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Highlights of the results obtained with Japanese X-ray astronomy satellite ‘Hakucho’ are reviewed. After a brief account of instrumentation (Section 2), some new features of non-bursting, non-pulsating objects are presented (Sections 3–5). The main part of the present review is devoted for X-ray bursts which are found more complex than one might have thought (Sections 6–11). The observation of X-ray pulsar, including a change of spin rate of Vela X-1, is described (Section 12). The main results obtained in the first two years are summarized in Section 13.

Publisher Summary This chapter provides an overview of the features and the objectives of the Italian Sirio satellite program and the characteristics of its systems. The principal objective is to investigate the applicability of frequencies above 10 GHz to satellite communication systems through an SHF propagation and communication experiment. Sirio is a spin-stabilized geostationary satellite with a mechanically despun antenna for the propagation and communication experiment. The nominal spin rate is 90 rpm. The Sirio program is developed in the frame of the Italian space program by the Consiglio Nazionale delle Ricerche (CNR). Project management is at the Servizio Attivita Spaziali (SAS) of CNR, while the experimental activity is under the scientific direction of the Centro Telecomunicazioni Spaziali of CNR at the Politecnico di Milano. Prime contractorship for the Sirio satellite has been entrusted to Compagnia Industriale Aerospaziale while the contractorship for the Sirio Operation Control Center and for the Sirio SHF ground stations has been entrusted to Telespazio. Telespazio is also giving technical and administrative assistance to CNR for the development of the program. NASA will take care of the satellite launch.

Publisher Summary This chapter provides an overview of the features and the objectives of the Italian Sirio satellite program and the characteristics of its systems. The principal objective is to investigate the applicability of frequencies above 10 GHz to satellite communication systems through an SHF propagation and communication experiment. Sirio is a spin-stabilized geostationary satellite with a mechanically despun antenna for the propagation and communication experiment. The nominal spin rate is 90 rpm. The Sirio program is developed in the frame of the Italian space program by the Consiglio Nazionale delle Ricerche (CNR). Project management is at the Servizio Attivita Spaziali (SAS) of CNR, while the experimental activity is under the scientific direction of the Centro Telecomunicazioni Spaziali of CNR at the Politecnico di Milano. Prime contractorship for the Sirio satellite has been entrusted to Compagnia Industriale Aerospaziale while the contractorship for the Sirio Operation Control Center and for the Sirio SHF ground stations has been entrusted to Telespazio. Telespazio is also giving technical and administrative assistance to CNR for the development of the program. NASA will take care of the satellite launch.

A space test of a pulsed-plasma engine was carried out on the Engineering Test Satellite-IV. The engine was operated successfully more than 300,000 times in space. The spin rate of the satellite was measured with a high accuracy for the impulse estimation of the engine. The spin rate change was, however, smaller than that given by simple estimation based on the impulse measured by the ground test. It was observed that the variation of the spin rate was the same order of magnitude as the variation due to the natural damping by air drag or the temperature variation of the satellite. The impulse of the engine calculated from the space test data taking account of these effects agreed with the impulse measured by ground tests using a pendulum.

The spin rate distributions of comet nuclei and small asteroids are compared, and it is shown that Whipple’s (1982) finding of a faster average rotation for the asteroid sample was due to observational biases. In fact, the presently available rotational data do not exhibit any clear differentiation among comet nuclei and asteroids, except possibly for a higher abundance of short rotational periods among the Apollo-Amor objects.

The effect of both gravitational and tidal torques on the spin rate of the planet Mercury is used as a model for a passage through resonance problem. Both the resonance and nonresonance aspects of the spin rate are studied by means of the method of averaging. On the basis of this analysis, it is concluded that the present 3:2 resonant state is due to nonresonant capture which evolved into resonant capture as the orbital eccentricity increased.

In the study, offsets, products of inertia, tip-off errors, and nominal spin rate were varied to find the relative importance of each on the accuracy of the mission. Since no requirements have been placed on maximum or minimum apogee altitude acquired from the final initial conditions agreed upon, a parametric study was made showing the relative effect of varying each parameter. Assumptions have led to suggested tolerances on the controlled parameter.

For the past ten years teams of the Western Satellite Research Network have undertaken an extensive program aimed at compiling and classifying satellite optical characteristics. In this the second optical characteristics catalog 7900 observations of the optical characteristics of 574 satellites are compiled, reduced and presented in tabular form. A detailed discussion of brightness data is included. This comprehensive summary of optical appearance data is a valuable aid for the identification of the nature or condition of satellites. For example, observations of spin rate increase have indicated leaks or ruptures in some orbiting vehicles' pressurized systems. Also, by noting such characteristics as flash pattern and magnitude variation, one may determine the general nature of a satellite's surface and orientation. Further reduction of these observations is intended in order to fully utilize existing data.

The results from photometric lightcurve observations of nine M-type asteroids are presented. New rotation periods were determined for 6 asteroids: 217 Eudora (12.54 h), 322 Phaeo (17.56 h), 572 Rebekka (5.65 h), 757 Portland (6.58 h), 857 Glasenappia (8.2

The basic principles behind cricket ball swing have been understood by scientists for years1–3; however, there has been only one published account of experiments on cricket ball swing4. Through a combination of flow visualization and measurements of surface pressures on a cricket ball, the individual parameters responsible for producing swing have been investigated. An accurate correlation between swing, seam angle, spin rate and flow speed was obtained in the more realistic projection tests where spinning cricket balls were projected into a wind tunnel5. For a ball to swing well, it should be released at a speed of between 15 and 30 m s−1 with the seam inclined at about 20° incidence and the ball spinning steadily along the seam at about 11 rev s−1. The present experiments do not support the popular view that swing increases in damp or humid conditions. In particular, measurements show that the cricket ball seam does not swell in such conditions.

A small, inexpensive device for determining the spin rate of a sounding rocket is described, which employs the variation in resistance of a magnetically sensitive diode when it is rotated in the earth's magnetic field.

H.H. Lamb (Climate, Present, Past and Future, vol. 2., Methuen Co., N.Y., 1977) postulated convincingly that there is a tight correlation between variations in the earth's climate and solar exposure (as represented by mean surface temperature 8). Given constant radiation and surface, solar exposure is a function of the length of day, and thus it has been tempting to correlate, as well, mechanisms that could cause or be the result of changes in the earth's rotation rate. Such mechanisms have been reviewed by Lambeck (The Earth's Variable Rotation, Geophysical Causes and Consequences, Cambridge University Press, London, 1980). Lambeck examined the variations in terms of fluid mechanical coupling between the earth's fluid core and the mantle but deduced that the electromagnetic coupling process between core and mantle probably plays the most dominant role in affecting the spin rate. The factors, climate (9), length of day, variation in the earth's rotation rate, and variations in the geomagnetic field, have been recently correlated by a group of French geophysicists (V. Courtillot et al., Nature, 297, 386, 1982) to form the basis of what is described as an ‘attractive causal chain’ to forecast future climatic variations. The predictive correlations are not subject to circular reasoning as to which—climate variations or variations within the core—was the ultimate cause. Courtillot et al. note a lag in time between core changes and climate changes—in terms of 0—of 15–25 years to predict the climate.