A new model of the ion composition at 75 to 1000 km for IRI

Ion composition of the ionosphere is an important parameter of any ionospheric model. The International Reference Ionosphere-1979 includes a program for the relative ion composition computation. The program was constructed on the basis of the Danilov and Semenov /1/ empirical model, which averaged 42 rocket measurements of the ion composition at middle latitudes below 200 km, on “AEROS” satellite measurements, and on Taylor's data /2/ above that altitude.     

Application potential of SPOT imagery for topographic mapping

The high resolution and good geometric configuration possible with SPOT gives a high potential for the production of 1:100 000 topographic maps. Studies at University College London have investigated this potential with the aid of a simple instrument which will introduce the necessary corrections to level 1b photographic images and orthophotographs and allow stereoscopic viewing of SPOT images and the ability to compile a line map. Accuracy has been investigated by computing ground co-ordinates from image co-ordinates and pixel positions. The methods used and results obtained in this work are described.Work is now going on to investigate the use of digital image processors in the mapping procedures and the use of analytical plotting instruments, and comments on this work and on future developments are made.     

SAMBO-GEOS: On three-dimensional substorm dynamics — A case study for 4 March 1979

For investigations of the isolated magnetospheric substorm the ground-based and satellite geophysical data are discussed. The active phase of the substorm has two parts: an active-convective phase and a classical active phase. The analysed data show that the breakup of the substorm takes place at closed and not very much stretched magnetic field lines.     

Aircraft Interrogation Scheduling with ASTRO-DABS

In the ASTRO-DABS concept for surveillance and data link, aircraft are interrogated by one of three geostationary transmitter satellites, each covering 1/3 of the contiguous United States. Interrogation scheduling involves a roll call such that aircraft responses to receiving satellites do not overlap (garble). A simple approach is developed which utilizes range ordering of aircraft with respect to transmitter satellites, but is independent of receiver satellite locations and aircraft distribution. Bounds on roll-call duration are established, showing that interrogation of 80 000 aircraft requires between 4.0 and 6.4 seconds with the ASTRO-DABS transmission format. If aircraft distribution is regionally concentrated (i.e., clustered), the roll-call duration nears the lower bound, since fewer gaps between interrogations are needed to preclude garbling.     

High-Resolution, Radar Coherent Linear FM Microwave Source

The microwave CLFM study was directed to generating 14 ?s S-band pulses of 1000 MHz bandwidth and an rms phase error of a few degrees. Over 972 MHz bandwidth, the sampled phase error relative to the reference was 7 degrees rms and 17 degrees peak, with a maximum Fourier component of 4 degrees. The FM pulse train is generated by a gated BWO driven by a stable linearizing waveform. Phase coherency during each pulse is obtained by a sampling technique, where the phase is corrected at intervals of 1/6 ?s, the RF phase having changed an integral number of cycles in each interval. Multiplication of the BWO signal by the sampling pulse train results in band-limited phase error pulses which are applied in a feedback loop. Pulse-to-pulse coherency is obtained by phase lock of the BWO starting frequency to the crystal reference. Feedback leveling holds the output constant to 0.3 dB. The basic MITRE technique was originally demonstrated at 10 MHz in 1964. Range results measured with the X-band model radar using the CLFM generator are given and confirm the phase errors of the CLFM.     

Optimization of entry-vehicle shapes during conceptual design

During the conceptual design of a re-entry vehicle, the vehicle shape and geometry can be varied and its impact on performance can be evaluated. In this study, the shape optimization of two classes of vehicles has been studied: a capsule and a winged vehicle. Their aerodynamic characteristics were analyzed using local-inclination methods, automatically selected per vehicle segment. Entry trajectories down to Mach 3 were calculated assuming trimmed conditions. For the winged vehicle, which has both a body flap and elevons, a guidance algorithm to track a reference heat-rate was used. Multi-objective particle swarm optimization was used to optimize the shape using objectives related to mass, volume and range. The optimizations show a large variation in vehicle performance over the explored parameter space. Areas of very strong non-linearity are observed in the direct neighborhood of the two-dimensional Pareto fronts. This indicates the need for robust exploration of the influence of vehicle shapes on system performance during engineering trade-offs, which are performed during conceptual design. A number of important aspects of the influence of vehicle behavior on the Pareto fronts are observed and discussed. There is a nearly complete convergence to narrow-wing solutions for the winged vehicle. Also, it is found that imposing pitch-stability for the winged vehicle at all angles of attack results in vehicle shapes which require upward control surface deflections during the majority of the entry.     

Neutral points on the boundary of the closed magnetosphere

Theoretical studies of a field-free plasma incident upon a magnetic dipole lead to a closed magnetosphere with two neutral points in the noon magnetic meridian, at a latitude of ± 70°–75° and a geocentric distance of approximately 10 R_E. The position of the neutral points with respect to the dipole axis is not greatly affected by the angle of incidence of the solar wind. Although the field magnitude near the neutral points is only a fraction of the dipole field, the direction is seen to reverse on opposite sides of the neutral point. Near the boundary the field direction is parallel to the boundary and tends to point towards the neutral point in the Northern hemisphere.