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At least 181 records · Page 10

Operational complexities of real tether systems in space

Some of the major operational concerns that have to be addressed in planning a real tether mission, such as the TTS-1 mission, which is due to fly on the Space Shuttle in the early 1990's, are discussed. Specifically, several operational hazards, such as the tether reel overtorque and the loss of tether system control, are considered from the viewpoint of flight crew, who must be able to detect the presence of a problem and to determine the corrective action to be taken. Various safety measures are discussed.

Hoffman, Jeffrey A.↗

Transportation monitoring unit qualification

Transportation monitoring unit (TMU) qualification testing was performed between 3 Mar. and 14 Dec. 1989. The purpose of the testing was to qualify the TMUs to monitor and store temperature and acceleration data on redesigned solid rocket motor segments and exit cones while they are being shipped from Utah's Thiokol Corporation, Space Operations, to Kennedy Space Center. TMUs were subjected to transportation tests that concerned the structural integrity of the TMUs only, and did not involve TMU measuring capability. This testing was terminated prior to completion due to mounting plate failures, high and low temperature shutdown failures, and data collection errors. Corrective actions taken by the vendor to eliminate high temperature shutdowns were ineffective. An evaluation was performed on the TMUs to determine the TMU vibration and temperature measuring accuracy at a variety of temperatures. This test demonstrated that TMU measured shock levels are high, and that TMUs are temperature sensitive because of decreased accuracy at high and low temperatures. It was determined that modifications to the current TMU system, such that it could be qualified for use, would require a complete redesign and remanufacture. Because the cost of redesigning and remanufacturing the present TMU system exceeds the cost of procuring a new system that could be qualified without modification, it is recommended that an alternate transportation monitoring system be qualified.

Cook, M.↗

StarPlan: A model-based diagnostic system for spacecraft

The Sunnyvale Division of Ford Aerospace created a model-based reasoning capability for diagnosing faults in space systems. The approach employs reasoning about a model of the domain (as it is designed to operate) to explain differences between expected and actual telemetry; i.e., to identify the root cause of the discrepancy (at an appropriate level of detail) and determine necessary corrective action. A development environment, named Paragon, was implemented to support both model-building and reasoning. The major benefit of the model-based approach is the capability for the intelligent system to handle faults that were not anticipated by a human expert. The feasibility of this approach for diagnosing problems in a spacecraft was demonstrated in a prototype system, named StarPlan. Reasoning modules within StarPlan detect anomalous telemetry, establish goals for returning the telemetry to nominal values, and create a command plan for attaining the goals. Before commands are implemented, their effects are simulated to assure convergence toward the goal. After the commands are issued, the telemetry is monitored to assure that the plan is successful. These features of StarPlan, along with associated concerns, issues and future directions, are discussed.

Heher, Dennis↗

A procedure concept for local reflex control of grasping

An architecture is proposed for the control of robotic devices, and in particular of anthropomorphic hands, characterized by a hierarchical structure in which every level of the architecture contains data and control function with varying degree of abstraction. Bottom levels of the hierarchy interface directly with sensors and actuators, and process raw data and motor commands. Higher levels perform more symbolic types of tasks, such as application of boolean rules and general planning operations. Layers implementation has to be consistent with the type of operation and its requirements for real time control. It is proposed to implement the rule level with a Boolean Artificial Neural Network characterized by a response time sufficient for producing reflex corrective action at the actuator level.

Fiorini, Paolo↗

Autonomous organization of grasping tasks

This paper describes an architecture for the control of robotic devices, and in particular of anthropomorphic hands, characterized by a hierarchical structure in which every level of the architecture contains data and control function with varying degree of abstraction. Bottom levels of the hierarchy interface directly with sensors and actuators, and process raw data and motor commands. Higher levels perform more symbolic types of tasks, such as application of Boolean rules and general planning operations. The implementation of the layer has to be consistent with the type of operation and its requirements for real time control. One implementation of the rule level, with a Boolean artificial neural network which would have a response time sufficient for producing reflex corrective action at the actuator level is presented.

Fiorini, Paolo↗

Artificial intelligence techniques for ground test monitoring of rocket engines

An expert system is being developed which can detect anomalies in Space Shuttle Main Engine (SSME) sensor data significantly earlier than the redline algorithm currently in use. The training of such an expert system focuses on two approaches which are based on low frequency and high frequency analyses of sensor data. Both approaches are being tested on data from SSME tests and their results compared with the findings of NASA and Rocketdyne experts. Prototype implementations have detected the presence of anomalies earlier than the redline algorithms that are in use currently. It therefore appears that these approaches have the potential of detecting anomalies early eneough to shut down the engine or take other corrective action before severe damage to the engine occurs.

Ali, Moonis↗

First incremental buy for Increment 2 of the Space Transportation System (STS)

Thiokol manufactured and delivered 9 flight motors to KSC on schedule. All test flights were successful. All spent SRMs were recovered. Design, development, manufacture, and delivery of required transportation, handling, and checkout equipment to MSFC and to KSC were completed on schedule. All items of data required by DPD 400 were prepared and delivered as directed. In the system requirements and analysis area, the point of departure from Buy 1 to the operational phase was developed in significant detail with a complete set of transition documentation available. The documentation prepared during the Buy 1 program was maintained and updated where required. The following flight support activities should be continued through other production programs: as-built materials usage tracking on all flight hardware; mass properties reporting for all flight hardware until sample size is large enough to verify that the weight limit requirements were met; ballistic predictions and postflight performance assessments for all production flights; and recovered SRM hardware inspection and anomaly identification. In the safety, reliability, and quality assurance area, activities accomplished were assurance oriented in nature and specifically formulated to prevent problems and hardware failures. The flight program to date has adequately demonstrated the success of this assurance approach. The attention focused on details of design, analysis, manufacture, and inspection to assure the production of high-quality hardware has resulted in the absence of flight failures. The few anomalies which did occur were evaluated, design or manufacturing changes incorporated, and corrective actions taken to preclude recurrence.

Source record↗

Flight Set 360L006 STS-34 field joint protection system, thermal protection system, and systems tunnel components, volume 4

The performance of the thermal protection system, field joint protection system, and systems tunnel components of Flight Set 360L006, are documented, as evaluated by postflight hardware inspection. The condition of both motors was similar to previous flights. Sixteen aft edge hits were noted on the ground environment instrumentation thermal protection system. Each hit left a clean substrate, indicating that the damage was caused by nozzle severance debris and/or water impact. No National Space and Transporation System debris criteria for missing thermal protection system were violated. One 5.0 by 1.0 in. unbond was observed on the left hand center field joint K5NA closeout and was elevated to an in-flight anomaly (STS-34-M-4) by the NASA Ice/Debris team. Aft edge damage to the K5NA and an associated black streak indicate that burning debris from the nozzle severance system was the likely cause of the damage. Minor divots caused by debris were seen on previous flights, but this is the first occurrence of a K5NA unbond. Since the unbond occurred after booster separation there is no impact on flight safety and no corrective actions was taken. The right hand center field joint primary heater failed the dielectric withstanding voltage test after joint closeout. The heater was then disabled by opening the circuit breaker, and the redundant heater was used. The redundant heater performed nominally during the launch countdown. A similar condition occurred on Flight 4 when a secondary joint heater failed the dielectric withstanding voltage test.

Wilkinson, J. P.↗

Some aspects of robotics calibration, design and control

The main objective is to introduce techniques in the areas of testing and calibration, design, and control of robotic systems. A statistical technique is described that analyzes a robot's performance and provides quantitative three-dimensional evaluation of its repeatability, accuracy, and linearity. Based on this analysis, a corrective action should be taken to compensate for any existing errors and enhance the robot's overall accuracy and performance. A comparison between robotics simulation software packages that were commercially available (SILMA, IGRIP) and that of Kennedy Space Center (ROBSIM) is also included. These computer codes simulate the kinematics and dynamics patterns of various robot arm geometries to help the design engineer in sizing and building the robot manipulator and control system. A brief discussion on an adaptive control algorithm is provided.

Tawfik, Hazem↗

The automatic human

An overview is presented of the growth and role of automation in civil aircraft operations for both cockpit management and ground control. NASA has initiated a research program centered on furthering automation and developing a consistent and rational philosophy of human centered aircraft and air traffic control automation. Introduction of the NASA Aviation Safety Reporting System (ASRS) has proved successful in bringing together pilots and ground controllers to report incidents of operational anomalies that can then be analyzed, leading to corrective action to prevent similar reoccurrences. Attention is given to the growing trend of extensive automation in the cockpit that appears to be leading to a diminution of management control of the aircraft by the decreasing number of flight crew members. A majority of reports indicate that there is a serious mismatch between new aircraft capabilities and ATC procedures, which were designed for older aircraft. ASRS has also kept research oriented toward real problems and community needs.

Billings, Charles↗

Five basic steps to problem trending

Five basic steps to problem trending evolved from experience in trending problems on Space Shuttle hardware are discussed: extracting data; constructing a Pareto chart of all failure modes; constructing normalized subsystem, component, and failure-mode trend charts; identifying trend direction; and providing a summary assessment. The five-step method has been useful for identifying failure modes of concern, evaluating the effectiveness of corrective actions, and determining funding allocation.

Bombara, Elwood L.↗

Investigative techniques used to locate the liquid hydrogen leakage on the Space Shuttle Main Propulsion System

Standard leak detection methods at ambient temperature have been developed in order to prevent excessive leakage from the Space Shuttle liquid oxygen and liquid hydrogen Main Propulsion System. Unacceptable hydrogen leakage was encountered on the Columbia and Atlantis flight vehicles in the summer of 1990 after the standard leak check requirements had been satisfied. The leakage was only detectable when the fuel system was exposed to subcooled liquid hydrogen during External Tank loading operations. Special instrumentation and analytical tools were utilized during a series of propellant tanking tests in order to identify the sources of the hydrogen leakage. After the leaks were located and corrected, the physical characteristics of the leak sources were analyzed in an effort to understand how the discrepancies were introduced and why the leakage had evaded the standard leak detection methods. As a result of the post-leak analysis, corrective actions and leak detection improvements have been implemented in order to preclude a similar incident.

Hammock, William R., Jr.↗

Optical Detection Of Ice On A Helicopter Rotor

Ice forming on helicopter rotor blades under adverse weather conditions detected via effect on polarization of reflected light, according to proposal. Ice-detection system based on this principal alerts helicopter pilot to need for corrective action, and/or turns on deicing equipment automatically.

Cornwell, Donald M., Jr.↗

Mission safety evaluation report for STS-39, postflight edition

After a delay of approximately 2 months due to a rollback from the pad to replace the External Tank door lug housing, Space Shuttle Discovery was launched from NASA-Kennedy at 7:33 a.m. Eastern Daylight Time on 28 April 1991. STS-39 was the first unclassified DoD Shuttle mission. On 28 April, countdown proceeded normally through the T-20 minute hold. No significant problems were encountered except for the Operations Sequence-2 recorder starting unexpectedly; it was stopped by an uplink command. Discovery landed on KSC runway 15 at 2:55 p.m. EDT on 6 May 1991. This was the second time in 6 months that the Space Shuttle was diverted to KSC for landing because of high winds at Edwards AFB, Calif. This was also the 7th of 40 Shuttle missions to land at KSC in the history of the Space Shuttle Program. The Main Landing Gear outer right tire shredded 3 of the 16 cords due to either an uneven landing or a maximum force breaking test during rollout. Contributing factors to the tire cord shredding were the development of last minute crosswinds and reluctance of the ground controllers to distract the Shuttle pilots with warnings of the low flight path. As a corrective action, communication procedures will be modified for future flights.

Hardie, Kenneth O.↗

The Spaceguard Survey - Protecting the earth from cosmic impacts

The conclusions of the NASA International Near-Earth-Object Detection Workshop (May 1991-January 1992) are summarized. Near-earth asteroids and short-period comets constitute about 90 percent of potential earth-impacting projectiles. The greatest risk is from those with diameters greater than 1 km. The objective of a near-earth object survey is to find such objects, calculate their long-term orbital trajectories, and identify any that may impact the earth over the next several centuries. There will generally be a period of at least several decades to take corrective action if any potential earth-impactors are found. A region of space extending outward from the earth to approximately the inner edge of the main asteroid belt must be monitored. Detection can be by reflected sunlight or infrared. Though faint, the objects should be readily detectable with ground-based telescopes, and thus there is no need for a more expensive space-based system.

Morrison, David↗

Galileo completing VEEGA - A mid-term report

In December Galileo will complete its Venus-Earth-Earth-Gravity Assist (VEEGA) mission phase and will be placed on a direct trajectory to Jupiter arriving in December 1995. Galileo will be the first aircraft to orbit Jupiter and send a probe into its atmosphere and will perform an intensive and comprehensive investigation of the planet. Observations made during the October 1991 encounter with the asteroid Gaspra are discussed. The observation plan to be used for earth and moon observations during the December 1992 gravity assist encounter is described. The Galileo High-Gain Antenna (HGA) deployment anomaly status is reported and future corrective actions are outlined. The low-gain antenna contingency mission to be implemented if the HGA cannot be deployed is described and overall performance and status of the space craft are discussed. The selected tour for the Galileo Jupiter satellite-gravity-assist orbital tour is described and the decision rationale for performing the August 1993 asteroid Ida flyby option is presented.

O'Neil, William J.↗

Systems engineering process and organization assessment

The purpose of this report is to briefly summarize the results of an eight week assessment of NASA/MSFC Phase A and Phase B systems engineering processes, methodologies, and activities. Specifically, fourteen inconsistencies or weaknesses were identified and recommendations for corrective action were generated. A 1.5 hour briefing on these results was given in EL51 on 8-11-92; that documentation is available from the author or either NASA Colleague.

Batson, Robert G.↗

A second generation expert system for checking and diagnosing AXAF's electric power system

AXAF - Advanced X-ray Astrophysics Facility - is a third NASA's great space observatory. Each of these observatories is intended to cover different parts of the electromagnetic spectrum (x-ray for AXAF) and to provide high resolution images of celestial sources in our universe. While the spacecraft is in orbit, the electric power system (EPS) performance is monitored via sensors measuring voltages, currents, pressures, and temperatures. The sensor data are sent from the spacecraft to the ground station as telemetry and analyzed on arrival. Monitoring, diagnosis and maintenance of such EPS is an arduous task which requires expertise and constant attention of the ground personnel. To help the ground crew in this task, much of it should be automated and delegated to expert systems, which draw engineer's attention to possible malfunctions and allows him to review the telemetry to determine the source of the trouble, diagnose the suspected fault and to propose a corrective action. Those systems are built on assumptions such as: (1) domain knowledge is available and can be represented as a set of rules; (2) domain knowledge is circumscribed, static, and monotonic; and (3) expert decision making can be emulated by a logical inference mechanism.

Bykat, Alex↗