Low-Noise Analog APDs with Impact Ionization Engineering and Negative Feedback

The technology can be used in active remote sensing optical instruments.

Goddard Space Flight Center, Greenbelt, Maryland

Silicon avalanche photodiodes (Si APDs) have low dark current and low excess noise factor, and are currently used in many of NASA’s missions. Noise equivalent power (NEP) of 40 to 50 fW/(Hz)1/2 over 140-MHz bandwidth has been demonstrated for Si APDs. Si APDs have very low responsivity for wavelengths longer than 1.1 mm, and cannot be used in future NASA lidar missions that require low noise and large-area photodetectors operated in the shortwave infrared (SWIR) region. The need for high-performance fiber optic communications receivers has provided the impetus for substantial progress during the last two decades in the understanding and performance of InP-based APDs that exhibit high responsivity in the wavelength range from 0.9 to 1.7 mm.

Posted in: Briefs, TSP, Communications, Optics, Radio equipment, Satellite communications, Optics, Radio equipment, Satellite communications, Noise, Noise

Method to Improve Wireless System Communication Coverage in a Bended Tunnel Environment

Lyndon B. Johnson Space Center, Houston, Texas

The conventional methods of improving wireless system coverage performance are to increase the transmitter power and/or antenna gain. The high transmit power could lead to more power consumption and RF exposure issues. The use of a high-gain antenna could lead to a larger antenna size and increased weight and volume. An alternative approach would be to capture the available signal power more efficiently without increasing the transmitter power and/or increasing antenna size.

Posted in: Briefs, TSP, Communications, Antennas, Antennas

Design for Improving the Flatness of Solar Sails

An optically flat solar sail could be useful in optical communication and solar energy applications.

NASA’s Jet Propulsion Laboratory, Pasadena, California

This work describes a discontinuous or segmented mirror whose overall flatness is less dependent on the limited tension that can be supplied by the booms. A solar sail is a large, nominally flat sheet of extremely thin reflectorized film rigidly attached to a spacecraft, enabling propulsion via solar radiation pressure. Rip-stop fibers embedded in the backside of the film — with diameters ≈100× the thickness of the film — are commonly used to arrest tear propagation, which can easily occur in the handling and/or deployment of these gossamer-thin structures. Typically, the thin film or membrane that is the sail is systematically folded to enable both volumetrically compact transportation to space and mechanized deployment. It is the aggressive folding and creasing of the thin film that limits the ultimate flatness that can be achieved.

Posted in: Briefs, TSP, Communications, Energy, Solar Power, Mechanical Components, Solar energy, Spacecraft

Army Equips Stryker Unit With New Communications Technology

The Army's Stryker vehicle, designed to quickly move soldiers into a combat zone, is swift and mobile. Now its communications equipment will be, too.

Posted in: News, Communications, Wireless, Defense, RF & Microwave Electronics

Frame Synchronization Without Attached Sync Markers

A means has been developed to detect the positions of code words directly.

NASA’s Jet Propulsion Laboratory, Pasadena, California

In communications systems, there must be a method to identify the beginning of a message at the receiving end, to know when the data stream of a specified structure begins. This is conventionally done by inserting attached sync markers (ASMs) between codewords, and looking for these ASMs in the transmitted data. Instead, a means has been developed to detect the positions of codewords directly, using the decoder to partially process a decoder attempt at each candidate synchronization position. A short decoding operation can successfully synchronize codewords in about two seconds in software.

Posted in: Briefs, TSP, Communications, Electronics & Computers, Information Sciences, Software, Communication protocols, Communication protocols, Data management

Serial Communication Cards

ACCES I/O Products, San Diego, CA, announced mPCIe-ICM Series PCI Express Mini Card isolated serial communication cards that measure 30 × 51 mm and feature a selection of four or two ports of isolated RS-232 serial communications. Features include 1.5kV isolation provided port-to-computer and 500V isolation port-to-port on all signals at the I/O connectors. The cards provide ±15kV ESD protection on all signal pins, and use 128-byte transmit/receive FIFO buffers to decrease CPU loading and protect against lost data in multitasking systems.

Posted in: Products, Communications, Electronic Components, Electronics & Computers

Method for Performing GPS L1 C/A Measurements in Wideband Jamming and Interference

John F. Kennedy Space Center, Florida

For effective range safety, global positioning system (GPS) metric tracking must be robust to interference with, and jamming of, GPS signals. The conventional approach to mitigating interference and jamming is to use a Controlled Reception Pattern Antenna (CRPA). These few-element phased arrays are used to steer nulls in the directions of interference sources, and/or to point beams in the directions of GPS satellites. The use of CRPAs is limited by their cost and size, as well as the difficulties of integrating the array into a platform. The problems are compounded for a launch vehicle, which must acquire and track GPS signals at high speed and acceleration, and undergo vibration and temperature conditions not common to CRPA use.

Posted in: Articles, Briefs, TSP, Communications, Test & Measurement, Antennas, Global positioning systems, Global positioning systems (GPS), Antennas, Global positioning systems, Global positioning systems (GPS), Satellites

Energy Harvesting Could Help Power Spacecraft of the Future

A consortium is working on a project to maximize energy harvesting on a spacecraft of the future. The initiative seeks to find energy-saving and -maximizing solutions to enable eco-friendly aircraft to stay in space for long periods of time without the need to return to Earth to re-fuel, or to avoid carrying vast amounts of heavy fuel on long-stay journeys.

Posted in: News, Aerospace, Aviation, Communications, Energy, Energy Efficiency, Energy Harvesting, Green Design & Manufacturing, Test & Measurement

Automatic Dependent Surveillance Broadcast System for Traffic Situational Awareness

An integrated communications and control system for unmanned aircraft systems (UAS) utilizes automatic dependent surveillance broadcast (ADS-B) technology. The prime objective of this system is to address safety concerns related to UAS sharing airspace with traditional aircraft. This system is capable of real-time traffic and weather updates in three-dimensional trajectories, and can be re-engineered for specific missions and applications.

Posted in: Briefs, TSP, Communications, Global positioning systems, Global positioning systems (GPS), Imaging, Imaging and visualization, Telecommunications, Global positioning systems, Global positioning systems (GPS), Imaging, Imaging and visualization, Telecommunications, Air traffic control, Unmanned aerial vehicles

E-Textile Antenna Tuning Stitches

This technique can be used to tune a microstrip patch antenna.

Lyndon B. Johnson Space Center, Houston, Texas

A variety of antenna tuning techniques exist for conventionally constructed antenna structures, such that when an antenna is converted from a design to an actual fabricated structure, slight adjustments can be made to the fabricated structure to match the performance expected from the design. For microstrip antenna structures, for example, shorting pins may be added to adjust the resonant frequency of the structure, or the conducting top layer of the antenna may be intentionally constructed in a fashion such that portions of it may be removed in post-production tuning.

Posted in: Articles, Briefs, TSP, Communications, Antennas, Antennas, Antennas, Textiles

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