Mechanical & Fluid Systems

Soft Landing of Spacecraft on Energy-Absorbing Self-Deployable Cushions

A report proposes the use of cold hibernated elastic memory (CHEM) foam structures to cushion impacts of small (1 to 50 kg) exploratory spacecraft on remote planets. Airbags, which are used on larger (800 to 1,000 kg) spacecraft have been found to (1) be too complex for smaller spacecraft; (2) provide insufficient thermal insulation between spacecraft and ground; (3) bounce on impact, thereby making it difficult to land spacecraft in precisely designated positions; and (4) be too unstable to serve as platforms for scientific observations. A CHEM foam pad according to the proposal would have a glass-transition temperature (Tg) well above ambient temperature. It would be compacted, at a temperature above Tg, to about a tenth or less of its original volume, then cooled below Tg, then installed on a spacecraft without compacting restraints. Upon entry of the spacecraft into a planetary atmosphere, the temperature would rise above Tg, causing the pad to expand to its original volume and shape. As the spacecraft decelerated and cooled, the temperature would fall below Tg, rigidifying the foam structure. The structure would absorb kinetic energy during ground impact by inelastic crushing, thus protecting the payload from damaging shocks. Thereafter, this pad would serve as a mechanically stable, thermally insulating platform for the landed spacecraft.

Posted in: Briefs, TSP

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Energy-Absorbing, Lightweight Wheels

Efficient structures would absorb impact energies and distribute contact loads. Improved energy- absorbing wheels are under development for use on special-purpose vehicles that must traverse rough terrain under conditions (e.g., extreme cold) in which rubber pneumatic tires would fail. The designs of these wheels differ from those of prior non-pneumatic energy-absorbing wheels in ways that result in lighter weights and more effective reduction of stresses generated by ground/wheel contact forces. These wheels could be made of metals and/or composite materials to withstand the expected extreme operating conditions.

Posted in: Briefs, TSP

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Viscoelastic Vibration Dampers for Turbomachine Blades

These dampers can be retrofitted to existing machines. Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines.

Posted in: Briefs

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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

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Minirovers as Test Beds for Robotic and Sensor-Web Concepts

These units would be highly functional, robust, repairable, and repro- grammable. 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: Machinery & Automation, Briefs, TSP

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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: Machinery & Automation, Briefs, TSP

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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: Machinery & Automation, Briefs, TSP

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