Mechanical & Fluid Systems

Optimization of Orientations of Spacecraft Reaction Wheels

A report presents a method of optimizing the orientations of three reaction wheels used to regulate the angular momentum of a spacecraft. The method yields an orientation matrix that minimizes mass, torque, and power demand of the reaction wheels while maximizing the allowable duration between successive angular-momentum dumps. Each reaction wheel is parameterized with its own unit vector, and a quadratic cost function is defined based on requirements for torque, storage of angular momentum, and power demand. Because management of angular momentum is a major issue in designing and operating an orbiting spacecraft, an angular-momentum-management strategy is parameterized and included as part of the overall optimization process. The report describes several case studies, including one of a spacecraft proposed to be placed in orbit around Europa (the fourth largest moon of Jupiter).

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Wheels, Flight management systems, Spacecraft

Flexure Rings for Centering Lenses

The rings accommodate fabrication tolerances and thermal-expansion mismatches.

Specially shaped mounting rings keep lenses precisely centered, regardless of temperature, in the lens housings of cameras and other optical systems. These rings feature (1) well-defined contact spots for alignment, plus (2) relieved surfaces that form flexures to accommodate small manufacturing tolerances and differences among the thermal expansions of lenses, lens housings, and the rings themselves. These rings are made by numerically controlled machining of recently developed clean, strong, machinable plastics.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Fiber optics, Plastics, Mountings, Parts

Variable Submillimeter-Wave Delay Line for Cryogenic Use

Stiffness, size, vacuum adhesion, range, and number of parts were considered in designing this device.

A variable delay line is being developed as part of a far-infrared or submillimeter- wavelength interferometer that would operate in a vacuum in the cryogenic temperature range. No such delay line for spatial interferometry has previously been built for operation under these conditions.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Optics, Waveguides, Optics, Waveguides, Product development

Precise Air Bearings Redesigned

A simplified design affords low friction at minimum airflow.

Highly precise air bearings for suspending objects over an epoxy flat floor in a laboratory have been developed. These bearings float on airgaps 3 to 5 mil (about 0.08 to 0.13 mm) thick. They are modern versions of precise air bearings, developed during the 1960s, that offer a working coefficient of friction of only 1/16,000. The basic design of these bearings can be scaled easily for different loads and airflows.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Bearings

User’s Guide for ENSAERO

A report summarizes the development, applications, and procedures for use of ENSAERO, a computer program for simulating aeroelastic phenomena (e.g., wing flutter) of aircraft and spacecraft. ENSAERO computes aeroelastic responses by simultaneously numerically integrating Euler and/or Navier-Stokes equations of airflow and modal finite-element equations of structural dynamics on aeroelastically adaptive dynamic grids. The numerical integrations are performed by time-accurate finitedifference schemes. The report describes the coupling of the governing equations of flow with the governing equations of structural dynamics and with equations that describe active controls and thermal loads. The criteria and procedures for generation of zonal adaptive grids are discussed. Results of simulations performed by use of ENSAERO are presented for examples that involve, variously, steady or unsteady flow about rigid full aircraft or elastic wing/body assemblies.

This work was done by Guru P. Guruswamy of Ames Research Center.

This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to the Patent Counsel, Ames Research Center, (650) 604-5104. Refer to ARC-14239.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Computer simulation, Computer software / hardware, Computer software and hardware, Computer software / hardware, Computer software and hardware, Aerodynamics, Aircraft, Spacecraft

Minimally Actuated Hopping Robot

This robot can traverse terrain that is too cluttered for wheeled vehicles.

A small robot that travels by hopping has been built and tested. This is a prototype of hopping robots that would carry video cameras and possibly other sensory devices and that are under consideration for use in exploring cluttered, unpredictable terrain on distant planets. On Earth, robots like this one might have value for entertainment and civilian and military reconnoitering of hazardous areas.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Springs, Optics, Sensors and actuators, Optics, Sensors and actuators, Robotics

Mobile Robot With Foveal Machine Vision

The Foveal Extra-Vehicular Activity Helper-Retriever (FEVAHR) is a mobile robot that features a hierarchical foveal machine-vision system (HFMV). The FEVAHR is a prototype of future robots that could detect, recognize, track, and pursue objects and avoid obstacles while operating autonomously, controlled by human operators via natural-language commands, or both. The design of the FEVAHR merges high- and low-level anthropomorphic designs. The high-level anthropomorphism is represented by (1) the Semantic Network Processing System (SNePS) software for semantic representation of information, inference, and natural-language interaction, and (2) the Grounded Layered Architecture With Integrated Reasoning (GLAIR) software, which acts as an interface between SNePS on the one hand and subconscious processes and sensors on the other hand. The low-level anthropomorphism is represented by the HFMV hardware and software, which exploit the neuromorphic multiacuity sensing and information processing prevalent among vertebrates to achieve an effective visual information-acquisition power that is higher than that of uniform-acuity active vision. SNePS, GLAIR, and HFMV work in unison, each driving and being controlled by the others, to accomplish physical tasks with constrained resources and maintain a high level perception necessary for autonomous interaction with humans.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Architecture, Computer software / hardware, Computer software and hardware, Imaging, Imaging and visualization, Sensors and actuators, Architecture, Computer software / hardware, Computer software and hardware, Imaging, Imaging and visualization, Sensors and actuators, Human machine interface (HMI), Robotics

Rotary Tool and Retractable Foot for Walking Robot

One end effector alternates between two roles.

A mechanism has been developed to serve as an end effector for one of the legs of the Legged Excursion Mechanical Utility Robot (LEMUR) — a walking robot designed for demon- strating robotic cap- abilities for maintenance and repair. [The LEMUR was described in “Six-Legged Experimental Robot” (NPO-20897), NASA Tech Briefs, Vol. 25, No. 12 (December 2001), page 58.] Through controlled actuation of this mechanism, the tip of the leg can become either (1) a foot for stable support during walking or (2) the robotic equivalent of a simple hand tool — a ballend hexagonal driver for a standard hexagonal-socket machine screw. More specifically, the foot can be extended to enable walking, or can be retracted to enable cameras that are parts of the robot to view the insertion of the tool bit in a socket. Retraction of the foot also enables the tool to be used in confined spaces in which the foot cannot fit.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Maintenance, Repair and Service Operations, Maintenance, repair, and service operations, Tools and equipment, Robotics, Fittings, Mountings

Minirovers as Test Beds for Robotic and Sensor-Web Concepts

These units would be highly functional, robust, repairable, and reprogrammable.

The figure depicts a proposed reconfigurable miniature exploratory robotic vehicle (mini- rover) that would serve as a versatile prototype in the development of exploratory robots and “smart”-sensor systems that contain them. For example, minirovers could serve as nodes of sensor webs — networks of spatially distributed autonomous cooperating robots — that have been contemplated for use in exploring large areas of terrain. [The concept of such networks was reported in more detail in “Sensor Webs” (NPO- 20616), NASA Tech Briefs, Vol. 23, No. 10 (October 1999), page 80.]

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Neural networks, Sensors and actuators, Neural networks, Sensors and actuators, Product development, Robotics

Mechanism for Docking a Miniature Spacecraft

This report discusses a proposed docking mechanism to be located in a small hangar on the outside of the International Space Station (ISS). The mechanism would enable docking of a miniature robotic spacecraft (or free flyer) that would carry a video camera and would operate in the vicinity of the ISS. The docking mechanism would include, among other things, (1) an electromagnet for actuation, (2) electrical connectors for transferring data to and from the free flyer and recharging the freeflyer power system, and (3) a quick-disconnect (QD) coupling for recharging a supply of gaseous N2. Once the free flyer had maneuvered into approximate docking alignment, an electromagnet in the mechanism would attract a ferromagnetic plate on the free flyer strongly enough to pull the free flyer in from a distance of as much as several inches (≈10 cm). The mechanism would include surfaces that would mate with surfaces on the free flyer to correct any misalignment as the free flyer was pulled in. Once docked, the free flyer would be held in place by either spring-loaded cam locks or the QD coupling itself. Data, power, and N2 can then be transferred to the vehicle.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Charging stations, Optics, Charging stations, Optics, Robotics, Entry, descent, and landing, Spacecraft

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