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An experimental system, called GPS-like tracking, was used to track TDRS and GPS satellites simultaneously from a small (3 station) ground network. Comparison with the operational precise orbit indicates that GLT determined the TDRS orbit to within 25 m.
The system described performs the tracking and communications functions of a tracking and data relay satellite system (TDRS). The spread-spectrum signal format is achieved through wide deviation FM by a sinusoidal subcarrier unique to each multiple-access user. A compound phase-locked loop tracks carrier and subcarrier and demodulates data and ranging signals. Design parameters of user and ground terminals for TDRS are given. Acquisition procedures are described. Performance analyses are presented including the effects of noise, RFI, multipath and other users.
The development and use of mathematical models of signals received through the multipath environmental of a TDRS-to-user spacecraft link and vice versa are discussed. The TDRS (tracking and data relay satellite) will be in synchronous orbit. The user spacecraft will be in a low altitude orbit between 200 and 4000 km.
Studies on the digital communication system for the direct communication links from ground to space shuttle and the links involving the Tracking and Data Relay Satellite (TDRS). Three main tasks were performed:(1) Channel encoding/decoding parameter optimization for forward and reverse TDRS links,(2)integration of command encoding/decoding and channel encoding/decoding; and (3) modulation coding interface study. The general communication environment is presented to provide the necessary background for the tasks and to provide an understanding of the implications of the results of the studies.
Study efforts directed at defining all TDRS system elements are summarized. Emphasis was placed on synthesis of a space segment design optimized to support low and medium data rate user spacecraft and launched with Delta 2914. A preliminary design of the satellite was developed and conceptual designs of the user spacecraft terminal and TDRS ground station were defined. As a result of the analyses and design effort it was determined that (1) a 3-axis-stabilized tracking and data relay satellite launched on a Delta 2914 provides telecommunications services considerably in excess of that required by the study statement; and (2) the design concept supports the needs of the space shuttle and has sufficient growth potential and flexibility to provide telecommunications services to high data rate users. Recommendations for further study are included.
The S-Band TDRS multimode transponder and its associated ground support equipment is described. The transponder demonstrates candidate modulation techniques to provide the required information for the design of an eventual S-band transponder suitable for installation in a user satellite, capable of operating as part of a Tracking and Data Relay Satellite (TDRS) system.
The results pertaining to the tradeoff analysis and performance of the Ku-band shuttle antenna pointing and signal acquisition system are presented. The square, hexagonal and spiral antenna trajectories were investigated assuming the TDRS postulated uncertainty region and a flexible statistical model for the location of the TDRS within the uncertainty volume. The scanning trajectories, shuttle/TDRS signal parameters and dynamics, and three signal acquisition algorithms were integrated into a hardware simulation. The hardware simulation is quite flexible in that it allows for the evaluation of signal acquisition performance for an arbitrary (programmable) antenna pattern, a large range of C/N sub O's, various TDRS/shuttle a priori uncertainty distributions, and three distinct signal search algorithms.
The TDRSS will consist initially of two geosynchronous satellites and a common ground station at White Sands, New Mexico. According to current schedules, operations are to begin in November 1980. The overall TDRSS will provide high and low bit-rate telemetry, commands, and satellite-to-satellite tracking services. Each Tracking and Data Relay Satellite (TDRS) will have four antenna systems for NASA use. The common ground station at White Sands will have three 18-meter K-band antennas. The tracking equipment at the ground station is required to meet the following specifications: (1) 0.1-radian root-mean-square (rms) phase noise on nondestruct Doppler measurements; (2) 10-nanosecond rms range noise; (3) 50-nanosecond maximum systematic range error. Attention is given to two-way range and Doppler measurements, the bilateration tracking of TDRS, and an experiment using differenced one-way Doppler measurements.
Various aspects of the shuttle orbiter S-band network communication system, the S-band payload communication system, and the Ku-band communication system are considered. A method is proposed for obtaining more accurate S-band antenna patterns of the actual shuttle orbiter vehicle during flight because the preliminary antenna patterns using mock-ups are not realistic that they do not include the effects of additional appendages such as wings and tail structures. The Ku-band communication system is discussed especially the TDRS antenna pointing accuracy with respect to the orbiter and the modifications required and resulting performance characteristics of the convolutionally encoded high data rate return link to maintain bit synchronizer lock on the ground. The TDRS user constraints on data bit clock jitter and data asymmetry on unbalanced QPSK with noisy phase references are included. The S-band payload communication system study is outlined including the advantages and experimental results of a peak regulator design built and evaluated by Axiomatrix for the bent-pipe link versus the existing RMS-type regulator. The nominal sweep rate for the deep-space transponder of 250 Hz/s, and effects of phase noise on the performance of a communication system are analyzed.
The modifications being considered by the NASA-ESA Working Group (NEWG) for space-data-systems standardization to maximize the commonality of the NASA and ESA RF and modulation systems linking spaceborne scientific experiments with ground stations are summarized. The first phase of the NEWG project shows that the NASA MK-IVA Deep Space Network and Shuttle Interrogator (SI) systems in place or planned for 1985 are generally compatible with the ESA Network, but that communications involving the Tracking and Data Relay Satellite (TDRS) are incompatible due to its use of spread-spectrum modulation, pseudonoise ranging, multiple-access channels, and Mbit/s data rates. Topics under study for the post-1985 period include low-bit-rate capability for the ESA Network, an optional 8-kHz command subcarrier for the SI, fixing the spacecraft-transponder frequency-multiplication ratios for possible X-band uplinks or X-band nondeep-space downlinks, review of incompatible TDRS features, and development of the 32-GHz band.
An analytical simulation package (LinCsim) which allows the analytical verification of data transmission performance through TDRSS satellites was modified. The work involved the modeling of the user transponder, TDRS, TDRS ground terminal, and link dynamics for forward and return links based on the TDRSS performance specifications (4) and the critical design reviews. The scope of this effort has recently been expanded to include the effects of radio frequency interference (RFI) on the bit error rate (BER) performance of the S-band return links. The RFI environment and the modified TDRSS satellite and ground station hardware are being modeled in accordance with their description in the applicable documents.
A detailed mission history is presented for the rescue of the Tracking and Data Relay Satellite (TDRS) in 1983, in the wake of a faulty rocket stage burn after reaching apogee. The 2.5-ton spacecraft began to spin out of control at 180 deg/s, still attached to its booster stage. An anomaly analysis was conducted, together with an attitude control subsystem simulation, as a result of which maneuvers were conducted that succeeded in boosting TDRS to geosynchronous orbit, using despin from the sun mode, three-axis stabilization during booster burn, and finally return to the sun mode.
The Mission Model for user support and NASA's plans to provide the necessary support resources are discussed. Particular attention is given to considerations which imply operation of up to two additional Tracking and Data Relay Satellites (TDRS), as well as potential interoperability with data relay satellite systems planned for launch in the mid-1990s by the ESA and by the NASDA of Japan. NASA activities related to the development of an Advanced TDRS system for the support of missions flying in the 21st century are also discussed.
Simultaneous orbit determination is demonstrated using live range and Doppler data for the NASA/Goddard tracking configuration defined by the White Sands Ground Terminal (WSGT), the Tracking and Data Relay Satellite (TDRS), and the Earth Radiation Budget Satellite (ERBS). A physically connected sequential filter-smoother was developed for this demonstration. Rigorous necessary conditions are used to show that the state error covariance functions are realistic; and this enables the assessment of orbit estimation accuracies for both TDRS and ERBS.
In July, 1989, Cosmic Background Explorer (COBE) will be launched from a Delta rocket to study the big bang theory. The COBE, which is in a LEO/Polar orbit, will have two 20 Ah NiCd batteries, and 18 cells per battery, made by McDonnell Douglas Company. In December, 1989, National Oceanic and Atmospheric Administration (NOAA-D) will be launched from an Atlas rocket for weather observation purposes. NOAA-D, which is in a LEO/Polar morning orbit, will have two 26.5 Ah NiCd batteries, and 17 cells per battery, made by Ge-Astro East Windor. NOAA-I, which is scheduled for May, 1991 launch in a LEO/Polar afternoon orbit, will have three 26.5 Ah NiCd batteries, 17 cells per battery, made by GE-Astro East Windor. In April, 1990, Gamma Ray Observatory (GRO) will be launched from STS37 to study the gamma ray radiation phenomenon. GRO, which is in a LEO orbit, will have two modular power systems (MPS) made by McDonnell Douglas, each MPS consisting of three 50 Ah NiCd batteries, 22 cells per battery. In July, 1990, Geostationary Operational Environmental Satellite (GOES-I) will be launched from an Atlas I rocket for weather observation purposes. GOES-I, which is in a GEO orbit, will have two 12 Ah NiCd batteries, 28 cells per battery, made by Ford Aerospace and Communications Company. In December, 1990, Tracking and Data Relay Satellite (TDRS-E) will be launched from STS43 for communication purposes. TDRS-E, which is in a GEO orbit, will have three 40 Ah NiCd batteries, 24 cells per battery, made by TRW. In August, 1991, Extreme Ultraviolet Explorer (EUVE) will be launched from a Delta rocket. EUVE, which is in a LEO orbit, will have one modular power system (MPS) made by McDonnell Douglas. In December, 1991, Upper Atmosphere Research Satellite (UARS) will be launched from STS50 to study the Earth's ozone layer and other environmental concerns. UARS, which is in a 56 deg inclination LEO orbit, will have one modular power systems (MPS) made by McDonnell Douglas.
The results of a study to analyze the dependence of TDRSS user spacecraft orbit determination consistencies on varying tracking schedules are presented. In this study, the TDRS-East orbit determination results obtained utilizing Bilateration Ranging Transponder System data were evaluated. Six state parameters, three position and three velocity components and the solar radiation pressure coefficient, are estimated for TDRS-East. It is concluded that, in order to achieve high-precision orbit determination, the tracking coverage should not fall below 10 minutes every two orbits as decreasing it to every four orbits will significantly degrade the accuracy; present state-of-the-art consistency in orbit determination using TDRSS tracking is approximately 15 to 20 meters.
In order to validate the operational and computational capabilities of the Preliminary Orbit Determination System (PODS), tests were performed using tracking measurements for several systems including the ERB satellite, the SMM, the STS and Landsat-4. POD procedures are utilized to generate a state vector following an unplanned orbital perturbation or spacecraft maneuver, when an estimation process such as a differential correction orbit determination cannot obtain a solution. Results are presented to demonstrate POD for several situations involving different qualities of a priori target state vectors, data type combinations, data arc lengths, and mixtures of single-TDRS, dual-TDRS, and GSTDN measurements. The system's ability to determine accurately the state vector for the spacecraft and the effectiveness of the solution screening process are discussed. It is shown that PODS is capable of determining a spacecraft vector when differential correction orbit determination processes fail.
A Modular Antenna Pointing System (MAPS) is described which was designed for on-orbit servicing and on-orbit exchange. The MAPS provides a data link between the Explorer Platform (EP) satellite and the Tracking and Data Relay Satellite (TDRS). The MAPS consists of a two axis gimbal set used fo position a High Gain Antenna (HGA) toward TDRS, system control electronics, and an extendable mast. The system was qualified and integrated with the EP satellite for an April 1992 launch.