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  • 1
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    High Gain Antenna Pointing on the Mars Exploration Rovers (2005)
    In:  Other Sources
    Details
    Publication Date: 2018-06-11
    Description: This paper describes the algorithm used to point the high gain antennae on NASA/JPL's Mars exploration rovers. Each rover's gimballed antenna must track the Earth as it moves across the Martian sky during communication sessions. The pointing algorithm accounts for obstacles to the line-of-sight posed by (1) features on the rover and in the surrounding environment (2) gimbal range limitations, and (3) kinematic singularities in the gimbal mechanism. The algorithm treats all obstacles with a generalized approach that computes the intercept-times to each obstacle. Where possible, the algorithm takes advantage of pairs of joint-space solutions arising from the mechanism design. The algorithm chooses the solution that provides the longest obstruction-free tracking time. Upon encountering an obstacle, the algorithm automatically switches to the other solution if it is not also obstructed. This algorithm has successfully provided obstruction-free pointing for both rovers throughout the mission.
    Keywords: Communications and Radar
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    NASA TECHNICAL REPORTS
  • 2
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    Attitude and position estimation on the Mars Exploration Rovers (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: NASA/JPL 's Mars Exploration Rovers acquire their attitude upon command and autonomously propagate their attitude and position. The rovers use accelerometers and images of the sun to acquire attitude, autonomously searching the sky for the sun with a pointable camera. To propagate the attitude and position the rovers use either accelerometer and gyro readings or gyro readings and wheel odometiy, depending on the nature of the movement ground operators are commanding. Where necessary, visual odometry is performed on images to fine tune the position updates, particularly in high slip environments. The capability also exists for visual odometry attitude updates. This paper describes the techniques used by the rovers to acquire and maintain attitude and position knowledge, the accuracy which is obtainable, and lessons learned after more than one year in operation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: IEEE Systems, Man and Cybernetics, International Conference; Oct 09, 2005 - Oct 12, 2005; Waikoloa, HI; United States
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    NASA TECHNICAL REPORTS
  • 3
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    Attitude and position estimation on the Mars Exploration Rovers (2005)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: This paper describes the techniques used by the rovers to acquire and maintain attitude and position knowledge, the accuracy which is obtainable, and lessons learned after more than one year in operation.
    Keywords: Lunar and Planetary Science and Exploration
    Type: IEEE Systems, Man and Cybernetics, International Conference; Oct 09, 2005 - Oct 12, 2005; Waikoloa, HI; United States
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  • 4
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    High gain antenna pointing on the Mars Exploration Rovers (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: This paper describes the algorithm used to point the high gain antennae on NASA/JPL's Mars Exploration Rovers. The gimballed antennae must track the Earth as it moves across the Martian sky during communication sessions. The algorithm accounts for (1) gimbal range limitations, (2) obstructions both on the rover and in the surrounding environment, (3) kinematic singularities in the gimbal design, and (4) up to two joint-space solutions for a given pointing direction. The algorithm computes the intercept-times for each of the occlusions and chooses the jointspace solution that provides the longest track time before encountering an occlusion. Upon encountering an occlusion, the pointing algorithm automatically switches to the other joint-space solution if it is not also occluded. The algorithm has successfully provided flop-free pointing for both rovers throughout the mission.
    Keywords: Lunar and Planetary Science and Exploration
    Type: IEEE International Conference on Systems, Man, and Cybernetics; Oct 10, 2005; Waikoloa, HI; United States
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  • 5
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    The Effects of Clock Drift on the Mars Exploration Rovers (2012)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: All clocks drift by some amount, and the mission clock on the Mars Exploration Rovers (MER) is no exception. The mission clock on both MER rovers drifted significantly since the rovers were launched, and it is still drifting on the Opportunity rover. The drift rate is temperature dependent. Clock drift causes problems for onboard behaviors and spacecraft operations, such as attitude estimation, driving, operation of the robotic arm, pointing for imaging, power analysis, and telecom analysis. The MER operations team has techniques to deal with some of these problems. There are a few techniques for reducing and eliminating the clock drift, but each has drawbacks. This paper presents an explanation of what is meant by clock drift on the rovers, its relationship to temperature, how we measure it, what problems it causes, how we deal with those problems, and techniques for reducing the drift.
    Keywords: Lunar and Planetary Science and Exploration; Cybernetics, Artificial Intelligence and Robotics
    Type: AIAA Space 2012; Sep 11, 2012 - Sep 13, 2012; Pasadena, CA; United States
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  • 6
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    Understanding Spacecraft Agility for Orbit Transfers on the Dawn Low-thrust Mission (2012)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Conventional maneuver design processes were inadequate. Long thrusting durations with the small force of SEP. Increased coupling between ACS and NAV teams. Definition of quantifiable constraints proved impractical. Specifically for the Dawn mission, because of the attitude steering algorithm. A time-efficient simulation tool, qSTAT, was developed and allowed fast verification of candidate thrust profile designs. This approach allowed Dawn to overcome the complications of low-thrust orbit transfers.
    Keywords: Spacecraft Design, Testing and Performance
    Type: Annual AAS Guidance & Control Conference; Feb 03, 2012 - Feb 08, 2012; Breckenridge, CO; United States
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  • 7
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    Verification of Pointing Constraints for the Dawn Spacecraft (2008)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: NASA's Dawn spacecraft, an ion-thrust science mission to Vesta and Ceres, has numerous pointing constraints critical for safe operation. Onboard software automatically chooses target attitudes but enforces only a simplified constraint set at slew endpoints. Onboard fault-protection also uses simplified constraints, and violations can result in safing events that dramatically consume mission margins for missed thrust. Lastly, for funding reasons the operations team is lean, forcing the development of month-long command sequences. These factors place a premium on reliable maneuver design, prediction, and verification against pointing constraints. This paper presents Slewth, a ground tool built to address these concerns.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking; Lunar and Planetary Science and Exploration
    Type: AIAA/AAS Astrodynamics Specialists Conference; Aug 18, 2008 - Aug 21, 2008; Honolulu, HI; United States
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