Galileo trajectory design

The Galileo spacecraft was launched by the Space Shuttle Atlantis on October 18, 1989. A two-stage Inertial Upper Stage propelled Galileo out of Earth parking orbit to begin its 6-year interplanetary transfer to Jupiter. Galileo has already received two gravity assists: from Venus on February 10, 1990 and from Earth on December 8, 1990. After a second gravity-assist flyby of Earth on December 8, 1992, Galileo will have achieved the energy necessary to reach Jupiter. Galileo's interplanetary trajectory includes a close flyby of asteroid 951-Gaspra on October 29, 1991, and, depending on propellant availability and other factors, there may be a second asteroid flyby of 243-Ida on August 28, 1993. Upon arrival at Jupiter on December 7, 1995, the Galileo Orbiter will relay data back to Earth from an atmospheric Probe which is released five months earlier. For about 75 min, data is transmitted to the Orbiter from the Probe as it descends on a parachute to a pressure depth of 20–30 bars in the Jovian atmosphere. Shortly after the end of Probe relay, the Orbiter ignites its rocket motor to insert into orbit about Jupiter. The orbital phase of the mission, referred to as the satellite tour, lasts nearly two years, during which time Galileo will complete 10 orbits about Jupiter. On each of these orbits, there will be a close encounter with one of the three outermost Galilean satellites (Europa, Ganymede, and Callisto). The gravity assist from each satellite is designed to target the spacecraft to the next encounter with minimal expenditure of propellant. The nominal mission is scheduled to end in October 1997 when the Orbiter enters Jupiter's magnetotail.List of Acronyms ASI Atmospheric Structure Instrument - EPI Energetic Particles Instrument - HGA High Gain Antenna - IUS Inertial Upper Stage - JOI Jupiter Orbit Insertion - JPL Jet Propulsion Laboratory - LRD Lightning and Radio Emissions Detector - NASA National Aeronautics and Space Administration - NEP Nephelometer - NIMS Near-Infrared Mapping Spectrometer - ODM Orbit Deflection Maneuver - OTM Orbit Trim Maneuver - PJR Perijove Raise Maneuver - PM Propellant Margin - PDT Pacific Daylight Time - PST Pacific Standard Time - RPM Retropropulsion Module - RRA Radio Relay Antenna - SSI Solid State Imaging - TCM Trajectory Correction Maneuver - UTC Universal Time Coordinated - UVS Ultraviolet Spectrometer - VEEGA Venus-Earth-Earth Gravity Assist     

Meteorological control of the D region

After a short review of the characteristics of ionized state and meteorology of the mesopause region, the winter anomaly of the D region electron density and its variability are described as manifestations of meteorological control. A major mechanism is the redistribution of nitric oxide, another important mechanism is the strong temperature dependence of cluster ion formation rates. The meteorological control can be described either in a ‘concerted’ scenario of more or less independently acting mechanisms, or in a ‘unitary’ scenario where all mechanisms are regarded as effects of a common cause, viz., the strong winter vortex circulation of the middle atmosphere.     

A sequence of five proton producing flares in McMath Plage 15266 28 April–7 May 1978 and their interplanetary consequences

McMath Plage 15266, which transited the solar disk during Carrington Rotation 1667, gave rise during its passage to a spectacular sequence of five proton producing flares. Solar circumstances leading up to the formation of the active plage are described. An account is given of the magnetic affiliations and optical characteristics of the flares themselves, and it is suggested that four of these events might be interpreted as two twin phase flares displaying secondary maxima and minima such that the second phase in each case could in some sense be deemed a consequence of phenomena initiated during the first phase. Those particle phenomena associated with the observed activity are reviewed, and it is suggested that the azimuthal propagation of solar cosmic rays in the corona may occur more efficiently for flares at eastern longitudes in which the magnetic axis is aligned in a roughly north to south rather than an east-to-west direction.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.     

A methodology for addressing support equipment obsolescence

The rapid growth of technology over the last twenty years is providing vastly improved capabilities for both avionics and avionics test systems. Unfortunately, an environment of rapid technological growth breeds a corresponding environment of rapid technological obsolescence. Test systems developed fifteen years ago are becoming increasingly more difficult to support due to obsolescence issues and, additionally, such a test system does not reflect the current state-of-the-art for automatic test equipment. The ability of a test system to evolve is essential to providing cost-effective support systems for electronic systems. The F-15 Tactical Electronic Warfare System (TEWS) Intermediate Support System (TISS) was developed under the Modular Automatic Test Equipment (MATE) guidelines to support the suite of F-15 electronic warfare LRUs. MATE imposed hardware architecture constraints, which were factors that contributed to its abandonment. However, the modular aspect of MATE has provided a system that can easily evolve with technological advancements. Modularity is the cornerstone of modern software systems and this is the aspect that has been exploited in the evolution of the TISS     

Ll-CFAR: a flexible and robust alternative

A new family of constant false alarm rate (CFAR) processors is introduced. An Ll-CFAR forms its noise power estimate by linearly filtering ranked samples from the reference set; the weights of this combination, however, depend not only on the rank, but also on the relative proximity of the sample to the cell under test. From the class of Ll-CFARs may be chosen members which effectively censor spurious targets; members which exhibit impressive control of false alarm in the presence of a clutter edge; and members which are robust against both such inhomogeneities. While the design of such schemes is involved, their implementation is not significantly more burdensome than that of plain ordered statistic CFAR (OS-CFAR). After a discussion of the stochastic training of Ll-CFAR, the performance is thoroughly assessed under the most commonly encountered instances of environmental conditions, and compared with those of classical CFAR techniques     

Investigation of corona initiation voltage at reduced pressures

The results of an experimental study of the 60 Hz ac corona inception voltage at reduced pressures for a cylindrical conductor and a parallel ground plane are presented. Several spacings and bare and insulated conductors of several diameters are considered. Empirical expressions from which a reasonably accurate prediction of the corona inception voltage (CIV) may be made have been inferred from experimental data     

Speech Data Rate Reduction Part II: Applicability of Sensitivity and Error Analysis

This paper deals with the application of modern estimation techniques to the problem of speech data rate reduction. It is desirable to adaptively identify and quantitize the parameters of the speech model. These paramaters cannot be identified and quantized exactly; the performance of the predictor is thereby degraded and this could prevent data reduction. In many cases it is desirable to emply a suboptimal predictor in order to simplify the algorithms, and predictor performance is again degraded. This paper develops sensitivity and error analysis as a potential method for determining quantitatively how speech data reduction system performance is degraded by imprecise parameter knowledge or suboptimal filtering. An intended use of the sensitivity and error analysis algorithms is to determine parameter identification and model structure requirements of configuration concepts for adaptive speech digitizers. First, sensitivity and error analysis algorithms are presented that form the basis for the remainder of the work. The algorithms are then used to determine how imprecise knowledge of vocal tract parameters degrades predictor performance in speech. Transversal filters have previously been proposed for this application. The sensitivity analysis algorithms are then used to determine when and by how much the transverse filter is suboptimal to the Kalman filter. In particular, the question of how effectively a higher order of all-pole model approximates a system with zeros is answered, as this question is of considerable importance in speech. Finally, the physical significance of the innovations process in speech data rate reduction is studied.     

A Systematic Approach to Blind-Speed Elimination

In radars that achieve a high subclutter visibility by coherent processing over several pulses, a serious problem appears in the form of blind Dopplers, or ?speeds,? at which target detection is impossible. Of the possible methods of eliminating these blind speeds, the most basic one that is employed when the performance requirements are high involves the use of several PRF's. These PRF's are chosen so that coverage is obtained at any Doppler with at least one PRF. The problem faced by the radar designer is to select the set of PRF's and the pulse numbers for each PRF so that the search frame time is minimized. This paper evolves a systematic method for the design of the blind-speed elimination scheme. A formalized approach is offered that shows the possible combinations of wavelength, PRF, and pulse number and the tradeoffs involved, without introducing the confusion ordinarily associated with multiparameter choices.