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A Shuttle-borne tethered satellite has the potential of contributing significantly to the scientific versatility of the Shuttle Orbiter, that will be launched by NASA in the early '80s. If the Shuttle is in a 200 km orbit, the use of a 100 km tether connected to the Shuttle at one end and to the satellite at the other makes the performance of various relevant electromagnetic measurements in the magnetosphere possible. The tethered satellite (a subsatellite) can also be lowered from the Shuttle down to heights in the vicinity of 100 km, to an altitude band that has great importance from the standpoint of both upper atmospheric experimentation and gravity-gradient measurements. From a preliminary analysis, we find that one of the major problem areas of the system — the heating of the wire and of the subsatellite due to air drag — can be solved within the present state of the art in wire technology and heat shielding. System masses are also reasonable: In fact, a system with a 100 km wire and a Shuttle-borne reel, tethering a 100 kg subsatellite, would have a mass no larger than 120 kg.

The release of PGF1alpha and PGF2alpha from superfused blood platelets was studied by the combined use of two radioimmunoassay systems with different specificities. PGF1alpha only accounted for approximately 30% of the total immunoreactivity. A substantially similar pattern of release was obtained with platelets of rat and human origin, although the latter released considerably lower amount of both compounds. Indomethacin, Femoprofen, Ditazole and Aspirin all inhibited PGF2alpha release from rat platelets in descending order of potency. Hydrocortisone was partically inactive. The release of PGF1alpha and PGF2alpha was inhibited to the same extent by both Indomethacin and Fenoprofen. Moreover, a quite similar inhibitory effect by the same drug on rat and human platelets was found in preliminary experiments. In agreement with a previous similar finding, Aspirin displayed a higher inhibitory activity than that reported in other tissues. The use of superfused platelets seems to provide a simple and reproducible model for studying pharmacologic influences upon PG formation.

A sounding link at HF established between tightly synchronized ground-based terminals located at shell conjugate sites (Jupiter, Florida, and Ushuaia, Argentina) has obtained echoes with 62 millisec delay. The echoes can be interpreted as being due to propagation along an enhancement of electron density aligned with the L=1.8 shell. The echoes are characterized by path losses 80 db worse than free space and were received at 7.46, 9.04, and 12.00 MHz for 7.6% of the over-all observing time, during night hours. Typically their strength was 15 db below noise and they were recovered with an integration time of 1 hour (3600 pulse repetition periods).

The OV4-1 (orbiting vehicle 4, experiment 1) dual satellite guided ionospheric propagation experiment has confirmed the existence of long-range, low-loss, earth-detached propagation paths in the bottomside ionosphere with mean path losses smaller than equivalent multihop and, in some instances, smaller than free-space propagation. Satellite-to-satellite signals at 34.3 MHz were received from 56 to 100% of the five-minute samples taken in real time by the ground telemetry network while the orbits of the two satellites were decaying from 300 to 250 km. Measured values of path losses range from between 124 and 159 db. Multipath spread was never found larger than 550 μsec, and there is some evidence that Doppler spread was less than 0.012 Hz. Signals at 20.75 and 46.8 MHz in the satellite-tosatellite link were rarely received beyond the line of sight.

The design of an experiment to provide conclusive proof of the existence of HF/VHF whispering gallery propagation in the ionosphere below F2Hmax (and to explore its characteristics) has recently been completed and the necessary instrumentation developed and built. The design has been performed on the basis of the results of the simulation of the phenomenon in a digital computer which has integrated in a self-consistent model the fragmentary, incomplete knowledge of the phenomenon available to date. A satellite-to-satellite configuration has be~n chosen, as suitable both to prove unambiguously the existence of whispering-gallery propagation in the lower ionosphere, and for gathering information basic to the evaluation of the practical usefulnes~ of the guided paths for communications, and to their channel characterization.

The objective of the radio science investigations is to extract the maximum scientific information from the data provided by the radio and radar systems on the Viking Orbiters and Landers. Unique features of the Viking missions include tracking of the landers on the surface of Mars, dual-frequency S- and X-band tracking data from the orbiters, lander-to-orbiter communications system data, and lander radar data, all of which provide sources of information for a number of scientific investigations. Post-flight analyses will provide both new and improved scientific information on physical and surface properties of Mars, on atmospheric and ionospheric properties of Mars, and on solar system properties.

An investigation has been carried on, based on a geometric-optics treatment, of HF and VHF propagation in the ionospheric whispering gallery, with emphasis on long-range paths between terminal points both embedded in the lower ionosphere and not involving earth surface reflections. The results of the investigation have proven that guided paths at HF and VHF are supported by the lower ionosphere despite sharp day-to-night transitions, refractive irregularities, and discontinuities, and have provided enough insight into their properties to allow the detailed design of a satellite-to-satellite experiment.