Gregory S. Hickey

LEMUR: Legged Excursion Mechanical Utility Rover

Although future orbital facilities will have immense scale, details will require intricate operations in restrictive, confined quarters. LEMUR is a small, agile and capable six-legged walking robot that has been built at the Jet Propulsion Laboratory to perform dexterous small-scale assembly, inspection and maintenance. It is intended to expand the operational envelope of robots in its size class (sub-5 kg) through the flexible use of its limbs and effectors, as well as through the modular changeout of those effectors. In short, LEMUR is intended as a robotic instantiation of a six-limbed primate with Swiss Army knife tendencies.LEMURs layout consists of six independently operated limbs arranged in two rows of three. The front two limbs have four active degrees of freedom while the rear four limbs have three each. Each limb is reconfigurable to allow the integration of a variety of mechanical tools.

Intelligent Mobile Systems for Assembly, Maintenance and Operations for Space Solar Power

NASA has been commissioned to investigate the feasibility of an orbiting Space Solar Power (SSP)system that is capable of generating power from space and transmitting the power to earth based rectennas. The structures for these systems would be large (1 km and greater) and would require robotic assembly, maintenance and operations. The robotic and autonomous operations required for SSP can be divided into three main areas: 1) initial assembly of the transmitter array and the photovoltaic power subsystem, 2) initial inspection of the assembled structure to determine that the assembly process has been correctly conducted and continued inspection of the system to evaluate its integrity and functionality, and 3) maintenance and repair of transmitter elements or tiles and the photovoltaic power subsystem. Due to the wide spectrum of the required operations, no single robotic system will suffice. Variation in robot design will be dictated both by the type of work performed, as well as the systems location relative to the SSP platform. For example, a heavy OMV hauler may be necessary to move large components into position, while a small legged robot may be needed to crawl into tight spaces for inspection and maintenance. However, the total number of unique systems can be reduced through reconfigurability of those systems. In the case of the small inspection/maintenance robot, the ability to freely switch end-effector tools would be invaulable. This paper will discuss design options and the technology development needs for the Space Solar Power system, after a brief introduction to some of the basic system configurations.

Micro-Control Actions of Segmented Actuators on Shallow Paraboloidal Shell Reflectors

Shallow paraboloidal shells of revolution are common components for reflectors, mirrors, etc. This study is to investigate the micro-control actions and distributed control effectiveness of precision paraboloidal shell structures laminated with segmented actuator patches. Mathematical models and governing equations of the paraboloidal shells laminated with distributed actuator layers segmented into patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components based on an assumed mode shape function and the Taylor series expansion. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a shallow paraboloidal shell are then analyzed in a case study. Analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent, 2) the meridional/circumferential membrane control actions dominate the overall control effect, 3) there are optimal actuator locations resulting in the maximal control effects at the minimal control cost for each natural mode. The analytical results provide generic design guidelines for actuator placement on precision shallow paraboloidal shell structures.Copyright

Thermal Insulation for Mars Surface Exploration

There is currently a significant amount of interest in Mars exploration by NASA to send a series of orbiting spacecrati and landers to Mars over the next decade. For the science and engineering systems that will land on the surface of Mars, there is a great challenge for thermal control. The Pathfinder mission will place a lander with an autonomous rover on Mars in July 1997; and the Mars ’98 mission set will have an orbiter and surface lander and surface penetrators. In the planning stages are additional landers and rovers, leading up to a Mars sample return mission for 2005 launch opportunity. The 8 torr C02 atmosphere and cryogenic temperatures are a unique thermal environment. The environment constrains the types and duration of missions that can be conducted and the thermal insulation required. All these factors add to a difficult challenge to design thermal control systems for Mars surface exploration. Current thermal insulation control approaches will be described and the needs for future missions.

Thermal outgassing behavior and photoemission studies of Haynes Alloy 214

Processing of many materials at high temperatures requires a high purity environment. The outgassing from hot surfaces of the processing chamber or the heating elements is a potential problem. The total amount of outgassing as well as the time‐ and temperature‐ dependent outgassing rates are important. The outgassing from Haynes Alloy 214 has been studied experimentally under a vacuum in the temperature range from room temperature to 600 °C. In addition to the outgassing rates, the composition of the outgassed species was determined through mass spectrometric analysis. Alloy surface composition was determined by x‐ray photoelectron spectroscopy. Changes in surface composition before and after heating can be accounted for by the outgassed species.

Selective molecular sorption by high surface area catalyst supports

Abstract Three high surface area catalyst supports were studied for the selective molecular sorption of organic compounds. The first was a carbon molecular sieve with a well-defined pore structure. The other two were silica gel and high surface area alumina. Both have a random pore structure. A mixture of phenol and acetic acid was used to qualitatively characterize the intermolecular force potentials and pore selectivity. Thermal gravimetric analysis and mass spectroscopy were used to characterize the desorption kinetics and differential scanning calorimetry was used to study the heats of desorption. The analyses illustrate an approach for characterizing adsorption-desorption processes in catalysts and high surface area materials.

Dynamic mechanical evaluation of a rubber toughened graphite-epoxy composite with application for laminate analysis

Abstract The dynamic mechanical properties of Hexcel F-155 rubber toughened epoxy was evaluated as a pure matrix and as a graphite-fiber composite. The materials were evaluated using a Dynastat mechanical analyzer at from −100°C to 200°C to provide temperature dependent elastic constants for composite laminate analysis. The pure matrix material showed a secondary transition, which has an effect on the mechanical properties of the composite laminate. The experimental results for complex modulus and thermal expansion of the pure matrix and unidirectional laminate were used to provide direct and indirect temperature dependent properties through micromechanics to predict properties of a composite laminate.

Precision Actuation of Micro-Space Structures

Space exploration and communication satellites and space structures need deployable precision mirrors, reflectors, and antennas. Conventional deployable space structures require motors and kinematic mechanisms to assist the deployment process. These mechanisms have the potential to jam or tangle and thus jeopardize the entire space mission. Recent development of smart structures and structronic systems opens many new design options in precision structures and systems. This paper reports a study of precision actuation and control for micro-shell laminated space structures made of smart materials. New design concepts of deployable micro-shell laminated structures are discussed and conceptual models fabricated. Analysis of precision parabolic struts is carried out and actuation authorities of proposed configurations are evaluated.

A comparison of the oxygen uptake characteristics of copper-exchanged zeolite with copper dispersed on a silica support

Abstract The kinetics of activated oxygen uptake by copper dispersed on catalytic supports was investigated. Two different adsorbents for oxygen were prepared: (a) Linde zeolite 13X was ion exchanged to replace sodium by copper, resulting in a uniform addition of copper to the zeolite; (b) dried silica gel was impregnated with copper oxide. The adsorbents were reduced by hydrogen to convert the copper oxide to elemental copper. The oxygen uptake by the reduced adsorbents was studied with the aid of a thermogravimetric analyser in the temperature range from 20 to 400°C. Global rate expressions were obtained from the kinetic data. Some insight into the role of the support in activating the copper oxidation was obtained from the rate expressions.

Thermal Engineering of Mars Entry Carbon/Carbon Non-Ablative Aeroshell - Part 2

Candidate Aeroshell Test models composed of a quasi-isotropic Carbon/Carbon (C/C) front face sheet (F/S), eggcrate core, C/C back F/S, Carbon Aerogel insulation, C/C radiation shield and the C/C close-out were constructed based on the analytical temperature predictions presented in Part One of this work.