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When the Tracking and Data Relay Satellite System (TDRSS)is completed, the system, together with its various NASA support elements will be known simply as the Space Networks. It will substantially increase information exchanges between low-orbiting spacecraft and the ground. The structural design, functions, earth-based links, and present and future use are discussed.
A desire for increased angular resolution at microwave frequencies has led to the development of radio telescopes with very lage effective apertures. Very long baseline interferometry (VLBI) has made it possible to synthesize telescopes with effective dimensions of a large fraction of an earth diameter. By using a satellite-borne radio telescope as part of a VLBI array, the dimensions of the earth cease to be a limitation. A demonstration was performed to show that the orbiting VLBI (OVLBI) concept is feasible. The Tracking and Data Relay Satellite System (TDRSS) was used as the orbiting element of the VLBI demonstration. Stability tests were made before the observations to determine the suitability of the TDRSS for OVLBI use. The first successful OVLBI observations were performed using the 64-m antenna observatories of NASA's Deep Space Network in Tidbinbilla, Australia, and of the Institute for Space and Astronautical Science in Usuda, Japan in conjunction with the TDRSS.
Very long baseline interferometry (VLBI) has been developed to the point where angular resolution at any given wavelength is limited by the dimensions of the earth. This limitation can be removed by placing a VLBI radio telescope in orbit. A demonstration of the feasibility of this approach was arranged. The Tracking and Data Relay Satellite System was used as an orbiting observatory in conjunction with the NASA Deep Space Network 64-m telescope in Tidbinbilla, Australia, and the Institute for Space and Astronautical Science 64-m antenna in Usuda, Japan. Interferometric fringes were successfully obtained from three quasars. The longest projected baseline was 1.4 earth diameters.
The Preliminary Orbit Determination System (PODS) provides early orbit determination capability in the Trajectory Computation and Orbital Products System (TCOPS) for a Tracking and Data Relay Satellite System (TDRSS)-tracked spacecraft. PODS computes a set of orbit states from an a priori estimate and six tracking measurements, consisting of any combination of TDRSS range and Doppler tracking measurements. PODS uses the homotopy continuation method to solve a set of nonlinear equations, and it is particularly effective for the case when the a priori estimate is not well known. Since range and Doppler measurements produce multiple states in PODS, a screening technique selects the desired state. PODS is executed in the TCOPS environment and can directly access all operational data sets. At the completion of the preliminary orbit determination, the PODS-generated state, along with additional tracking measurements, can be directly input to the differential correction (DC) process to generate an improved state. To validate the computational and operational capabilities of PODS, tests were performed using simulated TDRSS tracking measurements for the Cosmic Background Explorer (COBE) satellite and using real TDRSS measurements for the Earth Radiation Budget Satellite (ERBS) and the Solar Mesosphere Explorer (SME) spacecraft. The effects of various measurement combinations, varying arc lengths, and levels of degradation of the a priori state vector on the PODS solutions were considered.
The Tracking and Data Relay Satellite System (TDRSS) is an integral part of the overall NASA Space Network (SN) that will continue to evolve into the 1990's. Projections for the first decade of the 21st century indicate the need for an SN evolution that must accommodate growth int he LEO user population and must further support the introduction of new/improved user services. A central ingredient of this evolution is an Advanced TDRSS (ATDRSS) follow-on to the current TDRSS that must initiate operations by the late 1990's in a manner that permits an orderly transition from the TDRSS to the ATDRSS era. An SN/ATDRSS architectural and operational concept that will satisfy the above goals is being developed. To this date, an SN/ATDRSS baseline concept was established that provides users with an end-to-end data transport (ENDAT) service. An expanded description of the baseline ENDAT concept, from the user perspective, is provided with special emphasis on the TDRSS/ATDRSS evolution. A high-level description of the end-to-end system that identifies the role of ATDRSS is presented; also included is a description of the baseline ATDRSS architecture and its relationship with the TDRSS 1996 baseline. Other key features of the ENDAT service are then expanded upon, including the multiple grades of service, and the RF telecommunications/tracking services to be available. The ATDRSS service options are described.
The new AS&E Ultrahigh Resolution Soft X-ray Solar Research Rocket Payload has been successfully flown twice on Black Brant IX Sounding Rockets from White Sands Missile Range. These flights, conducted on 15 August 1987 and 11 December 1987, provided the first test of the new payload which consists of 3.8X magnifying hyperboloid-hyperboloid grazing incidence relay optic used in conjunction with an existing Wolter-I primary mirror. An RCA SID 500 series CCD detector was utilized in a thinned, back-illuminated configuration for recording the images. The 5.4 m effective focal length of the compound optics system resulted in a plate scale of 1 arc second per pixel which is comparable to the inherent resolution of the primary mirror. These flights represent the first use in X-ray astronomy of either of these two new technologies. These observations are presented with comparison to laboratory measurements and theoretical expectations of the instrument performance.
X-ray astronomy, both solar and celestial, has many needs for high spatial resolution observations which have to be performed with electronic detectors. If the resolution is not to be detector limited, plate scales in excess of 25 microns arc/sec, corresponding to focal lengths greater than 5 m, are required. In situations where the physical size is restricted, the problem can be solved by the use of grazing incidence relay optics. A system was developed which employs externally polished hyperboloid-hyperboloid surfaces to be used in conjunction with a Wolter-Schwarzschild primary. The secondary is located in front of the primary focus and provides a magnification of 4, while the system has a plate scale of 28 microns arc/sec and a length of 1.9 m. The design, tolerance specification, fabrication and performance at visible and X-ray wavelengths of this optical system are described.
The Tracking and Data Relay Satellite System (TDRSS) is currently in operation and is providing support to users. This paper describes a candidate satellite configuration which will continue system operation when the current satellite fleet is expended in the 1996 to 1997 time frame. The new system is intended to meet the growth in space network user population and service needs expected through approximately 2010. It is believed that the candidate architecture described will lead to a low-risk evolution from the TDRS architecture used prior to implementation of the ATDRS. NASA is using the architecture described herein as a reference, but has not selected an implementation architecture for the ATDRS system. This selection will be made when an implementing contractor is chosen and will be based on reducing life cycle costs and the ability to meet mission needs.
Analyses have indicated that the NASA Tracking and Data Relay Satellite System (TDRSS) can furnish its orbital users accurate, low cost onboard navigation services via two different modes: (1) Forward-Link Scheduled Tracking, designated 'Block-I', and (2) Forward-Link Beacon Tracking, designated 'Block II'. Attention is presently given to the Block-I and Block-II system configurations, signal definition, and observation data descriptions. Projected accuracies for orbit-determination, time-determination, and frequency-determination are presented, in conjunction with user-navigation scenarios and covariance analysis results detailing error sources and magnitudes. The status of the two navigation service modes in both TDRSS and Advanced TDRSS is noted.
An Advanced Tracking and Data Relay Satellite System (ATDRSS) reference architecture that embodies many of the system features and technological enhancements considered essential is presented and described. The architectural and user service features of the existing TDRSS are reviewed, and certain evolutionary features that will take place by the mid-1990s are discussed. NASAs projected user service requirements for the first decade at the next century, which are the principal drivers for the ATDRSS architecture, are described, including such aspects as the real-time data rates and the quantity of simultaneous services that must be supported. The discussion of the ATDRSS reference architecture covers rationale, technology considerations, and key features of the future ATDRSS user service. A status summary of the ATDRSS program is given.
The paper provides historical data and presents two parameters for evaluating the success of the Tracking and Data Relay Satellite System (TDRSS). The TDRSS provides high rate data from missions such as the Shuttle and Landsats, and lower rate data from missions such as the Solar Mesosphere Explorer and the Earth Radiation Budget Satellite. Two parameters have been established as measurements of the ability of the system to transmit user commands and telemetry data, i.e., availability and proficiency. Availability is the system's readiness to support any and all user requirements 24 hours per day, 7 days per week. Proficiency is the ratio of actual support provided to scheduled support.
As currently envisioned, NASA's Tracking and Data Relay Satellite System (TDRSS) will support the tracking and telecommunications requirements of LEO user satellites until the late 1990s, when existing TDRSS satellites will reach the end of their service lives. Spacecraft replacement is conceived as inseparable from network expansion for the accommodation of user population growth and the improvement of user services. The objective is to achieve a cost-effective/low-risk transition from TDRSS to Advanced TDRSS without interruption of user support. Attention is presently given to Advanced TDRSS architectural candidates studied and the choices which have emerged through technical tradeoff assessments.
The tracking and data relay satellite system (TDRSS) provides a flexible communications system for low-earth-orbit spacecraft and a source of tracking data to permit the location of the many orbital platforms to be accessed. Central to the TDRSS ground terminal is the integrated receiver which provides data demodulation, decoding, and deinterleaving over the range of 100 sps to 12 Msps, and all the tracking services in a single high-performance design. The requirements and design of the integrated receiver (IR), as well as an unbalanced quadriphase shift keying (UQPSK) receiver/demodulator under development for use in the TDRSS are discussed. The top level architecture of the IR is presented, and the implementation of the primary functions in the receiver is described. A single IR replaces the 12 different chassis currently required to support a single S-band single-access service. This approach has proven to be successful.
This investigation concerns the effects on Ocean Topography Experiment (TOPEX) spacecraft operational orbit determination of ionospheric refraction error affecting tracking measurements from the Tracking and Data Relay Satellite System (TDRSS). Although tracking error from this source is mitigated by the high frequencies (K-band) used for the space-to-ground links and by the high altitudes for the space-to-space links, these effects are of concern for the relatively high-altitude (1334 kilometers) TOPEX mission. This concern is due to the accuracy required for operational orbit-determination by the Goddard Space Flight Center (GSFC) and to the expectation that solar activity will still be relatively high at TOPEX launch in mid-1992. The ionospheric refraction error on S-band space-to-space links was calculated by a prototype observation-correction algorithm using the Bent model of ionosphere electron densities implemented in the context of the Goddard Trajectory Determination System (GTDS). Orbit determination error was evaluated by comparing parallel TOPEX orbit solutions, applying and omitting the correction, using the same simulated TDRSS tracking observations. The tracking scenarios simulated those planned for the observation phase of the TOPEX mission, with a preponderance of one-way return-link Doppler measurements. The results of the analysis showed most TOPEX operational accuracy requirements to be little affected by space-to-space ionospheric error. The determination of along-track velocity changes after ground-track adjustment maneuvers, however, is significantly affected when compared with the stringent 0.1-millimeter-per-second accuracy requirements, assuming uncoupled premaneuver and postmaneuver orbit determination. Space-to-space ionospheric refraction on the 24-hour postmaneuver arc alone causes 0.2 millimeter-per-second errors in along-track delta-v determination using uncoupled solutions. Coupling the premaneuver and postmaneuver solutions, however, appears likely to reduce this figure substantially. Plans and recommendations for response to these findings are presented.
A possible Data Relay Satellite System (DRSS) topology and network architecture is introduced. An asynchronous network concept, whereby each link (Inter-orbit, Inter-satellite, Feeder) is allowed to operate on its own clock, without causing loss of information, in conjunction with packet data structures, such as those specified by the CCSDS for advanced orbiting systems is discussed. A matching OBP payload architecture is described, highlighting the advantages provided by the OBP-based concept and then giving some indications on the OBP mass/power requirements.
The Tracking and Data Relay Satellite System (TDRSS), NASA's primary communications link between near-earth orbiting spacecraft and the ground, is addressed. The TDRSS supporting elements and their roles are described along with the different phases of the TDRSS life cycle. Users of TDRSS and the extent of support given to them are shown. TDRSS performance is evaluated in terms of availability and service proficiency.
The purpose of the Mars Environmental Survey (MESUR) mission is to put in place, over several launch opportunities, a constellation of Mars landers to make long-term surface observations of the circulation of the atmosphere and changes in climate, and to record the seismic activity of the planetary crust. Short-term objectives will also be addressed. An orbital communications infrastructure capable of providing regular high-rate data transfer to earth from the landers, which are scattered globally from pole to pole, is key to accomplishing the mission goals. A study is thereby presented of the orbit selection for the orbiter spacecraft, which will provide this support, and the relay communications operation. It is concluded that adequate communications support for the objectives of the MESUR mission can be provided by a single orbiter, provided care is taken in the selection of the size and orientation (i.e., inclination and apse line alignment) of the spacecraft orbit.
Correlation has been established between transient engine and control data obtained experimentally and data obtained by simulating the engine and control with an analog computer. This correlation was established at sea-level conditions for a turbine-propeller engine with a relay-type speed control. The behavior of the controlled engine at altitudes of 20,000 and 35,000 feet was determined with an analog computer using the altitude pressure and temperature generalization factors to calculate the new engine constants for these altitudes. Because the engine response varies considerably at altitude some type of compensation appears desirable and four methods of compensation are discussed.