Field test results prove GPS performance and utility

Statistical and operational results of extensive government field-testing of the Rockwell-Collins Global Positioning System (GPS) units are summarized. The equipment has exhibited better than 16-m spherical-error probable-position accuracy in over 6300 hours of testing conducted during the past two years. One-channel, two-channel, and five-channel receivers were subjected to thorough evaluation. Their respective signal-processing and data-processing architectures are described. Data highlighting dynamic position accuracy, static position accuracy, acquisition times, and field reliability are presented. GPS equipment integration and operation with nine different host vehicles is described. The results of mission scenarios, such as area navigation, rendezvous, and weapon delivery, are presented     

Airborne hyperspectral sensor systems

This paper presents brief profiles of 19 airborne hyperspectral sensor systems currently or nearly available for data acquisition. These systems represent various design concepts and innovations in hyperspectral information collection technology. A number of companies now have the ability to acquire data from these systems. As the scientific and commercial communities become aware of hyperspectral imaging data acquisition opportunities, more applications for this type of data will be investigated and implemented     

Progress in the study of homologous flares on the sun — Part II

Studies of groups of homologous flares in active regions in 1980 have been made using a variety of space and ground based instruments. Detailed properties of three of these groups have been studied, and are combined to form a possible sequence of events.     

Transport phenomena and crystal growth of the GeSe-Xenon system for different gravitational conditions

Previous chemical vapor transport experiments of the GeSe-GeI₄ system performed under reduced gravity conditions /1/ yielded crystals of considerably improved surface and bulk morphology. In addition, the mass transport rates observed in microgravity environment were significantly greater than predicted. A quantitative thermodynamic analysis of the solid-gas phase reactions of the GeSe-GeI₄ system revealed the multi-component, multi-reaction nature of the vapor phase /2/. Continued transport studies on ground of the GeSe-GeI₄ system in the presence of inert gases provided experimental evidence for the existence of a boundary layer /2/ and its thickness dependence on GeI₄ pressure in closed tube systems. Systematic transport rate measurements for different orientations of the density gradient relative to the gravity vector demonstrated the effects of ampoule inclination on mass flux /3/. Based on a computational model for simultaneous chemical vapor transport, sublimation, and Stefan flow /3/, the excellent agreement of predicted with ground-based experimental mass transport rates over wide pressure ranges /3/ confirmed the validity of the model and the discrepancy between observed and expected transport rates of the GeSe-GeI₄ system in microgravity.     

Thermal modeling of Halley's comet

The comet thermal model of Weissman and Kieffer is used to calculate gas production rates and other parameters for the 1986 perihelion passage of Halley's Comet. Gas production estimates are very close to revised pre-perihelion estimates by Newburn based on 1910 observations of Halley; the increase in observed gas production post-perihelion may be explained by a variety of factors. The energy contribution from multiply scattered sunlight and thermal emission by coma dust increases the total energy reaching the Halley nucleus at perihelion by a factor of 2.4. The high obliquity of the Halley nucleus found by Sekanina and Larson may help to explain the asymmetry in Halley's gas production rates around perihelion.     

Impact Potential of New Power Electronic Technologies

New technological advances in the area of power electronics are having an increasing impact on the design of aerospace control systems. These next generation power components promise improved system performance through increased electronic efficiencies. Applying state-of-the-art packaging concepts as an integral part of the system design will allow these devices to be utilized in a space efficient and reliable manner. The first portion of this paper looks at two such next generation components. The first is a High Voltage Integrated Circuit (HVIC) that provides a bridge between the low voltage controller logic and the high voltage motor winding invertor. This device achieves size reduction and an increase in reliability through integration of low and high voltage logic networks on a single integrated circuit. The second is the Insulated Gate Transistor (IGT). This device provides a high voltage switch with MOS-like drive characteristics. The present and future expectations of these power devices are discussed. This paper then looks at new packaging techniques for power devices. The impact of parasitic circuit effects have significant impact on power circuit performance. Finally, this paper looks at an example control application. The design is that of a permanent magnet motor driven actuator. The drive motor uses 270 vdc for supply voltage. Within the intelligent system controller, is the capability to control the current demands of the motor. The new power electronics devices are making the design feasible in both thermal and volume efficiency. This topic includes projected controller sizing into the 1990s.     

SIR-C/X-SAR: A multifaceted radar

The multifaceted Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) was successfully flown twice in 1994 aboard the Shuttle Endeavour as part of an international imaging radar mission. The United States SIR-C operated at L- and C-band, each with multiple polarization, utilizing an active phased array antenna. The German/Italian X-SAR operated at X-band with a single polarization. SIR-C and X-SAR operated synchronously to collect data over common sites. Data were collected for repeat-track interferometric processing at all three frequencies. A total of 143 hours (93 terabits) of SAR data were digitally recorded on tape over the two flights for subsequent processing in the U.S., Germany, and Italy. This advanced multifrequency/multipolarization system has produced a rich radar data set for Earth scientific investigation and demonstration of spaceborne radar remote sensing capabilities     

Flight test evaluation of a 35 GHz forward looking altimeter forterrain avoidance

Honeywell has conducted a series of flight tests of a 35 GHz digital microprocessor controlled forward looking radar altimeter. A Bell 206L Jet Ranger helicopter was used to evaluate the capability of the sensor as a detector of various types of terrain collision hazards. The sensor was composed of a covert, spread spectrum radar altimeter processor driving a 35 GHz converter and antenna assembly mounted on a steerable platform. Excellent correlation between predicted performance and observed performance was obtained     

Electrodeless ultraviolet communications system

The Laser Communications Laboratory (LCL) of the Wright Laboratory Avionics Directorate is heavily involved in designing optical communications systems covering the full optical spectrum to meet our current and future military communications requirements. This paper summarizes the in-house designed and built solar blind ultraviolet communications system used in the LCL to investigate non-line-of-sight data and voice links. It also summarizes some of the previous DoD work accomplished to exploit free space communications via ultraviolet radiation. In addition, safety factors peculiar to ultraviolet radiation in a closed cockpit environment are addressed. An evaluation of the current electrodeless ultraviolet communications system and a synopsis of planned future projects to improve the system are included in the paper