Agile attitude maneuver is a basic requirement for next generation imaging spacecraft and Control Moment Gyroscope (CMG) is an effective candidate for large space station and agile spacecraft attitude control because ...Agile attitude maneuver is a basic requirement for next generation imaging spacecraft and Control Moment Gyroscope (CMG) is an effective candidate for large space station and agile spacecraft attitude control because of its torque amplification capability. This paper provides a thorough survey of Single Gimbal Control Moment Gyroscope (SGCMG) in terms of configuration,evaluation,modeling,singularity analysis and steering logic,etc. For specific space missions,CMGs are logically mounted into different particular arrays which can be chosen by the proposed evaluation methods. From the dynamic model we find a tough inverse mapping problem which suffers the inherent geometric singularity. Different techniques and theories then are applied for singularity analysis and CMG steering logics design. The pyramid CMG cluster and singular robust logics are proven to be able to enhance the agility of spacecraft. Above work forms a systematic framework of SGCMG for agile spacecraft control with lots of illustrative examples,tables and figures,and will evoke further investigation for future missions.展开更多
Beijing City has suffered from groundwater-induced subsidence since the late 1930s and the over-exploration of groundwater could lead to subsidence as much as−12.0 cm yr−1.Previous studies on the ground deformation at...Beijing City has suffered from groundwater-induced subsidence since the late 1930s and the over-exploration of groundwater could lead to subsidence as much as−12.0 cm yr−1.Previous studies on the ground deformation at Beijing City mainly focused on the period before the year of 2014 when a mega-engineering project was launched to reduce water shortage in Beijing.To study the most recent ground deformation,19 L-band ALOS-1 PALSAR images(June 2007–January 2011),24 C-band Sentinel-1 SAR images(June 2015–November 2016)together with 9 ALOS-2 PALSAR acquisitions(September 2014–February 2017)were analysed in this work.Levelling measurements were exploited to verify the ALOS-1-based time series InSAR(TS-InSAR)result while Sentinel-1 and ALOS-2 result were cross-verified with each other.Furthermore,the whole study area was divided into four sub-zones,and the result indicated that the subsidence rates over five townships,Cuigezhuan,Jinzhan,Liyuan,Songzhuang and Yanjiao were accelerating and more attentions should be paid.On the contrary,the town centre of Douge Zhuang township experienced a decreasing trend between these two temporal-periods.Additionally,the time series measurements with respect to five selected measurement points and the profile line along the subsidence hot spots were analysed.展开更多
Coalbed methane(CBM)exploration generally refers to a technique that extracts natural gas from coal beds.The development of CBM in Liulin,China,has experienced a significantly growth period during the past two decades...Coalbed methane(CBM)exploration generally refers to a technique that extracts natural gas from coal beds.The development of CBM in Liulin,China,has experienced a significantly growth period during the past two decades.Previous research mainly focused on the coal geological background or CBM technique itself,while time series InSAR(TS-InSAR)technique was conducted in this work to study the potential land deformation induced by CBM extraction from 2003 to 2011.In total,21 ALOS-1 PALSAR images(acquired from 22 December 2006 to 2 January 2011)and 14 ENVISAT ASAR scenes(captured between 29 October 2003 and 7 November 2007)were used.The TS-InSAR outcome revealed that the annual deformation rates were ranging from 15 to−40 mm yr−1 over the study region.Then the time series deformation evolutions were analysed over 8 CBM sites(No.4 coal seam)out of 20,and the subsidence rates between 1.9 and−6.5 mm yr−1 were derived.In addition,the average subsidence rate and standard deviation among these eight measurements were−3.0 and 2.6 mm yr−1 respectively,suggesting that these CBM extraction sites were quite stable and no obvious subsidence had been observed during this eight-year period.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant No.61403197)the Natural Science Foundation of Jiangsu Province(Grant No.BK20140830)the Program of Shanghai Subject Chief Scientist(Grant No.14XD1423300)
文摘Agile attitude maneuver is a basic requirement for next generation imaging spacecraft and Control Moment Gyroscope (CMG) is an effective candidate for large space station and agile spacecraft attitude control because of its torque amplification capability. This paper provides a thorough survey of Single Gimbal Control Moment Gyroscope (SGCMG) in terms of configuration,evaluation,modeling,singularity analysis and steering logic,etc. For specific space missions,CMGs are logically mounted into different particular arrays which can be chosen by the proposed evaluation methods. From the dynamic model we find a tough inverse mapping problem which suffers the inherent geometric singularity. Different techniques and theories then are applied for singularity analysis and CMG steering logics design. The pyramid CMG cluster and singular robust logics are proven to be able to enhance the agility of spacecraft. Above work forms a systematic framework of SGCMG for agile spacecraft control with lots of illustrative examples,tables and figures,and will evoke further investigation for future missions.
基金This research was supported under Australian Research Council’s Discovery funding scheme[project number DP130101694]JAXA PI investigation project 1419–Automated interferometric analysis of L-band SAR satellite data for operational earthquake and volcano monitoring.
文摘Beijing City has suffered from groundwater-induced subsidence since the late 1930s and the over-exploration of groundwater could lead to subsidence as much as−12.0 cm yr−1.Previous studies on the ground deformation at Beijing City mainly focused on the period before the year of 2014 when a mega-engineering project was launched to reduce water shortage in Beijing.To study the most recent ground deformation,19 L-band ALOS-1 PALSAR images(June 2007–January 2011),24 C-band Sentinel-1 SAR images(June 2015–November 2016)together with 9 ALOS-2 PALSAR acquisitions(September 2014–February 2017)were analysed in this work.Levelling measurements were exploited to verify the ALOS-1-based time series InSAR(TS-InSAR)result while Sentinel-1 and ALOS-2 result were cross-verified with each other.Furthermore,the whole study area was divided into four sub-zones,and the result indicated that the subsidence rates over five townships,Cuigezhuan,Jinzhan,Liyuan,Songzhuang and Yanjiao were accelerating and more attentions should be paid.On the contrary,the town centre of Douge Zhuang township experienced a decreasing trend between these two temporal-periods.Additionally,the time series measurements with respect to five selected measurement points and the profile line along the subsidence hot spots were analysed.
基金This research was supported under Australian Research Council’s Discovery funding scheme[project number DP130101694]JAXA PI investigation project 1419–Automated interferometric analysis of L-band SAR satellite data for operational earthquake and volcano monitoring.
文摘Coalbed methane(CBM)exploration generally refers to a technique that extracts natural gas from coal beds.The development of CBM in Liulin,China,has experienced a significantly growth period during the past two decades.Previous research mainly focused on the coal geological background or CBM technique itself,while time series InSAR(TS-InSAR)technique was conducted in this work to study the potential land deformation induced by CBM extraction from 2003 to 2011.In total,21 ALOS-1 PALSAR images(acquired from 22 December 2006 to 2 January 2011)and 14 ENVISAT ASAR scenes(captured between 29 October 2003 and 7 November 2007)were used.The TS-InSAR outcome revealed that the annual deformation rates were ranging from 15 to−40 mm yr−1 over the study region.Then the time series deformation evolutions were analysed over 8 CBM sites(No.4 coal seam)out of 20,and the subsidence rates between 1.9 and−6.5 mm yr−1 were derived.In addition,the average subsidence rate and standard deviation among these eight measurements were−3.0 and 2.6 mm yr−1 respectively,suggesting that these CBM extraction sites were quite stable and no obvious subsidence had been observed during this eight-year period.
