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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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The paper deals with magnetic model suspension and balance systems for wind tunnel use. Particular attention is given to the extension of the electromagnetic position sensor (EPS) system producing roll position signals and the ac roll drive system producing closed loop control of rolling moment.
A tethered satellite system was conceived as a device to extend the capability of the Space Shuttle to perform scientific/applications investigations and operational activities. The concept envisions a multiple-use tethered system with closed-loop control, capable of supporting a payload or satellite suspended from the Shuttle cargo bay, toward or away from the Earth, at distances up to 100 kilometers from the Shuttle. The background and results of early analyses and feasibility studies are discussed and a design and operational description of the system are presented. Also presented are a discussion of potential applications of the Tethered Satellite System, and plans for an operational verification flight in 1982.
Ways in which autonomous behavior of spacecraft can be extended to treat situations wherein a closed loop control by a human may not be appropriate or even possible are explored. Predictive models that minimize mean least squared error and arbitrary cost functions are discussed. A methodology for extracting cyclic components for an arbitrary environment with respect to usual and arbitrary criteria is developed. An approach to prediction and control based on evolutionary programming is outlined. A computer program capable of predicting time series is presented. A design of a control system for a robotic dense with partially unknown physical properties is presented.
A U.S. Air Force technology spacecraft flight is scheduled to carry an Ion Auxiliary Propulsion System (IAPS) as part of its experimental payload. This paper presents the results of the successful flight-software qualification and system-level tests which were performed on IAPS. The software tests were performed with an operating engineering model ion thruster and power processing unit, and failure/off-normal recovery modes, operation with and without temperature telemetry from the thruster vaporizers, and with closed-loop control or fixed setpoint operation of the thruster vaporizers. The system-level tests cover a wide range of thermal and operating conditions with the entire system exposed to a simulated space environment.
The Skyhook concept is reviewed and the use of a tethered satellite system (TSS) to enable scientific investigations from the shuttle using a closed loop control system is examined. The tethered satellite system has capabilities for deployment toward or away from Earth, for multiple round trip missions, and for deployment at distances up to 100 KN from the orbiter. The deployer, which consists of an entendable boom, a reel for the tether, and the tether itself, permits deployment and retrieval at a safe distance, allows alignment of the force vector of the tether through the center of gravity of the shuttle, and gives some initial gravity gradient separation to aid in deployment and ultimate retrieval of the tethered satellite. Charts show TSS activities in terms of systems studies, key guidelines, Italian and U.S. responsibilities, user activities, and major science and applications accommodation features. Scientific objectives for TSS-1 and TSS-2 verification missions and the current status of the project are also given.
Reusable rocket engines such as the Space Shuttle Main Engines (SSME), the Orbital Transfer Vehicles (OTV), etc., have throttling capabilities that require real-time, closed-loop control systems of engine propellant flows, combustion temperatures and pressures, and turbopump rotary speeds. In the case of the SSME, there are four turbopumps that require real-time measurement and control of their rotary speeds. Variable-reluctance magnetic speed sensors were designed, fabricated, and tested for all four turbopumps, resulting in the successful implementation and operation of three of these speed sensors during each of the 12 Shuttle flights.
Remote displacement measurement is demonstrated using a Fabry-Perot cavity with a multimode optical fiber link. The sensing cavity modulates, as a function of its length, the spectrum of a light-emitting diode (LED). The light returns via the fiber and is analyzed by a tunable reference cavity. A closed-loop control causes the reference cavity to track the sensing cavity length within 2 x 10 to the -12th m. Displacement range is 2 x 10 to the -6th m. The reference cavity length is measured interferometrically, using a laser, to obtain the sensing cavity length. Advantages of this sensing technique include compatibility with multimode fiber-optic components, high immunity to optical losses, and large dynamic range.
NASA Marshall Space Flight Center has developed a facility in which closed loop control of Large Space Structures (LSS) can be demonstrated and verified. The main objective of the facility is to verify LSS control system techniques so that on-orbit performance can be ensured. The facility consists of an LSS test article or payload which is connected to a 3-axis angular pointing mount assembly that provides control torque commands. The angular pointing mount assembly is attached to a base excitation system which will simulate disturbances most likely to occur for Orbiter and DOD payloads. The control computer contains the calibration software, the reference systems, the alignment procedures, the telemetry software, and the control algorithms. The total system is suspended in such a fashion that the LSS test article has the characteristics common to all LSS.
An improved method is developed for eigenvalues and eigenvectors placement of a closed-loop control system using either state or output feedback. The method basically consists of three steps. First, the singular value of QR decomposition is used to generate an orthonormal basis that spans admissible eigenvector space corresponding to each assigned eigenvalue. Secondly, given a unitary matrix, the eigenvector set which best approximates the given matrix in the least-square sense and still satisfy eigenvalue cosntraints is determined. Thirdly, a unitary matrix is sought to minimize the error between the unitary matrix and the assignable eigenvector matrix. For use as the desired eigenvector set, two matrices, namely, the open-loop eigenvector matrix and its closest unitary matrix are proposed. The latter matrix generally encourages both minimum conditioning and control gains. In addition, the algorithm is formulated in real arithmetic for efficient implementation. To illustrate the basic concepts, numerical examples are included.
A real-time digital simulator of a Pratt and Whitney F 100 engine is discussed. This self-contained unit can operate in an open-loop stand-alone mode or as part of a closed-loop control system. It can also be used in control system design and development. It accepts five analog control inputs and its sixteen outputs are returned as analog signals.
Based upon the modified finite element-transfer matrix method, this paper presents a technique for reduced modeling of flexible structures for decentralized control. The modeling decisions are carried out at (finite-) element level, and are dictated by control objectives. A simply supported beam with two sets of actuators and sensors (linear force actuator and linear position and velocity sensors) is considered for illustration. In this case, it is conjectured that the decentrally controlled closed loop system is guaranteed to be at least marginally stable.
The potential importance of space telemanipulator systems is reviewed, along with past studies of master-slave manipulation using a generalized force reflecting master arm. Problems concerning their dynamic interaction with the human operator have been revealed in the use of these systems, with marked differences between 1-g and simulated weightless conditions. A study is outlined to investigate the optimization of the man machine dynamics of master-slave manipulation, and a set of specifications is determined for the apparatus necessary to perform this investigation. This apparatus is a one degree of freedom force reflecting hand controller with closed loop servo control which enables it to simulate arbitrary dynamic properties to high bandwidth. Design of the complete system and its performance is discussed. Finally, the experimental adjustment of the hand controller dynamics for smooth manual control performance with good operator force perception is described, resulting in low inertia, viscously damped hand controller dynamics.
This paper traces the development of Magnetic Suspension and Balance Systems (MSBSs) for use in wind tunnels. The expression MSBS implies a system that can both suspend a model and also measure the forces and moments acting on the model. This avoids the need for any mechanical support of the model. An MSBS uses electromagnets located outside the test section walls to create magnetic fields inside the test section. Measurement of the electrical current flowing in each of the electromagnets can be used to determine the forces and moments acting on the suspended model. An MSBS is capable of supporting a model with an internal magnetized core subject to gravity, aerodynamic, and inertial loads. The model must have a core made of either a permanent magnet, magnetized soft iron, or a solenoid. The position of the suspended body is inherently unstable. A closed-loop control system which includes a position sensing system has to control the position of the body by controlling the applied magnetic fields. This paper includes a discussion of all the known MSBSs and the outlook for larger systems.
Skin-friction balance (flight balance) for use in flight on aircraft fuselage incorporates type-one, closed-loop control to make direct skin-friction force measurements. Curved surface element 2 in. (5.08 cm) in diameter used to sense tangential force of airstream passed over it. Linear electromagnetic force motor exerts restoring force that nulls position of sensing element. Applied skin-friction force measured by sensing amount of current through motor necessary to maintain null position. Unit is rugged, accurate, reliable, and easy to operate. Insensitivity of balance to background rectilinear vibrations and ability to sustain large transient loads during takeoffs and landings make it attractive for flight testing.
A real-time digital simulator of a Pratt and Whitney F100 engine has been developed for real-time code verification and for actuator diagnosis during full-scale engine testing. This self-contained unit can operate in an open-loop stand-alone mode or as part of closed-loop control system. It can also be used for control system design and development. Tests conducted in conjunction with the NASA Advanced Detection, Isolation, and Accommodation program show that the simulator is a valuable tool for real-time code verification and as a real-time actuator simulator for actuator fault diagnosis. Although currently a small perturbation model, advances in microprocessor hardware should allow the simulator to evolve into a real-time, full-envelope, full engine simulation.
The design, operation, and performance of a wide-dynamic-range optical-quality actuator are discussed. The actuator uses a closed-loop control system to maintain accurate positioning and has an rms noise performance of 20 nm. A unique force offloading mechanism allows the actuator coil to dissipate less than 3 mW under quiescent conditions. The operation of an experimental segmented optical system that uses 18 of the actuators is examined to show how they are integrated into an actual system.
Over the past several years, there has been an increased awareness in the necessity for rocket engine health monitoring because of the cost and complexity of present and future systems. A current rocket engine system, the Space Shuttle Main Engine (SSME), combines a limited redline system with closed-loop control of the engine's thrust level and mixture ratio. Despite these features, 27 tests of the SSME have resulted in major incidents. A SSME transient model was used to examine the effect of variations in high pressure turbopump performance on various engine parameters. Based on analysis of the responses, several new parameters are proposed for further investigation as power-level specific redlines.
Over the past several years, there has been an increased awareness in the necessity for rocket engine health monitoring because of the cost and complexity of present and future systems. A current rocket engine system, the Space Shuttle Main Engine (SSME), combines a limited redline system with closed-loop control of the engine's thrust level and mixture ratio. Despite these features, 27 tests of the SSME have resulted in major incidents. An SSME transient model was used to examine the effect of variations in high pressure turbopump performance on various engine parameters. Based on analysis of the responses, several new parameters are proposed for further investigation as power-level specific redlines.