Human locomotion and workload for simulated lunar and Martian environments
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Newman, Dava J.↗
Engineering topics
Alexander, Harold L.
Publications and source records attributed to Alexander, Harold L..
Gravity and suspension effects on the dynamics of controlled structures
The effects of gravity on the actuators, sensors and structural plant of a controlled flexible structure are investigated. These influences include gravity stiffening, gravity induced deformations, gravity influence on inertial sensors and actuators, and the interaction with the suspension system. For each of the four influences, a simplified model is derived, from which the appropriate non-dimensional parameter can be identified, and the magnitude of the influence estimated. The construction of a detailed numerical model, which includes the four gravity influences, is outlined. This modeling procedure is then applied to a simplified model of the Middeck Active Control Eperiment (MACE). The influence on the poles and input-output transfer function is examined for several variations in the plant. The modeling procedure is also applied to the MACE experimental hardware. Experimental and model-based transfer functions are compared to demonstrate the significant improvement by incorporating gravity effects.
Rey, Daniel A.↗
Mental workload and performance experiment (15-IML-1)
Whether on Earth or in space, people tend to work more productively in settings designed for efficiency and comfort. Because comfortable and stress-free working environments enhance performance and contribute to congenial relationships among co-workers, the living and working arrangements for spacecraft to be used for missions lasting months or years assume particular importance. The Mental Workload and Performance Experiment (MWPE), in part, examines the appropriate design of workstations for performance of various tasks in microgravity, by providing a variable-configuration workstation that may be adjusted by the astronauts.
Alexander, Harold L.↗
The direct effects of gravity on the control and output matrices of controlled structure models
The effects of gravity on the dynamic performance of structural control actuators and sensors are dual forms of an additive perturbation that can attenuate or amplify the device response (input or output). The modal modeling of these perturbations is derived for the general case of arbitrarily oriented devices and arbitrarily oriented planes of deformation. A nondimensional sensitivity analysis to identify the circumstances under which the effects of gravity are important is presented. Results show that gravity effects become important when the product of the ratio of the normalized modal slope and the modal displacement is comparable to the ratio of the gravitational acceleration and the product of the beam length and the squared eigenfrequency for a given mode.
Rey, Daniel A.↗
Space engineering
Human productivity was studied for extravehicular tasks performed in microgravity, particularly including in-space assembly of truss structures and other large objects. Human factors research probed the anthropometric constraints imposed on microgravity task performance and the associated workstation design requirements. Anthropometric experiments included reach envelope tests conducted using the 3-D Acoustic Positioning System (3DAPS), which permitted measuring the range of reach possible for persons using foot restraints in neutral buoyancy, both with and without space suits. Much neutral buoyancy research was conducted using the support of water to simulate the weightlessness environment of space. It became clear over time that the anticipated EVA requirement associated with the Space Station and with in-space construction of interplanetary probes would heavily burden astronauts, and remotely operated robots (teleoperators) were increasingly considered to absorb the workload. Experience in human EVA productivity led naturally to teleoperation research into the remote performance of tasks through human controlled robots.
Alexander, Harold L.↗
Experiments in teleoperator and autonomous control of space robotic vehicles
A program of research embracing teleoperator and automatic navigational control of freely flying satellite robots is presented. Current research goals include: (1) developing visual operator interfaces for improved vehicle teleoperation; (2) determining the effects of different visual interface system designs on operator performance; and (3) achieving autonomous vision-based vehicle navigation and control. This research program combines virtual-environment teleoperation studies and neutral-buoyancy experiments using a space-robot simulator vehicle currently under development. Visual-interface design options under investigation include monoscopic versus stereoscopic displays and cameras, helmet-mounted versus panel-mounted display monitors, head-tracking versus fixed or manually steerable remote cameras, and the provision of vehicle-fixed visual cues, or markers, in the remote scene for improved sensing of vehicle position, orientation, and motion.
Alexander, Harold L.↗
An extended operational-space control algorithm for satellite manipulators
A new control algorithm, called the extended operational-space method, is presented for control of free-floating space robots. Experimental and simulation results are presented, for two-dimensional (laboratory) and three-dimensional (simulation) robot configurations. The method's significance is discussed for robot design, and for teleoperator and autonomous control of free-floating robots.
Alexander, Harold L.↗
Experiments in teleoperator and autonomous control of space robotic vehicles
A research program and strategy are described which include fundamental teleoperation issues and autonomous-control issues of sensing and navigation for satellite robots. The program consists of developing interfaces for visual operation and studying the consequences of interface designs as well as developing navigation and control technologies based on visual interaction. A space-robot-vehicle simulator is under development for use in virtual-environment teleoperation experiments and neutral-buoyancy investigations. These technologies can be utilized in a study of visual interfaces to address tradeoffs between head-tracking and manual remote cameras, panel-mounted and helmet-mounted displays, and stereoscopic and monoscopic display systems. The present program can provide significant data for the development of control experiments for autonomously controlled satellite robots.
Alexander, Harold L.↗