The radio science investigations planned for Galileo's 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements will be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system used for these investigations is based on Voyager heritage but with several important additions and modifications that provide linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. Collaboration between the investigators and the space-craft communications engineers has resulted in the first highly-stable, dual-frequency, spacecraft radio system suitable for simultaneous measurements of all the parameters normally attributed to radio waves.

The planned radio science investigations during the Voyager missions to the outer planets involve: (1) the use of the radio links to and from the spacecraft for occultation measurements of planetary and satellite atmospheres and ionospheres, the rings of Saturn, the solar corona, and the general-relativistic time delay for radiowave propagation through the Sun's gravity field; (2) radio link measurements of true or apparent spacecraft motion caused by the gravity fields of the planets, the masses of their larger satellites, and characteristics of the interplanetary medium; and (3) related measurements which could provide results in other areas, including the possible detection of long-wavelength gravitational radiation propagating through the Solar System. The measurements will be used to study: atmospheric and ionospheric structure, constituents, and dynamics; the sizes, radial distribution, total mass, and other characteristics of the particles in the rings of Saturn; interior models for the major planets and the mean density and bulk composition of a number of their satellites; the plasma density and dynamics of the solar corona and interplanetary medium; and certain fundamental questions involving gravitation and relativity. The instrumentation for these experiments is the same ground-based and spacecraft radio systems as will be used for tracking and communicating with the Voyager spacecraft, although several important features of these systems have been provided primarily for the radio science investigations.

Radar studies of the trails produced by 15th-magnitude meteors (trail electron densities of 1010 m-') have been conducted using a 100-kw transmitter at a wavelength of 13 m, and a 2000-ft linear array made up of 48 four-element Yagi antennas. Number-mass, number-velocity, and number-time distributions of these very small particles show some features similar to those predicted from studies of larger meteors, but other characteristics are markedly different. Of particular interest is the fact that the meteor echo rate, measured at the same time of day for several years, shows day-to-day fluctuations much greater than would be ob- tained from independent sporadic meteors, with little or no correlation with the well-known showers of larger particles. This rate variation does not appear to be due to radio-wave absorption or other atmospheric effects. It is suggested that the "sporadic" background of meteors is in reality a mixture of short-lived showers, with about 10 shower groupings being simultaneously present on the average.

The ionized medium between the earth and the moon is being studied at Stanford by means of lunar radar echoes. Of prime interest is the electron density beyond the earth's ionosphere, in regions (at distances of several to 60 earth radii) where the interplanetary gas may be dominant. Six related techniques for measuring the total integrated electron density are discussed. In practice the ionospheric part could be determined separately and subtracted from the total. These same techniques could be used to measure by radar the electron density between the earth and various planets, and to measure by one-way propagation the integrated electron density between a space probe and the earth. The moon's radar range exceeds the true range, especially at low frequencies, because of group retardation, which is a measure of integrated electron density. Density measurements based on absolute measures of radar range would require very high peak power (for pulse ranging) or very high equipment stability (for CW ranging); futhermore, the true lunar range is not known accurately. In two of the methods described here, the full average power capability of the transmitter can be used without need for high stability or precise knowledge of the lunar range. In effect, a reference is sent with the measuring quantities and only relative radar range is measured. Doppler frequency shifts and the earth's magnetic field cause only slight difficulties. However, path splitting, electron ‘blobs’ and lunar surface irregularities possibly could affect the waves more than the electrons do. The measurements might then yield information about the lunar surface or about the temporal and spatial variations of the cislunar medium.

The experimental evidence offered in support of Booker and Cohen's theory is examined point-by-point. It is concluded that the theory does not accurately represent the properties of meteoric echoes.

The discontinuous vhf signal, propagated over ranges up to 2000 km by reflections from meteor ionization trails, makes possible an important new technique for radio communication. With this technique, the required transmitter power and antenna sizes are considerably less than for communication by the continuous vhf scatter signal supported by smaller meteors and other scattering sources in the lower E region. The wavelength dependence of the information capacity of meteor-burst propagation is approximately λ2.7, which may be compared to approximately λ4.7 for the continuous signal. Thus, by adding the complexity in the terminal equipment needed for discontinuous operation, meteor-burst communication can fill an important need at the same wavelengths that are used in ionospheric-scatter communication, and can be used at shorter wavelengths than are feasible with continuous scatter. This extension to shorter wavelengths should make it possible to reduce the interference problem now being encountered in the lower vhf band, and to greatly increase the number of channels available for reliable longrange communication.

Certain characteristics of radio signals, propagated by reflection from meteor ionization trails from a low-power continuous-wave transmitter 960 km distant, were studied at radio frequencies of 23.2, 46.4, and 92.8 Mc. In particular, the percent of the total time that meteor reflections were detectable at each frequency is presented, and shown to be in qualitative agreement with theoretical expectations. Simultaneous recordings were also made of signals from a second remote transmitter operated at 23.1, 46.2, and 92.4 Mc, and located at various distances along, and at right-angles to, the propagation path. From the percent time that signals received from the second transmitter were coincident with those from the first, it is concluded that reradiation from the numerous, low-density trails is highly directional, and that the fading, long-enduring echoes from the relatively-infrequent, high-density trails are considerably less directional. When the transmitters were spaced in a direction perpendicular to the propagation path, the signal coincidence decreased much more rapidly with transmitter spacing than when the transmitters were spaced along the propagation path.

By a consideration of the amplitude and duration of echoes forward-scattered from individual meteor ionization trails, and of the probability of detecting randomly oriented trails over an oblique radio propagation path, an estimate of the contribution of meteoric ionization to extended range hf and vhf radio transmission has been obtained. It has been concluded that meteoric ionization alone would give a virtually continuous signal for a transmission path of about 1,000 km at frequencies near 15 mc. For the very high frequencies, scattering from meteor trails has been found to be at least an important contributing factor to the propagation of a signal over an oblique path. A precise evaluation of the role of this process must await a better determination of the number of trails as a function of their ionization density.

National Manpower Council _ 617 News and Notes First Palynology Conference: Calvin J. Heusser . 622 Technical Papers The Mass Isolation of Whole Cells from Rat Liver: Norman G. Anderson . 627 Purification and Crystallization of Hyperglycemic Glycogenolytic Factor (HGF): A Staub, L. Sinn, and 0. K. Behrens 628 Failure of Cyanide to Inhibit P-Amylase: Michinori Kakamura 629 Calorie Intake in Relation to Physique in Children: Penelope S. Peckos ____ 631 Protection Agapst X-rays and Therapy of Radiation Sickness with P-Mercaptoethylamine: Z. M. Bacq et al. 633 Incorporation of Tritium Oxide into Growing Chlorella pyrenoidosa Cells: D. Weinberger and J. W. Porter _ 636 Extended-Range High-Frequency Radio Communication at Relatively Low Power, by Means of Overlapping Oblique Reflections from Meteor Ionization Trails: 0. G. Vallard, Jr., et al. 638 Comments and Communications Rapid Aerial Survey of Gulf Stream with Camera and Radiation Thermometer: Henry Stommel et al. 639

It has been found that radio communication between relatively low-power stations operating at 14 megacycles and separated by distances of roughly 1200 km may be maintained at times when no layer transmission to any point on the earth's surface can be demonstrated to be present. The signal obtained is subject to considerable fading, but some signal is nearly always detectable. The contribution of overlapping oblique-incidence meteor reflections to the observed signal is considered in the light of some preliminary theoretical and experimental findings. It is clearly important to assess the meteoric contribution with care, since the possibility that meteoric reflections alone could account for the signal does not seem unreasonable.

A new theory is given for the way in which the number of echoes received from sporadic meteor ionization trails varies with radar wavelength and other system parameters. Previously-published explanations of the echo rate dependence on wavelength are critically examined. The present explanation of echo rate variations is based upon a more complete analysis of the radio reflection process than is afforded by the Lovell-Clegg theory. The effects of high electron density, the linear rate of trail formation, and the initial column radius are discussed. A number of apparent conflicts in earlier investigations are reconciled by the new theory.