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The assembly of the Large Precise Reflector Infrared Telescope is detailed. Also given are the specifications for the Aft Cargo Carrier and the Large Precision Reflector structure. Packaging concepts and options, stowage depth and support truss geometry are also considered. An example of a construction scenario is given.
The design of a high precision powered hinge is complicated by the unavoidable presence of parasitic drag torque resulting mainly from friction and transfer of power, signals, and fluids across the hinge. Regardless of the type of drive system selected, it is impossible to completely eliminate all parasitic drag. However, the mechanism described here comes very close to providing a drag free system. All sources of parasitic drag torque are collected on a shaft which is powered by an electric motor independent of the main hinge drive. Under control of a sensor, the electric motor applies a compensating torque equal to that of the parasitic drag torque, allowing the main hinge drive to operate in a practically drag free environment with very high positioning precision.
This paper is concerned with the results of a study designed to evaluate experimentally the accuracy and precision of electrochemical concentration cell (ECC) ozonesondes as prepared and flown by NASA, as a function of altitude. A combination of dual-instrument soundings and laboratory work using an environmental chamber was employed in the study. The ECC ozonesonde is a small, balloon-borne sensor developed for obtaining vertical profiles of atmospheric ozone. Attention is given to the design of the employed environmental chamber, ozone and temperature profiles used in simulated ozonesonde soundings, absolute and relative ECC ozonesonde precision estimates determined with the environmental chamber and from dual-instrument balloon soundings, and the ECC ozonesonde accuracy.
Experiments were conducted on simulators and on the Quiet Short-Haul Research Aircraft to evaluate the effect of highly augmented control modes and electronic displays on the ability of pilots to execute precision approaches and landings on a short runway. It is found that the primary benefits of highly augmented flightpath and airspeed controls and electronic displays are realized when the pilot is required to execute precisely a complex transition and approach under instrument conditions and in the presence of a wide range of wind and turbulence conditions. A flightpath and airspeed command and stabilization system incorporating nonlinear, inverse system concepts produced fully satisfactory flightpath control throughout the aircraft's terminal operating envelope.
Valve modification provides two operating modes fully open and small, precise leak. Copper insert with radially oriented holes allows small, controllable, precise effusion rate when valve closed or nearly unobstructed flow when valve open. Numerous applications in surface physics, vacuum physics, materials science, gas kinetics, thin films, and other areas of research requiring measured flows of gas into or out of system.
A study of the environmental constraints and engineering aspects of the acoustic portion of a system for making geodetic ties between undersea reference points and others on land is described. Important areas in which to make such observations initially would be from the California mainland out to oceanic points seaward of the San Andreas fault, and across the Aleutian Trench. The overall approach would be to operate a GPS receiver in a relative positioning (interferometric) mode to provide the long range element of the baseline determination (10 to 1,000 km) and an array of precision sea floor acoustic transponders to link the locally moving sea surface GPS antenna location to a fixed sea floor point. Analyses of various environmental constrants (tides, waves, currents, sound velocity variations) lead to the conclusion that, if one uses a properly designed transponder having a remotely controllable precise retransmission time delay, and is careful with regard to methods for installing these on the sea floor, one should, in many ocean locations, be able to achieve sub-decimeter overall system accuracy. Achievements of cm accuracy or better will require additional understanding of time and space scales of variation of sound velocity structure in the ocean at relevant locations.
Analysis of inflatable sphere measurements obtained during the Energy Budget and MAP/WINE campaigns led to questions concerning the precision of the MPS-36 radar used for tracking the spheres; the compatibility of the sphere program with the MPS-36 radar tracking data; and the oversmoothing of derived parameters at high altitudes. Simulations, with winds having sinusoidal vertical wavelengths, were done with the sphere program (HIROBIN) to determine the resolving capability of various filters. It is concluded that given a precision radar and a perfectly performing sphere, the HIROBIN filters can be adjusted to provide small-scale perturbation information to 70 km (i.e., sinusoidal wavelengths of 2 km). It is recommended that the HIROBIN program be modified to enable it to use a variable length filter, that adjusts to fall velocity and accelerations to provide wind data with small perturbations.
Recent technological developments have made viable a man-machine interface heavily dependent on graphics and pointing devices. This has led to new interest in classical reaction and movement time work by Human Factors specialists. Two experiments were designed and run to test the dependence of target capture time on information load (Hitt's Law) and movement precision (Fitts' Law). The proposed model linearly combines Hitt's and Fitts' results into a combination law which then might be called Hitts' Law. Subjects were required to react to stimuli by manipulating a joystick so as to cause a cursor to capture a target on a CRT screen. Response entropy and the relative precision of the capture movement were crossed in a factorial design and data obtained that were found to support the model.
The interplanetary navigation of a spacecraft requires precise calculation of trajectory correction maneuver parameters. Velocity increments must be found which make the required corrections, minimize propellant consumption, and do not violate hardware design constraints or scientific objectives. This process is illustrated by its application to the Galileo Mission. The paper describes inflight analysis techniques, mathematical modeling, and computational algorithms used in the precision maneuver calculation scenario.
The Hubble Space Telescope has the most stringent pointing requirements imposed on any spacecraft to date. The overall HST stability shall not exceed 0.007 arc-seconds rms. The Pointing Control System utilizes fine guidance sensors and rate gyros for attitude reference and rate information. Control torques are provided by reaction wheels. A digital computer collects the sensor data, performs the control law computations, and sends torque commands to the reaction wheels. To attain this precision pointing, improvements were made to the rate gyros to lower their noise characteristics and to the reaction wheels to reduce their emitted vibration levels. The control system design was validated in a test sequence which progressed from model verification tests on an air-bearing to operations-oriented, closed loop testing on the assembled vehicle. A test system is described which allowed the simultaneous production of test case command loads for the flight computer and plots of predicted profiles to assist in test data analysis. Workarounds were required during system test to accommodate gyro biases and noise introduced into the closed loop system. Testing and analysis indicate that the HST will provide the capability to meet the requirements for precision pointing.
Data from three different receiver types have been used to obtain precise orbits for the satellites of the Global Positioning System (GPS). The data were collected during the 1985 March-April GPS experiment to test and validate GPS techniques for precision orbit determination and geodesy. A new software package developed at the Jet Propulsion Laboratory (JPL), GIPSY (GPS Inferred Positioning SYstem), was used to process the data. To assess orbit accuracy, solutions are compared using integrated doppler data from various different receiver types, different fiducial sites, and independent data arcs, including one spanning six days. From these intercomparisons, orbit accuracy for a well-tracked GPS satellite of three meters in altitude and about five meters in each of down and cross-track components are inferred.
Semiconductors made to accept precise etching after pretreatment. Combination of material destabilization and anisotropic etching permits formation of precise perpendicular-wall cavities in silicon wafers and other semiconductors. New technique extends capabilities of current micromachining technology to fabrication of submillimeter waveguide arrays and filters. Pre-etching process currently used to fabricate thin-walled arrays of submillimeter waveguides for use as dichroic bandpass filters. Possible applications include integration of sensor probes and processing of circuitry on same silicon chip.
A portable, tactical approach guidance (PTAG) system, based on a novel, X-band, precision approach concept, was developed and flight tested as a part of NASA's Rotorcraft All-Weather Operations Research Program. The system is based on state-of-the-art X-band technology and digital processing techniques. The PTAG airborne hardware consists of an X-band receiver and a small microprocessor installed in conjunction with the aircraft instrument landing system (ILS) receiver. The microprocessor analyzes the X-band, PTAG pulses and outputs ILS compatible localizer and glide slope signals. The ground stations are inexpensive, portable units, each weighing less than 85 lb, including battery, that can be quickly deployed at a landing site. Results from the flight test program show that PTAG has a significant potential for providing tactical aircraft with low cost, portable, precision instrument approach capability.
The design and development of a mechanism for precise linear and angular adjustment is described. This work was in support of the development of a mechanical extensometer for biaxial strain measurement. A compact mechanism was required which would allow angular adjustments about perpendicular axes with better than 0.001 degree resolution. The approach adopted was first to develop a means of precise linear adjustment. To this end, a mechanism based on the toggle principle was built with inexpensive and easily manufactured parts. A detailed evaluation showed that the resolution of the mechanism was better than 1 micron and that adjustments made by using the device were repeatable. In the second stage of this work, the linear adjustment mechanisms were used in conjunction with a simple arrangement of flexural pivots and attachment blocks to provide the required angular adjustments. Attempts to use the mechanism in conjunction with the biaxial extensometer under development proved unsuccessful. Any form of in stitu adjustment was found to cause erratic changes in instrument output. These changes were due to problems with the suspension system. However, the subject mechanism performed well in its own right and appeared to have potential for use in other applications.
The first European remote sensing satellite ERS-1 will be launched by the European Space Agency (ESA) in 1989. The expected lifetime is two to three years. The spacecraft sensors will primarily support ocean investigations and to a limited extent also land applications. Prime sensor is the Active Microwave Instrumentation (AMI) operating in C-Band either as Synthetic Aperture Radar (SAR) or as Wave-Scatterometer and simultaneously as Wind-Scatterometer. In Europe there will be two distinct types of processing for ERS-1 SAR data, Fast Delivery Processing and Precision Processing. Fast Delivery Proceessing will be carried out at the ground stations and up to three Fast Delivery products per pass will be delivered to end users via satellite within three hours after data acquisition. Precision Processing will be carried out in delayed time and products will not be generated until several days or weeks after data acquisition. However, a wide range of products will be generated by several Processing and Archiving Facilities (PAF) in a joint effort coordinated by ESA. The German Remote Sensing Data Center (Deutsches Fernerkundungsdatenzentrum DFD) will develop and operate one of these facilities. The related activities include the acquisition, processing and evaluation of such data for scientific, public and commercial users. Based on this experience the German Remote Sensing Data Center is presently performing a Phase-B study regarding the development of a SAR processor for ERS-1. The conceptual design of this processing facility is briefly outlined.
A tunable microwave cavity containing ionizable metallic vapor or gases and an apparatus for precisely positioning a microwave coupling tip in the cavity and for precisely adjusting at least one dimension of the cavity are disclosed. With this combined structure, resonance may be achieved with various types of ionizable gases. A coaxial probe extends into a microwave cavity through a tube. One end of the tube is retained in a spherical joint attached in the cavity wall. This allows the coaxial probe to be pivotally rotated. The coaxial probe is slideable within the tube thus allowing the probe to be extended toward or retracted from the center of the cavity.
Results of simulated precision departures and missed approaches using MLS guidance concepts are presented. The study was conducted under the Terminal Configured Vehicle (TCV) Program, and is an extension of previous work by DAC under the Advanced Transport Operating System (ATOPS) Technology Studies Program. The study model included simulation of an MD-80 aircraft, an autopilot, and a MLS guidance computer that provided lateral and vertical steering commands. Precision departures were evaluated using a noise abatement procedure. Several curved path departures were simulated with MLS noise and under various environmental conditions. Missed approaches were considered for the same runway, where lateral MLS guidance maintained the aircraft along the extended runway centerline. In both the departures and the missed approach cases, pitch autopilot takeoff and go-around modes of operation were used in conjunction with MLS lateral guidance.
VLA C array configuration observations at 2 and 6 cm are presented for Europa, Ganymede, and Callisto at eastern and western elongations with respect to Jupiter, which allowed measurements in right ascension and declination of the satellites with an rms precision of about + or - 0.03 arcsec. The transfer of the mean offsets of Ganymede to Jupiter yields offsets of -0.185 + or - 0.03 arcsec and -0.06 + or - 0.03 arcsec, with respect to JPL-DE-200, at the mean epoch of April 28, 1983; the large offset in right ascension is a combination of the Jupiter ephemeris error and the error in the frame tie of the Jovian planets with the VLBI system of precise positions which was used as the absolute reference frame for the observations. A significant error is noted in the orbital position of Callisto with respect to Ganymede.