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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Evaluation of inertial devices for the control of large, flexible, space-based telerobotic arms

Inertial devices, including sensors and actuators, offer the potential of improving the tracking of telerobotic commands for space-based robots by smoothing payload motions and suppressing vibrations. In this paper, inertial actuators (specifically, torque-wheels and reaction-masses) are studied for that potential application. Batch simulation studies are presented which show that torque-wheels can reduce the overshoot in abrupt stop commands by 82 percent for a two-link arm. For man-in-the-loop evaluation, a real-time simulator has been developed which samples a hand-controller, solves the nonlinear equations of motion, and graphically displays the resulting motion on a computer workstation. Currently, two manipulator models, a two-link, rigid arm and a single-link, flexible arm, have been studied. Results are presented which show that, for a single-link arm, a reaction-mass/torque-wheel combination at the payload end can yield a settling time of 3 s for disturbances in the first flexible mode as opposed to 10 s using only a hub motor. A hardware apparatus, which consists of a single-link, highly flexible arm with a hub motor and a torque-wheel, has been assembled to evaluate the concept and is described herein.

Montgomery, Raymond C.↗
NASA NTRS1968

Spacecraft control

Partial inertial system integration tests, automatic lens design, and vibration and shock analyses of electrostatic gyroscope

Source record↗
NASA NTRS2016

Sampling and Control Circuit Board for an Inertial Measurement Unit

A circuit board that serves as a control and sampling interface to an inertial measurement unit ("IMU") is provided. The circuit board is also configured to interface with a local oscillator and an external trigger pulse. The circuit board is further configured to receive the external trigger pulse from an external source that time aligns the local oscillator and initiates sampling of the inertial measurement device for data at precise time intervals based on pulses from the local oscillator. The sampled data may be synchronized by the circuit board with other sensors of a navigation system via the trigger pulse.

Chelmins, David T↗
NASA NTRS2008

A Gyroless Safehold Control Law Using Angular Momentum as an Inertial Reference Vector

A novel safehold control law was developed for the nadir-pointing Vegetation Canopy Lidar (VCL) spacecraft, necessitated by a challenging combination of constraints. The instrument optics did not have a recloseable cover to protect them form potentially catastrophic damage if they were exposed to direct sunlight. The baseline safehold control law relied on a single-string inertial reference unit. A gyroless safehold law was developed to give a degree of robustness to gyro failures. Typical safehold solutions were not viable; thermal constraints made spin stabilization unsuitable, and an inertial hold based solely on magnetometer measurements wandered unaceptably during eclipse. The novel approach presented here maintains a momentum bias vector not for gyroscopic stiffness, but to use as an inertial reference direction during eclipse. The control law design is presented. The effect on stability of the rank-deficiency of magnetometer-based rate derivation is assessed. The control law's performance is evaluated by simulation.

Stoneking, Eric↗
NASA NTRS2008

A Gyroless Safehold Control Law using Angular Momentum as an Inertial Reference Vector

A novel safehold control law was developed for the nadir-pointing Vegetation Canopy Lidar (VCL) spacecraft, necessitated by a challenging combination of constraints. The instrument optics did not have a reclosable cover to protect them from potentially catastrophic damage if they were exposed to direct sunlight. The baseline safehold control law relied on a single-string inertial reference unit. A gyroless safehold law was developed to give a degree of rebustness to gyro failures. Typical safehold solutions were not viable; thermal constraints made spin stabilization unsuitable, and an inertial hold based solely on magnetometer measurements wandered unacceptably during eclipse. The novel approach presented here maintains a momentum bias vector not for gyroscopic stiffness, but to use as an inertial reference direction during eclipse. The control law design is presented. The effect on stability of the rate-deficiency of magnetometer-based rate derivation is assessed. The control law's performance is evaluated by simulation.

Stoneking, Eric↗
NASA NTRS1980

Pointing control for the International Comet Mission

The design of the pointing control system for the proposed International Comet Mission, intended to fly by Comet Halley and rendezvous with Comet Tempel-2 is presented. Following a review of mission objectives and the spacecraft configuration, design constraints on the pointing control system controlling the two-axis gimballed scan platform supporting the science instruments are discussed in relation to the scientific requirements of the mission. The primary design options considered for the pointing control system design for the baseline spacecraft are summarized, and the design selected, which employs a target-referenced, inertially stabilized control system, is described in detail. The four basic modes of operation of the pointing control subsystem (target acquisition, inertial hold, target track and slew) are discussed as they relate to operations at Halley and Tempel-2. It is pointed that the pointing control system design represents a significant advance in the state of the art of pointing controls for planetary missions.

Leblanc, D. R.↗
NASA NTRS1992

Evaluation of inertial devices for the control of large, flexible, space-based telerobotic arms

Batch simulation studies which show that torque-wheels can reduce the overshoot in abrupt stop commands by 82 percent for a two-link arm are presented. For man-in-the-loop evaluation, a real-time simulator has been developed that samples a hand-controller, solves the nonlinear equations of motion, and graphically displays the resulting motion on a computer workstation. It is shown that, for a single-link arm, a reaction-mass/torque-wheel combination at the payload end can yield a settling time of 3 s for disturbances in the first flexible mode as opposed to 10 s utilizing only a hub motor.

Montgomery, Raymond C.↗
NASA NTRS1967

Inertial navigation.

Strapdown and gimballed inertial navigation systems history, engineering progress and current developments

INERTIAL NAVIGATION↗
NASA NTRS1989

Effect of control surface mass unbalance on the stability of a closed-loop active control system

An inertial energy approach similar to the aerodynamic energy method for flutter suppression is used to investigate the effects of mass-unbalanced control surfaces on the stability of a closed-loop system. It is demonstrated that a spanwise section for sensor location can be obtained which ensures minimum sensitivity to the mode shapes of the aircraft. Leading-edge control is characterized by a compatibility between inertial stabilization and aerodynamic stabilization that trailing-edge control lacks.

Nissim, E.↗
NASA NTRS1968

Spacecraft control

Spacecraft control research - sterilizable inertial sensors, ion thrustor control loops, antenna pointing systems, and attitude control systems for electric powered vehicles

Source record↗
NASA NTRS1985

Technology research for strapdown inertial experiment and digital flight control and guidance

A helicopter flight-test program to evaluate the performance of Honeywell's Tetrad - a strapdown, laser gyro, inertial navitation system is discussed. The results of 34 flights showed a mean final navigational velocity error of 5.06 knots, with a standard deviation of 3.84 knots; a corresponding mean final position error of 2.66 n.mi., with a standard deviation of 1.48 n.m.; and a modeled mean-position-error growth rate for the 34 tests of 1.96 knots, with a standard deviation of 1.09 knots. Tetrad's four-ring laser gyros provided reliable and accurate angular rate sensing during the test program and on sensor failures were detected during the evaluation. Criteria suitable for investigating cockpit systems in rotorcraft were developed. This criteria led to the development of two basic simulators. The first was a standard simulator which could be used to obtain baseline information for studying pilot workload and interactions. The second was an advanced simulator which integrated the RODAAS developed by Honeywell into this simulator. The second area also included surveying the aerospace industry to determine the level of use and impact of microcomputers and related components on avionics systems.

Carestia, R. A.↗