Tech Briefs

A Broad-Band Phase-Contrast Wave-Front Sensor

The intrinsic 90° phase shift of an ideal beam splitter would be exploited. A broadband phase-contrast wave-front sensor has been proposed as a real-time wave-front sensor in an adaptive-optics system. The proposed sensor would offer an alternative to the Shack-Hartmann wave-front sensors now used in high order adaptive-optics systems of some astronomical telescopes. Broadband sensing gives higher sensitivity than does narrow- band sensing, and it appears that for a given bandwidth, the sensitivity of the proposed phase-contrast sensor could exceed that of a Shack-Hartmann sensor. Relative to a Shack-Hartmann sensor, the proposed sensor may be optically and mechanically simpler.

Posted in: Physical Sciences, Briefs, TSP

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Thermoelectric Air/Soil Energy-Harvesting Device

Small amounts of power would be extracted from natural temperature differences. A proposed thermoelectric device would exploit natural temperature differences between air and soil to harvest small amounts of electric energy. Because the air/soil temperature difference fluctuates between nighttime and daytime, it is almost never zero, and so there is almost always some energy available for harvesting. Unlike photovoltaic cells, the proposed device could operate in the absence of sunlight. Unlike a Stirling engine, which could be designed to extract energy from the air/soil temperature difference, the proposed device would contain no moving parts. The main attractive feature of the proposed device would be high reliability. In a typical application, this device would be used for low-power charging of a battery that would, in turn, supply high power at brief, infrequent intervals for operating an instrumentation package containing sensors and communication circuits.

Posted in: Physical Sciences, Briefs, TSP

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Actuated Hybrid Mirror Telescope

A new type of lightweight, wide-aperture, precise telescope is under development. The figure depicts the planned Actuated Hybrid Mirror Telescope (AHMT), which is intended to demonstrate a new approach to the design and construction of wide-aperture spaceborne telescopes for astronomy and Earth science. This technology is also appropriate for Earth-based telescopes.

Posted in: Physical Sciences, Briefs, TSP

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Stellar Gyroscope for Determining Attitude of a Spacecraft

A paper introduces the concept of a stellar gyroscope, currently at an early stage of development, for determining the attitude or spin axis, and spin rate of a spacecraft. Like star trackers, which are commercially available, a stellar gyroscope would capture and process images of stars to determine the orientation of a spacecraft in celestial coordinates. Star trackers utilize charge coupled devices as image detectors and are capable of tracking attitudes at spin rates of no more than a few degrees per second and update rates typically <5 Hz. In contrast, a stellar gyroscope would utilize an active pixel sensor as an image detector and would be capable of tracking attitude at a slew rate as high as 50°/s, with an update rate as high as 200 Hz. Moreover, a stellar gyroscope would be capable of measuring a slew rate up to 420°/s. Whereas a Sun sensor and a three-axis mechanical gyroscope are typically needed to complement a star tracker, a stellar gyroscope would function without them; consequently, the mass, power consumption, and mechanical complexity of an attitude-determination system could be reduced considerably.

Posted in: Physical Sciences, Briefs, TSP

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Fault-Tolerant Heat Exchanger

A single-point leak would not cause mixing of heat-transfer fluids.

Posted in: Physical Sciences, Briefs

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Optical Design of an Optical Communications Terminal

This airborne system would keep itself aimed at a ground station. An optical communications terminal (OCT) is being developed to enable transmission of data at a rate as high as 2.5 Gb/s, from an aircraft or spacecraft to a ground station. In addition to transmitting high data rates, OCT will also be capable of bidirectional communications. The OCT is meant to incorporate all of the design features of a prior apparatus denoted the Optical Communications Demonstrator (OCD), plus some improvements.

Posted in: Physical Sciences, Photonics, Briefs, TSP

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Atomic Clock Based on Opto-Electronic Oscillator

This apparatus would afford spectral purity plus long-term stability and accuracy.

Posted in: Physical Sciences, Briefs, TSP

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