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An investigation into the areas having an impact on producing reliable software including automated verification tools, software modeling, testing techniques, structured programming, and management techniques is presented. This final report contains the results of this investigation, analysis of each technique, and the definition of a methodology for producing reliable software.
The unique avionics design features of the Space Shuttle ascent flight control are described, along with the test article, test equipment, and test techniques used to verify the ascent flight control prior to commitment to the first orbital flight test. The ascent mission profiles are described, noting that upon ignition of the solid rocket boosters the Shuttle vehicle will rise vertically until achieving tower clearance. The Space Shuttle vehicle uses an integrated avionics system with the Orbiter avionics providing the command, control, and monitoring for the total mated Shuttle vehicle. The sensors and the actuator systems are discussed; the method of ascent flight control system verification is described, and it is concluded that the need for an advanced avionics integration and verification laboratory was recognized early in the program to provide maximum support to all program requirements.
Program documentation concerning the design, implementation, and verification of a computerized model for predicting the steady-state sinusoidal response of radial configured distribution feeders is presented in these appendices.
The various aspects of the conventional software development cycle are examined. This cycle was the basis of the augmented approach contained in the original grant proposal. This cycle was found inadequate for crucial software development, and the justification for this opinion is presented. Several possible enhancements to the conventional software cycle are discussed. Software fault tolerance, a possible enhancement of major importance, is discussed separately. Formal verification using mathematical proof is considered. Automatic programming is a radical alternative to the conventional cycle and is discussed. Recommendations for a comprehensive approach are presented, and various experiments which could be conducted in AIRLAB are described.
The wrap-rib deployable antenna concept development is based on a combination of hardware development and testing along with extensive supporting analysis. The proof-of-concept hardware models are large in size so they will address the same basic problems associated with the design fabrication, assembly and test as the full-scale systems which were selected to be 100 meters at the beginning of the program. The hardware evaluation program consists of functional performance tests, design verification tests and analytical model verification tests. Functional testing consists of kinematic deployment, mesh management and verification of mechanical packaging efficiencies. Design verification consists of rib contour precision measurement, rib cross-section variation evaluation, rib materials characterizations and manufacturing imperfections assessment. Analytical model verification and refinement include mesh stiffness measurement, rib static and dynamic testing, mass measurement, and rib cross-section characterization. This concept was considered for a number of potential applications that include mobile communications, VLBI, and aircraft surveillance. In fact, baseline system configurations were developed by JPL, using the appropriate wrap-rib antenna, for all three classes of applications.
The Tethered Satellite System has great prospects for extending orbital operations capability of the Space Transportation System to science, applications, and technology projects not otherwise attainable. The system will installed in the Shuttle Orbiter and will have the capability to deploy a captive satellite up to 100 km away from the Orbiter. Control and retrieval of the satellite are accomplished by means of a tether line connecting the satellite and the cargo bay mounted equipment in the Orbiter. At low satellite altitudes, the system will permit investigations of a duration that could not be pursued with sounding rockets of free-flying spacecraft. The propose of the Shuttle/Tethered Satellite System Definition Study was to produce the preliminary design, preliminary specifications, gross program plans, and program cost estimate for a 1982 operational verification flight. This was accomplished during a fifteen month effort under by the NASA George C. Marshall Space Flight Center (MSFC). The MSFC Phase 1 and related studies demonstrated the feasibility of the system and served as a starting point for the Phase 2 definition study.
At the beginning of the Get-Away Special (GAS) flight program, the GAS Project flew a Flight Verification Payload on STS-3 to make measurements of the vibrations, acoustic and magnetic environments of the canister, and to obtain thermal profiles of internal and external components of the GAS system. These data were used to verify pre-flight thermal models of the GAS system and results have been published in a GSFC Technical Note, X-732-83-8 (Butler, 1983). On somewhat later flights of the Orbiter, STS-7 and STS-8, the Naval Research Laboratory and the Goddard Space Flight Center jointly developed and flew a GAS payload whose primary objective was to evaluate the performance of ultraviolet-sensitive (Schumann) photographic emulsions in the Orbiter environment, including pre-flight integration, on-orbit exposure to the ambient environment of the Orbiter bay and post-flight conditions before removal of the experiment from the vehicle. These emulsions, used in spectrographs to record solar radiations with wavelengths between 100 A and 2000 A, have low gelatin content and no protective gelatin overcoating in order to maximize their UV sensitivity. Consequently, they are extremely sensitive to environmental conditions. Furthermore, they are exposed directly to space during the observations because any intervening protective window or lense would completely absorb the radiations to be studied. which was prepared at the Naval Research Laboratory under the direction of Robert Kreplin (Kreplin et al., 1984 a) also included two thermal sensors, whose output was recorded once an hour with a precision of 0.7O C. The experiment operated nominally on both missions and provided important data confirming that W - sensitive emulsions could tolerate integration and flight on the Shuttle with relatively little deterioration. The results of these studies have already been reported (Kreplin et al, 1984 b). The temperature measurements also were recorded successfully and are the basis for this paper. They are a useful complement to the thermal observations made on STS-3 and provide additional insight into the reaction of a payload to typical thermal environments that GAS experiments are subject to. Our GAS experiment and the circumstances of its flights were particularly useful in terms of modeling the thermal response of the GAS canister and our instrument. The Orbiter was held (except for interruptions for star tracker alignment, satellite deployments, etc., in specific attitudes for sufficiently long periods of time that the thermal response of the instrument to each attitude was well measured. Two types of GAS canister end cap, one, the insulated end cap and the other a silverized teflon covered end-cap, were used on the two flights so that a direct comparison of the thermal performance of the two types was obtained. This report is an attempt to compare these observations with a simple thermal model of the instrument in the GAS canister in order to assess whether such simple models can be useful to experimenters in predicting the thermal response of their payloads.
The philosophy of verification tests of the Ariane 5 launcher program is already established. It corresponds to the development and the ground and flight qualification phases for both unmanned and manned launches. The different types of test are outlined for the system, booster, main core and upper structures, allowing the identification of the associated test facilities which are described.
Preliminary design developed for validation experiment that addresses problems unique to assuring extremely high quality of multiple-version programs in process-control software. Approach takes into account inertia of controlled system in sense it takes more than one failure of control program to cause controlled system to fail. Verification procedure consists of two steps: experimentation (numerical simulation) and computation, with Markov model for each step.
The simulation of spacecraft attitude dynamics and control using the generic, multi-body code called TREETOPS and other codes written especially to simulate particular systems is discussed. Differences in the methods used to derive equations of motion--Kane's method for TREETOPS and the Lagrangian and Newton-Euler methods, respectively, for the other two codes--are considered. Simulation results from the TREETOPS code are compared with those from the other two codes for two example systems. One system is a chain of rigid bodies; the other consists of two rigid bodies attached to a flexible base body. Since the computer codes were developed independently, consistent results serve as a verification of the correctness of all the programs. Differences in the results are discussed. Results for the two-rigid-body, one-flexible-body system are useful also as information on multi-body, flexible, pointing payload dynamics.
Software is playing increasingly important roles in avionics systems. It is widely used in navigation and, in some cases, in control loops that maintain aircraft stability. To guarantee the safety of flight systems, the FAA requires that critical components have a probability of failure no greater than 10(exp -9) per hour of flight. Software is being used to diagnose system components for failure. SIFT (Software Implemented Fault Tolerance) was a computer system developed to study the use of software to check for failure and manage processor reconfiguration. To guarantee that software satisfies its specifications, formal verification can be used. With this a program and its specification are viewed as mathematical objects, and a mathematical proof is used to show that the program and its specification are equivalent. In previous research, a theory of checking was developed to offer assistance in analyzing specifications and designing run-time checks. In the theory, checking is considered abstractly in terms of n-ary relations much like those of relational database theory. Within the theory check are categorized, checks on input and checks on results are considered, and formal attention is given to the minimization and logical combination of checks. The focus is upon input checks and the obstacles in checking input to critical systems. A central concern is with a property referred to as independence. The concern is with circumstances under which it is possible to apply isolated, independent checks to separate sensor inputs and be assure that all illegal input will be properly detected. Presently, independence is being investigated and checked in the context of the GCS (Guidance and Control System). The GCS simulator is intended for testing software that implements control laws for landing spacecraft. The large number of inputs and their complex interrelationships provide an exciting context in which to investigate independence and the difficulties of supplying input checks.
Results to date on the application of two manufacturing techniques, fiber placement and single diaphragm/coconsolidation, to produce cost-effective, thermoplastic composite (TPC), primary fuselage structure are presented. Applications relative to fuselage upper cover structure indicate potential cost savings relative to conventional approaches. Progress is also presented on efforts concerned with other design details which take advantage of thermoplastic composites such as fastener less stiffener/frame attachments. In addition, results are presented on the development and verification testing of a composite lug analysis program which incorporates through-the-thickness effects.
This report describes the Applied Meteorology Unit's objective verification of the National Centers for Environmental Prediction 29-km eta model during separate warm and cool season periods from May 1996 through January 1998. The verification of surface and upper-air point forecasts was performed at three selected stations important for 45th Weather Squadron, Spaceflight Meteorology Group, and National Weather Service, Melbourne operational weather concerns. The statistical evaluation identified model biases that may result from inadequate parameterization of physical processes. Since model biases are relatively small compared to the random error component, most of the total model error results from day-to-day variability in the forecasts and/or observations. To some extent, these nonsystematic errors reflect the variability in point observations that sample spatial and temporal scales of atmospheric phenomena that cannot be resolved by the model. On average, Meso-Eta point forecasts provide useful guidance for predicting the evolution of the larger scale environment. A more substantial challenge facing model users in real time is the discrimination of nonsystematic errors that tend to inflate the total forecast error. It is important that model users maintain awareness of ongoing model changes. Such changes are likely to modify the basic error characteristics, particularly near the surface.
The process of verification, or determining the order of accuracy of computational codes, can be problematic when working with large, legacy computational methods that have been used extensively in industry or government. Verification does not ensure that the computer program is producing a physically correct solution, it ensures merely that the observed order of accuracy of solutions are the same as the theoretical order of accuracy. The Method of Manufactured Solutions (MMS) is one of several ways for determining the order of accuracy. MMS is used to verify a series of computer codes progressing in sophistication from "textbook" to "real life" applications. The degree of numerical precision in the computations considerably influenced the range of mesh density to achieve the theoretical order of accuracy even for 1-D problems. The choice of manufactured solutions and mesh form shifted the observed order in specific areas but not in general. Solution residual (iterative) convergence was not always achieved for 2-D Euler manufactured solutions. L(sub 2,norm) convergence differed variable to variable therefore an observed order of accuracy could not be determined conclusively in all cases, the cause of which is currently under investigation.
The NASA Engineering and Safety Center was requested to improve on the Best Practices document produced for the NESC assessment, Verification of Probabilistic Requirements for the Constellation Program, by giving a recommended procedure for using acceptance sampling by variables techniques. This recommended procedure would be used as an alternative to the potentially resource-intensive acceptance sampling by attributes method given in the document. This document contains the outcome of the assessment.
The NASA Engineering and Safety Center was requested to improve on the Best Practices document produced for the NESC assessment, Verification of Probabilistic Requirements for the Constellation Program, by giving a recommended procedure for using acceptance sampling by variables techniques as an alternative to the potentially resource-intensive acceptance sampling by attributes method given in the document. In this paper, the results of empirical tests intended to assess the accuracy of acceptance sampling plan calculators implemented for six variable distributions are presented.
NASA Glenn Research Center (GRC) is currently leading the development of multiple electric propulsion systems to flight readiness. The Advanced Electric Propulsion System is a 12.5 kW Hall thruster system that is being developed by the Solar Electric Propulsion Technology Demonstration Mission (SEP TDM) project, under the sponsorship of the Space Technology Mission Directorate. NASA's Evolutionary Xenon Thruster-Commercial (NEXT-C) is 7 kW class gridded ion thruster system that being developed under the sponsorship of the Science Mission Directorate. NASA GRC is also providing electric propulsion discipline support to the Power and Propulsion Element and the Double Asteroid Redirection Test (DART) missions, which will be the first applications for these technologies, respectively. Lower technology readiness level (TRL) projects are underway for applications including CubeSats, small spacecraft and Mars exploration vehicles. Under the sponsorship of the Small Spacecraft Technology Program, NASA GRC has performed numerous independent verification and validation tests of CubeSat class electric propulsion systems in support of a growing number of small US businesses that are developing these systems. Lastly, three technology development efforts focused on 100 kW EP strings led by Aerojet Rocketdyne, Ad Astra and MSNW were recently completed.
The NASA Engineering and Safety Center (NESC) has performed independent model development to support cross-model verification for the Space Launch System (SLS) Program since 2012 which culminated, for Artemis I, in a postflight reconciliation analysis of the Artemis I ascent trajectory (validation). This post-flight analysis was completed by both the NESC and the SLS Program. Upon successful completion of the Artemis I mission, multiple preflight simulations of the nominal ascent trajectory were updated with Day of Launch (DOL) conditions and simulated results were compared to reconstructed flight data derived from telemetry measurements. Dispersed trajectories were also produced using a combination of DOL conditions and preflight uncertainties, which ideally should bound the Artemis I flight data. Finally, multibody dynamics were simulated for some of the separation events to support clearance analyses. This paper focuses on validating and understanding the accuracy of the models by comparing simulated results against the Artemis I flight data. In addition, discrepancies uncovered between simulations led to opportunities to investigate areas for potential model improvement to refine preflight simulations for future Artemis missions. Included in this paper is background on the flight performance simulation tools, the postflight analysis approach, and a comparison of simulation results against the Artemis I flight data. Simulated results were found to generally be in close agreement with each other and the Artemis I flight data.