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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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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

High-Precision Temperature Control of a Crystal Growth Furnace at 1,500 C

For crystal growth of semiconductor materials a short-term temperature stability of 0.1 C at 1500 C is one of the essential parameters to be addressed for achieving high-quality crystals. Hence, for temperature monitoring and control with high precision in a floating zone furnace two sets of thermo-sensors, type B thermocouples and optical fibre thermometers, have been implemented and successfully operated in the furnace for more than 2000 h. The optical fibre thermometers consist of an optical system made of sapphire (two fibres plus a prism in between for deflection) and transmit the infra-red radiation of the heater to the outside of the hot core of the furnace for pyrometric temperature measurement. A dedicated control algorithm has been set up which controlled the power settings to the individual heaters. Both sensor types showed no degradation after this period and yielded a short-term stability at 1200 C of 0.05 C (optical fibre thermometers), respectively 0.08 C (thermocouples).

Stenzel, Ch.↗
NASA NTRS1992

Dynamics and control of high precision magnetically levitated vibration isolation systems

Vibration control of flexible structures has received a great deal of interest in recent years. Several authors have investigated this topic in the areas of robot manipulators, space structures, and flexible rotors. Key issues associated with the dynamics and control of vibration isolation systems are addressed. Among other important issues to consider in the control of such systems, the location and number of actuators and sensors are essential to effectively control and suppress vibration. We first address the selection of proper actuator and sensor locations leading to a controllable and observable system. The Rayleigh-Ritz modal analysis method is used to develop a lumped-parameter model of a flexible vibration isolation table top. This model is then used to investigate the system's controllability and observability including the coupling effects introduced by the magnetic bearing. This analysis results in necessary and sufficient conditions for proper selection of actuator and sensor locations. These locations are also important for both controller system's complexity and stability of point of views. A favorable pole-zero plot of the open loop transfer functions is presented. Necessary and sufficient conditions for reducing the controller complexity are derived. The results are illustrated by examples using approximate mode shape functions.

Youcef-Toumi, K.↗
NASA NTRS2010

High-Precision Shape Control of In-Space Deployable Large Membrane/Thin-Shell Reflectors

This innovation has been developed to improve the resolutions of future spacebased active and passive microwave antennas for earth-science remote sensing missions by maintaining surface figure precisions of large membrane/thin-shell reflectors during orbiting. The intention is for these sensing instruments to be deployable at orbit altitudes one or two orders of magnitude higher than Low Earth Orbit (LEO), but still being able to acquire measurements at spatial resolution and sensitivity similar to those of LEO. Because active and passive microwave remote sensors are able to penetrate through clouds to acquire vertical profile measurements of geophysical parameters, it is desirable to elevate them to the higher orbits to obtain orbital geometries that offer large spatial coverage and more frequent observations. This capability is essential for monitoring and for detailed understanding of the life cycles of natural hazards, such as hurricanes, tropical storms, flash floods, and tsunamis. Major components of this high-precision antenna-surface-control system include a membrane/thin shell reflector, a metrology sensor, a controller, actuators, and corresponding power amplifier and signal conditioning electronics (see figure). Actuators are attached to the back of the reflector to produce contraction/ expansion forces to adjust the shape of the thin-material reflector. The wavefront-sensing metrology system continuously measures the surface figure of the reflector, converts the surface figure to digital data and feeds the data to the controller. The controller determines the control parameters and generates commands to the actuator system. The flexible, piezoelectric polymer actuators are thus activated, providing the control forces needed to correct any distortions that exist in the reflector surface. Piezoelectric polymer actuators are very thin and flexible. They can be implemented on the back of the membrane/thin-shell reflector without introducing significant amounts of mass or stiffness to the reflector. They can be rolled up or folded to accommodate the packaging needed for launch. An analytical model of the system, which includes the membrane reflector, actuator, and controller has been developed to investigate the functionality of this control system on a 35-meter-diameter membrane reflector. The performance of this system under external disturbances such as in space thermal loads and W-error due to inflation has been investigated. A subscale breadboard has been developed, and the functionality of this control concept has been demonstrated by this breadboard.

Watkins, Ronald↗
NASA NTRS1981

Frequency and time generation and control

High precision quartz crystal oscillators, cesium beam atomic resonators, and cesium beam atomic standards for time and frequency generation equipment for ground, airborne, and space use are described. Because of the high risk factors involved, and the commercial applications of these products being too far off in the future, private capital for research and development is difficult if not impossible to obtain. More specific analysis and recommendations to overcome these difficulties are objectively presented.

Bloch, M.↗
NASA NTRS2003

ST7-DRS: A Step Towards Drag-free and High-precision Formation Control

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is an in-space technology demonstration within NASA's New Millennium Program. ST7-DRS is designed to validate system-level technologies that are required for future gravity missions (including the planned LISA gravitational-wave observatory) and for future formation-flying interferometer missions (including the planned MAXIM black-hole imager). ST7-DRS is based around a freely-floating test mass contained within a spacecraft structure that will shield this test mass from all external forces (aside from gravity). The spacecraft position will be continuously controlled, such that the spacecraft, itself, will remain centered about this test mass, essentially flying in formation with it. Colloidal micro-thrusters will be used to control the spacecraft s position to within a few nanometers, over time scales of tens to thousands of seconds. In order to detect the residual acceleration noise on the main test mass, a second test mass will be flown alongside the first, within the same physical spacecraft structure. This test mass will serve as a cross-reference for the first, and will also be used as a reference for the spacecraft's attitude control. The spacecraft's attitude will be controlled to an accuracy of a few milli-arc-seconds, also utilizing the colloidal micro-thrusters. ST7-DRS will consist of an instrument package (containing the test masses) and a set of micro-thrusters, which will be attached to the European Space Agency s SMART-2 spacecraft, set to launch in November 2007.

Houghton, M.↗
NASA NTRS2000

Enabling Spacecraft Formation Flying through Position Determination, Control and Enhanced Automation Technologies

Formation Flying is revolutionizing the way the space community conducts science missions around the Earth and in deep space. This technological revolution will provide new, innovative ways for the community to gather scientific information, share that information between space vehicles and the ground, and expedite the human exploration of space. Once fully matured, formation flying will result in numerous sciencecraft acting as virtual platforms and sensor webs, gathering significantly more and better science data than call be collected today. To achieve this goal, key technologies must be developed including those that address the following basic questions posed by the spacecraft: Where am I? Where is the rest of the fleet? Where do I need to be? What do I have to do (and what am I able to do) to get there? The answers to these questions and the means to implement those answers will depend oil the specific mission needs and formation configuration. However, certain critical technologies are common to most formations. These technologies include high-precision position and relative-position knowledge including Global Positioning System (GPS) mid celestial navigation; high degrees of spacecraft autonomy inter-spacecraft communication capabilities; targeting and control including distributed control algorithms, and high precision control thrusters and actuators. This paper provides an overview of a selection of the current activities NASA/DoD/Industry/Academia are working to develop Formation Flying technologies as quickly as possible, the hurdles that need to be overcome to achieve our formation flying vision, and the team's approach to transfer this technology to space. It will also describe several of the formation flying testbeds, such as Orion and University Nanosatellites, that are being developed to demonstrate and validate many of these innovative sensing and formation control technologies.

Bristow, John↗
NASA NTRS1985

The Galileo attitude and articulation control system - A radiation-hard, high precision, state-of-the-art control system

The Galileo mission and spacecraft, consisting of a Jupiter-orbiter and an atmospheric entry probe, are discussed. Components will include: magnetometers and plasma-wave antennas on a boom, high-gain antenna, probe vehicle, two different bus electronics packages, and a radioisotope thermoelectric generator. Instruments, investigators and objectives are tabulated for both probe science and orbiter science investigations. Requirements in the design of the attitude and articulation control system are very stringent because of the complex dynamics, flexible body effects, the need for autonomy, and the severe radiation environment in the Jupiter nighborhood. Galileo was intended to be ready for launch via Space Shuttle in May of 1986.

Stephenson, R. Rhoads↗
NASA NTRS1984

High precision active nutation control for a flexible momentum biased spacecraft

The controller design for the Solar Dynamics Observatory (SDO) is presented. SDO is a momentum biased spacecraft with three flexible appendages. Its primary scientific instrument, the solar oscillations imager (SOI), is rigidly attached to the spacecraft bus and has arc-second pointing requirements. Meeting these requirements necessitates the use of an active nutation controller (ANC) which is here mechanized with a small reaction wheel oriented along a bus transverse axis. The ANC does its job by orchestrating the transfer of angular momentum out of the bus transverse axes and into the momentum wheel. A simulation study verifies that the controller provides quick, stable, and accurate response.

Laskin, R. A.↗
NASA NTRS1986

The Galileo Attitude and Articulation Control System - A radiation-hard, high precision, state-of-the-art control system

The Galileo Mission and Spacecraft design impose tight requirements on the Attitude and Articulation Control System (AACS). These requirements, coupled with the flexible spacecraft, the need for autonomy, and a severe radiation environment, pose a great challenge for the AACS designer. The resulting design and implementation are described, along with the discovery and solution of the Single-Event Upset problem. The status of the testing of the AACS in the Integration and Test Laboratory as well as at the spacecraft level is summarized.

Rhoads Stephenson, R.↗
NASA NTRS1991

Experimental study of trajectory planning and control of a high precision robot manipulator

The kinematic and trajectory planning is presented for a 6 DOF end-effector whose design was based on the Stewart Platform mechanism. The end-effector was used as a testbed for studying robotic assembly of NASA hardware with passive compliance. Vector analysis was employed to derive a closed-form solution for the end-effector inverse kinematic transformation. A computationally efficient numerical solution was obtained for the end-effector forward kinematic transformation using Newton-Raphson method. Three trajectory planning schemes, two for fine motion and one for gross motion, were developed for the end-effector. Experiments conducted to evaluate the performance of the trajectory planning schemes showed excellent tracking quality with minimal errors. Current activities focus on implementing the developed trajectory planning schemes on mating and demating space-rated connectors and using the compliant platform to acquire forces/torques applied on the end-effector during the assembly task.

Nguyen, Charles C.↗