Mechanical & Fluid Systems

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

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Emergency Tether-Deployment-and-Recoil-Mitigating Systems

A report describes an emergency tether-deployment (ETD) system designed to minimize the harm caused by two events that can occur during deployment of tethered payloads from a space shuttle in orbit. One such event is snagging of the tether during payout while the payload is near the shuttle, causing rebound of the shuttle and payload toward each, thus possibly causing a collision. The other event is recoil of a tether that must be cut while it is under tension. If not suppressed, the recoil can cause the tether to become tangled around the shuttle. The ETD system includes a tether wound on a spool in a standard pattern that minimizes friction during payout, plus a rotating-arm mechanism that prevents snagging. The ETD system can be either (1) used as a primary deployment system or (2) activated automatically through breakage of a tether tiedown in the event of a snag or when the payload is at a safe distance from the shuttle. To suppress recoil, a core of solder is inserted along part of the length of the tether. When a wave of recoil reaches this part, the solder absorbs most of the recoil energy.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Cylindrical Shape-Memory Rotary/Linear Actuator

A shape-memory ribbon is wrapped around a cylinder to build up length. A compact actuator generates rotary or linear motion with a large torque or force, respectively. The original version of this actuator is designed to pull a wedge that, until pulled, prevents retraction of the proposed extended nose landing gear of the space shuttle. The original version is also required to fit into a volume that is severely limited by the size of the landing-gear assembly. The basic actuator design could be adapted to other applications in which there are requirements for compact, large-force actuators with similar geometries.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Formation Alignment of Multiple Autonomous Vehicles

Alignment is achieved by use of lasers, optical sensors, and rule-based controls. A table-top experiment on formation alignment of three air-levitated robotic vehicles has been performed to demonstrate the feasibility of a more general concept of controlling multiple robotic vehicles to make them move in specified positions and orientations with respect to each other. The original intended application of the concept is in the control of multiple spacecraft flying in formation, as described in “Synchronizing Attitudes and Maneuvers of Multiple Spacecraft” (NPO-20569) on page 64 in this issue of NASA Tech Briefs. In principle, the concept could also be applied on Earth to control formation flying of aircraft or to coordinate the motions of multiple robots, land vehicles, or ships.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Microfabricated Flow Controllers and Pressure Regulators

Efforts are underway to develop microfabricated flow controllers and pressure regulators that contain as few discrete components as feasible and that are cheaper, more robust, and orders of magnitude smaller than are currently commercially available devices that have similar capabilities. The developmental devices are designed to interact with electronic sensing and control circuits that include microprocessors that, in turn, communicate with host computers of digital feedback control systems. An example of the prototype devices constructed thus far is a hybrid device that includes a flow sensor, a valve containing a TiNi-alloy microribbon shape-memory actuator, and a temperature sensor, with wire-bonded leads for connection to electronic circuits. Windows™-based software for interaction between host computers and the microprocessors associated with these devices has been written. Contemplated further development efforts would be devoted to advancing from the concept of a flow controller on a ceramic substrate to that of a flow controller on an assembly of two or more semiconductor chips. In principle, fabrication on a semiconductor chip could be accomplished without need to assemble discrete components.

Posted in: Briefs, Mechanical Components, Mechanics

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Synchronizing Attitudes and Maneuvers of Multiple Spacecraft

A report discusses the problem of controlling the maneuvers of multiple spacecraft flying in formation and, more specifically, making the entire formation rotate about a given axis and synchronizing the rotations of the individual spacecraft with the rotation of the formation. Such formation flying is contemplated for mission in which the spacecraft would serve as platforms for long-baseline-interferometer elements and the synchronized rotations would be needed for slewing of the interferometers. Starting from (1) a particle model of the dynamics of the spacecraft formation, (2) a rigid-body model of the spacecraft-attitude dynamics, and (3) an assumption that one spacecraft would serve as the reference for the positions and orientations of the other spacecraft, the report presents a mathematical derivation of control laws for formation flying in the absence of gravitation and disturbances. A simplified control law suitable for implementation is also derived. Results of a computer simulation for three spacecraft flying in a triangular formation are presented to show that the control laws are effective.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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Mesoscopic Winch for Precise Extension and Retraction

A cable could be drawn in submicron steps over a range of ≈1 m. A proposed lightweight, micromachined winch would have microscopic structural details and mesoscopic overall dimensions and would be capable of generating bidirectional macro- scopic motion (maximum cable extension or retraction ≈1 m) with submicron increments. Winches like this one could be useful for actuating small mechanisms in scientific instruments and robots: examples of such mechanisms include translation stages; slide shutters and filters for imaging photodetector arrays; pan, tilt, or zoom actuators for cameras; mechanisms for dragging sampling scoops; and steering mechanisms for small robotic vehicles.

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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