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This paper discussed the MEC system and its mission from the viewpoint of orbit servicing. Information is provided on MEC system requirements, design for on orbit servicing, on orbit servicing operations and rationale and servicing costs.
Satellite systems in which the space segment operates in the 30/20 GHz frequency band are defined and compared as to their potential for providing various types of communications services to customer premises and the economic and technical feasibility of doing so. Technical tasks performed include: market postulation, definition of the ground segment, definition of the space segment, definition of the integrated satellite system, service costs for satellite systems, sensitivity analysis, and critical technology. Based on an analysis of market data, a sufficiently large market for services is projected so as to make the system economically viable. A large market, and hence a high capacity satellite system, is found to be necessary to minimize service costs, i.e., economy of scale is found to hold. The wide bandwidth expected to be available in the 30/20 GHz band, along with frequency reuse which further increases the effective system bandwidth, makes possible the high capacity system. Extensive ground networking is required in most systems to both connect users into the system and to interconnect Earth stations to provide spatial diversity. Earth station spatial diversity is found to be a cost effective means of compensating the large fading encountered in the 30/20 GHz operating band.
The potential United States domestic telecommunications demand for satellite provided customer premises voice, data and video services through the year 2000 were forecast, so that this information on service demand would be available to aid in NASA program planning. To accomplish this overall purpose the following objectives were achieved: development of a forecast of the total domestic telecommunications demand, identification of that portion of the telecommunications demand suitable for transmission by satellite systems, identification of that portion of the satellite market addressable by Computer premises services systems, identification of that portion of the satellite market addressabble by Ka-band CPS system, and postulation of a Ka-band CPS network on a nationwide and local level. The approach employed included the use of a variety of forecasting models, a market distribution model and a network optimization model. Forecasts were developed for; 1980, 1990, and 2000; voice, data and video services; terrestrial and satellite delivery modes; and C, Ku and Ka-bands.
The results of a life evaluation program on rigid explosive transfer lines, which are used to initiate aircraft emergency crew escape functions, are presented in order to provide quantitative information on rigid explosive transfer lines which can contribute to responsible, conservative, service life determinations. The program involved the development of a test methodology, testing of the three types of transfer lines in use in the U.S., testing of these lines following a repeat of the thermal test conducted in the original qualification, and conducting a degradation investigation. Results from the testing of more than 800 components showed that rigid explosive transfer lines were not affected by age, service, or a repeat of the thermal qualification tests on full-service lines. The explosive degradation limits were approximated and the mechanisms examined. It is concluded that the service lives of rigid explosive transfer lines should be considered for extension in order to provide cost savings and increased system reliability.
In computer program NOROCA populations statistics from National Center for Health Statistics used with computational procedure to estimate health service utilization rates, physician demands (by specialty) and hospital bed demands (by type of service). Computational procedure applicable to health service area of any size and even used to estimate statewide demands for health services.
A new capability regarding the U.S. space efforts will be related to the servicing of satellites in orbit utilizing first-generation space station as the collection point or base for Shuttle-delivered payloads. Orbital maneuvering vehicles could move payloads or spacecraft assembled at the Shuttle/space station terminus to other earth orbit locations. It is assumed that such a capability will be initially available in the early 1990's. The benefits provided by satellite servicing in orbit are discussed, taking into account extended satellite lifetimes, lower acquisition cost, improved satellite performance, the possibility to change a satellite's mission, optimized science, and higher satellite reliability. The requirements for Satellite Servicing Technology Development Missions (TDMs) are considered. It is found that existing technology is insufficient, in various areas, to perform the servicing operations. A list is provided of critical technologies which must be developed.
The similarities and differences between areas inside and outside U.S. metropolitan areas were evaluated in terms of their commercial/industrial and government employment characteristics. The comparison focuses on the levels, shares, and composition of employment in the commercial/industrial and government sectors that represent potential classes of land mobile communications users. The major findings of the analysis are as follows: (1) non-metropolitan commercial/industrial user classes of land mobile communication services exist in significant numbers; (2) the compositions of non-metropolitan and metropolitan commercial/industrial user classes of land mobile communication services closely resemble each other; (3) non-metropolitan areas have significant levels of the government user classes that represent potential markets for land mobile communication services; and (4) non-metropolitan local governments have a significantly larger proportion of their employment in the primary user classes of private land mobile radio service than do metropolitan local governments.
The overall purpose was to forecast the potential United States domestic telecommunications demand for satellite provided customer promises voice, data and video services through the year 2000, so that this information on service demand would be available to aid in NASA program planning. To accomplish this overall purpose the following objectives were achieved: (1) development of a forecast of the total domestic telecommunications demand; (2) identification of that portion of the telecommunications demand suitable for transmission by satellite systems; (3) identification of that portion of the satellite market addressable by consumer promises service (CPS) systems; (4) identification of that portion of the satellite market addressable by Ka-band CPS system; and (5) postulation of a Ka-band CPS network on a nationwide and local level. The approach employed included the use of a variety of forecasting models, a parametric cost model, a market distribution model and a network optimization model. Forecasts were developed for: 1980, 1990, and 2000; voice, data and video services; terrestrial and satellite delivery modes; and C, Ku and Ka-bands.
The developments in automation and robotics have increased the importance of applications for space based servicing using remotely operated systems. A study on three basic remote operating systems (teleoperation, telepresence and robotics) was performed in two phases. In phase one, requirements development, which consisted of one three-month task, a group of ten missions were selected. These included the servicing of user equipment on the station and the servicing of the station itself. In phase two, concepts development, which consisted of three tasks, overall system concepts were developed for the selected missions. These concepts, which include worksite servicing equipment, a carrier system, and payload handling equipment, were evaluated relative to the configurations of the overall worksite. It is found that the robotic/teleoperator concepts are appropriate for relatively simple structured tasks, while the telepresence/teleoperator concepts are applicable for missions that are complex, unstructured tasks.
A plan for advancing the state of automation and robotics technology as an integral part of the U.S. space station development effort was studied. This study was undertaken: (1) to determine the benefits that will accrue from using automated systems onboard the space station in support of satellite servicing; (2) to define methods for increasing the capacity for, and effectiveness of satellite servicing while reducing demands on crew time and effort and on ground support; (3) to find optimum combinations of men/machine activities in the performance of servicing functions; and (4) project the evolution of automation technology needed to enhance or enable satellite servicing capabilities to match the evolutionary growth of the space station. A secondary intent is to accelerate growth and utilization of robotics in terrestrial applications as a spin-off from the space station program.
Minimum satellite separations are calculated which satisfy a given carrier-to-interference protection ratio for the Fixed-Satellite Service (FSS) on a single-entry basis, assuming circular antenna beams. The results are presented in the form of universal contour curves, in which antenna-centered angles are the coordinates, and also in terms of the more conventional longitude and latitude separations. It is shown that orbit capacity increases with decreasing service-area size and that, for practical service areas, capacity is increased if the longitude of a satellite does not differ too greatly from that of the service area it serves.
The duplex space/ground/space data services for the Space Station are described. The need to separate the uplink data service functions from the command functions is discussed. Command management is a process shared by an operation control center and a command management system and consists of four functions: (1) uplink data communications, (2) management of the on-board computer, (3) flight resource allocation and management, and (4) real command management. The new data service capabilities provided by microprocessors, ground and flight nodes, and closed loop and open loop capabilities are studied. The need for and functions of a flight resource allocation management service are examined. The system is designed so only users can access the system; the problems encountered with open loop uplink access are analyzed. The procedures for delivery of operational, verification, computer, and surveillance and monitoring data directly to users are reviewed.
The capability to reservice spacecraft and satellites with expendable fluids will provide significant increases in the usability, operational efficiency and cost effectiveness of in-space systems. Initial resupply will be accomplished from the Orbiter cargo bay starting with monopropellant servicing which will eventually be extended to servicing of bipropellants and pressurants. Other fluids, such as freon, ammonia, methanol, superfluid helium, and liquid/gaseous nitrogen may also need to be resupplied once a space station becomes a reality. These fluids/gases are required for subsystem working fluid replacement and payload/experiment fluid replenishment. A logistics module operating on a 90 day schedule is planned for space station servicing. Resupplying hundreds of thousands of pounds of cryogenic propellants and reactants for users such as the Orbital Transfer Vehicle (OTV) also represents future logistics challenges. Implementation of on-orbit fluid transfer requires solving many problems including fluid management in the low-g environment, system docking and interface mating, configuration of user friendly avionics to monitor and control the entire servicing operation, and minimized maintenance and enhanced reliability. Candidate fluid transfer methods and possible gas transfer methods are discussed, and preliminary storable monopropellant and bipropellant tanker designs are summarized.
A history of on-orbit servicing and repair is given with emphasis placed on the Solar Maximum Repair Mission. The experience gained thus far in on-orbit servicing and the design of the Space Station's servicing capabilities impose the following requirements on users: (1) satellites must have a standard grapple for capture and a standard berthing interface, (2) Space Station safety requirements must meet to preclude damage to the Space Station or injury to the EVA crew, (3) sensitive instruments will need to implement remotely controlled protective devices to prevent damage, and (4) satellite thermal systems must be designed to maintain survival temperatures during transfer from orbit to the Space Station servicing facility.
NASA Space Station servicing support facilities will include both pressurized and unpressurized work areas. While the latter will allow astronauts operating in EVAs or aided by robots to accomplish Orbital Replacement Unit (ORU) and instrument changes, tests, assembly, refueling, and repairs, the former will furnish astronauts engaged in work requiring intravehicular activities (IVAs) the ability to enter through an airlock into a module in which they can more carefully service ORUs. Baseline IVA accommodations encompass (1) a staging/assembly area for ORUs brought in from satellites, orbital platforms or attached payloads, (2) a work station for monitoring and control of the external Servicing Bay facility, and (3) a large, laminar flow workbench which would provide highly controlled conditions, as well as (4) a 'glovebox' for delicate servicing and (5) an assortment of hand tools and test equipment.
The Spacecraft Assembly, Maintenance, and Servicing Study (SAMSS) is an effort to define and verify the most cost effective approach to spacecraft servicing, as a alternative to replacement, in the 1990's and beyond. The intent of the study is to assess the servicing of satellites in all orbit regimes. Elements of a space servicing infrastructure are developed and cost estimates are generated. Readiness is assessed and proof of concept demonstrations are identified. Cryogenic fuel resupply is discussed.
Tools, fixtures and systems being developed to improve the efficiency of extravehicular activity (EVA) servicing operations; and tools developed for EVA use being adapted for use in robot-assisted EVA, local robotic servicing, and remote robotic servicing, are presented. The basic types of satellite servicing operations, the various modes by which they can be accomplished, and the hardware which supports these modes are outlined. The program and hardware elements of the program infrastructure are reviewed.
The practicality of employing a combination of automated and extravehicular activity forms of servicing in-orbit was demonstrated with the STS 41-C Solar Maximum Repair Mission. This shows that modular Orbital Replacement Units (ORUs) designed for servicing can be readily accommodated. Successful replacement of an experiment ORU, not designed for replacement, was performed following extensive preparations. In a laboratory, spacecraft ORUs were replaced using a completely preplanned automated approach. This was later done using a completely unstructured teleoperations mode including the complicated exchange of the instrument ORU. As a result of this effort and work on powered tools, an approach for combining these techniques is underway to produce a flight support system servicing aid to increase the STS astronauts' effective in-orbit servicing capability by several fold.