Cross Sections and Radar Equation for Nonlinear Scatterers

The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects.     

Applications of stereoscopic height computations from dual geosynchronous satellite data/joint NASA-Japan stereo project

Stereoscopic heights of the top of an Oklahoma thunderstorm were computed, finding that high cloud tops are not always characterized by very cold IR temperature. The identical method was also applied to the computation of stereo heights based on GOES West and GMS stereo pairs obtained under the NASA-JAPAN cooperative program. It was found that stereo techniques are extremely useful in understanding the structure of thunderstorms in the United States, as well as that of hurricanes over the South Pacific.     

Development of 1000-mHz Distance Measuring Equipment

The major radio aids to air navigation are listed. Underlined are those whose signal format is standardized by the International Civil Aviation Organization (ICAO) and they have now all been the subject of the IEEE Aerospace and Electronic Systems Society Pioneer Award, as follows: airborne direction finder/nondirectional beacon (ADF/NDB), Busignies and Moseley, 1959; VHF omnidirectional range (VOR), Stuart, 1962; instrument landing system (ILS), Kramar 1964, Alford 1965; air traffic control radar beacon system (ATCRBS), Williams, Bowden, and Harris, 1973; distance measuring equipment (DME), Dodington, 1980. A brief history of the development of the distance measuring equipment, which also formed the basis for an IEEE National Aerospace Electronics Conference luncheon address, is given.     

Inertially fixed pitch stabilization of satellites by solar radiation pressure

Utilization of solar radiation pressure to stabilize the pitch attitude of an unsymmetrical satellite along an inertially-fixed orientation is investigated. A controller employing two rotatable highly reflective control surfaces is proposed and a control strategy involving both nominal and feedback controls is synthesized. Accounting for the apparent annual motion of the Sun, the validity of the concept throughout the year is established through a stability analysis of the system. The influence of the Earth's shadow on the controller performance is also analyzed. The speed of response as well as the pointing accuracy capabilities of the system appear to be quite acceptable for long-life scientific missions.     

The German space processing programme TEXUS with sounding rockets

This paper reports on the objectives of the German space processing programme with sounding rockets and the scientific results obtained thus far.     

Dynamics of solar cosmic ray events: Processes at large heliocentric distances (⪢1 AU)

Observations of solar cosmic ray events far from the sun (?1 AU) became possible after the launch of Pioneer 10 in 1972. Four spacecraft have now travelled beyond the orbit of Jupiter - Pioneer 10/11 and Voyager 1/2 — and are producing a growing body of distant observations of solar cosmic ray events. Initial studies using Pioneer 10/11 data out to ～6 AU interpreted flare particle observations in terms of a diffusion model, including the effects of convection and adiabatic energy loss. This model enjoyed general success in explaining the time-intensity profiles in cases where the spacecraft connection longitude at the sun did not change significantly with time. The results implied that the radial diffusion coefficient (K_r) increased slowly with distance over that radial range. More recent results at larger distances imply that K_r may begin to decrease beyond ～5 AU. It is not yet clear whether the standard diffusion model will be adequate to explain solar events well beyond 5 AU. The fact that large events at very large distances can last up to two solar rotations implies that solar wind stream structure will also play a role in the event dynamics. In general, however, observations at large distances offer perhaps the best hope of separating interplanetary propagation effects from coronal storage and propagation effects which frequently dominate observed event profiles at 1 AU.     

Fragmentation in rotating isothermal protostellar clouds

Summary From the extensive set of numerical calculations briefly described above, it seems apparent that rotating, isothermal gas clouds are unstable to fragmentation under a wide range of conditions. (Caution: This result for isothermal clouds cannot be generalized to all clouds, as is shown, for example, by Boss's analysis [these proceedings] of the stability of collapsing, adiabatic clouds.) It is of importance to note, however, that no fragmentation is apparent during a cloud's initial dynamic collapse toward a disk structure; rather it is the rotationally flattened disk/ring configuration that undergoes fragmentation. This is a considerably different picture of fragmentation than has been presented, for example, by Hoyle (1953).The degree of instability and the mode (ring vs. blob) of fragmentation is sensitive to , but insensitive to . The initial amplitude of a perturbation does not appear to be crucial--fragmentation should occur eventually even for low amplitude initial NAPs.Finally, it is of some interest to know what the properties are of the fragments that break out of these isothermal clouds. Before outlining these properties we emphasize that in this set of calculations we have specifically excited the m = 2 (binary) non-axisymmetric mode; hence we have in some sense suppressed the development of other modes and we have promoted the development of equal mass components in the binary systems. In these evolutions, a typical fragment contained 15% of the initial cloud mass; had a specific angular momentum 25–30% that of the original cloud; had a ratio of spin angular momentum to orbital angular momentum 0.2; and itself had a ratio of thermal to gravitational energy _frag < 0.1. The formation of a binary system has therefore resulted in a conversion of some of the original cloud's spin angular momentum into orbital angular momentum, and has produced protostars with reduced specific angular momenta. It is also evident that each fragment is unstable to further collapse (having low ) under the isothermal assumptions imposed here.     

The Engineer as a Radical?

Outdated and rigorous curricula are not only producing engineers unsuited to the challenges of the 1970's, but they are scaring off many of the most creative and intelligent students. Engineering education has become an endurance test; the excitement has been lost. Most students strive only to get out. Engineering schools have not yet realized the importance of the involvement of engineers in current environmental problems. They continue to present only the dry technical courses and seem unconcerned about the student's sense of social perspective or his motivation. This paper proposes a freshman awareness seminar plus project oriented learning in the following years as a remedy for this sad situation.     

Maximum Likelihood Elevation Angle Estimates of Radar Targets Using Subapertures

The maximum likelihood estimates of the elevation angles of two closely spaced targets within the beamwidth is considered. For an array divided into three subapertures, a simple, closed form solution is found whose accuracy compares favorably to the maximum likelihood estimate which uses all the individual elements. Simulation results are presented for the case of a radar target located over a smooth reflecting surface.