Mechanical & Fluid Systems

Thermoelectric Contact Cooler/Freezer

This cooler is efficient and quiet. A thermoelectric contact cooler/ freezer is designed to utilize thermal conduction to rapidly freeze blood and urine samples in test tubes and syringes. This apparatus is dependable, wastes little energy, contains no moving parts other than a fan, can operate in a wide temperature range and in any orientation (including in zero gravity), is quiet, and emits no chlorofluorocarbons or other greenhouse gases. It is a vast improvement over currently available convection-type cooler/freezers.

Posted in: Mechanics, Briefs, TSP

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Theory of Formation-Flying Control for Multiple Spacecraft

A report presents the mathematical basis of a method of controlling multiple spacecraft flying in formation, subject to control constraints. The spacecraft are assumed to be equipped with relative-position-sensing, relative-velocity-sensing, and communication infrastructure, and with maneuvering actuators. The method involves a leader-following control scheme. A graph is used to represent the hierarchy of, and the data dependencies among, the leading and following spacecraft. Graph-theoretic concepts are shown to play a vital role in determining the basic properties of the leader-following control architecture; hence, changes in the hierarchy (represented by changes in the graph) translate directly to the required changes in control.

Posted in: Mechanics, Briefs, TSP

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Onboard Estimation of Times of Periapsis During Aerobraking

A report proposes a technique for onboard updating of the orbital period of an aerobraking spacecraft in order to estimate the time of the next periapsis. The time of periapsis is nearly centered in the middle of the drag pass, and provides a convenient reference time for events in the sequence that controls the activities taking place onboard the spacecraft. Heretofore, updates of periapsis times have been computed on Earth on the basis of radio tracking data, then uplinked to the spacecraft. Onboard updating could increase operational efficiency and reduce costs by reducing the amount of ground and tracking support needed.

Posted in: Mechanics, Briefs, TSP

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Improved Micromachined Vaporizing-Liquid Microthruster

A report describes an improved micromachined vaporizing-liquid microthruster (VLM), now under development as a prototype of thrusters for microspacecraft. This thruster is of the resistojet type: the energy for vaporization and expansion of a propellant liquid is provided through electrical-resistance heating. A typical VLM of prior design, fabricated on a chip, was comparatively bulky and was energy-inefficient because much of the energy that should have gone into heating the propellant was wasted in heating the chip.

Posted in: Mechanics, Briefs, TSP

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Actuated Ball-and-Socket Joints

These joints would be relatively compact, lightweight, simple, and inexpensive. The term "actuated ball-and-socket" (ABS) characterizes a proposed class of ball-and-socket joints that would incorporate ultrasonic motors and other piezoelectric actuators to generate multidimensional actuation. In some applications, ABS joints could supplant traditional joint-and-actuator assemblies that include passive rotary joints actuated by electromagnetic motors via gears. In comparison with such assemblies, ABS joints offer potential advantages of compactness, relative mechanical simplicity, higher torque-to-weight ratios, no backlash, self-braking with power turned off, and lower cost. ABS joints are expected to be particularly attractive for use as robot joints and as general low-power orienting actuators for diverse applications that could include robot hands, tools, and mechanisms for aiming scientific instruments.

Posted in: Briefs, TSP

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Flex Wedges

Brakes and clutches could perform more reliably and predictably. Flex wedges have been proposed for use in brakes and clutches like those in which, heretofore, basic wedges have been used. Flex wedges (see Figure 1) offer advantages of superior braking and clutching performance and less weight, relative to basic wedges.

Posted in: Mechanics, Briefs, TSP

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Heat-Shield Panels in a 2D Shingling Arrangement

Adjacent panels are slid aside to make room for insertion or removal. Figure 1 depicts mockups of lightweight metal heat-shield panels that have been proposed for use on spacecraft of the reusable-launch-vehicle type. These panels are designed for simplicity of insertion and removal. The design could also be adapted to both insulating and noninsulating panels in nonspacecraft applications.

Posted in: Mechanics, Briefs, TSP

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