No abstract

The measurement of power spectra is a problem of steadily increasing importance which appears to some to be primarily a problem in statistical estimation. Others may see it as a problem of instrumentation, recording and analysis which vitally involves the ideas of transmission theory. Actually, ideas and techniques from both fields are needed. When they are combined, they provide a basis for developing the insight necessary (i) to plan both the acquisition of adequate data and sound procedures for its reduction to meaningful estimates and (ii) to interpret these estimates correctly and usefully. This account attempts to provide and relate the necessary ideas and techniques in reasonable detail. Part II of this article will appear in the March issue of The Journal.

The measurement of power spectra is a problem of steadily increasing importance which appears to some to be primarily a problem in statistical estimation. Others may see it as a problem of instrumentation, recording and analysis which vitally involves the ideas of transmission theory. Actually, ideas and techniques from both fields are needed. When they are combined, they provide a basis for developing the insight necessary (i) to plan both the acquisition of adequate data and sound procedures for its reduction to meaningful estimates and (ii) to interpret these estimates correctly and usefully. This account attempts to provide and relate the necessary ideas and techniques in reasonable detail. Part I of this article appeared in the January, 1958 issue of The Bell System Technical Journal.

During the past six or seven years, several methods of orbit refinement were developed specifically for use with artificial satellites and spacecraft. This article describes these methods, and the classical method, in a uniform mathematical formalism in order to facilitate comparisons of their relative advantages and disadvantages for practical systems applications. However, such comparisons are made in this article only to the extent that motivated the development of the new methods.

Orbit determination and prediction programs are needed to generate ephemerides for the satellite. Orbit determination is from tracking data consisting of angles only, and is based on a modified version of a method by R. E. Briggs and J. W. Slowey of the Smithsonian Institution. Trends in the data due to perturbations from a Keplerian orbit are removed before this process, and estimates of the orbital elements from individual passes are combined statistically to produce refined estimates. Ephemeris calculation is by a semi‐analytic method in which deviations from a Keplerian orbit are obtained by integrating the perturbing forces. The programs to implement these procedures have been written for both the IBM 7090 and the IBM 1620 computers.