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NASA NTRS1991

Proceedings of the 23rd Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting

A compilation of technical papers, from the 23rd annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting, is presented. Papers were given in the following categories: (1) developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; (2) international and transnational applications of PTTI technology with emphasis on satellite laser tracking networks, GLONASS timing, comparison of national time scales and international communications; (3) applications of PTTI technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; (4) applications of PTTI technology to evolving military communications and navigation systems; and (5) dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, Loran, and synchronous communications satellites.

Richard L. Sydnor↗

NASA NTRS1991

The role of clocks in operating deep space missions

Operation of deep space missions requires stable frequency references and clocks to perform several mission critical functions. These references are used in generating the telecommunication links to maintain communications between earth and spacecraft, in generating accurate doppler, range, and very long baseline interferometry (VLBI) observables for determining the spacecraft's time varying position, and to generate on-board timing information for clocking out timed commands and time tagging instrument data. In addition, science applications exist, particularly those utilizing radio instrumentation, which can require additional functions and levels of performance. The design necessary to support these functions affects both the spacecraft and the ground tracking stations. This paper provides a brief description of these functions and some of the key requirements needed to support them.

S. W. Asmar↗

NASA NTRS1991

The role of the Consultative Committee on International Radio (CCIR) in time and frequency

The Consultative Committee on International Radio (CCIR) is a technical advisory group that, within the International Telecommunications Union (ITU), provides formal recommendations, technical advice, and technical information related to the allocation and use of the radio spectrum. The CCIR does its work through a number of separate study groups, each of which deals primarily with one or more radio based services recognized by the ITU. One of these, Study Group 7, is called 'Science Services' and deals with, among other things, time and frequency services, and related topics. This part of CCIR is probably best known for its development and implementation of the UTC time system in 1972. The U.S. National Administration develops proposed recommendations and provides other technical input to the CCIR through an organization of U.S. Study Groups that parallel those functioning internationally. Both the private and government sectors participate actively under the general oversight of the U.S. State Department and its U.S. CCIR National Committee. Current and projected future activities of U.S. and international Study Group 7 are described, including some examples of current recommendations, handbooks, and other documentation that might be useful for working with time and frequency applications.

Roger E. Beehler↗

NASA NTRS1991

An experiment in remote manufacturing using the advanced communications technology satellite

The goal of the completed project was to develop an experiment in remote manufacturing that would use the capabilities of the ACTS satellite. A set of possible experiments that could be performed using the Advanced Communications Technology Satellite (ACTS), and which would perform remote manufacturing using a laser cutter and an integrated circuit testing machine are described in detail. The proposed design is shown to be a feasible solution to the offered problem and it takes into consideration the constraints that were placed on the experiment. In addition, we have developed two more experiments that are included in this report: backup of rural telecommunication networks, and remote use of Synthetic Aperture Radar (SAR) data analysis for on-site collection of glacier scattering data in the Antarctic.

Tsatsoulis, Costas↗

NASA NTRS1992

WARC's last act?

The upcoming 1992 World Administrative Radio Conference is discussed. The reasons for its importance are given, and three new types of services that are high on the list for consideration are examined. They are universal personal telecommunications, digital audio broadcasting, and high-definition satellite TV. U.S. preparations for the conference and important international alliances are discussed.

Taylor, Robert M.↗

NASA NTRS1992

The ACTS NASA Ground Station/Master Control Station

Two of the major components of the ACTS Ground Segment are the NASA Ground Station (NGS) and the Master Control Station (MCS), colocated at the NASA Lewis Research Center. Essentially, the NGS provides the communications links by which the MCS performs its various network control and monitoring functions. The NGS also provides telecommunications links capable of transmission/reception of up to approximately 70 Mbit/s of digital telephonic traffic. Operating as a system, the entire complex of equipment is referred to as the NGS/MCS. This paper provides an 'as-built' description of the NGS/MCS as a system.

Meadows, David N.↗

NASA NTRS1992

Proposed Ka-band array-fed near field Cassegrain system for NASA's Polar Probe Mission

A Ka-band array-fed near-field Cassegrain antenna envisioned for NASA's Solar Probe Mission is the basis of the present spacecraft telecommunications system, which is designed for operation at X-band up/downlink and Ka-band downlink. The hexagonal array employed, which is located at the Cassegrain point of the 0.75-m reflector, encompasses 37 active elements; each of these contains 1/4-W HEMT amplifiers. Relative to a TWTA-based system, this active array feed reduces mass, increases dc power efficiency, enhanced reliability, and reduces volume requirements.

Kellogg, K.↗

NASA NTRS1991

Design of mission operations systems for scientific remote sensing

The present work describes the mission operations system (MOS) design process for remote-sensing missions. A MOS is defined as the system required to perform, monitor, and control an operation, encompassing personnel, hardware, software and/or documentation. Attention is given to telecommunications and remote-sensing instrumentation, MOS definition program phases and reviews, and MOS organization, management, and staffing. Also treated are the uplink and downlink processes, anomalies and contingency plans, the illustrative case of the MOS for the Magellan radar sensing mission, and a projection of future MOSs incorporating AI.

Wall, Stephen D.↗

NASA NTRS1992

Satcom systems and technologies into the 21st century

The role of communications satellites in the domestic U.S. telecommunications market for the next 25 years is examined, the focus being on the new satellite communications systems concepts and their enabling technologies. A simple procedure for the identification of critical satellite technologies in the years 2000-2015 is described. Study results indicate that by the year 2015, satellites will find commercial applications in the distribution of space-gathered data, supercomputer network, scientific visualization to remote areas, mobile services, VSAT, broadband ISDN, and data services.

Kwan, Robert K.↗

NASA NTRS1992

Improving regional health care in West Africa using current space systems and technology

This paper discusses the issues involved with establishing an integrated satellite health network in West Africa based on currently available technology. The system proposed makes use of a central national facility capable of transmitting and receiving voice/data and video signals from the entire country. Regional, field and local facilities provides timely epidemiologic information, sharing of medical expertise through telemedical consultations, enhances optimized resource distribution and builds a framework for telecommunications for the entire country.

Jemison, Mae C.↗

NASA NTRS1992

The ITU as a means of facilitating international collaboration on space radiocommunication systems

The role of the International Telecommunication Union (ITU) in the international collaboration in the field of space radio communications is reviewed. The history of the ITU, its structure and activities, and the functions of the permanent organs of the ITU are briefly discussed. Attention is then given to new space service applications for communications around 400 MHz, space services near 2 GHz, new space service applications above 20 GHz, and links for future planetary missions. The discussion also covers deep space allocations near 32/34 GHz, space VLBI applications, new earth exploration satellite service applications, and future work.

Kimball, H.↗

NASA NTRS1993

Organic Materials For Optical Switching

Equations predict properties of candidate materials. Report presents results of theoretical study of nonlinear optical properties of organic materials. Such materials used in optical switching devices for computers and telecommunications, replacing electronic switches. Optical switching potentially offers extremely high information throughout in compact hardware.

Cardelino, Beatriz H.↗

NASA NTRS1993

Packet Controller For Wireless Headset

Packet-message controller implements communications protocol of network of wireless headsets. Designed for headset application, readily adapted to other uses; slight modification enables controller to implement Integrated Services Digital Network (ISDN) X.25 protocol, giving far-reaching applications in telecommunications. Circuit converts continuous voice signals into digital packets of data and vice versa. Operates in master or slave mode. Controller reduced to single complementary metal oxide/semiconductor integrated-circuit chip. Occupies minimal space in headset and consumes little power, extending life of headset battery.

Christensen, Kurt K.↗

NASA NTRS1993

On the performance of Trellis coded modulation with octal phase shift keying over the TDRSS channel

As the National Aeronautics and Space Administration moves into the 21st century with programs like Space Station Freedom, a manned mission to Mars, and the new Landsat mission, transmission demands on the Tracking and Data Relay Satellite System (TDRSS) will very likely exceed the available bandwidth. The Manual Lujan, Jr. Center for Space Telemetering and Telecommunications Systems (CSTTS) at New Mexico State University (NMSU) is studying techniques for increasing the data rate capabilities of TDRSS. These techniques include the use of advanced bandwidth efficient modulation formats to increase the data rate that can be sustained in a TDRSS transponder and the use of lossless bandwidth compression of the data to be transmitted to lower the data rate required from the user spacecraft. Based upon current technology the most promising bandwidth efficient modulation technique is Trellis Coded Modulation (TCM) operating with Octal Phase shift Keying (8PSK). Trellis Coded Modulation coding with 8PSK carrier modulation has the capability to increase the data rate which can be transmitted through the TDRSS spacecraft by a factor of 2 to 2.5 times that available with todays coded QPSK systems with only a small penalty in link performance relative to the existing systems. However, before NASA can safely employ TCM coding it is necessary to prove that this complex format can perform on the real TDRSS link as it does in labs and simulation studies. This proof-of-concept test over a live satellite channel was the objective of the construction and testing performed under this task of the NMSU NASA grant referenced above. In conjunction with NASA, NMSU's CSTTS has constructed a system to test a new candidate TDRSS modulation scheme, TCM 8PSK, that can enhance the information throughput of the TDRSS spacecraft. The test system for this project which was constructed over a period of 18 months by NMSU consisted of two racks of commercial and univeristy-designed and -built equipment. This project has included modifications of an existing White Sands Ground Terminal (WSGT) High Rate QPSK Demodulator to demodulate 8PSK as well as the construction of other support hardware. Also, two TCM codecs (coder/decoders) have been constructed to implement two levels of bandwidth efficiency. One was designed and built by the research team at NMSU while the other was created by the University of Notre Dame with the University of South Australia. The NMSU codec achieves a 2-to-1 increase in data rate per unit bandwidth with a coding gain relative to QPSK of about 3dB. The Notre Dame/South Australia codec achieves a 2.5-to-1 increase in data rate per unit of occupied bandwidth and a coding gain of about 2dB.

Osborne, William P.↗

NASA NTRS1992

MODIS algorithm development and data visualization using ACTS

The study of the Earth as a system will require the merger of scientific and data resources on a much larger scale than has been done in the past. New methods of scientific research, particularly in the development of geographically dispersed, interdisciplinary teams, are necessary if we are to understand the complexity of the Earth system. Even the planned satellite missions themselves, such as the Earth Observing System, will require much more interaction between researchers and engineers if they are to produce scientifically useful data products. A key component in these activities is the development of flexible, high bandwidth data networks that can be used to move large amounts of data as well as allow researchers to communicate in new ways, such as through video. The capabilities of the Advanced Communications Technology Satellite (ACTS) will allow the development of such networks. The Pathfinder global AVHRR data set and the upcoming SeaWiFS Earthprobe mission would serve as a testbed in which to develop the tools to share data and information among geographically distributed researchers. Our goal is to develop a 'Distributed Research Environment' that can be used as a model for scientific collaboration in the EOS era. The challenge is to unite the advances in telecommunications with the parallel advances in computing and networking.

Abbott, Mark R.↗

NASA NTRS1990

NASA/NSF Workshop on Antarctic Research

Viewgraphs that accompanied an Ames Research Center presentation address Ames' currently-supported life sciences activities. These include crew factor issues such as human, automation, and telecommunication systems; strategic behavior and workloads; sleep, fatigue, and circadian rhythms; and virtual reality and spatial instrumentation. The need, background, and examples of pertinent research are provided.

Connors, Mary M.↗

NASA NTRS1992

Systems analysis for ground-based optical navigation

Deep-space telecommunications systems will eventually operate at visible or near-infrared regions to provide increased information return from interplanetary spacecraft. This would require an onboard laser transponder in place of (or in addition to) the usual microwave transponder, as well as a network of ground-based and/or space-based optical observing stations. This article examines the expected navigation systems to meet these requirements. Special emphasis is given to optical astrometric (angular) measurements of stars, solar system target bodies, and (when available) laser-bearing spacecraft, since these observations can potentially provide the locations of both spacecraft and target bodies. The role of astrometry in the navigation system and the development options for astrometric observing systems are also discussed.

Null, G. W.↗

NASA NTRS1992

Correction of high-frequency noise-temperature inaccuracies

Deep-space mission data rates to Earth are limited by the system operating noise-temperature (T(sub op)) performance of the DSN. This article addresses some of the techniques and definitions used for measuring and reporting the effective noise temperature of receivers (Te) and T(sub op) of the DSN's ground receiving systems. Calibration loads are used to measure T(sub op) of the DSN antennas. At 32 GHz, a calibration load cooled to 2-K physical temperature requires a correction of 0.67 K to determine the noise temperature. Using corrected noise temperature for the calibration loads results in the correct values for T(sub op) such that the total system noise power can be defined by Pn = kT(sub op) B, as required for DSN telecommunications design control tables. T(sub op) and Te should not be converted to equivalent physical temperatures.

Stelzreid, C. T.↗