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The results are presented of a study of onboard checkout techniques, as they relate to space station subsystems, as a guide to those who may need to implement onboard checkout in similar subsystems. Guidance, navigation, and control subsystems, and their reliability and failure analyses are presented. Software and testing procedures are also given.
Onboard instruments have been shown to be an effective aid to navigation on missions to the outer planets. The relationship of two possible candidate navigation instruments, an image tube (television) and a scanning photometer, with other systems such as data processing and attitude control is discussed. Certain key problem areas relating to the design of each sensor are considered, and the scientific uses of each sensor are examined. The navigational efficacy of both instruments is illustrated by some selected results from a navigation and guidance simulation of outer planet missions. It is concluded that both devices are viable alternatives for onboard outer planet navigation.
The onboard data processor for OAO 3 flight applications executes instructions at the rate of 2 1/2 billion per day. The computer commands, processes data, and controls telemetry subsystem programs onboard the spacecraft.
A study was conducted to develop the functional requirements for onboard management of space shuttle consumables. A specific consumables management concept for the space shuttle vehicle was developed and the functional requirements for the onboard portion of the concept were generated. Consumables management is the process of controlling or influencing the usage of expendable materials involved in vehicle subsystem operation. The subsystems considered in the study are: (1) propulsion, (2) power generation, and (3) environmental and life support.
A flexible onboard encoder system was designed for the space shuttle. The following areas were covered: (1) implementation of the encoder design into hardware to demonstrate the various encoding algorithms/code formats, (2) modulation techniques in a single hardware package to maintain comparable reliability and link integrity of the existing link systems and to integrate the various techniques into a single design using current technology. The primary function of the command encoder is to accept input commands, generated either locally onboard the space shuttle or remotely from the ground, format and encode the commands in accordance with the payload input requirements and appropriately modulate a subcarrier for transmission by the baseband RF modulator. The following information was provided: command encoder system design, brassboard hardware design, test set hardware and system packaging, and software.
The Onboard Experimental Data Support Facility (OEDSF) is an inflight data processor based on a totally new architecture specifically developed to cost-effectively process the data of Shuttle payloads sensors. Processing data onboard fills the following needs: (1) reduction of data bulk by conversion to information (2)quick-look for evaluation, interactive operation, etc. (3) real-time computation of engineering representation of sensed phenomena. For example: Value of backscatter coefficient (sigma) of a scatterometer as a function of latitude and longitude (4) exploitation of the real-time availability of ancillary data, thereby obviating the need for time-tagging, recording, and recorrelation and (5) providing data or information immediately usable by the experimenter or user. The OEDSF is made up of modular and cascadable matrix processors. Each matrix has been sized to process the data of a full typical shuttle payload. Cost analyses indicate that significant savings are realized by processing data with the OEDSF compared with conventional ground facilities.
The potential use of real-time synthetic aperture radar (SAR) processing to produce 200 meter resolution imagery onboard a 1983 Venus orbiter imaging radar spacecraft is described. The VOIR SAR processing requirements are defined in terms of a nominal baseline design evolving from a 1977 VOIR mission study. A candidate onboard SAR processor architecture compatible with the VOIR requirements is next detailed. Finally, implementation characteristics, based upon currently available integrated circuits, are estimated in terms of chip count, power, and weight.
Analysis and simulation results are presented for magnetic field models for use in attitude acquisition onboard Solar Maximum Mission (SMM). A study was made of the degree of the spherical harmonic expansion of the magnetic field required, considering mission requirements, modeling errors, and magnetometer quantization and biases. It is shown that a fifth-degree field is sufficient to provide two-degree roll angle determination accuracy with a residual magnetic bias of 10 milligauss. Also, a spherical harmonic expansion for the McIlwain L-parameter is included for the first time. This parameter will be telemetered to ground with experimental data. The fifth-degree expansion will provide the L-parameter to within two percent of accepted values. The additional onboard computational burden is the storage of 36 coefficients and an increase of about 15% in computation time. Prototype flight code was developed which is anticipated to require about 2000 bytes of core storage and 30 milliseconds of computation time per orbit point on the NSSC-1 computer.
The space shuttle onboard navigation systems characteristics are described. A standard source of equations and numerical data for use in error analyses and mission simulations related to space shuttle development is reported. The sensor characteristics described are used for shuttle onboard navigation performance assessment. The use of complete models in the studies depend on the analyses to be performed, the capabilities of the computer programs, and the availability of computer resources.
A system to perform real time onboard geometric connection of LANDSAT D resolution satellite imagery is described. System requirements, algorithms, sensors, and other hardware components are defined. Feasibility of implementing the correction process is demonstrated using Kalman filter techniques to incorporate information from onboard ephemeris, attitude control, and ground control points. Random access sensor systems, such as charge injected devices and charge coupled devices are used to obtain pixel values at desired ground location, thus greatly reducing the data processing requirements.
There is a strong rationale for increasing the rate of information return from imaging class experiments aboard both terrestrial and planetary spacecraft. Future imaging systems will be designed with increased spatial resolution, broader spectral range and more spectral channels (or higher spectral resolution). The data rate implied by these improved performance characteristics can be expected to grow more rapidly than the projected telecommunications capability. One solution to this dilemma is the use of improved onboard data processing. The use of onboard classification processing in a multispectral imager can result in orders of magnitude increase in information transfer for very specific types of imaging tasks. Several of these processing functions are included in the conceptual design of an Infrared Multispectral Imager which would map the spatial distribution of characteristic geologic features associated with deposits of economic minerals.
The potential use of real-time SAR processing to produce 200-meter resolution imagery onboard a 1983 Venus Orbiter Imaging Radar (VOIR) spacecraft is discussed. The current NASA SAR processor development program and its relationship to the VOIR application are described. VOIR SAR processing requirements are defined in terms of a nominal baseline design evolving from a 1977 VOIR mission study by JPL. A candidate onboard SAR processor architecture compatible with the VOIR requirements is described. Detailed implementation characteristics, based on currently available integrated circuits, are estimated in terms of chip count, weight, and power.
This paper summarizes anticipated onboard navigation accuracies and user system characteristics for near-earth spacecraft. Alternate onboard systems configurations using inputs from the Tracking and Data Relay Satellite System (TDRSS) and the DOD NAVSTAR Global Positioning System (GPS) are described. Initial simulation results indicate that TDRSS will provide accuracies of 100 meters or less, and GPS can permit user spacecraft orbit determination to within 10 meters. Specific GPS user equipment developments for Landsat-D and Shuttle are outlined, along with future low-cost versions of these systems.
An orbit determination subsystem that will operate as an integral part of an autonomous, onboard navigation system is presented and analyzed. The navigation system is required to interface solely with the downlink telemetry stream and uplink command stream of an existing class of geostationary satellites. In particular, the orbit will be determined from a set of onboard sensors, which previously were used only for attitude determination. The design of the orbit determination subsystem is described in detail. The rationale behind the choice of each component of the design is given. Finally, the performance of the orbit determination subsystem, under a variety of assumptions, is determined by a combination of numerical simulation and analytical methods.
An ad-hoc committee was asked to review the following questions relevant to the space station program: (1) onboard maintainability and repair; (2) in-space research and technology program and facility plans; (3) solar thermodynamic research and technology development program planning; (4) program performance (cost estimating, management, and cost avoidance); (5) onboard versus ground-based mission control; and (6) technology development road maps from IOC to the growth station. The objective of these new assignments is to provide NASA with advice on ways and means for improving the content, performance, and/or effectiveness of these elements of the space station program.
Real-time onboard fault monitoring and diagnosis for aircraft applications, whether performed by the human pilot or by automation, presents many difficult problems. Quick response to failures may be critical, the pilot often must compensate for the failure while diagnosing it, his information about the state of the aircraft is often incomplete, and the behavior of the aircraft changes as the effect of the failure propagates through the system. A research effort was initiated to identify guidelines for automation of onboard fault monitoring and diagnosis and associated crew interfaces. The effort began by determining the flight crew's information requirements for fault monitoring and diagnosis and the various reasoning strategies they use. Based on this information, a conceptual architecture was developed for the fault monitoring and diagnosis process. This architecture represents an approach and a framework which, once incorporated with the necessary detail and knowledge, can be a fully operational fault monitoring and diagnosis system, as well as providing the basis for comparison of this approach to other fault monitoring and diagnosis concepts. The architecture encompasses all aspects of the aircraft's operation, including navigation, guidance and controls, and subsystem status. The portion of the architecture that encompasses subsystem monitoring and diagnosis was implemented for an aircraft turbofan engine to explore and demonstrate the AI concepts involved. This paper describes the architecture and the implementation for the engine subsystem.
In 1986, the Ada programming language was chosen by NASA as the primary computer programming language for the development of new software for the Space Station. Ada was selected based on the results of investigations coordinated through Johnson Space Center (JSC). These investigations resulted in the identification of a set of problems and risks associated with using software developed in Ada onboard the Space Station. But the risks associated with these problems were found to be of insufficient severity to outweigh the significant benefits and suitability of Ada for the project. However, since the selection of Ada for the Space Station Project, detailed investigations have continued at Johnson Space Center into the most important problems identified in using Ada. This paper discusses some of the specific solutions to problems which have been identified through these investigations and which are reducing the risks of using Ada onboard the Space Station.
It was determined that an onboard vortex wake detection system using existing, proven instrumentation is technically feasible. This system might be incorporated into existing onboard systems such as a wind shear detection system, and might provide the pilot with the location of a vortex wake, as well as an evasive maneuver so that the landing separations may be reduced. It is suggested that this system might be introduced into our nation's commuter aircraft fleet and major air carrier fleet and permit a reduction of current landing separation standards, thereby reducing takeoff and departure delays.