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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Multibeam Antenna Design and Development for NASA Advanced Communications Technology Satellite (ACTS)

The design of the ACTS multibeam antenna is described, and its performance is evaluated. The multibeam antenna is designed to cover the continential U.S. and provides three fixed spot beams for high burst rate operations and two scanning beams for low burst rate operations. The antenna has one main reflector, a dual polarized subreflector, and two orthogonal feed assemblies. The feed system is to receive a linearly polarized communication signal from 28.9-30.0 GHz and to provide the elevation and azimuth error tracking signals at 29.975 GHz with a 0.01 deg tracking accuracy. The feed system uses a single multiflare conical horn and a multimode coupler to provide a symmetric primary pattern for the communication signal. The sidelobe characteristics of the reflector, and the relation between the sidelobe level and surface distortion are studied. It is noted that the performance measurements for the multibeam antenna correlate well with predictions for secondary patterns and scan characteristics.

Choung, Youn H.↗
NASA NTRS1986

ACTS experiments program

NASA's Advanced Communications Technology Satellite which will flight test the advanced technologies associated with a Ka-band multibeam antenna, onboard signal processing and switching, and laser communications is described. The ACTS Experiment Program includes flight system technology experiments, ground system technology experiments, network control, propagation experiments, and end-to-end system experiments. Operational communications modes employing the baseband processor and microwave switch matrix are presented as well as the antenna coverage pattern.

Schertler, Ronald J.↗
NASA NTRS1990

LBR-2 earth stations for the ACTS program

Described in this paper is the 'LBR-2' earth station being developed for NASA's Advanced Communications Technology Satellite (ACTS). The LBR-2 is one of two earth station types that operate through the satellite's baseband processor. The LBR-2 is a small VSAT-like earth station that is easily sited on a user's premises, and provides up to 1.792 megabits per second (MBPS) of voice, video, and data communications. Addressed in the paper is the design of the antenna, the rf subsystems, the digital processing equipment, and the user interface equipment.

O'Reilly, Michael↗
NASA NTRS1990

ACTS propagation terminal prototype planning and design

The planning and design of a prototype propagation receiving terminal for beacon signals at 27 and 20 GHz bands are examined. The developmental plan is discussed, followed by technical design considerations including, the Advanced Communications Technology Satellite (ACTS) system salient features and frequency plan, beacon signal parameters and specifications, system calculations, and terminal hardware design issues.

Davarian, Faramaz↗
NASA NTRS1990

LBR-2 Earth stations for the ACTS program

The Low Burst Rate-2 (LBR-2) earth station being developed for NASA's Advanced Communications Technology Satellite (ACTS) is described. The LBR-2 is one of two earth station types that operate through the satellite's baseband processor. The LBR-2 is a small earth terminal (VSAT)-like earth station that is easily sited on a user's premises, and provides up to 1.792 megabits per second (MBPS) of voice, video, and data communications. Addressed here is the design of the antenna, the rf subsystems, the digital processing equipment, and the user interface equipment.

Oreilly, Michael↗
NASA NTRS1991

A software control system for the ACTS high-burst-rate link evaluation terminal

Control and performance monitoring of NASA's High Burst Rate Link Evaluation Terminal (HBR-LET) is accomplished by using several software control modules. Different software modules are responsible for controlling remote radio frequency (RF) instrumentation, supporting communication between a host and a remote computer, controlling the output power of the Link Evaluation Terminal and data display. Remote commanding of microwave RF instrumentation and the LET digital ground terminal allows computer control of various experiments, including bit error rate measurements. Computer communication allows system operators to transmit and receive from the Advanced Communications Technology Satellite (ACTS). Finally, the output power control software dynamically controls the uplink output power of the terminal to compensate for signal loss due to rain fade. Included is a discussion of each software module and its applications.

Reinhart, Richard C.↗
NASA NTRS1992

A 1-W, 30-ghz, CPW Amplifier for ACTS Small Terminal Uplink

The progress is described of the development of a 1 W, 30 GHz, coplanar waveguide (CPW) amplifier for the Advanced Communication Technology Satellite (ACTS)Small Terminal Uplink. The amplifier is based on Texas Instruments' monolithic microwave integrated circuit (MMIC) amplifiers; a three stage, low power amplifier, and a single stage, high power amplifier. The amplifiers have a power output of 190 mW and 0.710 W, gain of 23 and 4.2 dB, and efficiencies of 30.2 and 24 percent for the three stage and one stage amplifiers, respectively. The chips are to be combined via a CPW power divider/combiner circuit to yield the desired 1 W of output power.

Taub, Susan R.↗
NASA NTRS1992

Modeling radiation forces acting on TOPEX/Poseidon for precision orbit determination

Geodetic satellites such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon require accurate orbital computations to support the scientific data they collect. Until recently, gravity field mismodeling was the major source of error in precise orbit definition. However, albedo and infrared re-radiation, and spacecraft thermal imbalances produce in combination no more than a 6-cm radial root-mean-square (RMS) error over a 10-day period. This requires the development of nonconservative force models that take the satellite's complex geometry, attitude, and surface properties into account. For TOPEX/Poseidon, a 'box-wing' satellite form was investigated that models the satellite as a combination of flat plates arranged in a box shape with a connected solar array. The nonconservative forces acting on each of the eight surfaces are computed independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center-of-mass. In order to test the validity of this concept, 'micro-models' based on finite element analysis of TOPEX/Poseidon were used to generate acceleration histories in a wide variety of orbit orientations. These profiles are then compared to the box-wing model. The results of these simulations and their implication on the ability to precisely model the TOPEX/Poseidon orbit are discussed.

Marshall, J. A.↗
NASA NTRS1992

Airborne lidar mapping of vertical ozone distributions in support of the 1990 Clean Air Act Amendments

The 1990 Clean Air Act Amendments mandated attainment of the ozone standard established by the U.S. Environmental Protection Agency. Improved photochemical models validated by experimental data are needed to develop strategies for reducing near surface ozone concentrations downwind of urban and industrial centers. For more than 10 years, lidar has been used on large aircraft to provide unique information on ozone distributions in the atmosphere. However, compact airborne lidar systems are needed for operation on small aircraft of the type typically used on regional air quality investigations to collect data with which to develop and validate air quality models. Data presented in this paper will consist of a comparison between airborne differential absorption lidar (DIAL) and airborne in-situ ozone measurements. Also discussed are future plans to improve the airborne ultraviolet-DIAL for ozone and other gas observations and addition of a Fourier Transform Infrared (FTIR) emission spectrometer to investigate the effects of other gas species on vertical ozone distribution.

Uthe, Edward E.↗
NASA NTRS1992

Ka-band dual frequency array feed for a low cost ACTS ground terminal

Because of low cost and ease of fabrication, microstrip arrays are attractive as feeds for reflector antenna systems. The development of a 4 x 4 microstrip array which will be used as a feed for a low cost Advanced Communications Technology Satellite (ACTS) ground terminal is described. The array feed consisting of four 2 x 2 subarrays is fed with coplanar waveguide power dividing networks. The patch radiator is designed to excite two orthogonal, linearly polarized waves at Ka-band frequencies (around 20 and 30 GHz). Test results for the developed array are presented.

Lee, Richard Q.↗
NASA NTRS1992

A 1-W, 30-GHz, CPW amplifier for ACTS small terminal uplink

The progress to date of the development of a 1-W, 30-GHz, coplanar waveguide (CPW) amplifier for the Advanced Communication Technology Satellite (ACTS) Small Terminal Uplink is described. The amplifier is based on Texas Instruments' monolithic microwave integrated circuit (MMIC) amplifiers; a three-stage, low-power amplifier and a single stage, high-power amplifier. The amplifiers have a power output of 190 mW and 0.710 W, gain of 23 and 4.2 dB, and efficiencies of 30.2 and 24 percent for the three-stage and one-stage amplifiers, respectively. The chips are to be combined via a CPW power divider/combiner circuit to yield the desired 1 W of output power.

Taub, Susan R.↗
NASA NTRS1992

Ka-Band Dual Frequency Array Feed for a Low Cost ACTS Ground Terminal

Because of low cost and ease of fabrication, microstrip arrays are attractive as feeds for reflector antenna systems. This paper describes the development of a 4x4 microstrip array which will be used as a feed for a low cost ACTS ground terminal. The array feed consisting of four 2x2 subarrays is fed with coplanar waveguide power dividing networks. The patch radiator is designed to excite two orthogonal, linearly polarized waves at Ka-band frequencies (around 20 and 30 GHz). Test results for the developed array are presented.

Lee, Richard Q.↗
NASA NTRS1992

The ACTS Spacecraft

The tested physical and performance characteristics of the ACTS spacecraft are presented with emphasis placed on those for the multibeam antenna, the communications electronics panel, and the bus. Performance measurements for the multibeam antenna agree with predicted parameters, and the electronics panel provides four transponder channels for redundancy and system reliability. The spacecraft bus provides unique features including an attitude-control subsystem with autotrack for pitch accuracy, a sun sensor for yaw control, and thruster firing for dual spin turns.

Gargione, Frank↗
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

Network architectures and protocols for the integration of ACTS and ISDN

A close integration of satellite networks and the integrated services digital network (ISDN) is essential for satellite networks to carry ISDN traffic effectively. This also shows how a given (pre-ISDN) satellite network architecture can be enhanced to handle ISDN signaling and provide ISDN services. It also describes the functional architecture and high-level protocols that could be implemented in the NASA Advanced Communications Technology Satellite (ACTS) low burst rate communications system to provide ISDN services.

Chitre, D. M.↗
NASA NTRS1992

ACTS aeronautical experiments

A description of the two aeronautical mobile satellite experiments utilizing NASA's Advanced Communications Technology Satellite (ACTS) is presented. The low bit rate experiment is principally a Ka-band technology demonstration of a prototype 4.8 Kbps aeronautic mobile terminal employing three experimental active electronically steered arrays. The high bit rate experiment can demonstrate a 64 Kbps to 384 Kbps satellite link between a ground terminal and an aircraft.

Nguyen, Tien M.↗
NASA NTRS1992

Rain compensation algorithm for ACTS mobile terminal

The initial advanced communication technology satellite (ACTS) mobile terminal (AMT) demonstrations will involve two-way communications between the high-bit-rate link evaluation terminal (HBR-LET), which is a fixed terminal (FT), and a van-housed mobile terminal (MT). The HBR-LET has the capability of adjusting its transmitted uplink power over an approximately 10-dB range to compensate for forward uplink rain attenuation. However, because of size and weight limitations, the MT cannot use power control as a rain compensation technique. Consequently, the AMT rain compensation algorithm (RCA) is based on a formula for varying the transmitted data rate in either direction to maintain link performance within acceptable limits. The objective of the AMT RCA is to ensure reliable operation in both the forward and return directions despite the possibility of uplink or downlink fading due to rain events in the vicinity of the FT or MT. In particular, the RCA must maintain at least a 3-dB link margin at the highest possible transmission rate (AMT can operate at 9.6, 4.8, or 2.4 kb/s) permitted by the prevailing channel conditions. The 3-dB minimum link margin is a system design safety factor to accommodate conceivable implementation losses.

Levitt, Barry K.↗
NASA NTRS1992

Modeling radiation forces acting on satellites for precision orbit determination

Models of the TOPEX/Poseidon spacecraft are developed by means of finite-element analyses for use in generating acceleration histories for various orbit orientations which account for nonconservative radiation forces. The acceleration profiles are developed with an analysis based on the use of the 'box-wing' model in which the satellite is modeled as a combination of flat plates. The models account for the effects of solar, earth-albedo, earth-IR, and spacecraft-thermal radiation. The finite-element analysis gives the total force and induced accelerations acting on the satellite. The plate types used in the analysis have parameters that can be adjusted to optimize model performance according to the micromodel analysis and tracking observations. Acceleration related to solar radiation pressure is modeled effectively, and the techniques are shown to be useful for the precise orbit determinations required for spacecraft such as the TOPEX/Poseidon.

Marshall, J. A.↗