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Horan, Stephen

Publications and source records attributed to Horan, Stephen.

34 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Small Satellite Access of the Space Network

Small satellites have been perceived as having limited access to NASA's Space Network (SN). The potential for satellite access of the space network when the design utilizes a fixed antenna configuration and low-power, coded transmission is analyzed. From the analysis, satellites using this configuration in high-inclination orbits are shown to have a daily data throughput in the 100 to 1000 Mbit range using the multiple access communications service.

Horan, Stephen↗
NASA NTRS1999

Design of a Channel Error Simulator using Virtual Instrument Techniques for the Initial Testing of TCP/IP and SCPS Protocols

There exists a need for designers and developers to have a method to conveniently test a variety of communications parameters for an overall system design. This is no different when testing network protocols as when testing modulation formats. In this report, we discuss a means of providing a networking test device specifically designed to be used for space communications. This test device is a PC-based Virtual Instrument (VI) programmed using the LabVIEW(TM) version 5 software suite developed by National Instruments(TM)TM. This instrument was designed to be portable and usable by others without special, additional equipment. The programming was designed to replicate a VME-based hardware module developed earlier at New Mexico State University (NMSU) and to provide expanded capabilities exceeding the baseline configuration existing in that module. This report describes the design goals for the VI module in the next section and follows that with a description of the design of the VI instrument. This is followed with a description of the validation tests run on the VI. An application of the error-generating VI to networking protocols is then given.

Horan, Stephen↗
NASA NTRS1998

NASA Hitchhiker Program Customer Payload Requirements (CPR)

The mission objective is to demonstrate each of the three types of technology intended for future small-satellite communications system design. Each experiment in the overall package is designed to exercise a different technology objective that may be found in the overall satellite communications and telemetry system design. The data communications through TORSS portion is designed to demonstrate that low-power communications systems with non-gimbaled antenna systems can transport significant quantities of data through TDRSS to the ground based on only transmitting through a TDRS when the experiment is near the TDRS subsatellite point. The remaining time. the payload communications system is not active. The demand access experiment is to demonstrate that the request for a demand access service can be transmitted through TDRS and received and decoded at the ground station. In this mode, the TDRS does not track the experiment but signal processing components at the White Sands Complex are used to detect and track the transmitted request. The laser communications experiment is designed to demonstrate passive transmission of telemetry data from the experiment. This mode uses a ground-based laser source to illuminate the experiment and modulate the beam with the data. Ground-based reception recovers the data from the reflected beam back to the ground station.

Horan, Stephen↗
NASA NTRS1998

Telemetry Data Collection from Oscar Satellite

This paper discusses the design, configuration, and operation of a satellite station built for the Center for Space Telemetering and Telecommunications Laboratory in the Klipsch School of Electrical and Computer Engineering Engineering at New Mexico State University (NMSU). This satellite station consists of a computer-controlled antenna tracking system, 2m/70cm transceiver, satellite tracking software, and a demodulator. The satellite station receives satellite,telemetry, allows for voice communications, and will be used in future classes. Currently this satellite station is receiving telemetry from an amateur radio satellite, UoSAT-OSCAR-11. Amateur radio satellites are referred to as Orbiting Satellites Carrying Amateur Radio (OSCAR) satellites as discussed in the next section.

Haddock, Paul C.↗
NASA NTRS1998

Non-Gimbaled Antenna Pointing: Summary of Results and Analysis

There is considerable interest at this time in developing small satellites for quick-turnaround missions to investigate near-earth phenomena from space. One problem to be solved in mission planning is the means of communication between the control infrastructure in the ground segment and the satellite in the space segment. A nominal small-satellite mission design often includes an omni-directional or similar wide-pattern antenna on the satellite and a dedicated ground station for telemetry, tracking, and command support. These terminals typically provide up to 15 minutes of coverage during an orbit that is within the visibility of the ground station; however, not all orbits will pass over the ground station so that coverage gaps will exist in the data flow. To overcome this general limitation on data transmission for low-earth orbiting satellites, the Space Network (SN), operated by the National Aeronautics and Space Administration, (NASA) has been designed to transmit data to and from user satellites through the Tracking and Data Relay Satellites (TDRS) in geostationary orbit and interfacing to the White Sands Complex (WSC) in New Mexico for the data's ground entry point. The advantage of the SN over a fixed ground station is that all low-earth-satellite orbits will be within the visibility area of at least one TDRS within the SN for a large part of the orbit and the potential exists to establish a communications link if the user satellite can point an antenna in the direction of any one of the relay satellites. Within NASA, there is considerable interest in seeing that small satellite developers are aware of the advantages to the SN and that designs to include the SN are part of the satellite design. Small satellite users have not often considered using the SN because of: (1) The 26-dB link penalty differential between direct broadcast to a ground station and transmission through a TDRS to the ground; (2) The class of satellite is too small to support high-gain antennas and associated attitude control and drive electronics; (3) The class of satellites is severely weight and power limited; (4) There are perceived problems in scheduling communications for this class of user on the SN. This report addresses the potential for SN access using non-gimbaled, i.e. fixed-pointed, antennas in the design of the small satellite using modest transmission power to achieve the necessary space-to-ground transmissions. The advantage of using the SN is in the reduction of mission costs arising from using the SN infrastructure instead of a dedicated, proprietary ground station using a similar type of communications package. From the simulations and analysis presented, we will show that a modest satellite configuration can be used with the space network to achieve the data transmission goals of a number of users and thereby rival the performance achieved with proprietary ground stations. In this study, we will concentrate on the return data link (from the user satellite through a TDRS to the ground data entry point). The forward command link (from the ground data entry point through a TDRS to the user satellite) will usually be a lower data rate service and the data volume will also be considerably lower than the return link's requirement. Therefore, we assume that if the return link requirements are satisfied, then the forward link requirements can also be satisfied.

Horan, Stephen↗
NASA NTRS1997

Test Report: Low-Cost Access to TDRS Using TOPEX to Emulate Small Satellite Performance

This report lists the objectives and conclusions of a series of experimental contacts between the TOPEX and the TDRS satellites. These experiments are designed to verify the theoretical prediction that a spin-stabilized satellite with a broad-beam, zenith-pointing antenna can have regular, significant contacts with the TDRS and use those contacts for data services. This series of experiments is a joint project between the experimenters at New Mexico State University (NMSU), the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC), and the Jet Propulsion Laboratory (JPL). In these experiments, we show that: (1) The satellite contacts during the experiment begin and end as predicted prior to the experiment; (2) The data contact is held for the desired contact duration; (3) The data quality through the contact is high and similar to that required by actual project needs; and (4) The receiving hardware at the White Sands Complex (WSC) is able to track the signals better than expected by analysis of the antenna pattern effects alone predict. We believe that these experiments successfully demonstrate the basic concept and its validity with actual spacecraft systems.

Horan, Stephen↗
NASA NTRS1997

Rain Rate Statistics in Southern New Mexico

The methodology used in determining empirical rain-rate distributions for Southern New Mexico in the vicinity of White Sands APT site is discussed. The hardware and the software developed to extract rain rate from the rain accumulation data collected at White Sands APT site are described. The accuracy of Crane's Global Model for rain rate predictions is analyzed.

Paulic, Frank J., Jr.↗
NASA NTRS1996

Analysis of EUVE Experiment Results

A series of tests to validate an antenna pointing concept for spin-stabilized satellites using a data relay satellite are described. These tests show that proper antenna pointing on an inertially-stabilized spacecraft can lead to significant access time through the relay satellite even without active antenna pointing. We summarize the test results, the simulations to model the effects of antenna pattern and space loss, and the expected contact times. We also show how antenna beam width affects the results.

Horan, Stephen↗
NASA NTRS1996

Data Processing for NASA's TDRSS DAMA Channel

A concept for the addition of a Demand Assignment Multiple Access (DAMA) service to NASA's current Space Network (SN) is developed. Specifically, the design of a receiver for the DAMA channel is outlined. Also, an outline of the procedures taken to process the received service request is presented. The modifications to the (SN) system are minimal. The post reception processing is accomplished using standard commercial off the shelf (COTS) packages. The result is a random access system capable of receiving requests for service.

Long, Christopher C.↗
NASA NTRS1995

TDRS MA phased-array antenna simulations

The NASA's Space Network (SN) nominal user services are prescheduled to allocate service type and required equipment to a user of the network. The availability of a resource for a given user is then communicated back to the user prior to requested service time. A proposed Demand Assignment Multiple Access (DAMA) system for NASA's SN to make it easier to allow a real time changes to add new user to the service schedule, is presented. The goals of the project are to improve the current operational modes by (1) reducing the support overhead required to maintain the overall scheduling requirements in this area; (2) allowing for more users to access the system especially those who traditionally have not considered SN access available to them; and (3) providing additional scheduling flexibility.

Caballero, Ruben↗
NASA NTRS1994

Improved small satellite access of the space network

This report contains the results of a study performed under the sponsorship of the National Aeronautics and Space Administration (NASA) made as a grant to the Center for Space Telemetering and Telecommunication Systems at New Mexico State University. The purpose of this phase of the grant is to increase user access to the Space Network (SN) run by NASA for supplying space-to-ground communications for satellites and associated control centers. The identified need is to bring more users into the community of those accessing the SN, especially those in the small satellite class of users. The initial phase of the study concerned the potential for modifications to the standard transponder used in the SN. The results of that investigation are summarized in Section 4. As the hardware modifications were being investigated, a second option was developed, namely to consider changes to the operational mode for the small satellites. This operational concept was to use a single, fixed-pointing antenna in a spin-stabilized satellite and let the antenna pattern sweep past the Tracking and Data Relay Satellites (TDRS) in the SN. The question to be answered by this phase of the study was twofold: could enough contact time per day be made available using this simple operating mode and could the data rate be high enough to allow for sufficient data throughput to satisfy the user community using existing components. Section 2 outlines the methodology and simulation results to answer these questions. Section 3 contains a summary of an operational simulation of a simple satellite payload using these contact scenarios. The simulation is not all inclusive but shows how a payload simulation could be configured to utilize variable contact times. The answer to both of the questions desired to be answered is affirmative. By carefully choosing the correct system transmission power and antenna pattern, the system will allow support to the 50th percentile of expected systems. It is recommended that based on this initial study, further work be done to quantify the exact parameters for transmission through the space network and to optimize usage of the contact time to maximize throughput.

Horan, Stephen↗
NASA NTRS1992

Remote observatory access via the Advanced Communications Technology Satellite

An investigation of the potential for using the ACTS to provide the data distribution network for a distributed set of users of an astronomical observatory has been conducted. The investigation consisted of gathering the data and interface standards for the ACTS network and the observatory instrumentation and telecommunications devices. A simulation based on COMNET was then developed to test data transport configurations for real-time suitability. The investigation showed that the ACTS network should support the real-time requirements and allow for growth in the observatory needs for data transport.

Horan, Stephen↗
NASA NTRS1992

Making space part of general education

General education reform is on-going at many universities to, in part, make undergraduate students more technically literate. The space program provides an area of study that is still exciting to students, provides technical content, and can incorporate the other goals. Additionally, human space activity contains international and interdisciplinary dimensions that can reach students outside of the technical disciplines. The development and contents of a space education course to become part of the university's general education program open to all students is presented. Included in the presentation is a listing of the course materials to be used by the students.

Horan, Stephen↗
NASA NTRS1988

Modem simulations for possible use in Space Station

Two candidate modem structures for use in the Space Station Multiple-Access Communications System were simulated using a software simulation package to obtain symbol error-rate curves. These systems represent an evolutionary QPSK-through-8 PSK modulation format for the input data streams. It was found that the use of phase-staggered QPSK modems would give lower expected implementation loss than a modem based upon the polarity-Costas-loop method. However, the latter would represent a simpler hardware investment to realize the modem structure for both QPSK and 8 PSK.

Horan, Stephen↗
NASA NTRS1987

High data rate modem simulation for the space station multiple-access communications system

The communications system for the space station will require a space based multiple access component to provide communications between the space based program elements and the station. A study was undertaken to investigate two of the concerns of this multiple access system, namely, the issues related to the frequency spectrum utilization and the possibilities for higher order (than QPSK) modulation schemes for use in possible modulators and demodulators (modems). As a result of the investigation, many key questions about the frequency spectrum utilization were raised. At this point, frequency spectrum utilization is seen as an area requiring further work. Simulations were conducted using a computer aided communications system design package to provide a straw man modem structure to be used for both QPSK and 8-PSK channels.

Horan, Stephen↗