The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform

Eric K. Wang - One of the best experts on this subject based on the ideXlab platform.

  • feasibility study of two cassini reaction wheel thruster hybrid controllers
    Journal of Spacecraft and Rockets, 2014
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004–2008) and has since been approved for a first and second extended mission through September 2017. Cassini carries a set of four reaction wheels for attitude control when stable pointing of a science instrument is required. In 2002–2003, a prime reaction wheel exhibited signs of bearing-cage instability and was replaced by the backup wheel. To date, all Cassini wheels have accumulated >3.5 billion revolutions each. As such, in spite of careful management of the wheel rates by the Operation Team, there are observed symptoms of anomalous wheel-bearing drag torque. To prepare for the contingency scenario in which two reaction wheels had degraded, the feasibility of controlling Cassini using the two remaining wheels and four thrusters to meet the spacecraft pointing requirements is evaluated. Our results indicate that the hybrid controllers can achieve better attitude-cont...

  • Feasibility Study of Two Candidate Reaction Wheel/Thruster Hybrid Control Architecture Designs for the Cassini Spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

  • feasibility study of two candidate reaction wheel thruster hybrid control architecture designs for the cassini spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

Glenn A. Macala - One of the best experts on this subject based on the ideXlab platform.

  • feasibility study of two cassini reaction wheel thruster hybrid controllers
    Journal of Spacecraft and Rockets, 2014
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004–2008) and has since been approved for a first and second extended mission through September 2017. Cassini carries a set of four reaction wheels for attitude control when stable pointing of a science instrument is required. In 2002–2003, a prime reaction wheel exhibited signs of bearing-cage instability and was replaced by the backup wheel. To date, all Cassini wheels have accumulated >3.5 billion revolutions each. As such, in spite of careful management of the wheel rates by the Operation Team, there are observed symptoms of anomalous wheel-bearing drag torque. To prepare for the contingency scenario in which two reaction wheels had degraded, the feasibility of controlling Cassini using the two remaining wheels and four thrusters to meet the spacecraft pointing requirements is evaluated. Our results indicate that the hybrid controllers can achieve better attitude-cont...

  • Feasibility Study of Two Candidate Reaction Wheel/Thruster Hybrid Control Architecture Designs for the Cassini Spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

  • feasibility study of two candidate reaction wheel thruster hybrid control architecture designs for the cassini spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

Allan Y. Lee - One of the best experts on this subject based on the ideXlab platform.

  • feasibility study of two cassini reaction wheel thruster hybrid controllers
    Journal of Spacecraft and Rockets, 2014
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004–2008) and has since been approved for a first and second extended mission through September 2017. Cassini carries a set of four reaction wheels for attitude control when stable pointing of a science instrument is required. In 2002–2003, a prime reaction wheel exhibited signs of bearing-cage instability and was replaced by the backup wheel. To date, all Cassini wheels have accumulated >3.5 billion revolutions each. As such, in spite of careful management of the wheel rates by the Operation Team, there are observed symptoms of anomalous wheel-bearing drag torque. To prepare for the contingency scenario in which two reaction wheels had degraded, the feasibility of controlling Cassini using the two remaining wheels and four thrusters to meet the spacecraft pointing requirements is evaluated. Our results indicate that the hybrid controllers can achieve better attitude-cont...

  • Feasibility Study of Two Candidate Reaction Wheel/Thruster Hybrid Control Architecture Designs for the Cassini Spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

  • feasibility study of two candidate reaction wheel thruster hybrid control architecture designs for the cassini spacecraft
    AIAA Guidance Navigation and Control Conference, 2012
    Co-Authors: Glenn A. Macala, Allan Y. Lee, Eric K. Wang
    Abstract:

    As the first spacecraft to achieve orbit at Saturn in 2004, Cassini has collected science data throughout its four-year prime mission (2004-08), and has since been approved for a first and second extended mission through 2017. Cassini carries a set of three "fixed" reaction wheels and a backup reaction wheel (reaction wheel #4) is mounted on top of an articulable platform. If necessary, this platform could be articulated to orient the backup reaction wheel with the degraded wheel. The reaction wheels are used primarily for attitude control when precise and stable pointing of a science instrument such as the narrow angle camera is required. In 2001-02, reaction wheel #3 exhibited signs of bearing cage instability. As a result, reaction wheel #4 was articulated to align with reaction wheel #3. Beginning in July 2003, Cassini was controlled using wheel #1, #2, and #4. From their first use in the spring of 2000 until today, reaction wheels #1 and #2 have accumulated more than3.5 billions revolutions each. As such, in spite of very carefully management of the wheel spin rates by the mission Operation Team, there are some observed increases in the drag torque of the wheels' bearings. Hence, the mission Operations Team must prepare for the contingency scenario in which the reaction wheel #1 (in addition to wheel #3) had degraded. In this hypothetical fault scenario, the two remaining reaction wheels (#2 and #4) will not be able to provide precise and stable three-axis control of the spacecraft. In this study, we evaluate the feasibility of controlling Cassini using the two remaining reaction wheels and four thrusters to meet the science pointing requirements for two key science Operational modes: the Optical Remote Sensing and Downlink, Fields, Particles, & Waves Operation modes. The performance (e.g., pointing control error, pointing stability, hydrazine consumption rate, etc.) of the hybrid controllers in both Operations scenarios will be compared with those achieved using an all-thruster controller design. Strength and weaknesses of the hybrid control architecture are assessed quantitatively.

Nelander Maria - One of the best experts on this subject based on the ideXlab platform.

  • Ectopic pregnancy in simultaneous pancreas-kidney transplantation: A case report
    The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd., 2016
    Co-Authors: Yamamoto Shinji, Nelander Maria
    Abstract:

    AbstractIntroductionWe present a case report of ectopic pregnancy (EP) after simultaneous pancreas-kidney transplantation (SKPTx).Presentation of caseA 33-year-old female status post SKPTx suddenly got abdominal pain in the lower level. She had high human chorionic Gonadotropin test. Ultrasonography revealed that there was no fetus in the uterus but a dilated right fallopian tube, which strongly suggested ectopic pregnancy. An emergency Operation was performed and a dilated right side uterine tube was found with adhesions to her transplant. Salpingectomy was performed and no visible injury to the pancreas was found by the procedure. Pathological evaluation showed ectopic pregnant fetus, and no pancreas dysfunction was observed after the Operation.DiscussionThis is the first case and Operation report of EP after SKPTx. We should consider various causes of acute abdomen as well as several pathological condition in the transplanted pancreas such as pancreatitis, abscess, and thrombosis in vessels in the organ. Moreover, transplanted pancreas in abdomen is easily misrecognized as adipose tissue and there is high risk that the organ to get injured surgically.ConclusionEP should be included in the different diagnosis in SKPTx female patients who get acute abdominal pain. It is highly desirable that transplant surgeon is included in the Operation Team for EP of these patients

  • Ectopic pregnancy in simultaneous pancreas-kidney transplantation : A case report
    Department of surgery Uppsala University Hospital Uppsala SE-75185 Sweden., 2016
    Co-Authors: Yamamoto Shinji, Nelander Maria
    Abstract:

    INTRODUCTION: We present a case report of ectopic pregnancy (EP) after simultaneous pancreas-kidney transplantation (SKPTx). PRESENTATION OF CASE: A 33-year-old female status post SKPTx suddenly got abdominal pain in the lower level. She had high human chorionic Gonadotropin test. Ultrasonography revealed that there was no fetus in the uterus but a dilated right fallopian tube, which strongly suggested ectopic pregnancy. An emergency Operation was performed and a dilated right side uterine tube was found with adhesions to her transplant. Salpingectomy was performed and no visible injury to the pancreas was found by the procedure. Pathological evaluation showed ectopic pregnant fetus, and no pancreas dysfunction was observed after the Operation. DISCUSSION: This is the first case and Operation report of EP after SKPTx. We should consider various causes of acute abdomen as well as several pathological condition in the transplanted pancreas such as pancreatitis, abscess, and thrombosis in vessels in the organ. Moreover, transplanted pancreas in abdomen is easily misrecognized as adipose tissue and there is high risk that the organ to get injured surgically. CONCLUSION: EP should be included in the different diagnosis in SKPTx female patients who get acute abdominal pain. It is highly desirable that transplant surgeon is included in the Operation Team for EP of these patients. (C) 2016 The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd

Yamamoto Shinji - One of the best experts on this subject based on the ideXlab platform.

  • Ectopic pregnancy in simultaneous pancreas-kidney transplantation: A case report
    The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd., 2016
    Co-Authors: Yamamoto Shinji, Nelander Maria
    Abstract:

    AbstractIntroductionWe present a case report of ectopic pregnancy (EP) after simultaneous pancreas-kidney transplantation (SKPTx).Presentation of caseA 33-year-old female status post SKPTx suddenly got abdominal pain in the lower level. She had high human chorionic Gonadotropin test. Ultrasonography revealed that there was no fetus in the uterus but a dilated right fallopian tube, which strongly suggested ectopic pregnancy. An emergency Operation was performed and a dilated right side uterine tube was found with adhesions to her transplant. Salpingectomy was performed and no visible injury to the pancreas was found by the procedure. Pathological evaluation showed ectopic pregnant fetus, and no pancreas dysfunction was observed after the Operation.DiscussionThis is the first case and Operation report of EP after SKPTx. We should consider various causes of acute abdomen as well as several pathological condition in the transplanted pancreas such as pancreatitis, abscess, and thrombosis in vessels in the organ. Moreover, transplanted pancreas in abdomen is easily misrecognized as adipose tissue and there is high risk that the organ to get injured surgically.ConclusionEP should be included in the different diagnosis in SKPTx female patients who get acute abdominal pain. It is highly desirable that transplant surgeon is included in the Operation Team for EP of these patients

  • Ectopic pregnancy in simultaneous pancreas-kidney transplantation : A case report
    Department of surgery Uppsala University Hospital Uppsala SE-75185 Sweden., 2016
    Co-Authors: Yamamoto Shinji, Nelander Maria
    Abstract:

    INTRODUCTION: We present a case report of ectopic pregnancy (EP) after simultaneous pancreas-kidney transplantation (SKPTx). PRESENTATION OF CASE: A 33-year-old female status post SKPTx suddenly got abdominal pain in the lower level. She had high human chorionic Gonadotropin test. Ultrasonography revealed that there was no fetus in the uterus but a dilated right fallopian tube, which strongly suggested ectopic pregnancy. An emergency Operation was performed and a dilated right side uterine tube was found with adhesions to her transplant. Salpingectomy was performed and no visible injury to the pancreas was found by the procedure. Pathological evaluation showed ectopic pregnant fetus, and no pancreas dysfunction was observed after the Operation. DISCUSSION: This is the first case and Operation report of EP after SKPTx. We should consider various causes of acute abdomen as well as several pathological condition in the transplanted pancreas such as pancreatitis, abscess, and thrombosis in vessels in the organ. Moreover, transplanted pancreas in abdomen is easily misrecognized as adipose tissue and there is high risk that the organ to get injured surgically. CONCLUSION: EP should be included in the different diagnosis in SKPTx female patients who get acute abdominal pain. It is highly desirable that transplant surgeon is included in the Operation Team for EP of these patients. (C) 2016 The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd