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  • 1
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    Control of the ST7 Disturbance Reduction System Flight Experiment (2007)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: The Space Technology 7 (ST7) experiment will perform an on-orbit system-level validation of two specific Disturbance Reduction System technologies: colloidal micronewton thrusters and drag-free control. The ST7 Disturbance Reduction System (DRS) is designed to maintain the spacecraft s position with respect to a free-floating test mass while limiting the residual accelerations of that test mass over the frequency range of 1 to 30 mHz. This paper presents the overall design and analysis of the spacecraft drag-free and attitude controllers, with particular attention given to its primary mission mode. These controllers close the loop between the drag-free sensors and the colloidal micronewton thrusters.
    Keywords: Spacecraft Design, Testing and Performance
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Disturbance Reduction Control Design for the ST7 Flight Validation Experiment (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Space Technology 7 experiment will perform an on-orbit system-level validation of two specific Disturbance Reduction System technologies: a gravitational reference sensor employing a free-floating test mass, and a set of micro-Newton colloidal thrusters. The ST7 Disturbance Reduction System is designed to maintain the spacecraft's position with respect to a free-floating test mass to less than 10 nm/Hz, over the frequency range of 1 to 30 mHz. This paper presents the design and analysis of the coupled, drag-free and attitude control systems that close the loop between the gravitational reference sensor and the micro-Newton thrusters, while incorporating star tracker data at low frequencies. A full 18 degree-of-freedom model, which incorporates rigid-body models of the spacecraft and two test masses, is used to evaluate the effects of actuation and measurement noise and disturbances on the performance of the drag-free system.
    Keywords: Spacecraft Design, Testing and Performance
    Type: Flight Dynamics Symposium; Oct 29, 2003 - Oct 30, 2003; Greenbelt, MD; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    18-Degree-of-Freedom Controller Design for the ST7 Disturbance Reduction System (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Space Technology 7 experiment will perform an on-orbit system-level validation of a Disturbance Reduction System employing gravitational reference sensors and micronewton colloidal thrusters to maintain a spacecraft s position with respect to free-floating test masses in the gravitational reference sensors to less than 10 nm/dHz over the frequency range 1 to 30 mHz. This paper presents the design and analysis of the control system that closes the loop between the gravitational reference sensors and the micronewton thrusters while incorporating star tracker data at low frequencies. The effects of disturbances and actuation and measurement noise are evaluated in a eighteen-degree-of-freedom model.
    Keywords: Aircraft Stability and Control
    Type: AAS-03-586 , AAS Astrodynamics Specialist Conference; Aug 03, 2003 - Aug 07, 2003; Big Sky, MT; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Control Modes of the ST7 Disturbance Reduction System Flight Validation Experiment (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The Space Technology 7 experiment will perform an on-orbit system-level validation of two specific Disturbance Reduction System technologies: a gravitational reference sensor employing a free-floating test mass and a set of micro-Newton colloidal thrusters. The ST7 Disturbance Reduction System is designed to maintain the spacecraft s position with respect to a free-floating test mass to less than 10 nm/the square root of Hz over the frequency range of 1 to 30 mHz. This requirement will help ensure that the residual accelerations on the test masses (beyond gravitational acceleration) will be below the ST7 goal of 300 (1 + [f/3 mHz](sup 2)) pm/s(sup 2)/the square root of Hz. This paper presents the overall design and analysis of the spacecraft drag-free and attitude controllers being designed by NASA s Goddard Space Flight Center. These controllers close the loop between the GRS and the micro-Newton colloidal thrusters. The ST7 DRS comprises three control systems: the attitude control system to maintain a sun-pointing attitude, the drag free control to center the spacecraft about the test masses, and the test mass suspension control. There are five control modes in the operation of the ST7-DRS, starting from the attitude-only mode and leading to the challenging science mode. The design and analysis of each of the control modes are presented. An 18-DOF model is developed to capture the essential dynamics of the ST7-DRS package. It includes all rigid-body dynamics of the spacecraft and two test masses (three translations and three rotations for the spacecraft and each of the test masses). Actuation and measurement noise and major disturbance sources acting on the spacecraft and test masses are modeled.
    Keywords: Space Processing
    Type: Space Systems Optomechanics and Dynamics; Aug 02, 2004 - Aug 06, 2004; Denver, CO; United States
    Format: text
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  • 5
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    18-Degree-of-Freedom Controller Design for the ST7 Disturbance Reduction System (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents the overall design and analysis process of the spacecraft controller being developed at NASA's Goddard Space Flight Center to close the loop between the GRS and the micro-newton colloidal thrusters. The essential dynamics of the ST7-DRS are captured in a simulation including eighteen rigid-body dynamic degrees of freedom: three translations and three rotations for the spacecraft and for each test mass. The ST7 DRS comprises three control systems: the attitude control system (ACS) to maintain a sun-pointing attitude; the drag free control (DFC) to center the spacecraft about the test masses; and the test mass suspension control. This paper summarizes the control design and analysis of the ST7-DRS 18-DOF model, and is an extension of previous analyses employing a 7-DOF planar model of ST-7.
    Keywords: Aircraft Stability and Control
    Type: AAS Astrodynamics Specialist Conference; Aug 03, 2003 - Aug 07, 2003; Big Sky, MT; United States
    Format: text
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    NASA TECHNICAL REPORTS
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