DEVELOPMENT OF HIGH TEMPERATURE NOISE SOURCE (HTS) FOR ADVANCED MICROWAVE SCANNING RADIOMETER 2 (AMSR2).ppt

Editor's Notes

• #2: Thank you Mr. Chairman, and Good afternoon ladies and gentleman. Let me introduce myself. I’m Tatsuhiro Noguchi working for Mitsubishi Electric Corporation, Kamakura Works as a ｎ AMSR2 project manager. Today I’m going to talk about “Development of High Temperature Noise Source for Advanced Microwave Scanning Radiometer2”. AMSR2 is a passive microwave sensor mounted on the satellite named GCOM-W1. In the design of AMSR2, the thermal design of HTS is most critical to obtain the excellent calibration performance with keeping the temperature distribution of HTS uniform. In this presentation, I’d like to talk about the design of AMSR2, especially the design concepts of HTS.
• #3: My presentation consists of 5 parts. First of all, I’m going to explain the mission of GCOM satellites. Secondly, I’d like to talk about the summary of AMSR2 and design concept of HTS. Then, I will report the on-orbit thermal analysis results and the thermal vacuum test results for AMSR2. At the end, I will summarize of my presentation.
• #4: I will explain the GCOM which stands for Global Change Observation Mission. The entire GCOM consists of two series of satellites, named GCOM-W and GCOM-C. GCOM-W and GCOM-C are single mission satellite, and their mission is the data acquisition concerning the water cycle of the Earth, and the data acquisition concerning the climate change. For these purpose, GCOM-W1 and GCOM-C1 have microwave sensor AMSR2 and optical sensor SGLI, respectively. The entire GCOM has three generations and each satellite has 5 years design life. GCOM-W1 is the first satellite of this mission, and is scheduled for launch in FY 2011.
• #5: This figure shows GCOM-W1 satellite and AMSR2 which consists of Sensor Unit and Control Unit. AMSR2 observes the: Integrated Water Vapor, Integrated Cloud Liquid Water, Precipitation, Sea Surface Temperature, and Soil Moisture, etc. And these data are very useful for the construction of the Climate prediction models and the formulation of an international environmental strategy. They are also useful for people's lives, such as the improvement of the prediction accuracy of the weather forecast and the provision of the fishery information.
• #6: These are the pictures of AMSR2 flight model. Sensor Unit has a function of reflector deployment to realize the compact configuration at launch phase. These are the pictures of Control Unit and Momentum Wheel Assembly MWA is equipped to compensate the moment generated by the rotation of SU and installed in CU. In addition, the second MWA is equipped in AMSR2 for redundancy.
• #7: This table summarizes the key parameters of heritage AMSR. We have developed the series of microwave scanning radiometers as shown in the table. AMSR-E mounted on Aqua satellite and is still operational in orbit more than 9 years. AMSR2 is the successor of AMSR-E and has total 16 observation channels adding the 7.3GHz channels to AMSR-E channels for RF interference mitigation. In addition, antenna size of AMSR2 is enlarged to 2m from 1.6m of AMSR-E to improve the instant field of view (IFOV).
• #8: This figure shows AMSR2 schematic. AMSR2 receives the weak microwave radiation from the earth, and acquires the products from the observed data such as integrated water vapor, sea surface temperature, etc. One of the features of AMSR2 is that it enables to observe the Earth surface in 1450km width by scanning the AMSR2 Sensor Unit with 40rpm. The other is to calibrate the observation data of each scan on orbit in order to acquire the highly accurate observation data by using CSM and HTS. CSM and HTS are the cold and warm calibration loads of AMSR2.
• #9: There is a correlation between the microwave strength radiated from the earth and its brightness temperature. Therefore, by converting strength of the observed microwave into the brightness temperature, the temperature on the earth surface can be obtained. On the other hand, there is a temperature dependence in Feed, the measurement error is caused. Consequently, CSM has view in Outer Space at any position on orbit, and 3K microwave which outer space radiates is entered into Feed. Besides HTS irradiates Feed with the 20degC microwave by keeping the temperature of microwave absorbers in HTS constant. Then, the observational data is corrected by making the standard points from HTS and CSM which radiate constant brightness temperature. If the thermal environmental change on orbit, the measurement error is caused by variation of the correlation between acquired microwave strength and brightness temperature. Here, to sum up then, the HTS mission is to Uniform temperature distribution of microwave absorbers and Irradiate Feed with stabilized brightness temperature in the severe thermal environment on the orbit.
• #10: Let me give you the thermal design concepts of HTS. To obtain well-accurate data, the temperature distribution of the microwave absorbers should be minimized. As specifications, the reference temperature of HTS is 20degC and the allowed temperature distribution of microwave absorbers is 2.5degC or less. In order to show you how the HTS specification is demanding, there is an example of a normal satellite equipment for comparison. An allowed temperature range of a certain satellite equipment is from -10 to +50degC. Consequently, it is understood that the required specification of HTS is infinitely severe as a satellite equipment. To overcome the difficult problem, HTS was developed based on two design concepts, a heat radiation and an insulation. In the next slide, I will focus on those two design concepts of HTS.
• #11: The first concept is to control the surrounding temperature of microwave absorbers. Because the thermal conductivity of the microwave absorbers is very low, the temperature controlling by the thermal conduction has the possibility to increase the temperature distribution of the microwave absorbers. As you can see on the figure, Thermal Control Panel (TCP) is set up on Sensor Unit structure and opposite side of HTS aperture. In addition, the materials of HTS walls and TCP are aluminum alloys, and their all six planes’ temperature is controlled with the heaters. As a result, the temperature of the microwave absorbers are kept uniform by the heater radiation.
• #12: The other design concept is the thermal insulation. The thermal insulation design was conducted so that the microwave absorbers and the surrounding components were not connected thermally with the outside environment. Therefore, HTS equips Multi-Layered Insulator (MLI). The MLI surface layer has low solar absorption and high thermal emittance. In addition, TCP is equipped on Sensor Unit which is also useful for preventing the incidence of the solar light and heat radiation to the outer space. Moreover, the shields of HTS were installed for the same reason. Furthermore, both HTS and TCP are thermally insulated from Sensor Unit by the thermal insulation spacers made of the glass epoxy, in order to minimize thermal conductions from Sensor Unit and to make the thermal control of the HTS walls and TCP easier. The all of concepts about HTS design were given.
• #13: Next, I’m going to explain how to evaluate the validity of these design concepts. In order to validate HTS thermal design concepts, we conducted three evaluation methods, on-orbit analysis and two types of thermal vacuum tests, which are IR method and Solar method. Today, I will report the evaluation result of the on-orbit thermal analysis.
• #14: The thermal design conditions are shown in the left table. The analysis executed the high temperature case and the low temperature case. You can see the analysis results. It was able to be confirmed that the results of both severe cases met the specification 2.5degC or less. In addition, those analysis results and test results agreed well with each other. As for Solar light and IR, those values fluctuate on orbit depending on a season variation. Therefore, in the high temperature case, the maximum value of Solar light and IR were applied. In contrast, in the low temperature case, the minimum value of them were used. Then, about the thermal optical properties, EOL was used in the high temperature case and BOL was used in the low temperature case. Now, I’d like to take look at this next slide which shows that the temperature trends of the microwave absorbers in high temperature case.
• #15: Please take a look at this graph which shows the temperature trends of the microwave absorbers. GCOM-W1 rounds the earth at about 6000 seconds. The horizontal axis indicates the elapsed time from the center of sunset. The vertical axis shows the temperature at representative position of the microwave absorbers. According to the analysis results, there are two points where the temperature distributions of the microwave absorbers become large. Next, I’m going to show you the temperature contour figures of the microwave absorbers at those two instants of time.
• #16: This is the temperature contour figure of the microwave absorbers which is seen from the Feed side. At the first point, the temperature distribution is maximum 1.8degC which is shown as the temperature difference between red part and blue part in the contour figure. Because the temperature of Feed Cover which is not heater-controlled decrease in sunset by the radiation to outer Space, the low temperature of Feed cover influences microwave absorbers. As a result, the temperature in tips of microwave absorbers becomes low, and the temperature distribution is caused. In the next slide, I’d like to show you the second point of large temperature distribution.
• #17: This is the temperature contour figure of the microwave absorbers at 3900 seconds. In contrast, you will see the temperature increase of the tips. Because a solar light enters slightly from the gap between HTS walls and TCP into the tip of the microwave absorbers at that time.
• #18: Please look at the two temperature distribution figures of the microwave absorbers seen from the Feed side. The left figure shows the result of Case 1 and the right one indicates the result of Case 2. In Case1, the temperature distribution became only 0.6degC as a result of the same temperature control in all respects where the microwave absorber was enclosed. Hence, Validity verification of the thermal design concepts was completed. In Case2, the temperature distribution of the microwave absorbers become 1.2degC. By the influence of the low-temperature condition in Feed Covers, the tips’ temperature of microwave absorbers were low compared to the base side. Indeed, this phenomenon was corresponding to the analysis. Furthermore, as a result, it was confirmed to meet the specification of 2.5degC. Finally, the thermal math model's accuracy was improved by comparing the test analysis results with the test results.
• #19: This graph shows the temperature increase of the microwave absorbers. The horizontal axis indicates the elapsed time and its zero second shows the solar light irradiation beginning. The vertical axis shows the temperature at representative position of the microwave absorbers. Here, the time period that solar light enters into the microwave absorbers is about 150 seconds according to the analysis on orbit. As a result, the temperature increase when 150 seconds passed was about the maximum 0.3degC. Consequently, the influence of solar light incidence was small and able to be disregarded in the on-orbit operation. Furthermore, The test results and test analysis agreed well with each other, it was confirmed that the thermal math model was accurate.
• #20: In this slide, the conclusion will be given. Validity verification of the thermal design concepts of HTS was conducted by thermal analysis on orbit and thermal vacuum tests of development model. Moreover, the analysis results and the test result agreed well with each other, therefore it was confirmed that the thermal math model was accurate. As a result, the specification 2.5degC or less was met at any thermal environments. Furthermore, depending on the improvement of HTS thermal design, the calibration and measurement performance of AMSR2 will be improved more than AMSR-E. As a future plan, the launch of GCOM-W1 is scheduled for launch in the Japanese fiscal year 2011, and the on-orbit evaluation will be made.