Effects due to an artificial earth satellite in rapid motion through the ionosphere or the interplanetary medium

Conclusion

In this paper we have been concerned with the results of theoretical calculations of the interaction between a fast moving body and a tenuous plasma. Particular attention was paid to the case where the velocity of the body is much smaller than the velocity of neutral particles and ions, while the dimensions of the body are sufficiently large in comparison with the Debye radius. Such conditions are realized during the motion of artificial satellites or space rockets through the ionosphere, or through the interplanetary medium in the immediate neighborhood of the earth. Although this case has, on the whole, been investigated quite extensively, there are still a number of problems which require further analysis. Firstly, it is necessary to take into account the effect of the electric field on the motion of ions in the near zone at the rear of the body. Another important problem is that of magnetic disturbances. In the case of scattering of radio waves by the trail of the body, it would be interesting indeed to know the increase in the effective cross-section in the resonance region in which ɛ → 0. A number of other research problems which arise in the analysis of phenomena in the neighborhood of a moving body have been noted in the Introduction.

In the lower layers of the ionosphere it is important to allow for the fact that the dimensions of the body are comparable with the mean free path. Under these conditions there is the further interesting problem of the heating and additional ionization of the plasma, the disintegration of the surface, and the emission of waves. At large distances from the surface of the earth, the dimensions of the body may become comparable with the Debye radius, and the velocity of the body in the given region may become smaller than the thermal velocity of the particles. The character of the various disturbances introduced by the body under these conditions will also require a special investigation.

Thus, the interaction of a moving body with plasma leads to special and exceptionally varied effects. Disturbances due to the body are very considerable, so that the physical state of the region surrounding the body is very different from the state of the undisturbed medium.

The above results indicate that the phenomena in the neighborhood of satellites and space rockets in the ionosphere, or the interplanetary medium, must be taken into account, in the processing of experimental data when it is required to deduce information about the state of the undisturbed medium. This is particularly important in the analysis of the results of measurements obtained with various types of probes. Considerable errors may be introduced if these effects are not allowed for.

Further extensive experimental and theoretical studies of the structure of the disturbed region in the neighborhood of moving bodies in plasma are clearly necessary. Such investigations will, in particular, lead to the development of the most effective methods of studying the properties of the media through which satellites and space rockets travel.