火星进入、下降与着陆技术(entry,descent and landing,EDL)是火星着陆探测最为关键的环节。火星与地球再入返回过程相比,由于火星大气成分、物理性质与地球大气存在较大差别,且具有较大不确定性,使火星EDL过程历经时间短、状态变化快,...火星进入、下降与着陆技术(entry,descent and landing,EDL)是火星着陆探测最为关键的环节。火星与地球再入返回过程相比,由于火星大气成分、物理性质与地球大气存在较大差别,且具有较大不确定性,使火星EDL过程历经时间短、状态变化快,对减速性能要求高,时序紧张。从工程实现角度分阶段开展了任务分析,识别了火星EDL环节面临的问题和挑战,提出了关键环节技术途径选择。展开更多
Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerica...Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes （RANS） equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid （VOF） model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.展开更多
Background The insufficiency of the proximal landing zone (PLZ) is a frequent factor challenging the applicability and efficacy of endovascular repair (EVR) for thoracic aortic disorders. This study discusses two stra...Background The insufficiency of the proximal landing zone (PLZ) is a frequent factor challenging the applicability and efficacy of endovascular repair (EVR) for thoracic aortic disorders. This study discusses two strategies for conquering this challenge.Methods Ten patients underwent EVR for thoracic aortic diseases during a one-year period ending June 30, 2004. Nine patients had DeBakey type Ⅲ dissecting aortic aneurysm (DAA), and one had descending thoracic aortic aneurysm (DTAA). The PLZ, defined as the distance from the origin of the left subclavian artery (LSA) to the primary entry tear of the dissection or to the proximal aspect of DTAA, was less than 15 mm in all instances. EVR with intentional coverage of the LSA without any supportive bypass was employed in 6 patients with DAA, and the preliminary right-left carotid and left carotid-subclavian bypass combined with EVR in the DTAA and other 3 DAA cases. Results Technical success was achieved in all the patients. The patient with DTAA died from hemispheric cerebral infarction and subsequent multiple system organ failure following an uneventful recovery from the cervical reconstruction performed 1 week previously. In cases receiving the EVR with intentional coverage of the LSA, in two patients dizziness occurred, which noticeably resolved after intravenous administration of mannitol for 4 to 5 days, and a drop in blood pressure of the left arm was noted in all the cases, but remained clinically silent. No neurological deficits or limb ischaemia developed perioperatively or during the followup, ranging from 3 to 12 months, and complete thrombosis of the thoracic aortic false lumen was revealed on CT at 3 months in the 9 patients with DAA.Conclusions Both the intentional bypass absent coverage of the LSA and the adjunctive surgical bypass appear to be feasible and effective in managing the insufficiency of the PLZ during the endovascular thoracic aortic repair.展开更多
Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the R...Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet.For China’s 2020 Mars exploration mission to achieve success,many key technologies must be realized.In this paper,China’s 2020 Mars mission and the spacecraft architecture are first introduced.Then,the preliminary launch opportunity,Earth–Mars transfer,Mars capture,and mission orbits are described.Finally,the main navigation schemes are summarized.展开更多
This paper presents the comprehensive results of landing site topographic mapping and rover localization in Chang’e-3 mission.High-precision topographic products of the landing site with extremely high resolutions(up...This paper presents the comprehensive results of landing site topographic mapping and rover localization in Chang’e-3 mission.High-precision topographic products of the landing site with extremely high resolutions(up to 0.05 m)were generated from descent images and registered to CE-2 DOM.Local DEM and DOM with 0.02 m resolution were produced routinely at each waypoint along the rover traverse.The lander location was determined to be(19.51256°W,44.11884°N,-2615.451 m)using a method of DOM matching.In order to reduce error accumulation caused by wheel slippage and IMU drift in dead reckoning,cross-site visual localization and DOM matching localization methods were developed to localize the rover at waypoints;the overall traveled distance from the lander is 114.8 m from cross-site visual localization and 111.2 m from DOM matching localization.The latter is of highest accuracy and has been verified using a LRO NAC image where the rover trajeactory is directly identifiable.During CE-3 mission operations,landing site mapping and rover localization products including DEMs and DOMs,traverse maps,vertical traverse profiles were generated timely to support teleoperation tasks such as obstacle avoidance and rover path planning.展开更多
文摘火星进入、下降与着陆技术(entry,descent and landing,EDL)是火星着陆探测最为关键的环节。火星与地球再入返回过程相比,由于火星大气成分、物理性质与地球大气存在较大差别,且具有较大不确定性,使火星EDL过程历经时间短、状态变化快,对减速性能要求高,时序紧张。从工程实现角度分阶段开展了任务分析,识别了火星EDL环节面临的问题和挑战,提出了关键环节技术途径选择。
基金co-supported by Aeronautical Science Foundation of China (No.20102351023)Research Fund for the Doctoral Program of Higher Education of China (No. 20091102120021)
文摘Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes （RANS） equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid （VOF） model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.
文摘Background The insufficiency of the proximal landing zone (PLZ) is a frequent factor challenging the applicability and efficacy of endovascular repair (EVR) for thoracic aortic disorders. This study discusses two strategies for conquering this challenge.Methods Ten patients underwent EVR for thoracic aortic diseases during a one-year period ending June 30, 2004. Nine patients had DeBakey type Ⅲ dissecting aortic aneurysm (DAA), and one had descending thoracic aortic aneurysm (DTAA). The PLZ, defined as the distance from the origin of the left subclavian artery (LSA) to the primary entry tear of the dissection or to the proximal aspect of DTAA, was less than 15 mm in all instances. EVR with intentional coverage of the LSA without any supportive bypass was employed in 6 patients with DAA, and the preliminary right-left carotid and left carotid-subclavian bypass combined with EVR in the DTAA and other 3 DAA cases. Results Technical success was achieved in all the patients. The patient with DTAA died from hemispheric cerebral infarction and subsequent multiple system organ failure following an uneventful recovery from the cervical reconstruction performed 1 week previously. In cases receiving the EVR with intentional coverage of the LSA, in two patients dizziness occurred, which noticeably resolved after intravenous administration of mannitol for 4 to 5 days, and a drop in blood pressure of the left arm was noted in all the cases, but remained clinically silent. No neurological deficits or limb ischaemia developed perioperatively or during the followup, ranging from 3 to 12 months, and complete thrombosis of the thoracic aortic false lumen was revealed on CT at 3 months in the 9 patients with DAA.Conclusions Both the intentional bypass absent coverage of the LSA and the adjunctive surgical bypass appear to be feasible and effective in managing the insufficiency of the PLZ during the endovascular thoracic aortic repair.
基金the National Natural Science Foundation of China(Grant No.11672126)Innovation Funded Project of Shanghai Aerospace Science and Technology(Grant No.SAST2015036)+4 种基金the Opening Grant from the Key Laboratory of Space Utilization,Chinese Academy of Sciences(LSU-2016-07-01)Funding of Jiangsu Innovation Program for Graduate Education(Grant No.KYZZ160170)the Fundamental Research Funds for the Central UniversitiesFunding for Outstanding Doctoral Dissertation in NUAA(Grant No.BCXJ16-10)The authors fully appreciate their financial supports.
文摘Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet.For China’s 2020 Mars exploration mission to achieve success,many key technologies must be realized.In this paper,China’s 2020 Mars mission and the spacecraft architecture are first introduced.Then,the preliminary launch opportunity,Earth–Mars transfer,Mars capture,and mission orbits are described.Finally,the main navigation schemes are summarized.
基金supported by the National Natural Science Foundation of China(Grant Nos.41201480,41171355 and 41301528)the Key Research Program of the Chinese Academy of Sciences(Grant No.KGZD-EW-603)
文摘This paper presents the comprehensive results of landing site topographic mapping and rover localization in Chang’e-3 mission.High-precision topographic products of the landing site with extremely high resolutions(up to 0.05 m)were generated from descent images and registered to CE-2 DOM.Local DEM and DOM with 0.02 m resolution were produced routinely at each waypoint along the rover traverse.The lander location was determined to be(19.51256°W,44.11884°N,-2615.451 m)using a method of DOM matching.In order to reduce error accumulation caused by wheel slippage and IMU drift in dead reckoning,cross-site visual localization and DOM matching localization methods were developed to localize the rover at waypoints;the overall traveled distance from the lander is 114.8 m from cross-site visual localization and 111.2 m from DOM matching localization.The latter is of highest accuracy and has been verified using a LRO NAC image where the rover trajeactory is directly identifiable.During CE-3 mission operations,landing site mapping and rover localization products including DEMs and DOMs,traverse maps,vertical traverse profiles were generated timely to support teleoperation tasks such as obstacle avoidance and rover path planning.
