Cometary atmosphere (gas and dust)

There is important progress now in the identifications and measurements of primary (parent) molecules in the inner coma of Comet Halley. H₂O, CO₂ and CO are definitely in the list, CH and some complicate organic molecules are suspected. Gas production rate for water vapor is Q_H2O 10³⁰ s⁻¹. The bulk of data doesn't contradict to the Whipple model of nucleus (with clathrate modification). Pronounced spatial structure of gaseous flow in the coma was observed, but in general measured properties of neutral gas in the coma of Comet Halley are not very different from predicted. Situation for dust is different. In situ dust measurements show that size spectrum and optical properties of particles in coma are substantively declining from predicted on the base of groundbased photometry. However there are discrepancies between Vega and Giotto dust counter data. Dust in the inner coma didn't prevent the succesful imaging of nucleus by TV on Vega 1 and 2.     

Wide field cameras for SAX

SAX is an Italian X-ray satellite with a Dutch contribution that will be placed in orbit in 1994. The prime scientific object of SAX is to cover an energy bandwidth that ranges from 0.1 keV up to 200 keV. Among other instruments, SAX will consist of two X-ray Wide Field Cameras built by the Space Research Organisation Netherlands at Utrecht. The WFCs are based on the coded mask principle, the reconstruction of the image takes place on ground. The field of view is 20 degrees square full width at half maximum (FWHM), the angular resolution 5 arcminutes (FWHM) and the energy band ranges from 1.8 to 30 keV with a resolution of 18% at 6 keV. The sensitive area is 200 cm² at 6 keV. The mask pattern is based on a pseudo random array with 255 × 257 elements of 1 mm², 50% of which are transparent.     

Plasma effects of active ion beam injections in the ionosphere at rocket altitudes

Data from ARCS rocket ion beam injection experiments will be primarily discussed in this paper. There are three results from this series of active experiments that are of particular interest in space plasma physics. These are the transverse acceleration of ambient ions in the large beam volume, the scattering of beam ions near the release payload, and the possible acceleration of electrons very close to the plasma generator which produce intense high frequency waves. The ability of 100 ma ion beam injections into the upper E and F regions of the ionosphere to produce these phenomena appear to be related solely to the process by which the plasma release payload and the ion beam are neutralized. Since the electrons in the plasma release do not convect with the plasma ions, the neutralization of both the payload and beam must be accomplished by large field-aligned currents (milliamperes/square meter) which are very unstable to wave growth of various modes. Future work will concentrate on the wave production and wave-particle interactions that produce the plasma/energetic particle effects discussed in this paper and which have direct application to natural phenomena in the upper ionosphere and magnetosphere.     

Current collection through the transport of electrons across magnetic field lines

Collection of electrons by a long conducting cylinder in a flowing plasma is studied by means of numerical simulations. The plasma flow simulates the relative motion between a spacecraft and plasma. The sheath structures and the levels of electron current collections for the cases with and without an ambient magnetic field ( ) are studied. It is found that for the flow perpendicular to the magnetic field, the current is considerably enhanced depending on the relative drift velocity. In the case of a non-zero magnetic field perpendicular to the cylinder axis, the potential structure is a two-dimensional double layer with dimensions L L_|, where L and L_| are the dimensions perpendicular and parallel to , respectively. L is found to be the current limiting radius given by the Parker-Murphy model. For the flow along , the electron current is found to be smaller than that for the flow perpendicular to . This is explained in terms of the potential structures.     

Organization, selection, and training of crews for extended spaceflight: findings from analogs and implications

Ample research evidence from space analogs points to the crucial role that teamwork plays in the performance of small groups in isolation and confinement. This paper surveys findings about the impacts of group behavior and social interaction on crew morale, coordination, and productivity. Implications for the organization, selection, and training of crews for extended spaceflight are discussed.     

Radar Cross Section of Ships

A laboratory method to determine the magnitude and position of radar reflection sources on complex targets is described. In addition the method provides a way to measure the modification of the radar cross section (RCS) due to multipath. The method has application in modeling RCS for radar and electronic countermeasure (ECM) system performance analysis and in the study of the extent to which the signature of the target could be altered. The equipment described, termed MACROSCOPE, was developed for RCS studies by the U.S. Army and is described in limited distribution bution literature. The application to marine targets is new with this paper, as is the technique of measuring the RCS of parts of the target and analytically combining them to represent the whole. An illustration of the need for this type of laboratory equipment was illustrated by the extensive search for full scale data which could be compared to scale model data to validate the technique.     

Theory of physical libration of the Moon with the liquid core: Forced librations

For a two-layer model of the Moon that consists of a solid nonspherical mantle and an ellipsoidal homogeneous liquid core, a theory of forced librations under the effect of gravitational Earth’s moments has been developed. The motion of the Moon over its orbit has been described by the high-accuracy theory of DE/LE-4 orbital motion. Tables have been constructed that present forced librations of the Moon caused by the second harmonic of its force function, in the neighborhood of its motion according to the generalized Cassini laws. Disturbances of the first-order with respect to dynamic compressions of the Moon and its core are obtained in analytical form for Andoyer variables and Poincare variables and for the projection of the angular velocity vector of Moon’s mantle rotation and the Poincare coordinate system (relative to which core’s liquid accomplishes simple motion) on its major central axes of inertia, as well as for the classical variables in the Moon libration theory, etc. Constructed tables of the forced librations theory give the amplitudes and periods of librations and combinations of arguments of the orbital motion theory that correspond to libration parameters. The interpretation of basic variations has been given and a comparison with the previous theories has been carried out, in particular with the modern empirical theory constructed based on the laser observation data.     

Study of GNSS-measured ionospheric total electron content variations generated by powerful HF-heating

The purpose of this work is to report the experimental evidences for the influence of perturbations in the electron density in the dayside mid-latitude ionosphere, that are caused by high-frequency heating of the F2 layer, on the GNSS signals. The experiments were carried out at the Sura heater (Radio Physical Research Institute, N. Novgorod). During the sessions of ionospheric heating with different time modulations of the radiated power the rays linking the navigational satellites with the ground receiver intersected the heated region. Variations in the total electron content (TEC) were studied; these variations are proportional to the reduced phases of navigational signals. It is shown that with the square-wave modulation of the radiated power (with periods of 1, 6, 10 and 15 min), perturbations with periods of the main modulation of heating and its harmonics appear in the spectrum of TEC variations. Examples are presented of identification of the heating-induced variations in TEC, including determination of the amplitudes and time characteristics of these variations.     

An approach to forming the design performance of the attitude control system for small spacecraft

The elements for various types of attitude control systems used in a number of small spacecraft are considered. An approach for assessment of such system effectiveness based on design requirements for spacecraft purpose and restriction in accuracy, mass and energy is proposed.