SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
CLASS (Communications Link Analysis and Simulation System) is a software package developed for NASA to predict the communications and tracking performance of the Tracking and Data Relay Satellite System (TDRSS) services. This paper describes the capabilities of CLASS and the communications link model used and discusses typical applications for CLASS.
The Gamma Ray Observatory (GRO) has been undertaken by NASA to make the next major thrust in high-energy astrophysics. The GRO will be flown in a circular orbit at an altitude of 400 km with an inclination of 28.5 degrees. The Shuttle will take the GRO to its nominal orbit altitude. The GRO will be removed and will ascend to 400 km using its own propulsion system. The GRO will record and transmit data to the Tracking and Data Relay Satellite, which will then relay the signal to ground. The GRO will consist of four separate instruments that collectively span the photon spectrum from 0.05 to 30,000 MeV, almost six decades in energy. The photon sensitivity over the entire six-decade range will be improved by more than an order of magnitude over the best previously flown instruments. Significant improvements in angular resolution will also be made.
A computer interface has been designed for the Fault Isolation and Monitoring System, a system providing qualitative and quantitative assessment of the communications between the Tracking and Data Relay Satellite System Ground Segment and NASA's Network Control Center. The functional requirements for the interface and the design philosophy are discussed, as are the methods and protocol used to implement the operator support software required to configure the monitoring system and to display and report the results of the analysis. The system relies on the use of intelligent terminals, with the human interface removed from the host computer.
Using NASA's Tracking and Data Relay Satellite as a communications link, astronomers are able to receive scans from the Solar Maximum Mission (SMM) satellite immediately and regularly at the Goddard Space Flight Center. This major operational improvement permits the examination of SMM imagery and spectra as they arrive, as well as the formulation of future observational sequences on the basis of the solar activity in progress. Attention is given to aspects of the sun that change in the course of the 11-year sunspot cycle's movement from maximum to minimum. Proof has been obtained by means of SMM for the near-simultaneity of X-ray and UV bursts at flare onset.
Recommendations being developed by the NASA-ESA Working Group (NEWG) for Space Data Systems Standardization and the Consultative Committee for Space Data Systems (CCSDS) to standardize spacecraft telemetry and command coding are characterized. The telemetry convolutional codes used by JPL, ESA, and GSFC are found to be similar but incompatible, and it is recommended that a secondary capability for the other two schemes be developed at each facility, with the GSFC scheme as the ultimate standard, a periodic convolutional interleaving procedure for use with the NASA Tracking and Data Relay Satellite, and an optional concatenation of the convolutional code with a Reed-Solomon code to achieve up to 6.8 dB of gain. The telecommand-coding approach adopted by CCSDS is based on the schemes in use at JPL and GSFC.
Landsat-4 was launched on July 16, 1982, from Vandenberg Air Force Base in California. This launch culminated over a decade of planning, design, and implementation effort. During this period, many decisions and choices had to be made involving such items as the characteristics of the second-generation observing instrument named the Thematic Mapper (TM), the orbital altitude and coverage pattern, the configuration of the ground processing systems, etc. In total, the design and operation of Landsat-4 depart substantially from those of the successful Landsat 1, 2, and 3 series. Results derived from the operation of Landsat-4 systems and analyses of data products indicate that there have been very significant successes associated with Landsat-4. The TM provides observations that are considerably improved over the Multispectral Scanner (MSS). The middle-infrared bands at 1.6 and 2.2 micrometers, for example, are providing land-cover classification results that meet or exceed expectations. It is now hoped that successful operation of Landsat-4, Landsat-D' (D-prime), and the Tracking and Data Relay Satellite System (TDRSS) will permit the acquisition of a worldwide set of TM and MSS observations.
The Office of Space Tracking and Data Systems' Networks Consolidation Program (NCP), managed by the Jet Propulsion Laboratory (JPL), includes the implementation of a 26-meter Tracking and Communications Subnet as a part of the Mark IV A Deep Space Network (DSN). The incorporatin of this subnet into the DSN will contribute to the NCP goal of consolidating the two NASA ground tracking networks into one tracking network. The 26-meter Tracking and Communication Subnet was designed to provide the capability to support, at each Deep Space Communication Complex, the tracking and data communication requirements of the earth-orbital missions that cannot be supported by the Tracking and Data Relay Satellite System when it becomes operational. Implementation activities and planned capabilities of the subnet are discussed.
The Communications Link Analysis and Simulation System (CLASS) is a comprehensive, computerized communications and tracking system analysis tool under development by the Networks Directorate of the NASA/GSFC. The primary use of this system is to provide the capability to predict the performance of the Tracking and Data Relay Satellite system (TDRSS) User Communications and Tracking links through the TDRSS. The general capabilities and operational philosophy of the current and final versions of the CLASS are described along with some examples of analyses which have been performed utilizing the capabilities of this system.
CLASS (Communications Link Analysis and Simulation System) is a software package developed for NASA to predict the communication and tracking performance of the Tracking and Data Relay Satellite System (TDRSS) services. The modeling techniques used in CLASS are described. The components of TDRSS and the performance parameters to be computed by CLASS are too diverse to permit the use of a single technique to evaluate all performance measures. Hence, each CLASS module applies the modeling approach best suited for a particular subsystem and/or performance parameter in terms of model accuracy and computational speed.
CLASS (Communication Link Analysis and Simulation System) is a software package developed for NASA to predict the communication and tracking performance of the Tracking and Data Relay Satellite System (TDRSS) services. The methods used to verify CLASS are described. The usefulness of a software tool such as CLASS depends strongly on the reliability and accuracy of the results it produces. For this reason, considerable attention was paid to validation throughout the CLASS development.
Digital data scrambling has been considered for communication systems using NRZ (non-return to zero) symbol formats. The purpose is to increase the number of transitions in the data to improve the performance of the symbol synchronizer. This is accomplished without expanding the bandwidth but at the expense of increasing the data bit error rate (BER). Models for the scramblers/descramblers of practical interest are presented together with the appropriate link model. The effects of scrambling on the performance of coded and uncoded links are studied. The results are illustrated by application to the Tracking and Data Relay Satellite System links. Conclusions regarding the usefulness of scrambling are also given.
LANDSAT 4 and 5, launched in 1982 and 1984, not only carried the Thematic Mapper, but were redesigned to handle the increased data rates associated with it, and to communicate that data to Earth via geosynchronous orbiting Tracking and Data Relay Satellites (TDRS). The TM development program is summarized. A brief historical perspective is presented of the evolution of design requirements and hardware development. The basic performance parameters that serve as sensor design guidelines are presented.
The National Space Transportation System is a national resources serving the government, Department of Defense and commercial needs of the USA and others. Four orbital flight tests were completed July 4, 1982, and the first Operational Flight (STS-5) which placed two commercial communications into orbit was conducted November 11, 1982. February 1983 marked the first flight of the newest orbiter, Challenger. Planned firsts in 1983 include: use of higher performance main engines and solid rocket boosters, around-the-clock crew operations, a night landing, extra-vehicular activity, a dedicated DOD mission, and the first flight of a woman crew member. By the end of 1983, five commercial payloads and two tracking and data relay satellites should be deployed and thirty-seven crew members should have made flights aboard the space shuttle.
A formulation and many representative numerical results for mesh reflector antennas are presented. The reflection coefficient matrix for the prescribed mesh configuration was determined and the local coordinate system of the mesh cells at each point on the curved reflector surface was accentuated. A novel strip aperture model was used to formulate the transmission coefficient matrix for a variety of mesh cell configurations. Numerical data are tailored to the dimensions of a conceptually designed land mobile satellite system (LMSS) which employs a large mesh deployable offset parabolic antenna. Results are shown for an offset parabolic reflector with mesh surfaces similar to the mesh surface of tracking and data relay satellite system (TDRSS).
The information and control requirements of the investigator-users of future free-flying, platform-based, or Space Station-based scientific experiments are assessed, and the implications of these requirements for the design of the information systems are discussed. The principal requirements include near-real-time interaction with the payload, distributed or remote payload command and control, rapid access to quick-look data, flexibility of payload command sequences, on-demand uplink-downlink availability, system transparency, and modular design to facilitate replacement of system components. Current developments in systems architecture such as increased use of onboard microprocessors to select and preprocess data and transmit autonomous streams directly to the user, standardization of interfaces, and the NASA Tracking and Data Relay Satellite System are characterized, and block diagrams of present and future systems are provided.
The Tracking and Data Relay Satellite System (TDRSS) will consist of three identical satellites in geosynchronous orbits and a dedicated ground receiving station. The first two satellites (TDRS East and TDRS West) will form the operational TDRS service network providing near-global real-time user satellite coverage. The third TDRS satellite will act as an in-orbit spare. Since the TDRSS satellite are supported by a single ground station, a method of providing emergency support for TDRS and user satellites is needed. The support to be provided by JPL's Deep Space Network is described.
The requirements for future power for AF satellite mission vehicles, fall into two categories. The first category is in the 1 to 50 kW range for missions of a continuous nature such as communication, navigation, surveillance, data relay and meteorology. The second category is in the multi-megawatt range for either continuous or burst power durations and are for other than solar power sources. Requirements for longer life and survivability in varying degrees are there for all systems. While the power levels do not appear difficult to achieve in view of the large array developments pursued by NASA Space Station technology, the other military requirements are very challenging and continue to be system drivers. The development of solar cells arrays should be in conjunction with other power supply technologies such as regulation and control components and energy storage subsystems.
The Arecibo Observatory in Puerto Rico participated in the support of the U.S. International Cometary Explorer (ICE) mission when the ICE spacecraft passed through the tail of comet Giacobini-Zinner on September 11, 1985. The Arecibo Observatory is a research facility of the National Astronomy and Ionosphere Center (NAIC) operated by Cornell University under contract to the National Science Foundation (NSF). Coverage of the encounter involved the use of the observatory's 305-m (1000-ft) radio reflector antenna and RF and data system equipment fabricated or modified specifically for support of the ICE mission. The successful implementation, testing, and operation of this temporary receive, record, and data relay capability resulted from a cooperative effort by personnel at the Arecibo Observatory, the Goddard Space Flight Center, and the Jet Propulsion Laboratory.