples of the temperature anomaly. However, according to the monitoring of the TCS status, the temperature anomaly for the four sensors occurs every time when the β is in the discussed intervals. In preliminary simulation, these temperature anomalies cannot be simulated with the MERAT method because the geometry factor of the ISS component is simplified and combined into the MERAT. Technically, this temperature anomaly could be simulated with high-resolution model, customized interface and boundary settings, and by which the influence by the extra solar irradiation in an orbit could be quantified. 6. Data fit Technically the two radiators of AMS accept the most solar irradiation at the β ¼01, which leads to the orbit-averaged temperature should reach the highest value at β ¼01 and be symmetrically
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distributed. But since the AMS is not located at the geometric center of the ISS, the symmetric point of orbit-averaged temperature dependence on β is not at β ¼01. As shown in Fig. 6, the orbitaveraged temperature variation of RR2 and the four WR sensors in the entire β interval presents this characteristic, the cosine fit is used to describe the temperature variation. In addition, because of the temperature anomalies caused by the extra solar illumination on the inner sheet of the RAM radiator at specific β interval, it is better to fit the temperature dependence in this β interval individually using piecewise function, the fit during the anomaly internal is given in the form of original orbit-averaged temperature plus the increment by extra solar illumination. The fitted equations are listed in Table 2, and the fitted curves are combined into Fig. 6. It must be pointed out that the β of the ISS is not the only factor that affects AMS local temperature, as there are other factors such as heaters, the ISS configuration etc. Since those extra factors always work at specific β routinely, it is reasonable to simplify that the affections from the extra factors is the part of the characteristic of temperature dependence on β. In fact, when |β| 4671, the solar arrays are locked to block sunlight from illuminating the ISS continuously. That is not the normal situation for AMS. In the range of |β| o671, the fitted equations can more accurately describe the temperature dependence on β.
7. Conclusions
Fig. 16. Temperature curves of WR3 and surrounding electronic boxes when β ¼ 621. In an orbit, the sun starts to illuminate the inner sheet of WAKE radiator at point 1. At point 2, the solar illumination starts to be shaded by the ISS port solar arrays. At point 3, solar irradiation falls on the outer sheet of the WAKE radiator. At point 4, the WAKE radiator is shaded again. At point 5, AMS starts its night in this orbit.
The results show that in nominal operation, both RAM and WAKE radiator can work within the required temperature range, and also the regularity of orbit-averaged temperature of the selected sensors is given. According to the regularity, when β 301, the starboard side of the RAM radiator and the WAKE radiator are in hot case, and when the β is at extreme value, the both radiators are in cold case. In the hot case of the RAM radiator, the solar illumination falling on the inner sheet of the RAM radiator leads to temperature jump at a specific period of an orbit. On the WAKE radiator, a similarly temperature anomaly at WR3 sensor occurs when β 4 571 for the same reason.
Table 2 Fitted temperature (1C) dependence of the selected sensors on the β (Radian) of the ISS. Sensors RR1
Fitted equations π π βo ; β4 4 12 π π oβo T 0RR1 ¼ T RR1 þ 2:216 þ 2:236 cos ð 11:94 β 6:315Þ; 4 12 T RR1 ¼ 1:386 þ 1:282 cos ð 2:017 β þ 1:124Þ;
RR2
T RR2 ¼ 83:4þ 84:8 cos ð0:1643 β 0:02168Þ
RR3
T RR3 ¼ 0:8705 þ 0:6011 cos ð 2:982 β þ 1:659Þ;
RR4
T RR4 ¼ 48:45 cos ð 0:02391 β 1:557Þ;
π π βo ; β4 4 12 π π T 0RR3 ¼ T RR3 þ 2:135 þ 2:866 cos ð8:625 β þ 4:519Þ; oβo 4 12
T 0RR4 ¼ T RR4 þ 1:458 cos ð3:76 β 2:686Þ;
WR1
T WR1 ¼ 7:5 þ 5:85 cos ð1:355 β þ 0:797Þ
WR2
T WR2 ¼ 7:7 þ 6:8 cos ð1:443 β þ 0:7238Þ
WR3
T WR3 ¼ 9:03 4:43 cos ð1:631 β 2:131Þ
WR4
T WR4 ¼ 1:78 þ 8:64 cos ð1:08 β þ 0:6832Þ
βo β4
π 9
π 9
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This investigation of the general regularity of the TCS status of AMS provides references for the thermal design of equipment working on near-earth orbit, and also provides an approach in studying the status of TCS along with particular thermal factors. Acknowledgments The authors wish to give special thanks for the financial support from the Department of Science and Technology of Shandong Province, China (No. 2009ZHZX1A1105), and Chinese 973 program (No. 2013CB228305), sincere appreciation goes to Dr. Joseph Burger from Massachusetts Institute of Technology, USA, and Dr. Stefano Della Torre from Istituto Nazionale Di Fisica Nucleare, Italy, for the helpful discussions, Dr. Wenhao Sun from Southeast University, China, for his programming, Dr. Liang Ge from Shandong Computing Science Centre and Mr. Lipeng Song from Shandong University, China, for their valuable comments and suggestions in data fitting.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
F. Barao, Nuclear Instruments and Methods A 535 (2004) 134. V. Bindi, Nuclear Instruments and Methods A 617 (2010) 462. L. Amati, D. Baldassari, V. Bindi, et al., Nuclear Physics B 150 (2006) 276. T. Bruch, W. Wallraff, Nuclear Instruments and Methods A 572 (2007) 505. M. Buenerd, Nuclear Instruments and Methods A 502 (2003) 158. F. Cadoux, F. Cervelli, V. Chambert-Hermel, et al., Nuclear Physics B 113 (2002) 159. D. Haas, Nuclear Instruments and Methods A 530 (2004) 173. T. Kirn, T. Siedenburg, Nuclear Instruments and Methods A 535 (2004) 165. M. Aguilar, et al., Physical Review Letters 110 (2013) 141102. S. Coutu, Physics Online Journal 6 (2013) 40. X. Cai, On board computing system for AMS-02 mission, in: Proceedings of 29th International Cosmic Ray Conference Pune, 2005, pp. 373–376. M. Capell, E. Cortina, AMS Collaboration, AMS-02 electronics, in: Proceedings of 28th International Cosmic Ray Conference, 2003, pp. 2173-2176. Z. Cui, F. Luo, N. Wang, L. Cheng, Science China Technological Sciences 56 (2013) 2553.
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Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Operations of the thermal control system for Alpha Magnetic Spectrometer electronics following the beta angle of the International Space Station Kun Wang, Jinbo Li, Zheng Cui, Naihua Wang, Qie Sun, Lin Cheng n Institute of Thermal Science and Technology, Shandong University, 17923 Jingshi Road, 250061 Jinan, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 15 May 2014 Received in revised form 7 July 2014 Accepted 9 August 2014 Available online 10 September 2014
The Alpha Magnetic Spectrometer (AMS) has been running and measuring cosmic rays on the International Space Station (ISS) since May 19, 2011. The thermal control system (TCS) plays an important role in keeping all components and equipment working in an operational temperature range. Since the AMS started working on the ISS, AMS thermal engineers have been monitoring the on-orbit status of the TCS. During normal operation, the local temperature of AMS components regularly varies along with the β angle of the ISS. Based on the collected temperature data, the general characteristics of local temperature variations of TCS for AMS Electronics following the β of the ISS are discussed with the statistics of the orbit-averaged temperature and the orbit standard deviation of temperature. Furthermore some temperature anomalies at specific β are also studied. & 2014 Elsevier B.V. All rights reserved.
Keywords: Alpha Magnetic Spectrometer electronics Thermal control system Beta angle Regularity Temperature anomaly
1. Introduction The Alpha Magnetic Spectrometer (AMS) project is an international physical experiment whose aim is to use the unique environment on the International Space Station (ISS) to study the universe by searching for anti-matter and dark matter while performing precision measurements of cosmic rays composition and flux [1,2]. More than 48 billion cosmic-ray events (up to May 1, 2014) have been measured by six detectors since AMS started running on 19th May, 2011. Detailed information about the six detectors can be found in the referenced literature [3–8]. The first result of AMS experiment was published in 2013 [9]. The first result provides the largest set of cosmic-ray positron data, increasing the total world sample a hundredfold, while presenting a striking confirmation of positron fraction indicated in previous satellite experiments [10]. AMS will be working for the whole life of the ISS. Normally the ISS flies in the sun and the eclipse of earth, with the orbital period of about 91 min and altitude varying between 241 and 434 km. In this space environment, about 2500 W heat must be dissipated radiatively during operation. In addition to this, thermo-optical characteristics of materials are slowly degrading. For this reason, the temperature of all equipment must be controlled within its
n
Corresponding author. Tel.: þ 86 531 88393000. E-mail address: [email protected] (L. Cheng).
http://dx.doi.org/10.1016/j.nima.2014.08.010 0168-9002/& 2014 Elsevier B.V. All rights reserved.
own allowed range and furthermore, stability of the temperature of components is also required. Based on the issues mentioned above, an efficient and reliable thermal control system (TCS) is required in AMS to keep all components working within their allowed temperature range. On-orbit operation of AMS has proved that the TCS provides strong support for this experiment. In long-term monitoring, the AMS thermal group finds that the local temperature of AMS regularly varies along with the angle between the ISS orbit plane and sunlight (β angle) in normal operation. The AMS thermal group has also been trying to find the characteristic of local temperature change of AMS to give an approximate prediction of AMS local temperature at a certain moment with predictable thermal factors. In the preliminary simulation, the mean effective radiation temperature (MERAT) method was adopted, which means the external thermal factors were simplified as a MERAT which was provided by National Aeronautics and Space Administration (NASA), USA. In the simulation, the thermal status of AMS electronics in the operation of startup, running, power outage, and heater activities in worst hot and cold cases selected from 259 possible cases was given, which had proved that the TCS can support AMS effectively when working on the ISS. But the thermal status in general situations was not specifically given. In this paper, based on the collected temperature data, the general regularity of the temperature dependence on β will be investigated, and temperature anomaly at specific β will be studied.
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Table 1 Thermal limits (1C) of electronic elements.
β = 0° β < 0°
β > 0°
12°
Fig. 1. The sun's position relative to AMS at different β angles.
Fig. 2. Variation of β in 2012.
2.
β Angle of the ISS
The β is a very important parameter for the ISS external thermal factor. The regularity of β can be calculated with the parameter of the ISS orbit. Put simply, the angle between the ISS orbit plane and equatorial plan is 51.51 and the angle between equatorial plan and the ecliptic plane is 23.51, which results in a β angle of the ISS varying in the range [ 751, 751]. For AMS, different values of the β correspond to different configurations of Sun illumination, shown in Fig. 1. Since AMS is inclined to the port side of the ISS by about 121, when the β 4121, the sun illuminates AMS on the port side; when the β o 121, the sun illuminates AMS on the starboard side. However there is an express logistics carrier panel (ELC2) at the starboard side of AMS, and if the β is low enough, the ELC2 panel will shade AMS to a different extent. The author cannot get the specific dimension of the ISS but based on the observation of temperature data and approximately when β o 231, the ELC2 panel starts to shade the bottom of AMS from the sun; when β o 601, the AMS will be completely in the shadow of ELC2 during a certain period of an orbit. Fig. 2 presents the β variation in 2012. In fact, the variation of the β in each year is almost the same. The highest β always occurs between the end of May and the beginning of June, the lowest β always occurs between the end of December and the beginning of January.
3. TCS for AMS electronics The electronic system is a fundamental system that provides power supply\distribution, data collection and command interface [11,12]. Both passive thermal control hardware and active thermal control hardware are utilized in the AMS electronics thermal
xCrates J-group Crates xPD TTCB HV Bricks
Operational warning
Operational limits
Non-operational limits
Low
High
Low
High
Low
High
15 15 20 15 15
45 60 43 45 45
20 20 25 20 20
50 65 48 50 50
40 40 40 40 35
80 80 80 55 65
control [13]. The TCS protects the electronics from exceeding the allowed temperature range when AMS is running on the ISS. Relevant thermal limits are shown in Table 1, the low operational warning is also the minimum switch-on temperature of corresponding electronic elements. The two main radiators are arranged on RAM and WAKE side of AMS to dissipate heat generated by electronic boxes, shown in Fig. 3. The electronic boxes are mounted and fixed with screws on the inner sheet of the RAM radiator and the WAKE radiator. Heat pipes are used in radiators to diminish the temperature difference and homogenize the temperature distribution. A total of 40 heat pipes with various shapes are embedded into the interlayer of the main radiators: 16 are on the RAM radiator and 24 are on the WAKE radiator. Heaters are used on AMS main radiators including 38 heater patches and 132 thermostats (including spares) in order to keep the temperature of crucial electronic boxes above the required limit in cold conditions. There are two sets of heaters mounted on the RAM radiator. Set #1 includes 16 heaters, ten of which are glued onto the radiator while the other six are glued onto the walls of the boxes of J-group crates i.e. J, JT and JPD. Set #1 heaters aim to keep all the electronic boxes above the minimum nonoperational temperature with the exception of the J-group electronics, which has to be kept above the minimum switch-on temperature. The second heater set includes 9 heaters, which are glued onto the radiator directly. Set #2 heaters aim to bring all the electronics sitting on the RAM radiator panel to the minimum switch-on temperature together with the first set. The two sets work in parallel to reach this goal when AMS is on the ISS truss location. The WAKE radiator panel is equipped with 6 heaters glued onto the inner side of the panel itself. This heater set aims to warm all the electronics that are mounted on the WAKE radiator panel, with the exception of the Power Distribution System (PDS) box, to the minimum switch-on temperature together with the support of the PDS heaters set. Heater activities are controlled by means of PDS switches and mechanical thermostats. Two types of thermostats comprise the heater circuit: the control thermostats and the safety thermostats. The control thermostats regulate the normal (absence of failures) activity of the heaters cabled together, and the corresponding set points are 18 1C/ 12 1C. The tolerance on the set points is 71.7 1C. The safety thermostats have higher set points, namely þ42 1C/ þ 48 1C, and interrupt the heater circuit in case of failure if the temperature underneath the heater patch (close to the safety thermostat) exceeds þ 48 1C. Almost all visible surfaces on the inside and outside of the AMS are thermal-control finishes to increase emissivity and decrease absorptivity of surfaces. In addition, multilayer insulation (MLI) covers electronic units to minimize the thermal radiation to the inside detectors. On the main radiators, a total of 57 thermal sensors are arranged to collect the temperature of electronic units and main radiator panels: 28 thermal sensors are on the RAM radiator and
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Fig. 3. Radiators on AMS. The dimensions of AMS is about 3 m 3 m 3 m, with weight of about 7 tons. On a spacecraft, the ram side faces to the velocity vector, the wake side faces to the opposite of the velocity vector. When facing to ram direction, the left and right sides are respectively called port and starboard sides nautically. In addition, in the Cartesian coordinate of the ISS, the x-axis points to ram direction, the y-axis points to starboard direction, and z-axis points to the core of the earth.
Fig. 4. Arrangement of electronic boxes and thermal sensors on main radiators. The sensors marked as RR1-RR4 and WR1-WR4 are selected in this paper, each one is at a corner of the main radiators, and surrounded with several electronic boxes. In addition, about the names of electronic boxes, “E” represents Electromagnetic Calorimeter (ECAL), “R” represents Ring Imaging Cherenkov Detector (RICH), “S” represents Time of Flight detector (ToF), “U” represents Transition Radiation Detector (TRD), “UG” represents the TRD gas system, “T” represents Silicon Tracker. The six kinds of boxes are “Crates” referring to the readout/monitor/control electronics boxes. “TT” represents Tracker Thermal, “TTCBP” represents Tracker thermal control box primary, “TTCBS” represents Tracker thermal control box secondary, “J” represents Main Data Computer (MDC) and data handling interface, “JT” represents trigger and central data acquisition, “PD” represents power distribution, “HV” represents high voltage brick, “M” represents monitoring, “PDS” represents the power distribution system. The “CCEB” represents Cryo-Cooler Electronics Box which stopped working after the upgrade of AMS. (a) RAM radiator (b) WAKE radiator.
29 on the WAKE radiator. There are four sensors on each corner of the main radiators respectively RR1–RR4 and WR1–WR4 to record the local temperature of the radiator panel. The arrangement of electronic boxes and thermal sensors on the inner sheet of the main radiators is shown in Fig. 4.
4. General regularity of the TCS for AMS electronics 4.1. Method The AMS TCS gives a read out of temperature values once in a minute. In long-term monitoring, the quantity of temperature data
is extremely large. In this paper, based on the collected data, i.e. more than 1.4 million records for each sensor in total, from May 19, 2011 to January 31, 2014, the arithmetic average value and standard deviation of the local temperature in one orbit are calculated. Because of the illumination-varying characteristic, the local temperature of AMS has an oscillating behavior with the same period of the orbit around an average, and with and amplitude slowly varying with time, an example of which is shown in Fig. 5. In this case, the orbit-averaged temperature could represent the temperature level in a certain period, while the standard deviation could represent the variation range of local temperature in one orbit. In this paper, the relationship between orbit-averaged temperature and the β will be given, along with the orbit standard deviation versus the β.
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Fig. 5. Examples of temperature measured by RR3 and WR3 sensors in 8 h, plus the orbit averaged temperature. The period clearly visible corresponds to the ISS orbiting time of about 91 min.
Normally, the RAM side of the ISS faces to the velocity vector, the solar arrays rotate around the main truss of the ISS automatically following sunlight and locked parallel to the velocity vector to minimize the air resistance. According to the routine report of the ISS activity, for more than 90% of the time the ISS is in this normal operation. Using the above-mentioned method, the variation of temperature versus the β can be observed. Since there are 57 thermal sensors, most of which are used to read out the temperature of electronic boxes, eight sensors (RR1– RR4, WR1–WR4) are used to measure the temperature of the radiator panel. The RR1–RR4 sensors are located at the four corners of the RAM radiator, and the WR1–WR4 sensors are located at the four corners of WAKE radiator, Each of the sensors is surrounded with several electronic boxes. These eight sensors are more easily affected by various thermal factors, in normal operations of the ISS and AMS, β is the main external thermal parameter. In this paper, the data from the eight sensors will be utilized. 4.2. Results and discussion The results of orbit-averaged temperature versus β are shown in Fig. 6, the temperature dependence on the β is displayed. The duration of special operations of the ISS accounts for about 10%, which is shown as limited dots beyond the main trend, these dots will not significantly affect the general temperature dependence on β. According to the figures, the intervals of temperature variation of RR1–RR4 sensors at the entire β interval are respectively [ 5 1C, 5 1C], [ 2 1C, 5 1C], [ 2.5 1C, 75 1C], [ 4 1C, 3 1C]. The temperature of both RR1 and RR3 sensors which are located on the starboard side of the RAM radiator shows a similar variation with the β, with the highest temperature occurring when β ¼ 301, and in the interval [ 401, 101], a rapid rise and drop of temperature occurs. This is because in this β interval, the Sun illuminates the starboard side of AMS. In addition, at a specific period in an orbit the solar radiation can reach the starboard side of the inner sheet of the RAM radiator. Detailed discussion of this effect is in the next section. The temperature of RR2 remains stable in the entire β interval. For RR4, the temperature remains stable when β o201, however a rapid rise occurs when β rises from 201 to 301, and this relatively high temperature remains when β 4301, caused by the solar illumination on the port side of the inner sheet of the RAM radiator. The reason why the RR2 sensor which is at the same side as RR4 does not present a rapid temperature rise is because AMS is inclined to the port by 121, and this inclination means the solar illumination can hardly reach the point of the inner sheet of the radiator where RR2 is located.
The temperature of WR1–WR4 sensors shows a relatively uniform variation, the temperature variation range of these four sensors at entire β interval are respectively [0 1C, 15 1C], [0 1C, 17 1C], [0 1C, 14 1C], [ 5 1C, 13 1C]. It is obvious that the temperature interval of each RR and WR sensor is different from others, this phenomenon comes from two points. One is the different heat generated by different electronic units, the other is the influence from heater patches. The temperature of the four sensors goes up slowly when the β increases from the extremely negative value, with the highest level reached at about β ¼ 251, and the temperature slowly goes down for β 4 251. This is because the starboard thermal radiator panel of the ISS can reflect solar irradiation to AMS on the port side and wake side when the β is negative, and the reflection around β ¼ 251 is the greatest. The investigation about the influence of the starboard thermal radiator position to TCS for AMS electronics will feature in future research. The temperature value is not the same in different periods with the same β. The temperature difference between the highest and lowest temperature at the same nominal β is within about 7 1C. One reason is that the solar flux varies between 1322 W/m2 at aphelion and 1424 W/m2 perihelion. In a year, the ISS passes one value of β ( 501 o β o501) many times but with different solar flux levels, which causes the orbit-averaged temperature in the statistics at the same β to fall within a range rather than be a fixed value. It can be concluded from the statistics that, for electronic units, the hot case is when the β is between 301 and 201 in normal operation, while the cold condition is when the absolute β value is very high ( 4601). Figs. 7 and 8 display the approximate temperature distribution that is calculated using cubic spline interpolation. The comparison of the temperature distribution on the main radiators between the hot case and the cold case is visualized. The highest temperature on the RAM radiator occurs at the TMPD2 box and the highest temperature on the WAKE radiator occurs at the PDS box. According to the two figures, it is evident that all the electronic units on the radiators are in the requested temperature range in both normal hot and cold conditions. The statistics of the orbit standard deviation of temperature is presented in Fig. 9. The results show that the RR1–RR4 sensors do not display a similar variation of the orbit standard deviation with β. The RR1 sensor gives a smooth variation of orbit standard deviation following the β, but that of RR2 sensor shows an unstable variation. The largest orbit standard deviation of both of the two sensors occurs when β ¼301. The largest orbit standard deviation of RR3 occurs when β ¼ 201, however for RR4, the largest orbit standard deviation occurs when β ¼ 301. Considering the orbit-averaged temperature of RR3 and RR4 sensors at the two β, temperature anomaly occur here, and will be analyzed in the next section. The four WR sensors present uniform variation of orbit standard deviation except that there is a turning point when β ¼551, which means that the WR3 temperature fluctuates more, within a single orbit, as β increases. This anomalous behavior will be discussed in the next section.
5. Temperature anomaly discussion Based on the regularity in last section, temperature anomaly possibly occurs at RR3 and RR4 when the β is respectively 201 and 301, since both orbit-averaged temperature and orbit standard deviation of these two sensors show variation anomaly during a certain β period. Fig. 10 shows the temperature curve of RR3 and surrounding electronic boxes in a long-β interval. It is obvious that the orbithighest temperature of RR3 sensor in one orbit goes suddenly
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Fig. 6. Orbit-averaged temperature of the selected sensors. (a) RR1, (b) RR2, (c) RR3, (d) RR4, (e) WR1, (f) WR2, (g) WR3 and (h) WR4.
higher when β is in the interval ½ 301; 151, which usually lasts about four days, however the surrounding electronic boxes do not show the same phenomenon as RR3.
The change of thermal sensor temperature usually occurs for the following three reasons: change of thermal load of electronic units, change of heater activity and change of solar illumination.
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Fig. 7. Temperature distribution on RAM (left) and WAKE (right) radiators at β¼ 301. The temperature data in use is recorded on May 12, 2012.
Fig. 8. Temperature distribution on RAM (left) and WAKE (right) radiators at β¼ 701. The temperature data in use is recorded on June 5, 2012.
Here the sudden temperature change of RR3 is not caused by the first two reasons, since thermal load change will cause a sudden temperature change of electronic boxes, and heater activity change will influence a group of sensors in the area where heat can be transferred easily via heat pipes. When the β is around 201, the sunlight reaches AMS on the starboard side directly. Since the radiator is connected with the vacuum case by the unique support structure (USS), but not fitted together tightly, plus the RR3 sensor is located at the starboardbottom of the RAM radiator, in one orbit, there is a particular moment when the solar illumination can reach the inner side of the RAM radiator. The sudden rise in temperature of RR3 is caused by the solar illumination on the inner sheet of the RAM radiator (see Fig. 11). The inner sheet of the radiator is 0.5 mm-thick aluminum board with very little heat capacity and the electronic boxes are covered with MLI. However, the inner surface of the radiator is covered with white paint, so the sheet can be easily warmed. The detailed temperature variation of RR3 with surrounding electronic boxes is shown in Fig. 12. In the figure, T6 and S3 reach the highest temperature in an orbit at point 1, which means if the sun cannot shine on the inner side of the RAM radiator, point 1 is the highest temperature in one orbit. The sun starts shining on the inner side from point 2, and the temperature of RR3 reaches the highest point at moment 3. According to the thermal sensor arrangement, the E1R0PD Lower sensor is the closest sensor to RR3, though this electronic box is covered with MLI, the thermal sensor is easily influenced by temperature rise of RR3 and this is
why for E1R0PD Lower sensor at moment 3 is warmer than that at moment 1. RR1 displays a similar behavior for the same reason. This effect occurs at very specific position of the Sun relative to the ISS. If the β o 301, the ELC2 panel will block the sunlight from illuminating RR3, if the jβjo 101, the TRD detector will block the sunlight as well. However, the situation of RR4 is different from RR3 and the unusual temperature phenomenon of RR4 occurs when the β is around 301 (see Fig. 13). RR4 is located at the port-bottom position of the RAM radiator and only the port solar array panel could block the sunlight to AMS when β is extremely high which is why the temperature anomaly for RR4 occurs when 201 o β o 401. The temperature anomaly for RR4 generally lasts about five days. The detailed temperature variation of RR4 and surrounding sensors is shown in Fig. 14. The detailed information of the unusual temperature phenomenon is similar to that of RR3. The CCEB Power side sensor is the closest sensor to RR4, the sudden rise of temperature of RR4 influences the CCEB Power side sensor. The temperature anomaly for WR3 sensor mentioned above can be interpreted according to Fig. 15. The amplitude of temperature measured by this sensor rises when the β goes up to β 4 571 and the orbit-minimum temperature goes down stably, but the orbit-maximum temperature goes up. This phenomenon lasts longer than the above two because it occurs during the entire extreme-positive-β period, i.e. β 4 571 which usually last about nine days. Meanwhile, the temperature of the other sensors shows less and less amplitude. Bigger amplitude causes higher orbit standard deviation.
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Fig. 9. Orbit standard deviation of temperature of the selected sensors. (a) RR1, (b) RR2, (c) RR3, (d) RR4, (e) WR1, (f) WR2, (g) WR3 and (h) WR4.
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Fig. 10. Temperature variation of RR3 sensor when the β dropped from 01 to 301.
Fig. 11. Sunlight reaches the inner side of RAM radiator.
Fig. 13. Temperature variation of RR4 sensor when the β dropped from 401 to 151
Fig. 14. Temperature curves of RR4 and surrounding electronic boxes when β ¼ 301. At point 1, the electronic boxes reach the orbit-highest temperature with the solar illumination on outer sheet of RAM radiator, and the sun stops illuminating the outer sheet of RAM radiator after point 1 in the current orbit. At point 2, the sun starts to illuminate the port side of the inner sheet of the RAM radiator, which rapidly warms up only the RR4 sensor, and at point 3, the sun stops illuminating the inner sheet of the radiator, RR3 sensor reaches its orbit-highest temperature.
Fig. 12. Temperature curves of RR3 and surrounding electronic boxes when β ¼ 201. At point 1, the sun stops illuminating the outer sheet of RAM radiator, the electronic boxes reach the highest level; at point 2, the sun starts to illuminate the starboard side of the inner sheet of RAM radiator, but only the RR3 sensor is warmed up rapidly since no MLI is covered on the sensor; at point 3, the sun stops illuminating the inner sheet of RAM radiator, and at point 4, the sun starts to illuminate the outer sheet of RAM radiator again in a new orbit.
Fig. 15. Amplitude of WR3 temperature and surrounding sensors. According to the temperature curves, the amplitude of WR3 temperature is getting greater following the β increases, meanwhile the amplitude of the rest sensors is getting smaller.
Detailed temperature curves of WR3 and its surrounding sensors are shown in Fig. 16. On point 1 and point 5, the temperature turning at the three sensors of WR3, T4 and S2 is synchronous. The TTCBP box is not mounted on the WAKE radiator but fixed on the USS and is very close to the inner sheet of the WAKE radiator. The temperature turning at point 5 on the TTCBP is synchronous with the others, however the bottom of the temperature curve is smoother. In the figure, the sun (firstly on the ram side of the ISS) starts to illuminate the inner sheet of the WAKE radiator in an orbit at point 1, because much greater heat
capacity of electronic elements than the aluminum sheet, WR3 temperature rise much more rapidly. Since the β in this case is about 621, the solar illumination is easily blocked by the thermal radiators of the ISS and the port solar arrays. Between points 2 and 3, the sunlight falling on inner sheet of the WAKE radiator is blocked by solar arrays. After point 3 (the sun has moved on the wake side of the ISS), the sun illuminates the outer sheet of the WAKE radiator, but at point 4, the lower USS beam shades the WR3-sensor area, which causes a short and rapid temperature drop. At point 5, the WAKE radiator starts to be shaded by the
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starboard thermal radiator of the ISS, and soon after, the ISS goes into the eclipse of earth. The above discussion is based on specific examples of the temperature anomaly. However, according to the monitoring of the TCS status, the temperature anomaly for the four sensors occurs every time when the β is in the discussed intervals. In preliminary simulation, these temperature anomalies cannot be simulated with the MERAT method because the geometry factor of the ISS component is simplified and combined into the MERAT. Technically, this temperature anomaly could be simulated with high-resolution model, customized interface and boundary settings, and by which the influence by the extra solar irradiation in an orbit could be quantified. 6. Data fit Technically the two radiators of AMS accept the most solar irradiation at the β ¼01, which leads to the orbit-averaged temperature should reach the highest value at β ¼01 and be symmetrically
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distributed. But since the AMS is not located at the geometric center of the ISS, the symmetric point of orbit-averaged temperature dependence on β is not at β ¼01. As shown in Fig. 6, the orbitaveraged temperature variation of RR2 and the four WR sensors in the entire β interval presents this characteristic, the cosine fit is used to describe the temperature variation. In addition, because of the temperature anomalies caused by the extra solar illumination on the inner sheet of the RAM radiator at specific β interval, it is better to fit the temperature dependence in this β interval individually using piecewise function, the fit during the anomaly internal is given in the form of original orbit-averaged temperature plus the increment by extra solar illumination. The fitted equations are listed in Table 2, and the fitted curves are combined into Fig. 6. It must be pointed out that the β of the ISS is not the only factor that affects AMS local temperature, as there are other factors such as heaters, the ISS configuration etc. Since those extra factors always work at specific β routinely, it is reasonable to simplify that the affections from the extra factors is the part of the characteristic of temperature dependence on β. In fact, when |β| 4671, the solar arrays are locked to block sunlight from illuminating the ISS continuously. That is not the normal situation for AMS. In the range of |β| o671, the fitted equations can more accurately describe the temperature dependence on β.
7. Conclusions
Fig. 16. Temperature curves of WR3 and surrounding electronic boxes when β ¼ 621. In an orbit, the sun starts to illuminate the inner sheet of WAKE radiator at point 1. At point 2, the solar illumination starts to be shaded by the ISS port solar arrays. At point 3, solar irradiation falls on the outer sheet of the WAKE radiator. At point 4, the WAKE radiator is shaded again. At point 5, AMS starts its night in this orbit.
The results show that in nominal operation, both RAM and WAKE radiator can work within the required temperature range, and also the regularity of orbit-averaged temperature of the selected sensors is given. According to the regularity, when β 301, the starboard side of the RAM radiator and the WAKE radiator are in hot case, and when the β is at extreme value, the both radiators are in cold case. In the hot case of the RAM radiator, the solar illumination falling on the inner sheet of the RAM radiator leads to temperature jump at a specific period of an orbit. On the WAKE radiator, a similarly temperature anomaly at WR3 sensor occurs when β 4 571 for the same reason.
Table 2 Fitted temperature (1C) dependence of the selected sensors on the β (Radian) of the ISS. Sensors RR1
Fitted equations π π βo ; β4 4 12 π π oβo T 0RR1 ¼ T RR1 þ 2:216 þ 2:236 cos ð 11:94 β 6:315Þ; 4 12 T RR1 ¼ 1:386 þ 1:282 cos ð 2:017 β þ 1:124Þ;
RR2
T RR2 ¼ 83:4þ 84:8 cos ð0:1643 β 0:02168Þ
RR3
T RR3 ¼ 0:8705 þ 0:6011 cos ð 2:982 β þ 1:659Þ;
RR4
T RR4 ¼ 48:45 cos ð 0:02391 β 1:557Þ;
π π βo ; β4 4 12 π π T 0RR3 ¼ T RR3 þ 2:135 þ 2:866 cos ð8:625 β þ 4:519Þ; oβo 4 12
T 0RR4 ¼ T RR4 þ 1:458 cos ð3:76 β 2:686Þ;
WR1
T WR1 ¼ 7:5 þ 5:85 cos ð1:355 β þ 0:797Þ
WR2
T WR2 ¼ 7:7 þ 6:8 cos ð1:443 β þ 0:7238Þ
WR3
T WR3 ¼ 9:03 4:43 cos ð1:631 β 2:131Þ
WR4
T WR4 ¼ 1:78 þ 8:64 cos ð1:08 β þ 0:6832Þ
βo β4
π 9
π 9
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This investigation of the general regularity of the TCS status of AMS provides references for the thermal design of equipment working on near-earth orbit, and also provides an approach in studying the status of TCS along with particular thermal factors. Acknowledgments The authors wish to give special thanks for the financial support from the Department of Science and Technology of Shandong Province, China (No. 2009ZHZX1A1105), and Chinese 973 program (No. 2013CB228305), sincere appreciation goes to Dr. Joseph Burger from Massachusetts Institute of Technology, USA, and Dr. Stefano Della Torre from Istituto Nazionale Di Fisica Nucleare, Italy, for the helpful discussions, Dr. Wenhao Sun from Southeast University, China, for his programming, Dr. Liang Ge from Shandong Computing Science Centre and Mr. Lipeng Song from Shandong University, China, for their valuable comments and suggestions in data fitting.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
F. Barao, Nuclear Instruments and Methods A 535 (2004) 134. V. Bindi, Nuclear Instruments and Methods A 617 (2010) 462. L. Amati, D. Baldassari, V. Bindi, et al., Nuclear Physics B 150 (2006) 276. T. Bruch, W. Wallraff, Nuclear Instruments and Methods A 572 (2007) 505. M. Buenerd, Nuclear Instruments and Methods A 502 (2003) 158. F. Cadoux, F. Cervelli, V. Chambert-Hermel, et al., Nuclear Physics B 113 (2002) 159. D. Haas, Nuclear Instruments and Methods A 530 (2004) 173. T. Kirn, T. Siedenburg, Nuclear Instruments and Methods A 535 (2004) 165. M. Aguilar, et al., Physical Review Letters 110 (2013) 141102. S. Coutu, Physics Online Journal 6 (2013) 40. X. Cai, On board computing system for AMS-02 mission, in: Proceedings of 29th International Cosmic Ray Conference Pune, 2005, pp. 373–376. M. Capell, E. Cortina, AMS Collaboration, AMS-02 electronics, in: Proceedings of 28th International Cosmic Ray Conference, 2003, pp. 2173-2176. Z. Cui, F. Luo, N. Wang, L. Cheng, Science China Technological Sciences 56 (2013) 2553.